Using the Hubble Space Telescope astronomers have spotted an important and extraordinary event in planetary evolution for the first time. The researchers have observed volcanic activity on a distant rocky planet reforming that world’s atmosphere.
The planet–GJ 1132 b–is believed by the team to have previously possessed an atmosphere that was stripped by the intense radiation emitted by the bright young red dwarf star it closely orbits. After its thick blanket of hydrogen and helium was expunged the planet was left as a rocky core roughly the size of Earth.
The astronomers believe that much of the hydrogen from GJ 1132 b’s initial atmosphere was absorbed by the exoplanet’s molten magma mantle creating a reservoir of the element which is now being slowly dispersed back into the atmosphere. This dispersal replenishes hydrogen being lost to space.
The fact that the planet’s volcanic activity is generating a secondary atmosphere that is replacing the first has come as a huge suprise to the researchers.
What makes this replacement atmosphere so interesting and useful to astronomers is the fact that has come from the planet’s interior. Thus its chemical composition–with abundant hydrogen, hydrogen cyanide, methane and ammonia with glimmers of a hydrocarbons–means that astronomers should be able to study the interior of the exoplanet by proxy.
“This second atmosphere comes from the surface and interior of the planet, and so it is a window onto the geology of another world,” explains Paul Rimmer, University of Cambridge, UK, who was part of the team that made the discovery. “A lot more work needs to be done to properly look through it, but the discovery of this window is of great importance.”
The finding could change the way we think about highly irradiated exoplanets which astronomers normally expect to lack atmospheres. “We first thought that these highly radiated planets would be pretty boring because we believed that they lost their atmospheres,” explains Raissa Estrela of the Jet Propulsion Laboratory at the California Institute of Technology in Pasadena, California, USA, another member of the research team. “But we looked at existing observations of this planet with Hubble and realised that there is an atmosphere there.”
Like Earth, But Really Different
Whilst sharing some similarities with Earth, GJ 1132 b is actually a very different world. GJ 1132 b has a similar density, size and age–around 4.5 billion years. Additionally, both planets started life as molten balls of rock with hydrogen-dominated atmospheres. But, whereas our planet was able to hang on to its atmosphere, the intense radiation GJ 1132 b was exposed to stripped that world’s gaseous envelope.
The differences become more extreme when considering the formation of both worlds. GJ 1132 b is the surviving core of a sub-Neptune exoplanet–a planet resembling Neptune but with a smaller mass–so didn’t start its life as a terrestrial world like we believe Earth did. Possibly the most extreme difference between the two worlds, however, is their relationships with their respective parent stars.
Whilst Earth orbits the Sun at a comfortable distance, rotating on its axis as it does so, GJ 1132 b orbits its red dwarf parent star in blisteringly close proximity. So-close that the exoplanet’s orbit period is just 36 hours. That isn’t the only major orbital difference, however. GJ 1132 b is tidally locked, meaning that the same face points towards its parent star throughout its orbit.
This isn’t the only source of heating the exoplanet is experiencing. The tidal force that the planet experiences due to its proximity to its parent star and that star’s gravitational force is permanently stretching and squeezing it.
This deformation is converted to heat beneath the planet’s surface, maintaining its mantle’s molten state. It could be this tidal heating that is driving the extreme volcanism and also causing the planet’s thin crust to crack, allowing hydron to escape and replenish the atmosphere.
The findings raise the question; how many of the terrestrial worlds we see are actually the stripped cores of sub-Neptunes?
“How many terrestrial planets don’t begin as terrestrials? Some may start as sub-Neptunes, and they become terrestrials through a mechanism whereby light evaporates the primordial atmosphere,” says Mark Swain of NASA’s Jet Propulsion Laboratory who led the research. “This process works early in a planet’s life when the star is hotter. Then the star cools down and the planet’s just sitting there.”
“So you’ve got this mechanism that can cook off the atmosphere in the first 100 million years, and then things settle down. And if you can regenerate the atmosphere, maybe you can keep it.”
The observations made by the team were part of the Hubble observing program and raise the interesting possibility that if this secondary atmosphere is thin enough, astronomers could actually see down to the surface of the exoplanet.
