Sure we might have enormous gas giants and menacing asteroids, but compared to other corners of the universe, our solar system is pretty vanilla. There are black holes whose mass exceeds billions of solar masses, generating a gravitational pull so intense that they shape the formation and evolution of entire galaxies. Then there are magnetars, much less famous than black holes but incredibly powerful in their own right. Case in point, astronomers in Spain have witnessed such an object erupt with as much energy as the sun produces in 100,000 years, concentrating it in just 0.1 seconds.
When truly massive stars die, they do so with a bang, triggering a supernova explosion. In the aftermath, some collapse under their own weight, forming into black holes. Those that don’t make the cut, often become neutron stars, second only to black holes in their stupendous density. A teaspoon of neutron star material would weigh around a billion tons, for instance.
There are multiple types of neutron stars, including magnetars. These objects have extremely powerful magnetic fields, a thousand trillion times stronger than the Earth’s, and between 100 and 1,000 times stronger than that of a radio pulsar. They’re essentially the most powerful magnets in the universe.
Magnetars are quite rare, with only a couple dozen such objects having been identified so far. One of them, located in the Sculptor Galaxy about 13 million light-years away, was under observation by astronomers using the Atmosphere-Space Interactions Monitor (ASIM) aboard the International Space Station when a giant flare was detected.
The flare, known as the GRB 2001415 event, released roughly the energy the sun radiates in about 100,000 years in just two short quasi-periodic pulsations that lasted approximately 160 milliseconds.
“Even in an inactive state, magnetars can be one hundred thousand times more luminous than our Sun, but in the case of GRB 2001415, the energy that was released is equivalent to that which our Sun radiates in 100,000 years,” said Dr. Alberto Castro-Tirado, an astrophysicist with the Instituto de Astrofísica de Andalucía del Consejo Superior de Investigaciones Científicas (IAA-CSIC) and the Universidad de Málaga. “It’s a true cosmic monster,” added Professor Víctor Reglero, an astrophysicist at the Universitat de València and co-author of the new study.
The magnetar explosion was detected on April 15, 2020 thanks to an artificial intelligence system integrated with ASIM. If this kind of system wasn’t in place, the astronomers would have been oblivious to the event, whose signal decayed into background noise within a fraction of a second.
No one’s really sure what triggered the eruption, but the researchers believe it could have been due to instabilities in the magnetosphere or ‘earthquakes’ produced in their crust. Further research could help scientists reveal the mechanisms that trigger these frightening but, at the same time, fascinating cosmic burps.
“Although these eruptions had already been detected in two of the thirty known magnetars in our Galaxy and in some other nearby galaxies, GRB 2001415 would be the most distant magnetar eruption captured to date, being in the Sculptor group of galaxies about 11 million light-years,” said Professor Reglero.
“Seen in perspective, it has been as if the magnetar wanted to indicate its existence to us from its cosmic solitude, singing in the kHz with the force of a Pavarotti of a billion suns.”
The surfaces of neutron stars may feature mountains, albeit ones that are no more than millimetres tall, new research has revealed. The minuscule scale of neutron star mountains is a result of the intense gravity produced by these stellar remnants that are the second densest objects in the Universe after black holes.
Because neutron stars have the mass equivalent to a star like the Sun compressed into a diameter that is about the size of a city on Earth–about 10km– they have a gravitational pull at their surface that is as much as 40,000 billion times stronger than Earth’s.
This presses features on that surface flat, making for almost perfect spheres. Yet the new research, presented at the National Astronomy Meeting 2021 shows that these stellar remnants do feature some tiny topological deformations, analogous to mountains on a planet’s surface.
The finding was a result of complex computer modelling by a team of researchers led by the University of Southhampton’s Fabian Gittins. The Ph.D. student’s team simulated a realistic neutron star and then calculated the forces acting upon it. What the research really shows is how well neutron stars can support deviations from a perfect sphere without its crust being strained beyond breaking point.
This revealed how mountains could be created on such dense stellar remnants and demonstrated that such formations would be no taller than a fraction of a millimetre.
“For the past two decades, there has been much interest in understanding how large these mountains can be before the crust of the neutron star breaks, and the mountain can no longer be supported,” says Gittins. These results show how neutron stars truly are remarkably spherical objects. “Additionally, they suggest that observing gravitational waves from rotating neutron stars maybe even more challenging than previously thought”.”
Mountain formation has been formulated for neutron stars before, but these new findings suggest such features would be hundreds of times smaller than the mountains of a few centimetres previously predicted. This is because those older models took the crusts of neutron stars to the edge of breaking point at every single point; something the up-to-date research suggests is less than realistic.
Neutron stars form when massive stars run out of fuel to power nuclear fusion. This means that the toward force balancing against gravity’s inward pull is cancelled and leads to the gravitational collapse of the star. During the course of this collapse, the massive star ejects its outer material in supernova explosions and leaving behind a core of ultradense material. This stellar remnant is only protected from further collapse–and in turn, becoming a black hole–by the quantum mechanical properties of the neutron-rich material that composes it.
The finding may have implications that go beyond the modelling of neutron stars. Tiny deformations on the surface of rapidly spinning neutron stars called pulsars could launch gravitational waves–the tiny ripples in spacetime predicted by general relativity and detected here on Earth by the LIGO/Virgo collaboration.
Unfortunately, as precise and sensitive as the LIGO laser interferometer is, it is still not powerful enough to detect gravitational waves launched by these ant-hill like mountains. It is possible that future upgrades to these Earth-based detectors and advancements such as the space-based gravitational wave detector LISA could make observing the effect of these tiny bumps possible.
Astrophysicists have finally observed the spiralling merger between a neutron star and a black hole. The cataclysmic event was witnessed in a gravitational wave signal by the LIGO/Virgo/KAGRA collaboration and is the first time that one of these elusive but titanic ‘mixed’ merger events has been spotted and had its nature confirmed. And just like buses, you wait for an age for one to come and then two arrive at once.
The researchers also detected a gravitational wave signal from another event of the same nature just ten days after the first, with the signals picked up by LIGO/Virgo on 5th January 2020 and the 15th January 2020 respectively.
The finding is significant because of the three types of mergers between stellar remnant binaries–neutron star/neutron star mergers, black hole/ black hole mergers, and neutron star/ black hole or mixed mergers–this latter category is the only one we hadn’t detected until now and has proved fairly elusive.
“With this new discovery of neutron star- black hole mergers outside our galaxy, we have found the missing type of binary,” says Astrid Lamberts, a CNRS researcher at Observatoire de la Côte d’Azur, in Nice, France. “We can finally begin to understand how many of these systems exist, how often they merge, and why we have not yet seen examples in the Milky Way.”
These detections of signals from separate mixed merger events come just six years after the LIGO/Virgo collaboration first detected the gravitational waves confirming predictions regarding ripples in the fabric of spacetime by Einstein’s theory of general relativity a century previous.
Though further observations are needed, the results produced by the team could help astronomers and astrophysicists refine their knowledge of systems in which these elusive mergers occur determining both how these mixed binary pairings form and how frequently their components spiral together and merge.
“Gravitational waves have allowed us to detect collisions of pairs of black holes and pairs of neutron stars, but the mixed collision of a black hole with a neutron star has been the elusive missing piece of the family picture of compact object mergers,” says Chase Kimball, a Northwestern University graduate student. “Completing this picture is crucial to constraining the host of astrophysical models of compact object formation and binary evolution. Inherent to these models are their predictions of the rates that black holes and neutron stars merge amongst themselves.
“With these detections, we finally have measurements of the merger rates across all three categories of compact binary mergers.”
Chase Kimball, Northwestern University
Kimball is the co-author of a study published in the Astrophysical Journal Letters and part of a team that includes researchers from the LIGO Scientific Collaboration (LSC), the Virgo Collaboration and the Kamioka Gravitational Wave Detector (KAGRA) project.
A Gravitational-Wave Signal Signal One Billion Years in the Making
One of the most astounding things about the detection of gravitational waves is just how precise a piece of equipment has to be to detect these tiny ripples in the fabric of spacetime. Since that first key detection in 2015, the National Science Foundation’s (NSF) operators at the LIGO laser interferometer and their counterparts at the Virgo detector in Italy have detected over 50 gravitational wave signals from mergers between black hole pairs and neutron star binaries.
The first mixed neutron star/black hole merger spotted by the collaboration on January 5th is believed to be the result of a merger of a black hole six times the mass of the Sun and a neutron star with a mass 1.5 times that of our star. The event which has been designated GW200105 occurred 900 million light-years away from Earth and was picked up as a strong signal at the LIGO detector located in Livingstone, Louisiana.
LIGO Livingstone’s partner detector located in Hanford, Washington, missed the signal as it was offline at the time. Virgo on the other hand caught the signal but it was somewhat obscured by noise. “Even though we see a strong signal in only one detector, we conclude that it is real and not just detector noise,” says Harald Pfeiffer, group leader in the Astrophysical and Cosmological Relativity department at Max Planck Institute for Gravitational Physics (AEI) in Potsdam, Germany. “It passes all our stringent quality checks and sticks out from all noise events we see in the third observing run.”
The fact that GW200105 was only strongly picked up by one detector makes it difficult to pinpoint in the sky with the international team only able to ascertain that it came from a region about 34 thousand times the size of the Moon.
“While the gravitational waves alone don’t reveal the structure of the lighter object, we can infer its maximum mass,” says Bhooshan Gadre, a postdoctoral researcher at the AEI. “By combining this information with theoretical predictions of expected neutron star masses in such a binary system, we conclude that a neutron star is the most likely explanation.”
