Researchers at the University of Warwick report finding a white dwarf barreling through space at great speed. The source, they say, was likey a “partial supernova” which ejected the core of the star.
Sitting at about 40% the mass of our sun, white dwarf SDSS J1240+6710 is much smaller, and denser. Data from the Hubble telescope allowed researchers to confirm that its atmosphere is an unusual mix of gases.
A peculiar star
“There is a clear absence of what is known as the ‘iron group’ of elements, iron, nickel, chromium and manganese,” explains a statement from the University of Warwick.
“These heavier elements are normally cooked up from the lighter ones and make up the defining features of thermonuclear supernovae.”
White dwarfs are born when a star completely consumes its fuel. Most of its mass blows away to form a nebula, leaving behind a white-hot core. They usually have atmospheres consisting of hydrogen or helium, the researchers add, with traces of carbon and oxygen produced as the star grew old.
This particular one, however, was made from oxygen, neon, magnesium and silicon. Furthermore, the lack of elements in the iron group points to it undergoing a “partial supernova” before it died. Heavier elements are formed by light atoms being pushed together in stars as they explode.
Its speed — this solar remnant is travelling at around 559,234 mph — would indicate that it was thrown out in the event.
“This star is unique because it has all the key features of a white dwarf but it has this very high velocity and unusual abundances that make no sense when combined with its low mass,” says Professor Boris Gaensicke from the Department of Physics at the University of Warwick, lead author of the paper.
“It has a chemical composition which is the fingerprint of nuclear burning, a low mass and a very high velocity: all of these facts imply that it must have come from some kind of close binary system and it must have undergone thermonuclear ignition.”
The paper “SDSS J124043.01+671034.68: the partially burned remnant of a low-mass white dwarf that underwent thermonuclear ignition?” has been published in the journal Monthly Notices of the Royal Astronomical Society.
The term was first used in 2006 to describe celestial bodies that were comparable in size to Pluto. Since then it has taken on a broader usage, with the IAU (International Astronomers’ Union) currently recognizing five bodies in the Solar System as being dwarf planets — and an extra six more await a decision.
However, since its addition to the old classification system (which held that nine planets were orbiting the Sun), the term ‘dwarf planet’ has caused quite a lot of confusion (and controversy). So let’s see what it’s meant to represent and whether Pluto does actually deserve to be called as such.
A dwarf planet is “(a) in orbit around the Sun [or another star], (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, (c) has not cleared the neighborhood around its orbit, and (d) is not a satellite,” according to the IAU’s RESOLUTION B5 on the Definition of a Planet in the Solar System.
In essence, that definition says that dwarf planets are objects in stable orbit around a star that are massive enough to maintain a round shape but not massive enough to clear all other material out of their orbit, and that they don’t orbit another planet.
It’s basically these last two points that differentiate a dwarf planet from a regular one and from moons. Full-blown planets always clear their orbits, according to the current definition, but neither they nor dwarf planets can orbit another planet — only moons do that.
There are currently five dwarf planets recognized as such by the IAU in the Solar System: Pluto, Ceres, Eris, Makemake, and Haumea. There is still some debate whether Eris, Makemake, or Haumea fit the bill, however, as our observations of these bodies are still far from perfect. Other nearby contenders include Orcus, 2002 MS4, Salacia, Quaoar, 2007 OR10, and Sedna; the IAU further decided that Trans-Neptunian Objects (TNOs) with an absolute magnitude higher than +1 and a diameter of 838 km or more are to be considered dwarf planets until more data can be gathered on their nature.
On the matter of shape
The roundedness criteria is actually pretty central in how we think about planets. Roundedness in the case of stellar objects is largely the product of gravity. Planets become round (sorry, Flat Earthers) when their gravity becomes strong enough to plastically deform their surfaces and to overpower all other forces affecting them. Strong gravity is necessary to impart a rounded shape to a planet by flattening high-elevation areas and filling in low-lying ones.
It’s a pretty reliable indicator of planethood, all things considered. Asteroids or comets are small and don’t have the mass to round themselves out; their final shape is the product of outside forces acting on the body. Centrifugal forces generated by rotation, friction, impacts, or the tidal pull of other bodies are what create their irregular shapes.