“This result is significant because it gives exoplanet scientists a way to figure out something about a planet’s geology from its atmosphere,” concludes Rimmer. “It is also important for understanding where the rocky planets in our own Solar System — Mercury, Venus, Earth and Mars, fit into the bigger picture of comparative planetology, in terms of the availability of hydrogen versus oxygen in the atmosphere.”
A team of researchers from the University of Bern has discovered a very different binary system 450 light-years from Earth. The system — CFHTWIR-Oph 98 or Oph 98 for short — has twin occupants that appeared at first sight to be exoplanets existing in a star-less system. A deeper examination has revealed that they are brown dwarfs — Oph 98 A and Oph 98 B respectively — astronomical objects that are similar to stars but smaller and cooler.
These brown dwarfs wander the galaxy together, orbiting each other at an incredibly large distance equivalent to 200 times the distance between Earth and the Sun.
The discovery of the curious Oph 98 system by the research team led by Clémence Fontanive from the Center for Space and Habitability (CSH) and National Centre of Competence in Research PlanetS (NCCR PlanetS) is documented in a paper published in The Astrophysical Journal Letters.
A Star that Failed
The Oph 98 is a relativity new-born system in astrophysical terms, forming just 3 million years ago in the Ophiuchus stellar nursery (hence the ‘Oph’ element of its name). Its relative youth has some interesting consequences for the bodies that comprise it and led the team to properly identify its constituent bodies.
The system has not existed for long enough for it to start forming planets. This means that Oph 98 A and B must have both formed via the same mechanisms that give rise to stars. This conclusion is also supported by the fact that Oph 98 B is roughly the right size to be a planet, but Oph A is too small to have the reservoir of material needed to form a planet so large. That means they must be brown dwarfs.
“This tells us that Oph 98 B, like its host, must have formed through the same mechanisms that produce stars and shows that the processes that create binary stars operate on scaled-down versions all the way down to these planetary masses,” says Fontanive.
The fact that brown dwarfs form in ways that are similar to stars and share similar masses, but do not ignite with the nuclear processes that power stars, has often led to them being nicknamed ‘failed stars.’ It is extremely rare for star-forming processes to create worlds that go on to exist in a system such as this.
The objects are rare examples of astronomical bodies similar to giant exoplanets that orbit each other without a parent star. Both are young brown dwarfs, with Oph 98 A being the larger of the two with a mass 15 times that of Jupiter. Its smaller companion — Oph 98 B — has a mass equivalent to 8 times that of the gas giant, which is the largest body other than the Sun in our solar system.
This isn’t the only thing that makes Oph 98 unique, however.
Brown Dwarfs with a Weak Bond
Another thing that makes the Oph 98 system so remarkable is the fact that, like all binary systems, the bodies are gravitationally bound. These bonds are greater with objects of greater mass but follow an inverse square law — meaning the bond’s strength falls off quickly as separation distances increase. Because these objects have relatively small mass coupled with an extremely large separation, the gravitational bond between them is one of the weakest in terms of energy that astronomers have ever observed.
Observing this system at all is no mean feat as brown dwarfs — especially low-mass ones — emit very little electromagnetic radiation and are thus, not easy to spot.
“Low-mass brown dwarfs are very cold and emit very little light, only through infrared thermal radiation,” explains Fontanive. “This heat glow is extremely faint and red, and brown dwarfs are hence only visible in infrared light.”
This visibility challenge was further compounded by the fact that Oph 98 and the Ophiuchus galaxy cluster itself is embedded in a dense cloud of dust that scatters visible light. “Infrared observations are the only way to see through this dust,” the researcher adds.
In fact, the team’s discovery was only made possible by the impressive power of the Hubble Space Telescope and the fact that it makes its observations from above Earth.
Hubble Shines Through Again
The Hubble Space Telescope is one of the only telescopes capable of observing objects as faint as the Oph 98 A and B and resolving the image of the brown dwarfs at such tight angles.
“Detecting a system like Oph 98 also requires a camera with a very high resolution, as the angle separating Oph 98 A and B is a thousand times smaller than the size of the moon in the sky,” Fontanive continues.
Hubble’s space-based vantage point is also crucial for the observation of such objects. This is because the infrared signatures that are used to observe brown dwarfs arise from water vapors that form in their upper atmospheres. As Earth’s atmosphere is full of water also producing this signal, the fainter trace from distant brown dwarfs is almost always obscured beyond detection for telescopes at the planet’s surface.
