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I love it when scientists discover something unusual in nature. They have no idea what it is, and then over decades of research, evidence builds, and scientists grow to understand what’s going on.
My favorite example? Quasars.
Astronomers first knew they had a mystery on their hands in the 1960s when they turned the first radio telescopes to the sky.
They detected the radio waves streaming off the Sun, the Milky Way and a few stars, but they also turned up bizarre objects they couldn’t explain. These objects were small and incredibly bright.
They named them quasi-stellar-objects or “quasars”, and then began to argue about what might be causing them. The first was found to be moving away at more than a third the speed of light.
But was it really?
An artist’s conception of jets protruding from an AGN.Maybe we were seeing the distortion of gravity from a black hole, or could it be the white hole end of a wormhole. And If it was that fast, then it was really, really far… 4 billion light years away. And it generating as much energy as an entire galaxy with a hundred billion stars.
What could do this?
Here’s where Astronomers got creative. Maybe quasars weren’t really that bright, and it was our understanding of the size and expansion of the Universe that was wrong. Or maybe we were seeing the results of a civilization, who had harnessed all stars in their galaxy into some kind of energy source.
Then in the 1980s, astronomers started to agree on the active galaxy theory as the source of quasars. That, in fact, several different kinds of objects: quasars, blazars and radio galaxies were all the same thing, just seen from different angles. And that some mechanism was causing galaxies to blast out jets of radiation from their cores.
But what was that mechanism?
This artist’s concept illustrates a quasar, or feeding black hole, similar to APM 08279+5255, where astronomers discovered huge amounts of water vapor. Gas and dust likely form a torus around the central black hole, with clouds of charged gas above and below. Image credit: NASA/ESAWe now know that all galaxies have supermassive black holes at their centers; some billions of times the mass of the Sun. When material gets too close, it forms an accretion disk around the black hole. It heats up to millions of degrees, blasting out an enormous amount of radiation.
The magnetic environment around the black hole forms twin jets of material which flow out into space for millions of light-years. This is an AGN, an active galactic nucleus.
When the jets are perpendicular to our view, we see a radio galaxy. If they’re at an angle, we see a quasar. And when we’re staring right down the barrel of the jet, that’s a blazar. It’s the same object, seen from three different perspectives.
Supermassive black holes aren’t always feeding. If a black hole runs out of food, the jets run out of power and shut down. Right up until something else gets too close, and the whole system starts up again.
The Milky Way has a supermassive black hole at its center, and it’s all out of food. It doesn’t have an active galactic nucleus, and so, we don’t appear as a quasar to some distant galaxy.
We may have in the past, and may again in the future. In 10 billion years or so, when the Milky way collides with Andromeda, our supermassive black hole may roar to life as a quasar, consuming all this new material.
An artist's conception of jets protruding from a quasar. Credit: ESO/M. Kornmesser
Understanding the formation of stars and galaxies early in the Universe’s history continues to be somewhat of an enigma, and a new study may have turned our current understanding on its head. A recent survey used archival data from four different telescopes to analyze hundreds of galaxies. The results provided overwhelming evidence that radio jets protruding from a galactic center enhance star formation – a result that directly contradicts current models, where star formation is hindered or even stopped.
All early galaxies consist of intensely luminous cores powered by huge black holes. These so-called active galactic nuclei, or AGN for short, are still the topic of intense study. One specific mechanism astronomers are studying is known as AGN feedback.
“Feedback is the astronomer’s slang term for the way in which an AGN – with its large amount of energy release – influences its host galaxy,” Dr. Zinn, lead researcher on this study, recently told Universe Today. He explained there is both positive feedback, in which the AGN will foster the main activity of the galaxy: star formation, and negative feedback, in which the AGN will hinder or even stop star formation.
Current simulations of galaxy growth invoke strong negative feedback.
“In most cosmological simulations, AGN feedback is used to truncate star formation in the host galaxy,” said Zinn. “This is necessary to prevent the simulated galaxies from becoming too bright/massive.”
Zinn et al. found strong evidence that this is not the case for a large number of early galaxies, claiming that the presence of an AGN actually enhances star formation. In such cases the total star formation rate of a galaxy may be boosted by a factor of 2 – 5.
Furthermore the team showed that positive feedback occurs in radio-luminous AGN. There is strong correlation between the far infrared (indicative of star formation) and the radio.