Those bodies for which gravity is a significant but not dominant factor morph into spheroid (sphere-like) shapes. This is a bit of a middle-ground between the shape gravity works towards and the irregular mess promoted by outside forces.
An object with high gravity will come as close to a perfect sphere as possible, reaching ‘hydrostatic equilibrium‘. To illustrate, the Earth isn’t perfectly round — it’s an oblate spheroid. This is due to the planet’s rotation around its own axis, which generates centrifugal forces that pull on the equator, making the Earth look a bit like a sphere you pressed down on. The faster a body rotates, the more deformation it will experience around its equator. The dwarf planet Haumea, for example, is almost twice as long at its equator as it is at the poles.
Tidal forces are the gravitational pull of other planets and/or celestial bodies on an object. This helps deform it (on Earth we see this as the waxing and waning of the tide) and can tidally-lock an object in relation to another. The moon is tidally locked to Earth; no matter when you look at it, it’s always showing the same hemisphere.
The IAU’s definition uses shape instead of mass because particularities of a given celestial body, such as its chemical composition, also have a part to play in their overall shape. Mass alone isn’t a reliable indicator of a body’s overall characteristics. Water ice, for example, is much more easily deformed by gravity than a chunk of solid rock.
On the matter of its neighborhood
A celestial body’s ability to remove all smaller ones along its orbit is also known as ‘orbital dominance’. Planets have virtually complete orbital dominance through collision, capture, or other interaction with other space-born bodies they come into contact with; dwarf planets do not.
Orbital dominance once again ties into a body’s mass, which dictates its gravitational force (do keep in mind that gravitational pull is inversely proportional to the squared distance between two bodies).
An easy way to think about this factor is that planets have enough mass to ‘overpower’ all other bodies of similar size in the volume of space they transit. Dwarf planets, being smaller, need to share their space with other chunks of matter.
This is the most contentious point in the definition. For one, an argument can be made that a planet’s orbit is never fully cleared as objects come and go through space. Secondly, there’s also the question of how can we reliably say that a planet did in fact clear its orbital neighborhood; and also, for that matter, where does a planet’s neighborhood end? The IAU doesn’t put any actual figures on its definition of dwarf planets. The definition can thus be seen as more of a theoretical guideline than a hard criterion; it has drawn criticism for this fact.
“In no other branch of science am I familiar with something that absurd,” said New Horizons principal investigator Alan Stern for Space.com in 2011. “A river is a river, independent of whether there are other rivers nearby.”
“In science, we call things what they are based on their attributes, not what they’re next to.”
Stern says that Earth, Mars, Jupiter, and Neptune have not fully cleared their orbital zones either, but we still call them planets. Some 10,000 near-Earth asteroids orbit the Sun alongside our planet, he explains. Jupiter drags some 100,000 Trojan asteroids on its way through space, Stern adds. The main criticism leveled at his approach is that these planets completely control the other asteroids and bodies within their orbit via gravitational pull.
The debate is especially heated because Pluto’s status as a planet hinges on this particular point of the IAU’s definition. Pluto is gravitationally dominated by Neptune, which constrains its orbit. It also has to share its neighborhood with several objects in the Kuiper belt of similar size, effectively dooming it to a dwarf planet status under the current definition.
It’s also relevant for exoplanets. Our current equipment and techniques can’t directly determine whether a planet very far away has cleared its orbit. Here, however, the IAU has taken some steps to clarify matters: it established a separate working definition for extrasolar planets in 2001, and decided that the minimum size and mass requirements for planets in the Solar System apply to exoplanets as well.
“As new claims are made in the future, the WGESP [Working Group on Extrasolar Planets] will weigh their individual merits and circumstances and will try to fit the new objects into the WGESP definition of a “planet”, revising this definition as necessary,” the statement reads.
“This is a gradualist approach with an evolving definition, guided by the observations that will decide all in the end.”
The main current issues with the IAU’s classification system is that while it’s easy to understand, it doesn’t really withstand impact with reality on the ground. Space is a big place and it doesn’t abide by simple rules you can fit in a four-point list.
However, we’re still in a very early stage of space exploration. The exact difference between planets, dwarf planets, and moons is pretty inconsequential to our lives, even if it does rile up the spirits. As our reach into space extends, such classifications will become more important. But our ability to clearly define the multitude of shapes, sizes, and types of matter we’ll find in space will also be much better by then.