“Both objects looked very red and showed clear signs of water molecules. This immediately confirmed that the faint source we saw next to Oph 98 A was very likely to also be a cold brown dwarf, rather than a random star that happened to be aligned with the brown dwarf in the sky,” says Fontanive.
Interestingly, the team’s findings have helped confirm the fact that the Oph 98 system has actually been spotted before. The binary was also visible in data collected by the Canada-France-Hawaii Telescope (CFHT), located atop the summit of Mauna Kea, Hawaii, 14 years ago. This older data helped the team confirm how Oph 98 A and B move together across the galaxy as a pair.
“We observed the system again this summer from another Hawaiian observatory, the United Kingdom Infra-Red Telescope. Using these data, we were able to confirm that Oph 98 A and B are moving together across the sky over time, relative to other stars located behind them, which is evidence that they are bound to each other in a binary pair”, explains Fontanive. “We are really witnessing an incredibly rare output of stellar formation processes.”
Fontanive. C., et al, ‘A wide planetary-mass companion to a young low-mass brown dwarf in Ophiuchus,’ The Astrophysical Journal Letters, , [https://arxiv.org/abs/2011.08871]
Time is running out to catch a glimpse of the comet NEOWISE. The comet — the brightest object to grace the skies over the Northern Hemisphere in 25 years — will soon disappear from view. At least as far as the naked eye is concerned. Fortunately, the Hubble Space Telescope is on hand to capture stunning images of the comet — discovered on March 27th by NASA’s Wide-field Infrared Survey Explorer (WISE) space telescope during its mission to search for near-Earth objects.
The image taken by Hubble on 8th August — which represents the closest ever taken of the comet since it first lit up the sky — shows NEOWISE as it sweeps past the Sun. This is the first time that astronomers have managed to capture such a bright object as it passes our star.
Hubble snapped the object as it rapidly makes its way out of the solar system, with it not scheduled to return for 6,800 years. The comet caused a stir amongst amateur star watchers and the general public as it was visible with the naked eye under the right conditions.
“Nothing captures the imagination better than actually seeing its tails stretching into the sky in person,” Qicheng Zhang, a graduate student studying planetary science at Caltech, Pasadena, CA, who has been heavily involved in the study of NEOWISE. “The comet last came around about 4,500 years ago. This was around when the Egyptian pyramids were being built.”
“My research area covers comets and their evolution under solar heating,” Zhang explains to ZME Science. “I also like to keep track of potentially bright comets to actually see in the sky, which included this particular comet.”
The image shows NEOWISE’s halo of glowing gas and dust illuminated by light from the Sun surrounding the icy nucleus of the comet, too small at little more than 4.8km across to be fully resolved by the telescope. In contrast, the dust halo that surrounds the comet’s heart is too large to be fully resolved by the space telescope, with its diameter measuring an estimated 18,000 km.
Zhang points out that as NEOWISE moves past the Sun, there is a chance we could still glimpse its icy core: “As the comet recedes from the Sun, the dust with clear and reveal the solid nucleus currently buried within, providing an opportunity to directly observe the source of all the activity that made the comet impressive last month.”
Let’s Stick Together: Why NEOWISE Survived and ATLAS Didn’t
Previous attempts to capture other bright comets as they pass the Sun have failed because these objects have disintegrated as they passed too close to the star. This break-up is driven by both the incredible heat of the Sun causing the icy heart of the comets to fragment, and the powerful gravitational influence of our star further pulling the comets apart.
The most striking example of this came shortly after the discovery of NEOWISE, with the observation of the fragmentation of the comet ATLAS in April this year. The collapse of this comet — believed at the time to offer our best look at such an icy body — in 30 separate pieces was also caught by Hubble.
Unlike comet ATLAS, itself only discovered in December 2019, comet NEOWISE somehow survived its close passage to the Sun–with its solid, icy nucleus able to withstand the blistering heat of the star– enabling Hubble to capture the comet in an intact state.
As the latest image of NEOWISE shows, however, it is not going to escape its encounter with the Sun completely unscathed. Jets can clearly be seen blasting out in opposite directions from the poles of the comet’s icy nucleus. These jets represent material being sublimated–turning straight from a solid to a gas skipping a liquid stage–beneath the surface of the comet. This ultimately results in cones of gas and dust erupting from the comet, broadening out as the move away from the main body, forming an almost fan-like shape.