Now, a correlation between the radio and the far infrared is no stranger to galactic astronomy. Stars form in extremely dusty regions. This dust absorbs the starlight and re-emits it in the far infrared. The stars then die in huge supernova explosions, causing powerful shock-fronts, which accelerate electrons and lead to the emission of strong synchrotron radiation in the radio.
This correlation however is a stranger to AGN studies. The key lies in the radio jets, which penetrate far into the host galaxy itself. A “jet which is launched from the AGN hits the interstellar gas of the host galaxy and thereby induces supersonic shocks and turbulence,” explains Zinn. “This shortens the clumping time of gas so that it can condense into stars much more quick and efficiently.”
This new finding conveys that the exact mechanisms in which AGN interact with their host galaxies is much more complicated than previously thought. Future observations will likely shed a new understanding of the evolution of galaxies.
Hubble Space Telescope image of J1148+5251. Credit: NASA/ESA/M. Mechtley, R. Windhorst, Arizona State University
Quasars have been the best and most easily observed beacons for astronomers to probe the distant Universe, and one of the most distant and brightest quasars is providing a bit of a surprise. Astronomers studying a distant galaxy, dubbed J1148+5251 and which contains a bright quasar, are seeing only the quasar and not the host galaxy itself. It has been thought that the quasar has been feeding on a handful of stars every year in order to bulk up to its size of three billion solar masses over just a few hundred million years. But where are all the stars?
Likely, the quasar hasn’t gone on a feeding frenzy and eaten everything in sight! But it might be eating on the sly. Near infrared views with the Hubble Space Telescope’s Wide Field Camera 3 are only providing hints of what might be taking place: the galaxy is so enshrouded with dust that none of the starlight can be seen; only the bright, blaring quasar shines through. Just how many stars this quasar is eating is now uncertain, as the carnage is taking place undercover.
While most early galaxies contain hardly any dust — the early universe was dust-free until the first generation of stars started making dust through nuclear fusion – previous submillimeter observations showed this galaxy harbors large amounts of dust, so that is somewhat of a mystery, too.
So how could this all be happening?
Artist’s impression of one of the most distant, oldest, brightest quasars ever seen is hidden behind dust. The dust is also hiding the view of the underlying galaxy of stars that the quasar is presumably embedded in. (Credit: NASA/ESA/G.Bacon, STScI)
“If you want to hide the stars with dust, you need to make lots of short-lived massive stars earlier on that lose their mass at the end of their lifetime. You need to do this very quickly, so supernovae and other stellar mass-loss channels can fill the environment with dust very quickly,” said Rogier Windhorst of Arizona State University (ASU), Tempe, Ariz.
“You also have to be forming them throughout the galaxy to spread the dust throughout the galaxy,” added Matt Mechtley, also of ASU.
This quasar was first identified in the Sloan Digital Sky Survey (SDSS) and the follow-up submillimeter observations showed significant dust but not how and where it was distributed.
Windhorst and his team used Hubble to very carefully subtract light from the quasar image and look for the glow of surrounding stars. They did this by looking at the glow of a reference star in the sky near the quasar and using it as a template to remove the quasar light from the image. Once the quasar was removed, no significant underlying starlight was detected. The underlying galaxy’s stars could have been easily detected, had they been present and relatively unobscured by dust in at least some locations.
“It is remarkable that Hubble didn’t find any of the underlying galaxy,” said Windhorst. “The underlying galaxy is everywhere much fainter than expected, and therefore must be in a very dusty environment throughout. It’s one of the most rip-roaring forest fires in the universe. It’s creating so much smoke that you’re not seeing any starlight, anywhere. The forest fire is complete, not a tree is spared.”
Because we don’t see the stars, we can rule out that the galaxy that hosts this quasar is a normal galaxy,” said Mechtley. “It’s among the dustiest galaxies in the universe, and the dust is so widely distributed that not even a single clump of stars is peeking through. We’re very close to a plausible detection, in the sense that if we had gone a factor of two deeper we might have detected some light from its young stars, even in such a dusty galaxy.”
This result was published in the Sept. 10 issue of the Astrophysical Journal Letters in the team’s paper.
The only way to get to the bottom of this mystery, Windhorst said, is to wait for the James Webb Space Telescope to launch and come online.
“The Webb telescope is designed to make a definitive detection of this,” he said. “ We will get solid detections of the stars with Webb’s better sensitivity to longer wavelengths of light, which will better probe the dusty regions in these young galaxies.”