The European Space Observatory’s SPHERE instrument has spotted what may be the smallest small planet in our solar system.
The object christened Hygiea is currently considered an asteroid — but it might be classified as a dwarf planet. It’s the fourth largest body in the asteroid belt after Ceres, Vesta, and Pallas. The reclassification follows on the heels of new observations: for the first time, astronomers were able to look at Hygiea with a sufficiently-high resolution to study its surface and to determine that it is spherical (a condition necessary to be considered a planet).
Hygiea might thus officially become the smallest dwarf planet in our solar system — a title currently held by Ceres,
Small but significant
“Thanks to the unique capability of the SPHERE instrument on the VLT (Very Large Telescope), which is one of the most powerful imaging systems in the world, we could resolve Hygiea’s shape, which turns out to be nearly spherical,” says lead researcher Pierre Vernazza from the Laboratoire d’Astrophysique de Marseille in France.
“Thanks to these images, Hygiea may be reclassified as a dwarf planet, so far the smallest in the Solar System.”
Prior to this discovery, we already knew that Hygiea satisfied three of the four requirements to be considered a dwarf planet: it orbits around the Sun, it is not a moon, and it has not cleared the neighborhood around its orbit (like a proper planet would). The final requirement is for it to have enough gravitational force to pull itself into a roughly spherical shape. Thanks to new observations, we now know that Hygiea passes this criterion as well.
Based on the SPHERE data, the team estimated Hygiea’s size to be around 430 km in diameter. Ceres is closer to 950 km in diameter while Pluto, the largest dwarf planet, comes close to 2400 km.
One surprising find was that Hygiea lacks any large impact craters on its surface. The team really expected to find such a structure on its surface as Hygiea is the main member of one of the largest asteroid families (with around 7000 members) that all come from the same parent body. It was believed that Hygiea would have been left scarred by the event that led to that original body breaking apart. Although the astronomers observed Hygiea’s surface with a 95% coverage, they could only identify two relatively small craters.
“This result came as a real surprise as we were expecting the presence of a large impact basin, as is the case on Vesta,” says Vernazza.
“Neither of these two craters could have been caused by the impact that originated the Hygiea family of asteroids whose volume is comparable to that of a 100 km-sized object. They are too small,” explains study co-author Miroslav Bro of the Astronomical Institute of Charles University in Prague, Czech Republic.
Computer simulations suggest that Hygiea’s shape and the large number of members in its asteroid family were the result of a major head-on collision between the parent body and an object between 75 and 150 km in diameter around 2 billion years ago, The simulations showed that this violent impact completely shattered the parent body. Hygiea, the simulations suggest, is the product of left-over pieces that reassembled themselves into a round shape surrounded by companion asteroids.
“Such a collision between two large bodies in the asteroid belt is unique in the last 3-4 billion years,” says Pavel Ševeček, a PhD student at the Astronomical Institute of Charles University and paper co-author.
“Thanks to the VLT and the new generation adaptive-optics instrument SPHERE, we are now imaging main belt asteroids with unprecedented resolution, closing the gap between Earth-based and interplanetary mission observations,” Vernazza concludes.
The paper “A basin-free spherical shape as outcome of a giant impact on asteroid Hygiea” has been published in the journal Nature Astronomy.
Researchers report finding a new exoplanet orbiting a three-star system.
Artist’s view of planets transiting red dwarf star in TRAPPIST-1 system. Image credits Hubble ESA / Flickr.
The excitingly-named LTT 1445Ab orbits one star from a group of three red dwarves that constitute the system LTT 1445, located around 22.5 light-years away. While definitely rocky in nature, high surface temperatures on LTT 1445Ab make it completely unwelcoming for life as we know it. However, researchers are still excited for the find — its atmosphere makes it a perfect test subject to help us refine our long-distance planetary analysis techniques.
LTT 1445Ab and the three red dwarves
“If you’re standing on the surface of that planet, there are three suns in the sky, but two of them are pretty far away and small-looking,” Jennifer Winters, an astronomer at the Harvard-Smithsonian Center for Astrophysics and the paper’s first author told New Scientist.
“They’re like two red, ominous eyes in the sky.”