Far from being just a stunning image of a comet as it passes through the inner solar system, the Hubble images stand to teach astronomers much about NEOWISE and about comets in general.
“It’s a fairly large comet that approached closer to the Sun than the vast majority of comets of its size do,” Zhangs says. “These factors contributed to its high brightness and also made it a good candidate to see how solar heating alters comets, as the effects are theoretically amplified by its close approach to the Sun.
“That information is useful for interpreting observed characteristics of other comets that don’t approach as close to the Sun, and thus where the changes are more gradual and might not be directly observable.”
In particular, the colour of the comet’s dust halo, and the way it changes as NEOWISE moves away from the Sun, gives researchers a hint as to the effect of heat on such materials. This could, in-turn, help better determine the properties of the dust and gas that form what is known as the ‘coma’ around a comet.
“We took images to show the colour and polarization of the dust released by the comet, to get a sense of what it looks like before it’s broken down by sunlight,” says Zhang. “That analysis is ongoing–and will take a while to do properly–but as the published images show, we’ve caught at least a couple of jets carrying dust out from the rotating nucleus.”
The information contained in the Hubble data will become clearer as researchers delve deeper into it. But, the investigation of NEOWISE’s cometary counterparts will benefit from future telescope technological breakthroughs. This will include spotting comets much more quickly and thus, further out from the Sun.
“When this comet was discovered by the NEOWISE mission, it was only 3 months from its close approach to the Sun and had already begun ramping up activity,” Zhang says. “More sensitive surveys, like the upcoming Legacy Survey of Space and Time (LSST) at the Rubin Observatory, will allow us to find such comets much earlier before they become active, enabling us to track them throughout their apparition from beginning to end.
“This will facilitate a more precise comparison of what changes the comets undergo during their solar encounter.”
The next step in Zhang’s research, however, will be comparing the qualities of comet NEOWISE to other such objects, particularly a recent interstellar visitor to our solar system: “This is one of three comets I have observed or have planned to observe in this manner, the others being the interstellar comet 2I/Borisov and the distant solar system comet C/2017 K2 (PANSTARRS),” the researcher concludes. “My team of collaborators and I will be evaluating all three comets to see how their differences in present location and formation/dynamical history translate into differences in physical properties.”
“Liftoff of the space shuttle Discovery, with the Hubble Space Telescope, our window on the universe,” were the words uttered by George Diller as STS-31 lifted off into a partly-cloudy Florida sky. That day — April 24, 1990 – was one, indeed, that would shape how we saw the unending expanse of space. The cargo aboard Discovery, 30 years ago, would end up becoming the most prolific space telescope in history and would change not only how we thought about the universe, but the creation of it itself.
The United States space program was still reeling from the Challenger explosion four years prior, and the launch of Hubble was not only a chance to learn more than ever about the universe, but a chance for NASA to remake its image with the public as well.
However, the story of Hubble started much earlier than that.
The road to Hubble
From the dawn of humankind to a mere 400 years ago, all that we knew about our universe came through observations with the naked eye. When Galileo turned his telescope toward the heavens in 1610, the world was in for an awakening.
Saturn, we learned, had rings. Jupiter had moons. That nebulous patch across the center of the sky called the Milky Way was not a cloud, but a collection of countless stars. Within but a few years, our notion of the natural world would be forever changed. A scientific and societal revolution quickly ensued.
In the centuries that followed, telescopes grew in size and complexity and, of course, power. They were placed on mountains far from city lights and as far above the haze of the atmosphere as possible. Edwin Hubble, for whom the Hubble Telescope is named, used the largest telescope of his day in the 1920s at the Mt. Wilson Observatory near Pasadena, California, to discover galaxies much further than our own.
the 1970s, NASA and the European Space Agency (ESA) began planning
for a space telescope that could transcend the blurring effects of
the atmosphere and take clearer images of the Universe than ever
The Hubble telescope was the first major optical telescope to be
placed in space, the ultimate mountaintop. Without the atmosphere to
hinder its observations, and far removed from rain clouds and light
pollution, Hubble has an unobstructed view of the universe.
“Hubble is really a time machine,” said Larry Dunham, Hubble’s chief systems engineer at NASA’s Goddard Space Flight Center, in an interview. “We’re looking at data from light years in the past. Hubble is giving us the opportunity to look back in time to see how things were formed.”