Despite the fact that the second mixed merger occurred farther away–1 billion light-years distant from Earth– its signal was spotted by both LIGO detectors and the Virgo detector. This means that the team have been able to localise the merger–named GW200115– more precisely, to a region of the sky that is around three thousand times the size of Earth’s moon. This second merger is believed to have occurred between a black hole nine times the mass of our Sun and a neutron star almost twice the size of the Sun.
These Black Holes Weren’t Messy Eaters
Because of the extraordinary distances involved, astronomers have yet to confirm either merger in the electromagnetic spectrum upon which traditional astronomy is based. Despite being informed of the event almost immediately astronomers could not find telltale flashes of light indicating the mergers.
This is unsurprising as any light from such distant events would be incredibly dim after one billion years of journeying to Earth no matter what wavelength it is observed in, or how powerful the telescope is that is used to attempt the follow-up observation.
There also remains another possibility why no light could be seen from these events. The lack of a signal in electromagnetic radiation could be because the neutron star elements of these mergers were swallowed whole by their black hole partners.
“These were not events where the black holes munched on the neutron stars like the cookie monster and flung bits and pieces about,” explains Patrick Brady, a professor at the University of Wisconsin-Milwaukee and Spokesperson of the LIGO Scientific Collaboration, colourfully. “That ‘flinging about’ is what would produce light, and we don’t think that happened in these cases.”
Whilst these are the first two confirmed examples of such mixed mergers, there have been suspects spotted by their gravitational-wave signals in the past. In August 2019 a signal designated GW190814 was detected which researchers say involved a collision of a 23-solar-mass black hole with an object of about 2.6 solar masses. This second object could have been eitherthe heaviest known neutron star or the lightest known black hole ever found. That ambiguity left this signal unconfirmed as the product of a mixed merger event and other similar finds have been plagued with similar ambiguities.
Now that two confirmed detections of mixed mergers have been made, astrophysicists can set about discovering if current estimates that say such collisions should occur at a frequency of around one per month within a distance of 1 billion light-years of Earth are correct.
They can also set about discovering the origins of such binaries, possibly eliminating one or two of the proposed locations in which such events are believed to occur: stellar binary systems, dense stellar environments including young star clusters, and the centers of galaxies.
Key to these investigations will be the fourth observation run of the laser interferometers that act as our gravitational wave detectors, set to begin in summer 2022.
“The detector groups at LIGO, Virgo, and KAGRA are improving their detectors in preparation for the next observing run scheduled to begin in summer 2022,” concludes Brady. “With the improved sensitivity, we hope to detect merger waves up to once per day and to better measure the properties of black holes and super-dense matter that makes up neutron stars.”
Whilst it may not have the snappiest name, the event GW150914 is pretty significant in terms of our understanding of the Universe. This event, with a name that includes ‘GW’ as a prefix which is an abbreviation of ‘Gravitational Wave’ and the date of observation–15/09/14– marked humanity’s first direct detection of gravitational waves.
This was groundbreaking on two fronts; firstly it successfully confirmed a prediction made by Albert Einstein’s theory of general relativity almost a century before. A prediction that stated events occurring in the Universe do not just warp spacetime, but in certain cases, can actually send ripples through this cosmic fabric.
The second significant aspect of this observation was the fact that it represented an entirely new way to ‘see’ the Universe, its events and objects. This new method of investigating the cosmos has given rise to an entirely new form of astronomy; multimessenger astronomy. This combines ‘traditional’ observations of the Universe in the electromagnetic spectrum with the detection of gravitational waves, thus allowing us to observe objects that were previously invisible to us.
Thus, the discovery of gravitational waves truly opened up an entirely new window on the cosmos, but what are gravitational waves, what do they reveal about the objects that create them, and how do we detect such tiny tremblings in reality itself?
Gravitational Waves: The Basics
Gravitational waves are ripples in the fabric of spacetime.
These ripples travel from their source at the speed of light.
The passage of gravitational waves squash and stretch space itself.
Gravitational waves can be detected by measuring these infinitesimally small changes in the distance between objects.
They are created when an object or an event that curves spacetime causes that curvature to change shape.
Amongst the causes of gravitational waves are colliding black holes and neutron stars, supernovae, and stars that are undergoing gravitational collapse.
Imagine sitting at the side of a lake, quietly observing the tranquil surface of the water undisturbed by nature, the wind, or even by the slightest breeze. Suddenly a small child runs past hurling a pebble into the lake. The tranquillity is momentarily shattered. But, even as peace returns, you watch ripples spread from the centre of the lake diminishing as they reach the banks, often splitting or reflecting back when they encounter an obstacle.
The surface of the lake is a loose 2D analogy for the fabric of spacetime, the pebble represents an event like the collision of two black holes, and our position on Earth is equivalent to a blade of grass on the bank barely feeling the ripple which has diminished tremendously in its journey to us.
Gravitational waves were first predicted by Henri Poincare in 1905 as disturbances in the fabric of spacetime that propagate at the speed of light, but it would take another ten years for the concept to really be seized upon by physicists. This happened when Albert Einstein predicted the same phenomenon as part of his revolutionary 1916 geometric theory of gravity, better known as general relativity.
Whilst this theory is most well-known for suggesting that objects with mass would cause warping of spacetime, it also went a step further positing that an accelerating object should change this curvature and cause a ripple to echo through spacetime. Such disturbances in spacetime would not have been permissible in the Newtonian view of gravity which saw the fabric of space and time as separate entities upon which the events of the Universe simply play out.
But upon Einstein’s dynamic and changing stage of united spacetime, such ripples were permissible.
Gravitational waves arose from the possibility of finding a wave-like solution to the tensor equations at the heart of general relativity. Einstein believed that gravitational waves should be generated en masse by the interaction of massive bodies such as binary systems of super-dense neutron stars and merging black holes.
The truth is that such ripples in spacetime should be generated by any accelerating objects but Earth-bound accelerating objects cause perturbations that are far too small to detect. Hence why our investigations must turn to areas of space where nature provides us with objects that are far more massive.
As these ripples radiate outwards from their source in all directions and at the speed of light, they carry information about the event or object that created them. Not only this, but gravitational waves can tell us a great deal about the nature of spacetime itself.
Where do Gravitational Waves Come From?
There are a number of events that can launch gravitational waves powerful enough for us to detect with incredibly precise equipment here on Earth. These events are some of the most powerful and violent occurrences that the Universe has to offer. For instance, the strongest undulations in spacetime are probably caused by the collision of black holes.
Other collision events are associated with the production of strong gravitational waves; for example the merger between a black hole and a neutron star, or two neutron stars colliding with each other.
But, a cosmic body doesn’t always need a partner to make waves. Stellar collapse through supernova explosion–the process that leaves behind stellar remnants like black holes and neutron stars– also causes the production of gravitational waves.
To understand how gravitational waves are produced, it is useful to look to pulsars–binary systems of two neutron stars that emit regular pulses of electromagnetic radiation in the radio region of the spectrum.
Einstein’s theory suggests that a system such as this should be losing energy by the emission of gravitational waves. This would mean that the system’s orbital period should be decreasing in a very predictable way.
The stars draw together as there is less energy in the system to resist their mutual gravitational attraction, and as a result, their orbit increases in speed, and thus the pulses of radio waves are emitted at shorter intervals. This would mean that the time it takes for the radio wave to be directly facing our line of sight would be reduced; something we can measure.
This is exactly what was observed in the Hulse-Taylor system (PSR B1913±16), discovered in 1974, which is comprised of two rapidly rotating neutron stars. This observation earned Russell A. Hulse and Joseph H. Taylor, Jr, both of Princeton University, the 1993 Nobel Prize in Physics. The reason given by the Nobel Committee was: “for the discovery of a new type of pulsar, a discovery that has opened up new possibilities for the study of gravitation.”
Though inarguably an impressive and important scientific achievement, this was still only indirect evidence of gravitational waves. Whilst the effect Einstein predicted of shortening of the pulsar’s spin was definitely present, this wasn’t an actual direct detection.
In fact, though not alive to witness this momentous achievement, Einstein had predicted that this would be the only way we could ever garner any hint of gravitational waves. The great physicist believed those spacetime ripples would be so faint that they would remain impossible to detect by any technological means imaginable at that time.
Fortunately, Einstein was wrong.
How do we Detect Gravitational Waves?
It should come as no surprise that actually detecting a gravitational wave requires a piece of equipment of tremendous sensitivity. Whilst the effect of gravitational waves–the squashing and stretching space itself–sounds like something that should pre-eminently visible, the degree by which this disturbance occurs is so tiny it is totally imperceptible.
Fortunately, there is a branch of physics that is pretty adept at deal with the tiny. To spot gravitational waves, researchers would use an effect called interference, something demonstrated in the most famous quantum physics experiment of all time; the double-slit experiment.
Physicists realised that a laser interferometer could be used to measure the tiny squashing and stretching of space as it would cause the arms of the equipment to shrink by a minute amount. This means when splitting a laser and sending it through the arms of an interferometer the squeezing of space caused by the passage of a gravitational wave would cause one laser to arrive slightly ahead of the other–meaning they are out of phase and causing destructive interference. Thus, this difference in arrival times causes interference that gives an indication that gravitational waves have rippled across one of the arms.
But, not just any laser interferometer would do. Physicists would need an interferometer so large that it constituents a legitimate feat in engineering. Enter the Laser Interferometer Gravitational-wave Observatory (LIGO).
The LIGO detector uses two laser emitters based at the Hanford and Livingstone observatories, separated by thousands of kilometres apart to form an incredibly sensitive interferometer. From these emitters, lasers are sent down the ‘arms’ of the interferometer which are actually 4km long vacuum chambers.