Stars in multiple-star systems are gravitationally locked around a mutual center of gravity, which they all orbit. LTT 1445 is home to three such stars. The new exoplanet was discovered in this system by the Transiting Exoplanet Survey Satellite (TESS), NASA’s planet-hunting space telescope. TESS was designed to spot exoplanets as they pass between Earth and their home star by detecting the slight dimming the planet causes as it blocks part of the star’s light.
Based on the amount of dimming and on the tiny, almost imperceptible, movements stars make under the effect of an orbiting planet’s gravity (in the case of LTT 1445Ab this was measured with other telescopes than TESS), researchers can estimate the size and mass of the planet. The new planet is about 1.35 times the physical size of Earth but it packs up to 8.4 times Earth’s mass, so it’s a lot denser than our home planet.
Judging by its size and mass, this is definitely a rocky planet — like Earth, Venus, or Mars — not an ice or gas giant. However, don’t break out your colonizing gear just yet. The planet is so close to its host star that it only has a 5.36 day-long orbit. At this distance, surface temperatures likely hover around 428 Kelvin (155 °C; 311 °F), the authors report.
While LTT 1445Ab won’t be a welcoming home for us anytime soon, it’s still an exciting planet for astronomers because it might have an atmosphere. Rocky planets with atmospheres that transit in front of their stars are good test subjects for the detection tools we use to spot gases such as methane and carbon dioxide on alien worlds. Such a planet won’t just dim a star’s light as it transited in front of it but, based on the atmosphere’s chemical composition, would also change the properties of the light.
By analyzing at this change, researchers can estimate the chemical make-up of an alien world’s atmosphere. Our current technology and know-how in this field can still use some tweaking, one which LTT 1445Ab can help provide. With Hubble’s successor, the James Webb Space Telescope due to be launched in 2021, astronomers are already making a list of targets they’d like it to study. LTT 1445Ab could be a perfect candidate.
Among the properties that recommend it for this role is that it transits in front of its star very often, meaning the James Webb Space Telescope can take many readings in a short span of time. The planet is also relatively close in astronomical terms, which makes it easier to take high-quality images, and its red dwarf star is just right for this kind of observation — bright enough to back-light the atmosphere, but not so bright that the planet is hard to see.
Mind you, we don’t know whether LTT 1445Ab has an atmosphere or not right now. But even if it doesn’t, or if its atmosphere contains no biosignatures, it could tell us more about what we can expect to find on rocky planets that orbit red dwarfs.
The paper “Three Red Suns in the Sky: A Transiting, Terrestrial Planet in a Triple M Dwarf System at 6.9 Parsecs” has been submitted to the The Astronomical Journal and is available on the preprint server arXiv.
Astronomers have snapped the first pictures of a planet forming.
This is the first clear image of a planet forming around the dwarf star PDS 70. Image credits ESO / Müller et al., 2018, A&A.
Researchers led by a group at the Max Plank Institute for Astronomy in Heidelberg, Germany, are spying on a baby planet. The object of their attention is a still-forming planet that orbits around PDS 70, a young dwarf star. This is the first time we’ve captured clear images of a forming planet and its travels through the dust cloud surrounding young stars.
The images were captured using the SPHERE instrument installed on Unit Telescope 3 of the European Southern Observatory (ESO’s) Very Large Telescope (VTL) array in Chile. SPHERE, the Spectro-Polarimetric High-contrast Exoplanet REsearch instrument, is one of the most powerful planet-finding tools astronomers have at their disposal today. What makes SPHERE stand out in the field of exoplanet exploration is that, unlike the majority of its contenders, it relies on direct imaging — SPHERE takes actual photographs of planets millions or billions of kilometers away.
SPHERE relies on a technique known as high-contrast imaging to produce such amazing shots. The device uses complex observation techniques and powerful data processing algorithms to tease out the faint traces of light incoming from planets around bright stars. Astronomers draw on the Earth’s rotation to help them better observe such planets — SPHERE continuously takes images of the star over a period of several hours, while keeping the instrument as stable as possible. This creates images of a certain planet taken from slightly different angles and at different points in the stellar halo, giving the impression that it’s slowly rotating or moving about. The stellar halo, meanwhile, appears immobile. The last step is to combine all the images and filter out all the parts that do not appear to move — blocking out signals that don’t originate from the planet itself.