Like every good love story, this one has its ups and downs with Hubble being the knot that ties the marriage of human curiosity and the science with satisfies it. Also, like a good marriage – and unlike most satellites – it gets better and stronger with age. Fifteen years after its expected lifespan, she has still not given up the ghost and has some of her most important discoveries just ahead.
The most marvelous part of the telescope, of course, is the 94.5-inch (2.4-meter-wide) mirror. As Eric Chaisson, an American astrophysicist and author wrote in his book The Hubble Wars, “While not the largest ever built, Hubble’s mirror is assuredly the cleanest and most finely polished mirror of its size. If Hubble’s mirror were scaled up to equal the width of the North American continent, the highest hill or lowest valley would be a mere few inches from the average surface.”
Up to a slow start
The mirror was also the headline when Hubble’s debut picture was snapped. Four weeks after leaving Discovery’s payload bay, the telescope’s initial offering to the public was that of a somewhat blurry photo of binary star HD96755, about 1,300 light-years away. A spherical aberration caused by a manufacturing error was causing the telescope to bring in only 10 to 15 percent of a star’s light into focus, as opposed to the 70 percent it should be gathering. Picture after picture revealed in no clearer images. Engineers eventually found that the shape of the concave mirror, moving from the center to the outer edge, was too shallow by up to two microns — 1/50 the width of a human hair.
slight, the error turned what was the most heralded telescope in
NASA’s history into the laughingstock of the world. In fact, it
wouldn’t be until December of 1993, three and a half years later,
that the crew of Columbia would come to the rescue with a set of
corrective optics to restore Hubble’s vision.
“The mirror flaw was a disappointment,” said Dunham. “It was really a disappointment that it showed up in the news. Even with the spherical aberration, the images we were getting were still better than anything we had ever had in the past.”
Replacing the mirror was not practical, so the best solution was to build replacement instruments that fixed the flaw much the same way a pair of glasses correct the vision of someone who is near-sighted. The corrective optics and new instruments were built and installed on Hubble by spacewalking astronauts during the STS-61 mission in 1993. The Corrective Optics Space Telescope Axial Replacement (COSTAR) instrument, which was about the size of a telephone booth, placed into Hubble five pairs of corrective mirrors that countered the effects of the flaw.
Once the mirror had a new set of spectacles, she now had the ability to look farther into universe than anything humans had ever produced. When astronomers pointed her to before had been an empty patch of sky in Ursa Major in 1995, they captured an image of over 3,000 galaxies too distant to be detected by other telescopes. (This was later called the Hubble Deep Field). Some of the galaxies Hubble found were so young, they had not yet begun serious star formation. Other deep field findings in the same area were performed, peering deeper into space each time. These were called the Hubble Ultra-Deep Field (released in 2004) and the Hubble eXtreme Deep Field (released in 2012).
Besides the extraordinary finds, Hubble was famous for another reason. Unlike other satellites, Hubble was made into a better machine as time wore on. Each service mission would renew and improve her capabilities.
“With the servicing missions have allowed us to upgrade both the science instruments as well as the spacecraft hardware,” said Dunham. “Actually, it took us so long to get it up there initially (due to the delay after the Challenger explosion), that by the time we finally got Hubble up, a lot of its hardware was already obsolete. The recorders we launched with were tape, and now we have upgraded those to digital. The original computer we had was six-point binary assembly coding with a huge 32k of memory. Now we’ve got a 46 computer up there that has megabytes.”
In February 1997 the second servicing mission took place, resulting in the replacement of degrading spacecraft components, and the installation of new instruments such as the Space Telescope Imaging Spectrograph (STIS) and the Near Infrared Camera and Multi-Object Spectrometer (NICMOS). STIS separated the light the telescope took in, and “dissected” it so that the composition, temperature, motion and other properties could be analyzed. With NICMOS, astronomers could see the first clear views of the universe at near-infrared wavelengths.
On November 13, 1999, the fourth of six gyroscopes failed, and the telescope temporarily closed its eyes on the universe. Traveling at speeds of five miles per second, the gyros measure the spacecraft’s rate of motion and help point Hubble toward its observation target. Unable to conduct science without three working gyros, Hubble entered a state of safe mode dormancy. Essentially, Hubble took a nap while it waited for help.