This results in a system that is so sensitive it can measure a deviation in spacetime that is as small as 1/10,000 the size of an atomic nucleus. To put this into an astronomical context; it is equivalent to spotting a star at a distance of 4.2 light-years and pinpointing its location to within the width of a human hair! This constitutes the smallest measurement ever practically attempted in any science experiment.
And in 2015, this painstaking operation paid off.
On 14th September 2015, the LIGO and Virgo collaboration spotted a gravitational wave signal emanating from the spiralling in and eventual merger of two black holes, one 29 times the mass of the Sun, the other 36 times our star’s mass. From changes in the signal received the scientists were also able to observe the resultant single black hole.
The signal, named GW150914, represented not just the first observation of gravitational waves, but also the first time humanity had ‘seen’ a binary stellar-mass black hole system, proving that such mergers could exist in the Universe’s current epoch.
Different Kinds of Gravitational Waves
Since the initial detection of gravitational waves, researchers have made a series of important and revelatory detections. These have allowed scientists to classify different types of gravitational waves and the objects that may produce them.
Continuous Gravitational Waves
A single spinning massive object like a neutron star is believed to cause a continuous gravitational wave signal as a result of imperfections in the spherical shape of this star. if the rate of spin remains constant, so too are the gravitational waves it emits–it is continuously the same frequency and amplitude much like a singer holding a single note. Researchers have created simulations of what an arriving continuous gravitational wave would sound like if the signal LIGO detected was converted into a sound.
The sound of a continuous gravitational wave of the kind produced by a neutron star can be heard below.
Compact Binary Inspiral Gravitational Waves
All of the signals detected by LIGO thus far fit into this category as gravitational waves created by pairs of massive orbiting objects like black holes or neutron stars.
The sources fit into three distinct sub-categories:
Binary Black Hole (BBH)
Binary Neutron Star (BNS)
Neutron Star-Black Hole Binary (NSBH)
Each of these types of binary pairing creates its own unique pattern of gravitational waves but shares the same overall mechanism of wave-generation–inspiral generation. This process occurs over millions of years with gravitational waves carrying away energy from the system and causing the objects to spiral closer and closer until they meet. This also results in the objects moving more quickly and thus creating gravitational waves of increasing strength.
The ‘chirp’ of an eventual merger between neutron stars has been translated to sound waves and can be heard below.
Stochastic Gravitational Waves
Small gravitational waves that even LIGO is unable to precisely pinpoint could be passing over Earth from all directions at all times. These are known as stochastic gravitational waves due to their random nature. At least part of this stochastic signal is likely to have originated in the Big Bang.
Should we eventually be able to detect this signal it would allow us to ‘see’ further back into the history of the Universe than any electromagnetic signal could, back to the epoch before photons could freely travel through space.
The simulated sound of this stochastic signal can be heard below.
It is extremely likely given the variety of objects and events in the Universe that other types of gravitational wave signals exist. This means that the quest to detect such signals is really an exploration of the unknown. Fortunately, our capacity to explore the cosmos has been boosted tremendously by our ability to detect gravitational waves.
A New Age of Astronomy
GW150914 conformed precisely to the predictions of general relativity, confirming Einstein’s most revolutionary theory almost exactly six decades after his death in 1955. That doesn’t mean that gravitational waves are done teaching us about the Universe. In fact, these ripples in spacetime have given us a whole new way to view the cosmos.
Before the discovery of gravitational waves, astronomers were restricted to a view of the Universe painted in electromagnetic radiation and therefore our observations have been confined to that particular spectrum.
Using the electromagnetic spectrum alone, astronomers have been able to discover astronomical bodies and even thecosmic microwave background (CMB) radiation, a ‘relic’ of one of the very first events in the early universe, the recombination epoch when electrons joined with protons thus allowing photons to begin travelling rather than endlessly scattering. Therefore, the CMB is a marker of the point the universe began to be transparent to light.
Yet despite the strides traditional astronomy has allowed us to make in our understanding of the cosmos, the use of electromagnetic radiation is severely limited. It does not allow us to directly ‘see’ black holes, from which light cannot escape. Nor does it allow us to see non-baryonic, non-luminous dark matter, the predominant form of matter in galaxies–accounting for around 85% of the universe’s total mass. As the term ‘non-luminous’ suggests dark matter does not interact with the electromagnetic spectrum, it neither absorbs nor emits light. This means that observations in the electromagnetic spectrum alone will never allow us to see the majority of the matter in the universe.
Clearly, this is a problem. But one that can be avoided by using the gravitational wave spectrum as both black holes and dark matter do have considerable gravitational effects.
Gravitational waves also have another significant advantage over electromagnetic radiation.
This new form of astronomy measures the amplitude of the travelling wave, whilst electromagnetic wave astronomy measures the energy of the wave, which is proportional to the amplitude of the wave squared.
Therefore the brightness of an object in traditional astronomy is given by 1/distance² whilst ‘gravitational brightness’ falls off by just 1/distance. This means that the visibility of stars persists in gravitational waves for a much greater distance than the same factor persists in the electromagnetic spectrum.
Of course, none of this is to suggest that gravitational wave astronomy will ‘replace’ traditional electromagnetic spectrum astronomy. In fact the two are most powerful when they are unified in an exciting new discipline–multimessenger astronomy
Sources and Further Reading
Maggiore. M., Gravitational Waves: Theory and Experiments, Oxford University Press, 
Maggiore. M., Gravitational Waves: Astrophysics and Cosmology, Oxford University Press, 
Collins. H., Gravity’s Kiss: The Detection of Gravitational Waves, MIT Press, 
Without question, black holes and neutron stars are the most mysterious objects in the known universe. One of the mysteries that has surrounded these dense objects that arise at the conclusion of a star’s lifetime is the source of the electromagnetic radiation emitted from regions of space that host them.
Astrophysicists have suspected for decades that this high-energy radiation is a product of electrons moving at near light speeds around black holes and neutron stars.
The missing piece of the puzzle, however, is exactly what process causes these electrons to be accelerated to such relativistic speeds.
Now, in a study published in theAstrophysical Journal, astrophysicists Luca Comisso and Lorenzo Sironi discuss massive supercomputer simulations that they have employed to uncover this mystery mechanism behind this acceleration.
The conclusion reached by the duo from Columbia University is that this velocity is granted by an interaction between chaotic motion and a phenomenon called ‘reconnection’ found in tremendously powerful magnetic fields.
“Turbulence and magnetic reconnection–a process in which magnetic field lines tear and rapidly reconnect–conspire together to accelerate particles, boosting them to velocities that approach the speed of light,” says Comisso, a postdoctoral research scientist at Columbia and first author on the study.
The researcher goes on to explain that regions that host black holes and neutron stars are permeated by a sea of extremely hot gas particles. As these gas particles move chaotically they drag magnetic field lines with them. This drives vigorous magnetic reconnection.
“It is thanks to the electric field induced by reconnection and turbulence that particles are accelerated to the most extreme energies, much higher than in the most powerful accelerators on Earth, like the Large Hadron Collider at CERN,” Comisso continues.
The difficulty in studying such turbulent gas is that chaotic motion is impossible to predict precisely. In fact, the problem of dealing with the mathematics of turbulence is so well-known that it is one of the seven problems that make up the Millennium Prize challenge in mathematics.
Comisso and Sironi tackled this issue from an astrophysical standpoint by designing and employing extensive supercomputer simulations to solve equations which describe turbulence of charged particles in a gas. These simulations are some of the largest ever created in this research area.
“We used the most precise technique–the particle-in-cell method–for calculating the trajectories of hundreds of billions of charged particles that self-consistently dictate the electromagnetic fields. And it is this electromagnetic field that tells them how to move,” adds Sironi, assistant professor of astronomy at Columbia and the study’s principal investigator.
The researchers point out that the most critical element of the study was the identification of the role played by magnetic reconnection in this turbulent environment.
Their simulations suggest that reconnection ‘selects’ particles that will be accelerated to magnetic fields to near relativistic speeds. It simulations also show that particles in this environment gained most of their energy by bouncing off the turbulent fluctuations at random.
The stronger the magnetic field involved in this process, the more rapid the acceleration of the electrons. These strong fields also cause the particles to travel in a curved trajectory, with such acceleration causing the emission of electromagnetic radiation.
“This is indeed the radiation emitted around black holes and neutron stars that make them shine, a phenomenon we can observe on Earth,” Sironi says.
Understanding the extreme environments around Black Holes and Neutron Stars
The duo of researchers point out that the ultimate aim of their study is to better understand the extreme environments surrounding both black holes and neutron stars and the events that occur in them.
This could, in turn, shine additional light on both fundamental physics and our understanding of how the universe functions.
But there is still much work to be done.
The team plan to compare the predictions revealed by their simulations to observations of electromagnetic radiation emitted by the Crab Nebula. By analysing the electromagnetic spectrum of this bright supernova debris leftover from the violent explosion of a star they can connect their work with actual observations.
“We figured out an important connection between turbulence and magnetic reconnection for accelerating particles, but there is still so much work to be done,” Comisso concedes. “Advances in this field of research are rarely the contribution of a handful of scientists, but they are the result of a large collaborative effort.”
Heavier elements like iron, calcium, and nickel are made after atoms fuse in massive stellar explosions known as supernovae. Other relatively light elements, like aluminum, are made inside giant stars and blown out into space by stellar winds. But until now astronomers weren’t sure how much heavier elements such as gold, silver, or strontium formed.
This is where a groundbreaking new study comes in — the findings suggest that strontium, and likely other heavy-weight elements, is produced in the aftermath of a merger of two neutron stars.