The new planet, christened PDS 70b, stands out very clearly in the images SPHERE recorded. It appears as a bright point to the right of that blackened blob in the middle of the image. That blob is a coronagraph — a mask that researchers apply directly onto the star, lest its light blocks out everything else in the image.
Some examples of how such images from different angles helps astronomers tease out the light incoming from exoplanets. Image credits Müller et al., 2018, A&A.
PDS 70b is a gas giant with a mass several times that of Jupiter. It’s about as far from its host star as Uranus is to the Sun. Currently, PDS 70d is busy carving a path through the planet-forming material surrounding the young star, the researchers note, making it instantly stand out.
“These discs around young stars are the birthplaces of planets, but so far only a handful of observations have detected hints of baby planets in them,” explains Miriam Keppler, who lead the team behind the discovery of PDS 70’s still-forming planet. “The problem is that until now, most of these planet candidates could just have been features in the disc.”
PDS 70d is already drawing a lot of attention from astronomers. A second paper, which Keppler also co-authored, has followed-up on the initial observations with a few months of study. The data from SPHERE also allowed the team to measure the planet’s brightness over different wavelengths — based on which they estimated the properties of its atmosphere. The planet is blanketed in thick clouds, the team explained, and its surface is currently revolving around a crisp 1000°C (1832°F), which is much hotter than any planet in the Solar System.
The findings also helped researchers make heads and tails of a structure known as a transition disc. This is a ring-like protoplanetary (meaning it is involved in early planetary formation) structure. Transitional disks roughly resemble a stadium, with a clean area in the middle (from which planets drew their matter), surrounded by a ring of dust and gas. While these gaps have been known for several decades now and speculated to be produced by the interaction between forming planets and its host star’s disk, this is the first time we’ve actually seen them.
“These objects represent […] disks whose inner regions are relatively devoid of distributed matter, although the outer regions still contain substantial amounts of dust,” explains a paper published by Strom et al. in 1989.
All this data helps flesh out our understanding of the early stages of planetary evolution — which are quite complex and, up to now, “poorly-understood”, according to André Müller, leader of the second team to investigate the young planet.
“We needed to observe a planet in a young star’s disc to really understand the processes behind planet formation,” he explains.
The findings further help improve our overall knowledge of how planets form. By determining PDS 70d’s atmospheric and physical properties, astronomers now have a reliable data point from which to extrapolate — which will help improve the accuracy of our planetary formation models.
Not bad for a bunch of photographs.
The first paper, “Discovery of a planetary-mass companion within the gap of the transition disk around PDS 70” has been published in the journal Astronomy & Astrophysics.
The second paper, “Orbital and atmospheric characterization of the planet within the gap of the PDS 70 transition disk,” has also been published in the journal Astronomy & Astrophysics
Until some 17,000 years ago, we humans shared the Earth with another close relative: Homo floresiensis. Often called the ‘hobbit’ because of its dwarfish stature, scientists have long debated the origin of this species first discovered as recently as 2003 in the Liang Bua cave on the remote Indonesian island of Flores. Now, scientists who embarked on the most comprehensive analysis of H. floresiensis yet claim the debate is over. The hominid is a distant relative to modern humans and, instead, likely evolved from another branch of hominid from Africa.
Homo Floresiensis skull. Credit: Stuart Hay – ANU.
During the misty years following the discovery of the Flores hobbits, one of the most promising hypotheses explaining their origin posited that the 1.1-meter-tall creatures evolved from Homo erectus populations settled in Asia. Homo erectus is basically the first hominid that looked like a human.
Homo erectus had a long tenure. The earliest Homo erectus fossils are dated to roughly 1.8 million years ago, while the youngest fossils assigned to this species date to roughly 300 thousand years ago. The stature of Homo erectus is considered to be very similar to that of living humans having a hindlimb that’s much longer than in earlier forms. Its skulls were generally thicker and more massively built than those of H. sapiens, but all other features point to striking similarities between the two species.
Initial surveys of H. floresiensis remains suggested it was a direct descendant of H. erectus, but some critics have pointed out the evidence presented thus far is inconclusive. To get to the bottom of things Australian researchers led by Dr. Debbie Argue from the Australian National University examined 133 cranial, postcranial, mandibular, and dental remains coming from H. floresiensis but also other hominid species. No other study collected or examined these many samples before and previously scientists focused on finding the best match for the skull and lower jaw only.