The third servicing mission was originally conceived as one of maintenance, but when the fourth gyro failed, NASA divided the work into two missions — and in the process, upheld the time-honored tradition of governments just making things more confusing by instead of calling them a third and fourth service mission, called them Servicing Mission 3A (SM3A) and Servicing Mission 3B (SM3B).
SM3A flew in December 1999 and the second in March 2002. During SM3A astronauts replaced all six gyroscopes with new ones, and installed a faster, more powerful main computer, a next-generation solid-state data recorder, a new transmitter, new insulation and other equipment. During SM3B, astronauts installed a new science instrument called the Advanced Camera for Surveys (ACS). ACS sees in wavelengths ranging from visible to far-ultraviolet, and can produce 10 times the science results in the same amount of time than the camera it replaced, the Faint Object Camera (FOC).
Servicing Mission 4 (SM4), the fifth – and last — visit to Hubble, occurred in May 2009. Astronauts installed two new scientific instruments: the Cosmic Origins Spectrograph (COS) and Wide Field Camera 3 (WFC3). Two failed instruments, the Space Telescope Imaging Spectrograph (STIS) and the Advanced Camera for Surveys (ACS), were brought back to life by the first-ever on-orbit instrument repairs. In order to prolong Hubble’s life, other components were replaced including new batteries, new gyroscopes and a new science computer. In addition, a device was attached to the base of the telescope to facilitate de-orbiting when the telescope is eventually decommissioned.
As things are now, that decommissioning date looks like it will be long in the future. Originally given a shelf life of 15 years, Dunham says that reentry of the satellite probably won’t occur until 2046, a 56-year span since it lifted off aboard Discovery. To put that in perspective, that is only five years less than when the telescope’s namesake reached his expiration date.
With the launch of the highly touted James Webb Telescope approaching nearer, the Hubble’s capabilities should only increase.“There are a lot of observations that people want to do in parallel with the Webb,” said Dunham. “The two spacecraft look at different light spectrums, so you can look at something with the Webb and get once sense of the object you’re looking at and then look at it with the Hubble and get another sense. Together you can produce some amazing science.”
Maybe it was appropriate that Discovery was the ship that took Hubble into orbit. The opportunities and discoveries we have made are more than the number of coins it took to produce it.
Famed poet Walt Whitman might have pegged it when he wrote:
“O to realize space! The plenteous of all, that there are no bounds, To emerge and be of the sky, of the sun and moon and flying clouds, as one with them.”
Astronomers believe that globular clusters — found around giant galaxies in the centre of galactic clusters — are ancient relics remaining from the earliest formative stages of galaxies. But, despite this well-founded belief, the physical origins of these clusters — most common around elliptical galaxies — remains something of a mystery.
New research conducted by Dr Jeremy Lim and his Research Assistant, Miss Emily Wong, at the Department of Physics of The University of Hong Kong (HKU) have used data collected by the Hubble Space Telescope in order to find a surprising answer to this cosmic conundrum.
Dr Lim’s team discovered that globular clusters around the giant galaxy at the centre of the Perseus galaxy cluster are not all ancient objects. Whilst most globular clusters are believed by scientists to have formed shortly after the Universe began 13.8 billion years ago, a few thousand of the clusters studied by the team seem to have formed over at least the past 1 billion years. Even more, could have possibly formed later in cosmic history the research suggests.
These younger globular clusters seem to be associated with a complex filamentary network of cool gas which extends to the outer reaches of this giant galaxy. This seems to suggest that these clusters were born in this same network. This is significant as this cool gas is thought to have been deposited by the hot gas that infuses the entire Perseus galaxy cluster. The density of this hot gas and thus the rate at which it cools rises in the direction of the galactic cluster’s centre.
After formation, the newly born galactic clusters are no longer bound to the network of cool gas and begin to fall inwards onto the giant galaxies. This can be considered almost analogous to raindrops condensing in clouds and falling to the ground.
This inward gathering of younger globular clusters after formation in a network of cool gas is in stark contrast to the formation and dispersion of more ancient globular clusters.
These older clusters form from gas compressed in the spiral arms of galaxies or from dense gas at the centre of galaxy clusters. After their formation, the random dispersion of older clusters across the giant galaxy is a result of them scattering off each other during the course of their orbit around this galaxy.