In 2017, astronomers detected a cosmic cataclysmic event: The merger of two neutron stars from 130 million years ago. The force of the collision was so strong that it literally shook the fabric of space-time, generating gravitational waves that eventually reached Earth, where they were detected. The two neutron stars either merged into a huge single neutron star or collapsed into a black hole.
A neutron star is the collapsed core of a large star — they’re the smallest and, at the same time, densest stars we know of. Most models suggest that they are made almost exclusively of neutrons — hence the name.
The existence of gravitational waves, which were first predicted by Einstein’s Theory of General Relativity about a hundred years ago, was confirmed only in 2016. The event was recorded by the Laser Interferometer Gravitational-Wave Observatory (LIGO), whose founders were awarded this year’s Nobel Prize in Physics.
Gravity waves are essentially ripples in the fabric of spacetime which are generated by interactions between very massive accelerating cosmic objects, such as neutron stars or black holes. Physicists liken gravity waves to the waves generated when a stone is thrown into a pond.
But, it’s not just gravitational waves that emerged out of the neutron star merger. The merger, known as GW170817, also generated a kilonova — a massive explosion that is much brighter than a regular nova but less so than a supernova. This was the first time that this type of nova was ever witnessed.
Scientists had suspected for some time that heavier elements may be forged during neutron star collisions. In a new study published in Nature, astronomers used ESO’s X-shooter spectrograph on the Very Large Telescope (VLT) to look for signatures of such elements in the kilonova.
Astronomers recorded a series of spectra from the ultraviolet to the near-infrared, which, when analyzed, revealed the presence of strontium.
Strontium is naturally found in the soil and some minerals. It’s what gives fireworks their dazzling red color.
To make strontium, other atoms need to be bombarded very rapidly with a huge number of neutrons under high pressure and temperature. The process, known as rapid neutron capture, needs to happen fast enough for an atomic nucleus to capture some of the neutrons before they decay in order to produce very heavy elements.
“By reanalysing the 2017 data from the merger, we have now identified the signature of one heavy element in this fireball, strontium, proving that the collision of neutron stars creates this element in the Universe,” says the study’s lead author Darach Watson from the University of Copenhagen in Denmark.
“This is the final stage of a decades-long chase to pin down the origin of the elements,” says Watson. “We know now that the processes that created the elements happened mostly in ordinary stars, in supernova explosions, or in the outer layers of old stars. But, until now, we did not know the location of the final, undiscovered process, known as rapid neutron capture, that created the heavier elements in the periodic table.”
This kind of research is still in its infancy. There is still much to learn about how neutron stars merge and their subsequent kilonovae. In the future, by analyzing more such events, astronomers hope to identify other heavy elements.
“This is the first time that we can directly associate newly created material formed via neutron capture with a neutron star merger, confirming that neutron stars are made of neutrons and tying the long-debated rapid neutron capture process to such mergers,” says Camilla Juul Hansen from the Max Planck Institute for Astronomy in Heidelberg, who played a major role in the study.
“We actually came up with the idea that we might be seeing strontium quite quickly after the event. However, showing that this was demonstrably the case turned out to be very difficult. This difficulty was due to our highly incomplete knowledge of the spectral appearance of the heavier elements in the periodic table,” says University of Copenhagen researcher Jonatan Selsing, who was a key author on the paper.
Pulsars are rotating neutron stars that emit a focused beam of electromagnetic radiation, resulting in their nickname as “lighthouses” of the universe. Pulsars come in all shapes and sizes, and some behave quite weirdly and seemingly chaotic — but that doesn’t mean there isn’t a pattern.
Vela, a neutron star located nearly 1,000 light-years away from Earth in the southern sky, is famous among astronomers because it “glitches” once every three years, suddenly speeding up its rotational period before slowing down back to normal.
Scientists aren’t sure why this weird star is behaving this way but new observations suggest that Vela seems to slow down its rotation rate immediately before the glitch. This was the first time astronomers have ever seen anything like this.
Neutron stars are the remnants of huge dead stars and represent some of the densest objects in the universe. Imagine an object with the mass of a sun squashed down to the size of a city — that’s how dense these objects can get.
Most neutron stars are observed as pulsars, which rotate at very regular intervals ranging from milliseconds to seconds.
For their new study, astronomers at the Monash University School of Physics and Astronomy reanalyzed observations of the Vela glitch made in December 2016.
This more thorough analysis revealed that Vela — which normally makes 11 rotations per second — started rotating even faster and then slowed down to a more normal speed very quickly.
Although astronomers aren’t sure why this happens, the observation is consistent with theoretical models that suggest that neutron stars have three internal components.
“One of these components, a soup of superfluid neutrons in the inner layer of the crust, moves outwards first and hits the rigid outer crust of the star causing it to spin up,” said Dr. Paul Lasky, an astronomer at the Monash School of Physics and Astronomy and co-author of the new study published in the journal Nature Astronomy.
“But then, a second soup of superfluid that moves in the core catches up to the first causing the spin of the star to slow back down.”
Ultimately, what this new study shows is that a pulsar glitch isn’t a straightforward, single-step process. Instead, a complex interplay of internal forces seems to generate sophisticated behaviors in the neutron stars, although the exact mechanisms are still a mystery. In the future, new observations and theoretical models may reveal more.
The strongest material in the known universe is a strange form of pasta — it’s not campanelle, gnocchi, or penne, but rather an esoteric-like concoction called nuclear pasta, which is formed by the ungodly pressure found inside a neutron star. By scientists’ calculations, nuclear pasta is about 10 billion times stronger than steel.
The ultimate pressure cooker
Different shapes that nuclear pasta takes on at varying layers of a neutron stars, from crust to core. Credit: Physical Review Letters.
When some stars die, they go supernova — the biggest kind of explosion man has ever measured. In the aftermath of a supernova, the outer layers of the star are stripped, exposing a dense core that collapses inward, forming a neutron star. These dense objects cram the mass of several suns into an object the size of a city. To illustrate the mind-boggling kind of density we’re referring to here, imagine cramming Mt. Everest into a sugar cube.
These sort of densities can trigger all sorts of quirky physics, among them the so-called nuclear pasta. The immense gravity makes the outer layer of the neutron star freeze solid, similar to how Earth’s thin crust envelops a liquid core. Below this crust, competing forces between protons and neutrons push and squeeze them into different directions, causing the material to take on tangled shapes that resemble pasta. The deeper you travel into the neutron star, the more elongated the neutrons become. In the spirit of the analogy, it’s like transitioning from gnocchi-like bubbles into thin rods that resemble spaghetti.
An international team comprised of researchers from McGill University, Indiana University and the California Institute of Technology has now crunched the numbers, simulating how the nuclear particles interact at different layers of the neutron star.
Over the course of these simulations — which required 2 million hours worth of processor time or the equivalent of 250 years on a laptop with a single good GPU — virtual nuclear pasta was stretched and deformed until it was pushed to its limits. The results suggest that the neutron star’s density made the nuclear pasta an astounding 10 billion times stronger than steel. It’s by far the strongest material in the universe.
“A lot of interesting physics is going on here under extreme conditions and so understanding the physical properties of a neutron star is a way for scientists to test their theories and models,” says Matthew Caplan, co-author of the study. “With this result, many problems need to be revisited. How large a mountain can you build on a neutron star before the crust breaks and it collapses? What will it look like? And most importantly, how can astronomers observe it?”
Understanding the strength of the nuclear pasta is important for astrophysicists, whose observations of neutron stars are confined to the crust. The findings published in Physical Review Letterscould also help scientists better understand gravitational waves like those detected last year when two neutron stars collided.
A group of misbehaving neutron stars is breaking the limits of physics, and astronomers are struggling to understand why. Now, a recent study sheds new light on these incredibly bright structures.
Image of the Whirlpool galaxy, or M51. X-ray light seen by NASA’s Chandra X-ray Observatory is shown in purple, and optical light from NASA’s Hubble Space Telescope is red, green and blue. The ultraluminous X-ray source, or ULX, in the new Caltech-led study is indicated. Image credits: NASA/CXC/Caltech/M.Brightman et al.; Optical: NASA/STScI
They’re some of the brightest objects in the universe, and they surprised researchers from the moment they were discovered. In the 1980s, astronomers spotted bright sources of X-rays in the outer portions of galaxies — far away from the center, dominated by black holes. They called these bright structures ultraluminous X-ray sources, or ULXs, and initially, they assumed they were black holes. But in 2014, data from NASA’s NuSTAR and other space telescopes found that that’s not really the case. Instead, ULXs are extremely bright neutron stars.
Neutron stars are the burnt-out cores of massive stars that exploded, formed by the gravitational collapse of the remnants. This process is so violent that protons and electrons essentially melt into each other, creating neutrons, hence the name of the stars.
As a result, neutron stars are extremely dense, with one teaspoon of material weighing over one billion tons — as much as a mountain.
Somewhat like black holes, they pull surrounding material from them. As this material is pulled towards the neutron star, it heats up and glows with X-rays. However, at one point in the process, there comes a time when the push of the X-rays is stronger than the gravitational draw, and matter is simply pushed away. This point, the limit at which neutron stars can’t accumulate matter and give off X-rays, is called the Eddington limit. But here’s the problem: these massive neutron stars we call ULXs are breaking the Edington limit.
“In the same that we can only eat so much food at a time, there are limits to how fast neutron stars can accrete matter,” says Murray Brightman, a postdoctoral scholar at Caltech and lead author of a new report on the findings in Nature Astronomy. “But ULXs are somehow breaking this limit to give off such incredibly bright X-rays, and we don’t know why.”