A digital reconstruction of the face of H. floresiensis. Credit: ANU.
The examination showed that H. floresiensis doesn’t share that as many features with H. erectus as some believed. Instead, the hobbits seem much more similar to Homo habilis, the earliest representative of theHomo genus which lived between 1.6 million and 2.4 million years ago.
“The analyses show that on the family tree, Homo floresiensis was likely a sister species of Homo habilis. It means these two shared a common ancestor,” Dr Argue said.
“It’s possible that Homo floresiensis evolved in Africa and migrated, or the common ancestor moved from Africa then evolved into Homo floresiensis somewhere.”
Virtual endocast of H. floresiensis (left) vs H. sapiens (right). Credit: rofessor Peter Brown, University of New England.
The findings refute the idea that the hobbits evolved from Asian Homo erectus which presumably underwent island dwarfing. Instead, a counter-hypothesis which suggests the hobbits evolved from an earlier ancestor in Africa, who was most likely Homo habilis, seems more favorable.The hobbits either evolved in Africa then migrated to Asia where they eventually reached the island of Flores in Indonesia or the common ancestor migrated from Africa then evolved into H. floresiensis somewhere on route or on the famous island itself.
The biggest takeaway is that H. floresiensis was far more primitive than previously thought, though it went extinct less than 15,000 years ago.
“We can be 99 per cent sure it’s not related to Homo erectus, and nearly 100 per cent chance it isn’t a malformed Homo sapiens,” said Professor Mike Lee of Flinders University and the South Australian Museum, and co-author of the study published in the Journal of Human Evolution.
An international research team has found the largest brown dwarf we’ve ever seen, and it has ‘the purest’ composition to boot. Known as SDSS J0104+1535, the dwarf trails at the edges of the Milky Way.
An artists’ representation of a brown dwarf with polar auroras. Image credits NASA / JPL.
Brown dwarfs — they’re like stars, but without the spark of love. They’re much too big to be planets but they’re too small to ignite and sustain fusion, so they’re not (that) bright and warm and so on. Your coffee is probably warmer than some Y-class brown dwarfs, which sit on the lower end of their energy spectrum. The coldest such body we know of, a Y2 class known as WISE 0855−0714, is actually so cold (−48 to −13 degrees C / −55 to 8 degrees F) your tongue would stick to it if you could lick it.
But they can still become really massive, as an international team of researchers recently discovered: nestled among the oldest of stars in the galaxy at the halo of our Milky Way, some 750 light years away from the constellation Pisces, they have found a brown dwarf which seems to be 90 times more massive than Jupiter — making it the biggest, most massive brown dwarf we’ve ever seen.
Named SDSS J0104+1535, the body is also surprisingly homogeneous as far as chemistry is concerned. Starting from its optical and near-infrared spectrum measured using the European Southern Observatory’s Very Large Telescope, the team says that this star is “the most metal-poor and highest mass substellar object known to-date”, made up of an estimated 99.99% hydrogen and helium. This would make the 10-billion-year-old star some 250 times purer than the Sun.
Y u so cold? Image credits NASA / JPL-Caltech.
“We really didn’t expect to see brown dwarfs that are this pure,” said Dr Zeng Hua Zhang of the Institute of Astrophysics in the Canary Islands, who led the team.
“Having found one though often suggests a much larger hitherto undiscovered population — I’d be very surprised if there aren’t many more similar objects out there waiting to be found.”
From its optical and infrared spectrum, measured using the Very Large Telescope, SDSS J0104+1535 has been classified as an L-type ultra-cool subdwarf — based on a classification scheme established by Dr Zhang.
The paper “Primeval very low-mass stars and brown dwarfs – II. The most metal-poor substellar object” has been published in the journal Monthly Notices of the Royal Astronomical Society.
Scientists at the University of Warwick have discovered the first white dwarf pulsar we’ve ever seen. The super-dense body is housed in an exotic binary star system 380 light-years away from Earth.
Image credits Mark Garlick / University of Warwick.
Professors Tom Marsh and Boris Gänsicke of the University’s Astrophysics Group together with Dr David Buckley from the South African Astronomical Observatory, have made astronomical history — they have identified the first white dwarf pulsar humanity has ever seen, in the neighboring system of AR Scorpii (AR Sco). Astronomers have been on the lookout for this class of pulsar for over half a century now.