Globular clusters can contain anywhere from hundreds of thousands to several million stars — all of which are born at the same time. These stars are packed incredibly densely, with the clusters having spherical volumes thousands of times smaller than the diameter of our galaxy — the milky way.
One puzzling aspect of these clusters has been the sheer numbers at which they exist — and how they could have formed at the same point in cosmic history. By showing that some of these clusters form later than others and fall into place — this new research may have solved that puzzle.
Another puzzling aspect of these global clusters is the broad range of colours they display around giant galaxies. Again, this could be a result of the clusters have different respective ages. Globular clusters likely change from blue to red as they age. This is a result of more massive stars burning through their fuel more quickly as nucleosynthesis progresses more quickly in larger stars. As these stars are bluer than smaller stars, as they die it leaves the cluster to take a redder hue. Thus, a broad range of ages would result in a broad range of colours — which is indeed what astronomers observe.
The team’s research does indicate that despite forming at different times, both older and younger globular clusters in the Perseus galaxy share a common formation mechanism. Irrespective of age, the globular clusters span a broad range of masses — with fewer at the larger mass end of the spectrum. This similar mass trend suggests a common formation mechanism for star clusters across the mass scale regardless of the environment in which they formed.
This sustained formation of globular clusters over a long range of time could also explain the enormous size of giant galaxies — which can be in excess of ten times that of the Milky Way. As more massive globular clusters within these galaxies endure, their more diminutive counterparts could be ripped apart during their orbits. This leaves the stars which form these smaller globular clusters to be spread through the giant galaxies contributing to their growth in size.
Original research: ‘Sustained Formation of Progenitor Globular Clusters in a Giant Elliptical Galaxy’ by Jeremy Lim, Emily Wong, Youichi Ohyama, Tom Broadhurst & Elinor Medezinski in Nature Astronomy.
The discovery of 39 ‘hidden’ ancient galaxies urges scientists to rethink their theories of fundamental aspects of the Universe — including supermassive black holes, star formation rates, and the ever-elusive, dark matter.
In an unprecedented discovery of astronomers, researchers have utilised the combined power of a multitude of observatories across the globe to discover a vast array of 39 previously hidden galaxies.
The finding — described by the researchers from the University of Tokyo as a ‘treasure trove’ — is the first multiple discoveries of this kind. But the finding is significant for more than its size alone.
In addition to containing a wealth of newly discovered ancient galaxies, an abundance of this particular type of galaxy suggests that scientists may have to refine current models of the universe.
This is because our current understanding of the universe and how it formed is built upon observations of galaxies in ultraviolet light. But observations in these wavelengths under-represent the most massive galaxies — those with high dust content and crucially, the most ancient.
This means that a discovery of such galaxies — such as the one just made — must force us to reconsider the rates of star formation in the early universe. The study explains that the population of stars discovered may mean that star formation rates were actually ten times greater in early epochs than previous estimates held.
There are also particular ramifications for our understanding of both supermassive black holes and their distribution, and for the concept of dark matter — the elusive substance which makes up 80% of the matter in the universe.
Despite the wealth of astronomical data that has become available to scientists since the launch of the Hubble Space Telescope, researchers at the Institute of Astronomy in Toyko were aware there were things that Hubble simply couldn’t show us. It was these things — fundamental pieces of the cosmic puzzle — that they wanted to investigate.
They achieved this by unifying different observatories, using them to look more deeply in the Universe than Hubble alone could do. This is what led them to this huge collection of galaxies.
Researcher Tao Wang describes the uniqueness and magnitude of the team’s discovery: “This is the first time that such a large population of massive galaxies was confirmed during the first two billion years of the 13.7-billion-year life of the universe.
“These were previously invisible to us.”
Wang continues: “This finding contravenes current models for that period of cosmic evolution and will help to add some details, which have been missing until now.”
A different view of the universe
Wang explains that if we could see these galaxies and the light they shed, our view from the Milky way would be significantly different: “For one thing, the night sky would appear far more majestic. The greater density of stars means there would be many more stars close by appearing larger and brighter.
“But conversely, the large amount of dust means farther-away stars would be far less visible, so the background to these bright close stars might be a vast dark void.”
The galaxies have been difficult to see from Earth due to how faint they are. Were we able to see these stars, their density would make the night sky majestic, Wang says.