In the new study, Brightman and his colleagues analyzed such a ULX in the Whirlpool galaxy, also known as M51, which lies about 28 million light-years away. Their attention was drawn by an unusual dip in the luminosity of this ULX. After ruling out all other possible explanations, they concluded that the cause of this dip is a phenomenon called cyclotron resonance scattering. This phenomenon occurs when charged particles (protons or electrons) circle around in a magnetic field.
Since black holes don’t have a magnetic field but neutron stars do, this is a telltale sign that M51 is, indeed, a neutron star. But this study says even more about the nature of M51, and might even allow astronomers to finally understand what gives ULXs the necessary fuel to keep burning up when they shouldn’t.
“The cyclotron absorption feature we found in the ULX in M51 could be caused by electrons or protons,” Brightman told ZME Science. “If protons, it would imply a very strong magnetic field helping the star to break the Eddington limit. If electrons, the magnetic field strength would be quite typical for a neutron star. It may still shine brighter than the Eddington limit in this case because the matter is channeled down an accretion column on to the star whereas the X-ray light escapes from the sides of the column. This reduces the interaction between the matter and radiation.”
However, if the cyclotron is from electrons, then the magnetic field wouldn’t be strong enough to help these stars break the Eddington limit. So it’s an important clue, but it might or might not be the decisive one.
Now, researchers want to carry out further investigations, acquiring more X-ray data on M51, and look for more cyclotron evidence around other ULXs.
“The discovery that these very bright objects, long thought to be black holes with masses up to 1,000 times that of the sun, are powered by much less massive neutron stars, was a huge scientific surprise,” says Fiona Harrison, the principal investigator of the NuSTAR mission. “Now we might actually be getting firm physical clues as to how these small objects can be so mighty.”
Unfortunately, there aren’t that many ULXs to go around, but researchers are working hard on solving these issues. It’s a tough riddle, but it’s certainly one that’s worth cracking.
“Since there are only a few neutron stars known that shine as ULXs, we still don’t know for sure what makes them different. We are working on figuring it out though!” Murray concluded.
The study, “Magnetic field strength of a neutron-star-powered ultraluminous X-ray source,” has been published in Nature Astronomy.
It was, by far, the most spectacular discovery of 2017. Gravitational waves not only confirmed a theory proposed by Albert Einstein 100 years ago but also opened up a whole new field of observational science. But they’ve done even more: they’ve shown us how gold was formed.
Artistic depiction of spinning / colliding neutron stars. Credits: Los Alamos National Laboratory.
After astronomers observed gravitational waves coming from the collision of two black holes, they’ve now observed the same phenomenon from a different collision: between neutron stars. Neutron stars are the collapsed cores of large stars between 10 and 29 solar masses. After a massive supernova explosion which ejects most of the star’s material, the gravitational collapse compresses the core to incredible densities. Neutron stars are the smallest stars (often measuring only kilometers across), but they’re also the densest. Most models suggest that they comprise almost exclusively of neutrons — hence the name.
For the first time, scientists have observed a collision between two neutron stars. Some 130 light years away, the two stars began an unstoppable dance, drawing closer and closer to each other, until they were spinning around each other more than 500 times per second, distorting space and time as they did so.
The ripples they created spread through the Universe, some of them reaching a planet we call Earth. There, scientists all over the world recorded the observation, realizing its massive importance. Andrew Levan, Professor in the Astronomy & Astrophysics group at the University of Warwick, commented:
“Once we saw the data, we realised we had caught a new kind of astrophysical object. This ushers in the era of multi-messenger astronomy, it is like being able to see and hear for the first time.”
Not only did astronomers record the gravitational waves, but they also used this event to answer several questions. Dr. Samantha Oates, also from the University of Warwick added:
“This discovery has answered three questions that astronomers have been puzzling for decades: what happens when neutron stars merge? What causes the short duration gamma-ray bursts? Where are the heavy elements, like gold, made? In the space of about a week, all three of these mysteries were solved.”
Gold, like most heavier elements, is formed through a process of stellar fusion. In the earlier stages of the universe, only lighter elements like hydrogen and helium existed (in significant quantities, at least). So where did all the others come from?
Well, the early stars burned more and more mass, fusing existing atoms and creating new ones. Going higher and higher on the periodic table, they ultimately reached heavier metals like gold and iron. In a previous article, ZME’s Tibi Puiu explains:
“Finally, as they burnt silicon to make iron, they exploded as a supernova, and for a few short moments, each star would release as much energy as all the regular stars in that galaxy put together. In that cataclysmic explosion, for the first time, atoms of gold were manufactured — and then hurled out into the Universe, along with the other debris from that explosion.”
Scientists had a pretty good idea that this is how gold originated, but this is the first time we’ve seen it live. The neutron stars’ collision created as much gold as the mass of the Earth, and also created heavier elements such as platinum and uranium, pumping them into space.
Dr. Joe Lyman, who was watching the collision at the European Southern Observatory, was the first to alert the community of these findings, emphasizing the importance of having direct confirmation of previous theories.
“The exquisite observations obtained in a few days showed we were observing a kilonova, an object whose light is powered by extreme nuclear reactions. This tells us that the heavy elements, like the gold or platinum in jewellery are the cinders, forged in the billion degree remnants of a merging neutron star.”
I’ve never been a big fan of gold, but knowing how it’s formed somehow makes it much more beautiful. It somehow makes everything much more beautiful.
Two merging neutron stars were detected on Aug. 17 in the galaxy NGC 4993m about 130 million light-years from Earth. Credit: NASA.
In a galaxy far, far away, some 130 million years ago, two neutron stars smashed into each other in an event called a ‘kilonova’ event, which astronomers have just witnessed for the first time. The collision sent out a burst of gamma rays and ripples through space-time known as gravitational waves. On August 17, both signals, which travel at the same speed of light, reached Earth, where they were picked up by the LIGO and Virgo detectors in the US and Italy, respectively. This was the first time signals originating from the same source were detected with both traditional telescopes that detect light, and gravitational wave detectors that sense wrinkles in the fabric of space-time.
A milestone in astronomy
The existence of gravitational waves, which were first predicted by Einstein’s Theory of General Relativity about a hundred years ago, was confirmed only last year. The event was recorded by the Laser Interferometer Gravitational-Wave Observatory (LIGO), whose founders were awarded this year’s Nobel Prize in Physics.
Gravity waves are essentially ripples in the fabric of spacetime that are generated by interactions between very massive accelerating cosmic objects, such as neutron stars or black holes. Physicists liken gravity waves to the waves generated when a stone is thrown into a pond.
LIGO was founded in 1992, so it took them 25 years to prove their existence. That’s because detecting a gravity wave is no easy feat. To spot gravitational waves directly for the first time, scientists had to measure a distance change 1,000 times smaller than the width of a proton using interferometers, which are essential mirrors placed 4 kilometers apart.
In the case of the September 14, 2015 observation which was announced on February 11, 2016, scientists observed gravitational waves produced by the collision of two black holes. This week’s announcement marks not one but a number of unprecedented observations in science. This was the first time astronomers witnessed a new type of nova called a kilonova, which is a large explosion following the merger of two neutron stars. A neutron star is the collapsed core of a large star — they’re the smallest and, at the same time, densest stars we know of. Kilonovas are 1,000 times brighter than a typical nova, which is already intense. Their existence was purely theoretical until this summer.
The biggest hype around this week’s announcement is that both light and gravitational waves were observed from the same source. At 8:41 a.m. Eastern time on August 17, a gravitational wave hit the Virgo detector in Italy and, 22 milliseconds later, set off the LIGO detector. Later, over several days, the source was detected from its light emissions at many different wavelengths, ranging from gamma-rays through to radio waves.
The black dot on the right shows where the kilonova signal originated. The left image shows the same patch of the sky in an image taken by the Hubble telescope in April before the two neutron stars collided. Credit: Swope Supernova Survey, UC Santa Cruz.
Within 24 hours of the initial readings, telescopes all over the world were directed towards the same patch of the sky. Astronomers eventually managed to find the source around a galaxy called NGC 4993, located 130 million light-years away. The event was named Swope Supernova Survey 2017a (SSS17a), after the telescope which first detected it.
At this point, it’s not clear what was left in the wake of the kilonova event. It could be that the two stars merged into a single neutron star or if the two bodies collapsed into a black hole, which can’t be detected directly.
This week’s discovery could revolutionize astronomy, since measuring both optical and gravitational signals from the same source could vastly improve how scientists measure the expansion of the universe. Edwin Hubble first realized in 1929 that the further away you look, the faster galaxies recede from us. By measuring the distance and velocity of a large number of stars, it’s possible to infer the age of the universe. Being able to sense gravitational waves and light from the same source at the same time will enable scientists to keep the error bar low for this estimate. As more and more gravitational waves are detected, scientists hope that within 10 years they’ll be able to determine the age of the universe from these sorts of signals alone, which they can then compare to traditional methods to spot inconsistencies.
All in all, this was an amazing week in science, with more than a dozen published papers about various aspects of SSS17a. We’ve likely only seen a glimpse of what gravity waves can teach us.
Heavier chemical elements could be the love child of two very spectacular and exotic lovers — neutron stars and tiny black holes.
“Papa?” Image via Digitaltrends.
We are, as Carl Sagan once put it, “made of star stuff.” Considering that what we call a star is actually a ginormous reactor mashing hydrogen and helium atoms into more complex elements, such as carbon, oxygen, or iron, that’s pretty true. But we needn’t look very hard around us for elements that outshine our particularly starry heritage. R-process elements (which are much heavier than iron — such as gold or uranium) could be sired by nature’s two most extreme creations.