Small but lively
AR Sco is only 380 light-years away from Earth, in the Scorpius constellation. It has two stars — a very rapidly spinning former star known as a white dwarf pulsar, and an actual star known as a red dwarf — locked together in a 3.6-hour orbit.
The red dwarf isn’t very noticeable in and of itself. It weighs one-third of a Solar mass (the biggest ones reach one-half of a solar mass). It ‘burns’ hydrogen just like our Sun but at a much slower rate. So it’s not particularly hot or very bright at all. Standard red dwarf across the board.
However, its choice of companions creates some spectacular interaction which brought the scientists’ attention to the system in the first place. Its neighboring pulsar isn’t much bigger than Earth, but it’s an estimated 200,000 times denser. Like other pulsars, it’s a very lively celestial body.
What sets it apart is the way it formed. Neutron stars/pulsars are the naked cores of huge stars squashed by supernovae into pure matter — they’re one huge atomic nuclei, without any empty space for electron orbits or personal space or whatnot. It’s the closest a star can get to a black hole without turning to the dark side. The white dwarf pulsar is smaller, less dense, and formed after the outer layers of a Sun-like star breezed away into a planetary nebula.
“White dwarfs and pulsars represent distinct classes of compact objects that are born in the wake of stellar death,” NASA explains.
“A white dwarf forms when a star similar in mass to our sun runs out of nuclear fuel. As the outer layers puff off into space, the core gravitationally contracts into a sphere about the size of Earth, but with roughly the mass of our sun. […] neutron stars are even denser, cramming roughly 1.3 solar masses into a city-sized sphere.”
“Pulsars give off radio and X-ray pulsations in lighthouse-like beams.”
A white dwarf pulsar, like AR Sco, doesn’t cool off into a black dwarf but retains enough energy to accelerate subatomic particles as a pulsar.
“Similar to neutron-star pulsars, the pulsed luminosity of AR Sco is powered by the spin-down of the rapidly rotating white dwarf that is highly magnetized,” the paper reads.
It has an electromagnetic field 100 million times more powerful than our planet’s and makes a full rotation in just under two minutes. Because of this gargantuan magnetic field, AR Sco acts kind of like a natural particle accelerator. We’re talking about monumental levels of energy here. Matter inside it is squashed down to extreme conditions and emits huge levels of radiation and charged particles as focused ‘beams’. These occasionally whip at its neighbor, causing the entire system to spectacularly brighten and fade every two minutes.
“The new data show that AR Sco’s light is highly polarised, showing that the magnetic field controls the emission of the entire system, and a dead ringer for similar behaviour seen from the more traditional neutron star pulsars,” Prof Marsh says.
The beams radiate outwards from the pulsar’s magnetic poles. Think of it like a huge lighthouse in space spinning really fast. Each time the beam hits the atmosphere of the red dwarf, it speeds up electrons there to almost the speed of light. This interaction is what causes the red dwarf’s brightness to flicker. It suggests that the star’s inner workings are dominated by its neighbor’s kinetic energy — an effect which has never been observed before, not even in similar types of binary stars.
Graphical simulation of a pulsar. Credit: Giphy.
“AR Sco is like a gigantic dynamo: a magnet, size of the Earth, with a field that is ~10.000 stronger than any field we can produce in a laboratory, and it is rotating every two minutes. This generates an enormous electric current in the companion star, which then produces the variations in the light we detect,” Professor Boris Gänsicke added.
The distance between the two stars is around 1.4 million kilometers — which is three times the distance between the Moon and the Earth.
The full paper ‘Polarimetric evidence of a white dwarf pulsar in the binary system AR Scorpii’, has been published in the journal Nature Astronomy.
Researchers working with the Gemini North telescope in Hawaii have made a stunning discovery: they found evidence of water clouds around a brown dwarf.
Artist’s rendering of WISE 0855 as it might appear if viewed up close in infrared light. (Illustration by Joy Pollard, Gemini Observatory/AURA)
Since its discovery, the brown dwarf known as WISE 0855 has fascinated astronomers. It lies just 7.2 light-years from Earth and it’s the coldest confirmed object outside of our solar system at temperatures ranging between −48 to −13 °C (that’s −55 to 8 °F). The team working on the star have now obtained the star’s infrared spectrum — providing the first details of the object’s composition and chemistry. Among the findings is water, in the form of clouds.