The light from these galaxies also has to battle extinction — the absorption of light) by intervening interstellar dust clouds. The light from the galaxies also has to travel great distances meaning the wavelength is redshifted by the expansion of the universe making it even less visible.
Professor Kotaro Kohno explains that this phenomenon is how the galaxies escaped Hubble’s gaze: “The light from these galaxies is very faint with long wavelengths invisible to our eyes and undetectable by Hubble.
“So we turned to the Atacama Large Millimeter/submillimeter Array (ALMA), which is ideal for viewing these kinds of things. I have a long history with that facility and so knew it would deliver good results.”
This redshift due to cosmic expansion does have its advantages, however. It allows astronomers to estimate not just the distances to the galaxies in question, but it also allows them to calculate just how long ago the light was emitted.
The hidden implications of these hidden galaxies
The team’s finding is so controversial and poses such a radical rethink that they found their fellow astronomers were initially reluctant to believe they had found what they claimed.
Wang explains: “It was tough to convince our peers these galaxies were as old as we suspected them to be. Our initial suspicions about their existence came from the Spitzer Space Telescope’s infrared data.
“But ALMA has sharp eyes and revealed details at submillimeter wavelengths, the best wavelength to peer through dust present in the early universe. Even so, it took further data from the imaginatively named Very Large Telescope in Chile to really prove we were seeing ancient massive galaxies where none had been seen before.”
The discovery has the potential to reshape our ideas of the supermassive black holes that scientists currently believe nestle at the centre of most galaxies.
Kohno elaborates: “The more massive a galaxy, the more massive the supermassive black hole at its heart.
“So the study of these galaxies and their evolution will tell us more about the evolution of supermassive black holes, too.”
Kohno also explains that some ideas regarding dark matter may have to be revised, too: “Massive galaxies are also intimately connected with the distribution of invisible dark matter. This plays a role in shaping the structure and distribution of galaxies. Theoretical researchers will need to update their theories now.”
In addition to the potential shake up the team believes that their findings may already present, they expect more surprises to come.
Wang concludes: These gargantuan galaxies are invisible in optical wavelengths so it’s extremely hard to do spectroscopy, a way to investigate stellar populations and chemical composition of galaxies. ALMA is not good at this and we need something more.
“I’m eager for upcoming observatories like the space-based James Webb Space Telescope to show us what these primordial beasts are really made of.”
Original research: T. Wang, C. Schreiber, D. Elbaz, Y. Yoshimura, K. Kohno, X. Shu, Y. Yamaguchi, M. Pannella, M. Franco, J. Huang, C.F. Lim & W.H. Wang. A dominant population of optically invisible massive galaxies in the early Universe. Nature. DOI: 10.1038/s41586–019–1452–4
NASA’s Hubble Space Telescope recently completed one of its most thorough and ambitious mozaic projectes. Astronomers at Hubble, stitched together some 438 separate images, both in visible and infra-red light, to complete the most accurate picture of the Tarantula Nebula so far, spanning across no less than 600 light-years. The Tarantula nebula contains some 800,000 newly born or developing stars, and these latest developments will hopefully help scientists answer some puzzling questions on star formation.
One such question is whether super-massive stars – stars with mass at least 50 times greater than the sun – form exclusively in star clusters or not. The Tarantula Nebula, located 170,000 light-years away in the Large Magellanic Cloud, contains the nearest observable super-cluster of stars. Coupled with the fact the nebula is still a massive star hatchery, makes it an ideal candidate for investigating super-massive star formation in isolation.
Click for magnefied view. (c) NASA
Hubble is sensitive enough to resolve individual stars and many red protostars as well as aging red giants and supergiants, giving astronomers new insights into the stars’ birth and evolution. The telescope had to be wired to ‘see’ in infra-red however, since only these light wavelengths can peer through the ubiquitous clouds of dust and gas which are aggregated in star formation.
“Because of the mosaic’s exquisite detail and sheer breadth, we can follow how episodes of star birth migrate across the region in space and time,” said Elena Sabbi, an astronomer at the Space Telescope Science Institute in Baltimore, Md., and the principal investigator of the observing team.
So far, astronomers have identified a multitude of star formation pockets, which most likely will merge into large clusters. When the program will be completed, astronomers will have a more refined view of various star formation properties.