So let’s take a step back and look at how elements form. The lightest, simplest atom, hydrogen, was created during of the Big Bang, with some helium and traces of lithium and beryllium peppered in. This mix started to clump together in areas of higher density (accrete), which eventually led to the formation of the first stars. Stars that formed more complex elements. But there is a caveat. A living star simply isn’t powerful enough to fuse stuff past iron. Even supermassive stars, the biggest out there, can’t do it.
Think of a star as an explosion so massive, its sheer weight and gravitational pull causes it to fall back on itself. So a star can only exist while there’s a balance between two forces — the energy of fusion reactions trying to blast it apart, and gravity straining to keep it together. This works quite well for our granddaddy’os up to the point where they build up a respectable silicon core.
Because, as aging stars everywhere find out, fusing silicon into iron doesn’t return on investment. Even in the ultra-hot, uber-dense conditions of a star’s core, making atoms merge takes a lot of energy — needed to overcome protons’ (positively charged particles) tendency to push other positively charged particles away. However, once you do make them merge, protons and neutrons get along just great thanks to the nuclear force, which makes them stick together.
The simpler the atom, the stronger this nuclear force. So when you go from hydrogen (1 proton) to helium (2 protons), and then on to lithium (3 protons) it gets progressively weaker — it has ‘less power’ so to speak. At the same time, all that leftover power needs to go somewhere and it does so by degrading into the heat and light of stars. But there is a turning point where you end up needing to pump more energy into the atom to make it fuse than you get from its final nuclear force.
The flip-side is that this turning point works both ways — that’s why fusion reactors work with hydrogen but fission reactors work with uranium. You can extract the extra energy by lowering the nuclear force of simple elements (hydrogen), or you can get it by splitting heavier atoms (uranium) and cashing back on the energy it took to fuse them together. But that’s a story for another time.
What matters right now is that this turning point is iron.
Ms and Mr Dense
“Maman?! Image credits Kevin Gill / Flickr.
Up to now, supernovas and binary star mergers were believed to be the only environments that could supply the conditions needed for higher fusion. But now, a team of three theoretical astrophysicists at UCLA — George Fuller, Alex Kusenko and Volodymyr Takhistov — offer another event that could produce these elements: the merger between a tiny black hole and a neutron star.
“A different kind of furnace was needed to forge gold, platinum, uranium and most other elements heavier than iron,” Fuller, a theoretical astrophysicist and professor of physics who directs UC San Diego’s Center for Astrophysics and Space Sciences and first author of the paper, explained in a statement.
“These elements most likely formed in an environment rich with neutrons.”
Neutron stars are immensely dense. They’re what’s left in the wake of stellar collapses and supernovae, a kernel of ultra-packed matter. A ‘normal’ atom has a nucleus, an electron shell, and a lot of empty space between the two. Neutron stars are like a huge atomic nucleus, made of back-to-back neutrons held together by gravity. To get an idea of what “immensely dense” means, it’s estimated that a spoonful of the stuff neutron stars’ surfaces are made of weighs about three billion tons.
The other half of this lovely couple is even denser — a tiny black hole, weighing between 10-14 and 10-8 solar masses. Unlike neutron stars, we’re not really sure that they really exist. But a lot of researchers (including Stephen Hawking) do believe they’re out there, a byproduct of the Big Bang, and could make up part of the dark matter — which has been proven to exist. If these micro black holes follow the distribution of dark matter in space, they’ll often co-exist with neutron stars. And this, the team argues, sets the stage for heavier elements to form.
Their calculations show that if a neutron star captures such a black hole and get devoured from the inside out by it, some of the dense neutron star matter can get thrown out into space by the ferocity of the event. Even a tiny bit of this matter is enough to seed the formation of a huge quantity of heavy elements, since it’s so dense.
“As the neutron stars are devoured,” Fuller explains, “they spin up and eject cold neutron matter, which decompresses, heats up and make these elements.”
“In the last milliseconds of the neutron star’s demise, the amount of ejected neutron-rich material is sufficient to explain the observed abundances of heavy elements.”
The team’s theory is especially intriguing since it also helps explain a few other unanswered questions about the universe. For example, it explains why there aren’t that many neutron stars in the galactic core, where there are a lot of black holes to hunt them down. Even more, the team says that the ejection of nuclear matter from tiny black holes chowing on neutron stars would explain three mysterious astronomical phenomena.
“They are a distinctive display of infrared light [‘kilonovas’], a radio emission that may explain the mysterious Fast Radio Bursts from unknown sources deep in the cosmos, and the positrons detected in the galactic center by X-ray observations,” Fuller concludes.
“Each of these represent long-standing mysteries. It is indeed surprising that the solutions of these seemingly unrelated phenomena may be connected with the violent end of neutron stars at the hands of tiny black holes.”
The paper “Primordial Black Holes and r-Process Nucleosynthesis” has been published in the preprint archive arXiv.
Researchers have found an intriguing resemblance between the human cells and neutron stars, some of the the smallest and densest stars known to exist.
Similar shapes — structures consisting of stacked sheets connected by helical ramps — have been found in cell cytoplasm (left) and neutron stars (right). Credit: University of California – Santa Barbara
When I was a kid and I learned about cells and planets, I had a strange idea: what if our planets are just cells inside a gargantuan organism, which itself lives on a planet which itself is a cell… and so on. Well, we’re still a while away from confirming my childhood, but cells and stars might have more in common than you’d think — at least some stars.
In 2014, UC Santa Barbara soft condensed-matter physicist Greg Huber and colleagues explored the geometry of a cellular organelle called the endoplasmic reticulum (ER). They found a distinctive shape, something like a multi-story parking garage. They dubbed them Terasaki ramps after their discoverer, Mark Terasaki, a cell biologist at the University of Connecticut. They found that this shape was virtually unique, reserved for thes specific organelles inside the human body — or so they thought. At one point, they stumbled upon the work of nuclear physicist Charles Horowitz at Indiana University, who was studying neutron stars. Using computer models, he concluded that deep inside neutron stars, similar shapes emerged. Huber was shocked.
“I called Chuck and asked if he was aware that we had seen these structures in cells and had come up with a model for them,” said Huber, the deputy director of UCSB’s Kavli Institute for Theoretical Physics (KITP). “It was news to him, so I realized then that there could be some fruitful interaction.”
Crossing an interdisciplinary border is not easy, especially when it comes to two fields which are so different from one another. But, as it usually happens with these collaborations, the results were outstanding. Astrophysicists have their own terminology for the class of shapes they see in their high-performance computer simulations of neutron stars: nuclear pasta. The surprisingly suitable name has subcategories such as tubes (spaghetti) and parallel sheets (lasagna) connected by helical shapes that resemble Terasaki ramps.
“They see a variety of shapes that we see in the cell,” Huber explained. “We see a tubular network; we see parallel sheets. We see sheets connected to each other through topological defects we call Terasaki ramps. So the parallels are pretty deep.”
However, once you start to look deep enough, differences also start emerging. The relevant physical parameters (temperature and pressure for example) are widely different at cellular and stellar scales.
“For neutron stars, the strong nuclear force and the electromagnetic force create what is fundamentally a quantum-mechanical problem,” Huber explained. “In the interior of cells, the forces that hold together membranes are fundamentally entropic and have to do with the minimization of the overall free energy of the system. At first glance, these couldn’t be more different.”
Still, the similarities are riveting for both biologists and astrophysicists. Is there some intrinsic phenomenon which shapes both things this way, some way of preserving energy or distributing matter, or is it all a grand, cosmic coincidence? Horowitz believes they’re on to something here.
“Seeing very similar shapes in such strikingly different systems suggests that the energy of a system may depend on its shape in a simple and universal way,” he said.
Huber noted that these similarities are still rather mysterious.
“Our paper is not the end of something,” he said. “It’s really the beginning of looking at these two models.”
Two mysterious objects which erupted into dramatic X-ray bursts have been detected, and astronomers are hard at work trying to understand just what they are.
Galaxy NGC 5128, with the flaring object highlighted in the square. Image credits NASA / J.Irwin et al. 2016
University of Alabama astronomer Jimmy Irwin set out to look for unusual X-ray activity following the detection of an extremely bright flaring near the NGC 4697 galaxy. The flaring took place in 2005, but nobody had any idea what caused it. So Irwin and his team set to work on finding similar phenomena by shifting through archival data collected by NASA’s Chandra Observatory recording 70 different galaxies. The team found two X-ray sources in two different galaxies that might be the same thing as the mysterious NGC source.
At their peak emissions, these objects qualify as ultraluminous X-ray sources (ULX). However, their flaring behavior doesn’t resemble anything we’ve seen up to now, leaving astronomers quite baffled.
“We’ve never seen anything like this,” says astronomer Jimmy Irwin from the University of Alabama. “Astronomers have seen many different objects that flare up, but these may be examples of an entirely new phenomenon.”
The first object was found near NGC 4636, roughly 47 million light-years away from us, and flared in February of 2003. The second one, which was captured five times between 2007 and 2014, is found near galaxy NGC 5128, only 14 million light-years from Earth.
While that could make it sound that the flares take place only rarely, it may not necessarily be the case. Since Chandra has had a limited amount of time to look at each galaxy, these events could be taking place much more frequently, and we’d have no way of knowing about them. They could go off every day, and we’d have no idea.
“These flares are extraordinary,” says co-author Peter Maksym from the Harvard-Smithsonian Centre for Astrophysics. “For a brief period, one of the sources became one of the brightest ULX to ever be seen in an elliptical galaxy.”