“We would expect an object that cold to have water clouds, and this is the best evidence that it does,” said Andrew Skemer, assistant professor of astronomy and astrophysics at UC Santa Cruz.
“It’s five times fainter than any other object detected with ground-based spectroscopy at this wavelength,” Skemer said. “Now that we have a spectrum, we can really start thinking about what’s going on in this object. Our spectrum shows that WISE 0855 is dominated by water vapor and clouds, with an overall appearance that is strikingly similar to Jupiter.”
Brown dwarfs are failed stars, which never picked up enough steam and mass to spark the nuclear fusion necessary to become “real” stars. In a way, they’re more similar to gas giants than stars, but they formed from the collapse of nebular gases, not from the accretion disc.
But having about five times the mass of Jupiter, WISE 0855 resembles that gas giant planet in many respects. In fact, astronomers believe that by studying WISE 0855 we could learn more about Jupiter.
“WISE 0855 is our first opportunity to study an extrasolar planetary-mass object that is nearly as cold as our own gas giants,” Skemer said.
Another interesting similarity is that they seem to share similar spectrum features. Namely, their spectra have similar water-absorption features, which likely indicates that they both have water vapours in their respective atmospheres. However, Jupiter also has a significant amount of phosphine (a compound of phosphorous and hydrogen) in its atmosphere, while WISE 0855 does not, which would indicate that Jupiter’s atmosphere is much more turbulent, and WISE 0855 is a calmer place.
WISE 0855 and brown dwarfs in general still have many secrets which await uncovering, but the mere fact that we know about a star with water vapours in its atmosphere is mind blowing.
A new dwarf planet, designated V774104 has been identified and now takes the crown of most distant object in our solar system, being three times farther away than Pluto. The dwarf planet is estimated to be between 500 and 1000 kilometers across. Astronomers don’t yet have enough data to estimate its orbit and estimate that about an year of observations is needed to gather enough data for a precise answer. They suspect that V774104 will end up joining an emerging class of extreme solar system objects whose strange orbits point to the hypothetical influence of rogue planets or nearby stars.
“We can’t explain these objects’ orbits from what we know about the solar system,” says Scott Sheppard, an astronomer at the Carnegie Institution for Science in Washington, D.C., who announced the discoverytoday at a meeting of the American Astronomical Society.
V774104 currently sits 15.4 billion kilometers from the sun, or 103 astronomical units (AU) away. One AU is the distance between Earth and the sun. Image via sciencemag
V774104 could join one of two groups, depending on it’s exact orbit. Should it come closer to the Sun on part of its trajectory, it will be classified together with a more common population of icy worlds whose orbits can be explained by gravitational interactions with Neptune. Should it stay relatively far away from our star it will join two other worlds, Sedna and 2012 VP113, who keep between 50 AU and 1000 AU distance from the Sun.
Sheppard calls them “inner Oort cloud objects” to distinguish them from icy Kuiper Belt objects, that reside between 30 and 50 AU. The Oort cloud is a hypothetical, thinly populated sphere of icy bodies, thousands of AU away, that marks the edge of the solar system and the end of the sun’s gravitational influence.
Oort cloud objects have eccentric orbits that cannot be explained by the current known structure of the solar system, and it is suspected that other factors come into play when shaping their orbits too — such as an yet-undiscovered giant planet that disturbs Oort cloud objects, or even remnant movement from the creation of the Solar system.
“They carry the signature of whatever else happened,” says Mike Brown, a planetary astronomer at the California Institute of Technology in Pasadena, unaffiliated with the discovery.
Currently, Brown holds the claim of having discovered the most distant solar system object, which came in 2005 when he found the dwarf planet Eris at a distance of 97 AU from the sun.
“I have held the record for 10 years,” he says, jokingly. “I have to relinquish it. So I’m sad.”
Sheppard made his discovery with colleagues using Japan’s 8-meter Subaru Telescope in Hawaii. Unlike many searches for distant objects, which peer into the solar system’s plane, Sheppard is training Subaru on swaths of the sky an average of 15° away from the ecliptic, the better to find other weird objects.