The most similar activity to these flarings come from magnetars, young neutron stars with hugely powerful magnetic fields. When these “pop”, however, the X-rays decline in just a few seconds after the burst. These mysterious sources build-up more slowly, taking about a minute to peak, then taking about an hour to decline. From what we know to date, the phenomena seems to originate from normal binary systems, which are composed of a black hole or neutron star accompanied by a regular star just like our Sun. Whatever their source may be, the bursts don’t seem to disrupt the systems in which the sources are located.
So while we don’t know for sure what causes these bursts, astronomers have advanced a few theories. It’s possible that the X-rays are generated by matter being sucked from the companion star into the black hole or neutron star. Whatever the case may be, scientists are now eager to get to the bottom of the truth — especially since the NGC 4697 outbursts don’t seem to have been a fluke.
“Now that we’ve discovered these flaring objects, observational astronomers and theorists alike are going to be working hard to figure out what’s happening,” says Gregory Sivakoff from the University of Alberta.
The full paper titled “Ultraluminous X-ray bursts in two ultracompact companions to nearby elliptical galaxies” was published in the journal Nature.
NASA released the breathtaking image you see below, announcing that it is basically X-ray light echoes reflecting off clouds of dust. But this image does more than thrill us amateur stargazers – it helps astronomers figure out how far away the double star system Circinus X-1 is from Earth.
A light echo in X-rays detected by NASA’s Chandra X-ray Observatory has provided a rare opportunity to precisely measure the distance to an object on the other side of the Milky Way galaxy. The rings exceed the field-of-view of Chandra’s detectors, resulting in a partial image of X-ray data. Credits: NASA/CXC/U. Wisconsin/S. Heinz
“It’s really hard to get accurate distance measurements in astronomy and we only have a handful of methods,” said Sebastian Heinz of the University of Wisconsin in Madison, who led the study. “But just as bats use sonar to triangulate their location, we can use the X-rays from Circinus X-1 to figure out exactly where it is.”
Circinus X-1 is an X-ray binary star system that includes a neutron star, a type of stellar remnant that can result from the gravitational collapse of a massive star after a supernova. Neutron stars are the densest and smallest stars known to exist in the universe; with a radius of only about 12–13 km (7 mi), they can have a mass of about two times that of the Sun. Observation of Circinus X-1 in July 2007 revealed the presence of X-ray jets normally found in black hole systems, the first neutron star ever observed that displays this similarity to black holes.
“Circinus X-1 acts in some ways like a neutron star and in some like a black hole,” said co-author Catherine Braiding, also of the University of New South Wales. “It’s extremely unusual to find an object that has such a blend of these properties.”
In 2013, the Circinus system created a burst of X-rays; the X-rays bounced off clouds of interstellar dust, resulting in rings of X-ray light which were ultimately picked up by the Chandra X-Ray observatory. The results are as beautiful as they are useful for astronomers.
“We like to call this system the “Lord of the Rings,” but this one has nothing to do with Sauron,” says study co-author Michael Burton of the University of New South Wales in Australia. “The beautiful match between the Chandra X-ray rings and the Mopra radio images of the different clouds is really a first in astronomy.”
By comparing the Chandra data to prior images of dust clouds detected by the Mopra radio telescope in Australia, astronomers learned that each ring was actually the result of X-Ray reflections of a different dust cloud. Knowing that X-rays travel at the speed of light, this lets them know what the distance to different clouds is, and the X-ray echo then lets them determine the relative position of Circinus X-1 to the clouds. By analyzing the rings and the combined radio data and using simple geometry, researchers managed to accurately determine the distance of Circinus X-1 from Earth. These results have been published in The Astrophysical Journal and are available online.
The system is also interesting from another point of view: astronomers believe it is the youngest X-ray binary yet discovered, starting emitting X-rays only 2,500 years ago.
Scientists have observed a massive burst of radio waves, helping them narrow down the potential sources of these huge bursts of energy. These events, also called blitzars, last about a millisecond but give off as much energy as the sun does in a million years.
Image via The Register.
These are quite possibly the most interesting and shocking sources of energy in the Universe. It’s not clear how they form, and the best theory is that blitzars start when a spinning neutron star with a big mass starts to collapse. The necessary condition is that the star is spinning very fast. Over a few million years, the pulsar’s strong magnetic field radiates energy away and slows its spin. Eventually the weakening centrifugal force is no longer able to stop the pulsar from its transformation into a black hole. At this moment of blitzar formation, part of the pulsar’s magnetic field outside the black hole is suddenly cut off from its vanished source – and this is where the burst starts.
A total of nine blitzars have been reported since the first was discovered in 2007, but none of them were captured “live” – all of them were found by looking through older data. Now, astronomers have finally surprised such an event in the act using the Parkes Telescope.
“This is a major breakthrough,” says Duncan Lorimer of West Virginia University in Morgantown, who was part of the team that discovered the first fast radio burst.
Within only a few hours, other telescopes also tuned in to see the blitzar, but none of them observed any afterglow – which is a neat finding in itself, Emily Petroff of Swinburne University in Melbourne, Australia said. This observation also revealed a new, interesting property – the waves appear to be circularly polarised rather than linearly polarised. This means that they don’t vibrate in a single plane, but in two.
“It’s something nobody has ever measured before,” Petroff says. But it’s hard to know how to interpret it, she says.
So far, while this is very exciting data, scientists are still not clear what conclusions to draw. Keith Bannister from Australia’s national science agency in Sydney said:
“Nobody knows what to make of it,” he says. “All the ideas are very exotic so ruling them out is all you can do at the moment.”
A striking artifact discovered in Panama, dated 700-1000 CE. “Winged Pendant, Gran Coclé.” Image credits: Gilcrease Museum
Revered for its aesthetic and metallurgical properties for thousands of years, gold is still one of the most sought after precious metals. There’s no question about it — for better or for worse, gold has played a unique role for humanity. Today, we’ll explore the fascinating science behind the origin of gold atoms and see how the prized element got to where it is today, here on Earth.
Why Gold is important
From Copper Age Israeli hills to the Bulgarian Varna Necropolis in the 4th millennium, from the Egyptian pharaohs to the Spanish conquistadors, the allure of gold – its powerful effect on us – has been consistent and unmistakable. In fact, the Egyptians called gold “the breath of God”. And it’s not just the ancients that held gold in high esteem.
To display his imperial glory, Napoleon gilded Paris in gold, while even more recently Hitler sought to control all of Europe’s gold as support for his “1000-year Reich.” What myths made gold such a prized commodity and what factual properties still support it as a precious metal to this very day?
Gold nuggets. Credit: Sick Chirpse
First and foremost, what makes a precious metal is its rarity. Rarer than silver or copper, two other metals mined since antiquity, its value was proportionately larger. Second, gold has fantastic properties. It does not tarnish, it’s very easy to work, can be drawn into wire, hammered into thin sheets, it alloys with many other metals, can be melted and cast into highly detailed shapes, has a wonderful color and a brilliant luster. All of these properties could be harnessed since ancient times, like today, just by heating gold nuggets at high temperatures and using simple tools like hammers or molds.
In short, gold is very memorable, so it shouldn’t come as a surprise that its main use is in jewelry.
Since time immemorial the noble metal’s resplendent luster allows it to be designed into the world’s most coveted and exquisite jewelry — fit for queens or kings. Today, most of the gold that is newly mined or recycled is used in the manufacture of jewelry. About 78% of the gold that’s available, as opposed to stored, each year is used for this purpose.
Because gold is highly valued and in very limited supply it has long been used as a medium of exchange or money. The first known use of gold in transactions dates back over 6000 years.
Early transactions were done using pieces of gold or pieces of silver. The rarity, usefulness, and desirability of gold make it a substance of long-term value.
The first gold coins were minted under the order of King Croesus of Lydia (a region of present-day Turkey) in about 560 BC. Gold coins were commonly used in transactions up through the early 1900s when paper currency became a more common form of exchange. The United States once used a “gold standard” and maintained a stockpile of gold to back every dollar in circulation. Under this gold standard, any person could present paper currency to the government and demand in exchange an equal value of gold.
Possibly gold’s greatest use to mankind didn’t become evident until early last century when its fantastic electrical conductivity properties came to light. Solid state electronic devices use very low voltages and currents which are easily interrupted by corrosion or tarnish at the contact points. Gold is the highly efficient conductor that can carry these tiny currents and remain free of corrosion, which is why electronics made using gold are highly reliable. A small amount of gold is used in almost every sophisticated electronic device. This includes cell phones, calculators, personal digital assistants, global positioning system units and other small electronic devices.
Facts about gold
The atomic number of gold, which means there are 79 protons in the nucleus of every atom of gold.
One ounce of gold can be stretched to a length of 50 miles; the resulting wire would be just five microns wide.
One ounce of pure gold could be hammered into a single sheet of nine square meters.
Over 90 percent of the world’s gold has been mined since the California Gold Rush.
Julius Caesar gave two hundred gold coins to each of his soldiers from the spoils of war in defeating Gaul.
Fort Knox holds 4,600 tonnes of gold.
And the US Federal Reserve holds 6,200.
The temperature of the human body is 37 degrees centigrade. Because of gold’s unique conductivity, gold jewelry rapidly matches your body’s heat, becoming part of you.
In 95 BC, Chinese Emperor Hsiao Wu I minted gold commemorative piece to celebrate the sighting of a unicorn.
Gold is edible. Some Asian countries put gold in fruit, jelly snacks, coffee, and tea. Since at least the 1500s, Europeans have been putting gold leaf in bottles of liquor, such as Danziger Goldwasser and Goldschlager. Some Native American tribes believed consuming gold could allow humans to levitate.
The chemical symbol for gold is Au, from the Latin word aurum meaning “shining dawn” and from Aurora, the Roman goddess of the dawn. In 50 B.C., Romans began issuing gold coins called the Aureus and the smaller solidus.
Between A.D. 307 and 324, the worth of one pound of gold in Rome rose from 100,000 denarii (a Roman coin) to 300,000 denarii. By the middle of the fourth century, a pound of gold was worth 2,120,000,000 denarii—an early example of runaway inflation, which was partly responsible for the collapse of the Roman Empire.
Where did gold come from?
We’re all made out of “star stuff”, and gold is no exception. Image: NASA
The ancient Aztecs believed gold was in fact “the sweat of the sun”. Though this isn’t true, the phrase is a highly accurate metaphor.
Gold, like most heavy metals, are forged inside stars through a process called nuclear fusion. In the beginning, following the Big Bang, only two elements were formed: hydrogen and helium. A few hundred million years after the Big Bang, the first stars were blazing away with their nuclear fires. These nuclear fires forced lighter elements together to make slightly heavier elements, and these nuclear reactions released a huge amount of energy.
Gradually, these early stars began making elements such as carbon, nitrogen, oxygen — working their way up through the periodic table towards iron. But there was still no gold in the Universe. Once these earlier stars ran out of light elements to burn, they kicked in on the heavier ones.
Finally, as they burnt silicon to make iron, they exploded as a supernova, and for a few short moments, each star would release as much energy as all the regular stars in that galaxy put together.In that cataclysmic explosion, for the first time, atoms of gold were manufactured — and then hurled out into the Universe, along with the other debris from that explosion.
On Earth, gold finally reached us some 200 million years after the formation of the planet when meteorites packed with gold and other metals bombarded its surface. During the formation of Earth, molten iron sank to its centre to make the core. This took with it the vast majority of the planet’s precious metals — such as gold and platinum. In fact, there are enough precious metals in the core to cover the entire surface of Earth with a four-metre thick layer.
Another theory concerning the formation of gold that’s been gaining a lot of traction today is that the element can form following the collision of two neutron stars. Following the collapse of a massive star – at least eight times more massive than the Sun – what remains is a extremely dense core. They have masses comparable to a star, but that mass is compressed into an object roughly 10 kilometers in diameter, or the size of a city on Earth. Another way to look at this would be to imagine cramming Mount Everest into your morning cup of coffee to achieve the same density as a neutron star. At these huge densities, the fabric and space and time is stretched by exotic physics.
Two neutron stars in mutual orbit can collide when gravitational waves carry enough energy away from the system to destabilize the orbit. When this happens, a type of gamma-ray burst can occur – these are the most powerful explosions in the universe. The intense energy would be enough to create gold and other heavy elements, according to a paper published in the Astrophysical Journal Letters.
Check out the video below for a brief explanation of the neutron star gold formation hypothesis.
Physicist Kip Thorne and astronomer Anna Zytkow proposed a new theoretical class of stars back in 1975, but it was only very recently that such an example of hybrid star was identified in the universe. The Thorne-Zytkow Objects (TZOs) are a combination between red supergiant and neutron stars, superficially looking like normal red supergiants, for example Betelgeuse in the Orion constellation. The main difference consists in the chemical signatures resulting from particular activity in their stellar interiors.
The formation of the TZOs is believed to happen when the two massive types of stars interact – the red supergiant and the neutron star shaped during the explosion of a supernova – in a close binary system. The exact interaction is still undetermined, but the most popular theory holds that during the evolutionary interaction of the two bodies the neutron star is swallowed by its substantially more massive interaction partner, the red supergiant. It is also believed that the neutron star spirals into the core of the red supergiant.
As it is scientifically agreed upon the fact that the red supergiants classically derive their energy from nuclear fusion in their cores, the TZOs are powered by the odd activity of the absorbed neutron stars in their cores. The discovery provides evidence of a new model of stellar interiors, which wasn’t detected by astronomers until the new finding. The declaration of project leader Emily Levesque of the University of Colorado Colder (who was awarded the American Astronomical Society’s Annie Jump Cannon Award this year) is that:
‘Studying these objects is exciting because it represents a completely new model of how stellar interiors can work. In these interiors we also have a new way of producing heavy elements in our universe. You’ve heard that everything is mae of ‘stellar stuff’ – inside these stars we might now havea new way to make some of it.’
The discovery was made on Las Campanas, in Chile, with a 6.5-meter Magellan Clay telescope. Astronomers investigated the spectrum of light that was emitted from the apparent red supergiants, which allowed them to determine what elements made up the stars. The first time when the spectrum of a particular star, HV 2112 in the Small Magellanic Cloud, was displayed, even the observers were surprised by its unusual features.
At a closer look, Levesque and her colleagues found that the spectrum contained excess rubidium, lithium, and molybdenum. Previous scientific research showed that each of these elements could be created through normal stellar processes. But finding so much of them together at the temperatures that are typical to the red supergiants represents a feature unique for TZOs.
‘Since Kip Thorne and I proposed our models of stars with neutron cores, people were not able to disprove our work. If theory is sound, experimental confirmation shows up sooner or later. So it was a matter of identification of a promising group of stars, getting telescope time and proceeding with the object’, declared astronomer Anna Zytkow.
The team does take prevention measures and points out the chemical characteristics not matching the theoretical models proposed by the two researchers. Phillip Massey, co-author of the study, underlines that:
‘We could, of course, be wrong. There are some minor inconsitencies between some of the details of what we found and what theory predicts. But the theoretical predictions are quite old, and there have been a lot of improvements in the theory since then. Hopefully our discovery will spur additional work on the theoretical side now’.
While there is some level of uncertainty, the detection of a TZO provides the first direct, observable evidence for a completely new model of stellar interiors, which implies never-before-seen nucleosynthesis processes.
The overwhelming part of the universe is still a mystery to astronomers – and most of what we know is a result of deduction and analysis. So it should be no big surprise that when radio waves from 11 billion light years was received, they couldn’t pinpoint its origin.
Their brightness and distance suggest that they originated when the Universe was half its current age, and judging by the very high energy levels, astronomers believe they originated in an extreme, relativistic object – such as a neutron star, or a black hole. Lead author Dan Thornton, a PhD student at Australia’s Commonwealth Scientific and Industrial Research Organization, explained that only such an extreme event could be the cause.
But, as always, with such little understood phenomena, the good news is that it will help improve our understanding of the Universe in which we live in. Astrophysicists still aren’t sure exactly what happens in the space between galaxies, and this will likely help them solve this mystery.
In a never-before seen feat, astronomers using NASA’s Swift X-ray Telescope have observed a spinning neutron star suddenly slowing down, something which can provide valuable clues to understanding these mysterious objects.
Neutron stars are the cores of former high-mass stars, the remains of supernovae after the blow-up. As the core of the massive star is compressed during a supernova, and collapses into a neutron star, it retains most of its angular momentum. However, since it only has a small fraction of its original mass and radius, a neutron star is formed with very high rotation speed, and then gradually slows down; we’re talking about massive speeds, some neutron stars have been known to have rotation periods from about 1.4 ms to 30 seconds.
They emit a beam of radiation as it spins, and this can make it look like a blinking pulsar to us, which has a very precise period. By analyzing that blink, astrophysicists can analyze how the neutron star is rotating.
However, some neutron stars, like the one in case, have a much stronger magnetic field than most, and they spin slower.
A surprising observation
This neutron star, 1E 2259+586, is located about 10,000 light-years away toward the constellation Cassiopeia. It is one of about two dozen observed neutron stars called magnetars. Last year, on April 28, , data showed the spin rate had decreased abruptly, by 2.2 millionths of a second, and the magnetar was spinning down at a faster rate.
The opposite has been observed on several occasions and can be accounted for, but this case is unique so far.
“Astronomers have witnessed hundreds of events, called glitches, associated with sudden increases in the spin of neutron stars, but this sudden spin-down caught us off guard,” said Victoria Kaspi, a professor of physics at McGill University in Montreal. She leads a team that uses Swift to monitor magnetars routinely.
This “anti-glitch” has pretty much baffled astronomers, who are trying to find a valid explanation.
“It affected the magnetar in exactly the opposite manner of every other clearly identified glitch seen in neutron stars.”, said co-author Neil Gehrels, principal investigator of the Swift mission at NASA’s Goddard Space Flight Center in Greenbelt, Md.
This could also have significant implications for understanding the extreme environment of the neutron stars. Since no lab on Earth can simulate them, we have to rely on observations conducted in outer space. A report on the findings appears today,in the May 30 edition of the journal Nature.
This adds yet another mystery to the already long list regarding neutron stars. Current theories suggest that a neutron star has a crust made up of electrons and ions, while the interior is made up of very bizarre… stuff – a neutron superfluid (a state of matter that has 0 viscosity and 0 friction) and a surface that accelerates streams of high-energy particles through the star’s intense magnetic field.
This theory can explain the “glitch”, but not the “anti-glitch” (as far as we can tell so far) – the particles which are ejected from the star drain the energy, but as the crust slows down as a result, the interior (which remember, is frictionless) resists being slowed. The crust fractures under the strain. When this happens, a glitch occurs. There is an X-ray outburst and the star gets a speedup kick from the faster-spinning interior. But for the opposite, there’s no explanation with what we know now.
“What is really remarkable about this event is the combination of the magnetar’s abrupt slowdown, the X-ray outburst, and the fact we now observe the star spinning down at a faster rate than before,” said lead author Robert Archibald, a graduate student at McGill.