The Webb telescope will also have the infrared sensitivity to peer all the way back to 200 million years after the Big Bang. If galaxies started forming stars at this early epoch, Webb is designed and being built to detect them.
So only then will the true nature – and potential carnage – of this system be revealed.
An international team of astronomers has observed the heart of a distant quasar with unprecedented sharpness, two million times finer than human vision. The observations, made by connecting the Atacama Pathfinder Experiment (APEX) telescope to two others on different continents for the first time, is a crucial step towards the dramatic scientific goal of the “Event Horizon Telescope” project: imaging the supermassive black holes at the centre of our own galaxy and others.
Astronomers connected APEX, in Chile, to the Submillimeter Array (SMA) in Hawaii, USA, and the Submillimeter Telescope (SMT) in Arizona, USA. They were able to make the sharpest direct observation ever of the center of a distant galaxy, the bright quasar 3C 279, which contains a supermassive black hole with a mass about one billion times that of the Sun, and is so far from Earth that its light has taken more than 5 billion years to reach us. APEX is a collaboration between the Max Planck Institute for Radio Astronomy (MPIfR), the Onsala Space Observatory (OSO) and ESO. APEX is operated by ESO.
The telescopes were linked using a technique known as Very Long Baseline Interferometry (VLBI). Larger telescopes can make sharper observations, and interferometry allows multiple telescopes to act like a single telescope as large as the separation — or “baseline” — between them. Using VLBI, the sharpest observations can be achieved by making the separation between telescopes as large as possible. For their quasar observations, the team used the three telescopes to create an interferometer with transcontinental baseline lengths of 9447 km from Chile to Hawaii, 7174 km from Chile to Arizona and 4627 km from Arizona to Hawaii. Connecting APEX in Chile to the network was crucial, as it contributed the longest baselines.
The observations were made in radio waves with a wavelength of 1.3 millimetres. This is the first time observations at a wavelength as short as this have been made using such long baselines. The observations achieved a sharpness, or angular resolution, of just 28 microarcseconds — about 8 billionths of a degree. This represents the ability to distinguish details an amazing two million times sharper than human vision. Observations this sharp can probe scales of less than a light-year across the quasar — a remarkable achievement for a target that is billions of light-years away.
The observations represent a new milestone towards imaging supermassive black holes and the regions around them. In future it is planned to connect even more telescopes in this way to create the so-called Event Horizon Telescope. The Event Horizon Telescope will be able to image the shadow of the supermassive black hole in the centre of our Milky Way galaxy, as well as others in nearby galaxies. The shadow — a dark region seen against a brighter background — is caused by the bending of light by the black hole, and would be the first direct observational evidence for the existence of a black hole’s event horizon, the boundary from within which not even light can escape.
The experiment marks the first time that APEX has taken part in VLBI observations, and is the culmination of three years hard work at APEX’s high altitude site on the 5000-metre plateau of Chajnantor in the Chilean Andes, where the atmospheric pressure is only about half that at sea level. To make APEX ready for VLBI, scientists from Germany and Sweden installed new digital data acquisition systems, a very precise atomic clock, and pressurized data recorders capable of recording 4 gigabits per second for many hours under challenging environmental conditions. The data — 4 terabytes from each telescope — were shipped to Germany on hard drives and processed at the Max Planck Institute for Radio Astronomy in Bonn.
The successful addition of APEX is also important for another reason. It shares its location and many aspects of its technology with the new Atacama Large Millimeter/submillimeter Array (ALMA) telescope. ALMA is currently under construction and will finally consist of 54 dishes with the same 12-metre diameter as APEX, plus 12 smaller dishes with a diameter of 7 metres. The possibility of connecting ALMA to the network is currently being studied. With the vastly increased collecting area of ALMA’s dishes, the observations could achieve 10 times better sensitivity than these initial tests. This would put the shadow of the Milky Way’s supermassive black hole within reach for future observations.
Black holes powering distant quasars in the early Universe grazed on patches of gas or passing galaxies rather than glutting themselves in dramatic collisions according to new observations from NASA’s Spitzer and Hubble space telescopes.
A black hole doesn’t need much gas to satisfy its hunger and turn into a quasar, says study leader Kevin Schawinski of Yale “There’s more than enough gas within a few light-years from the center of our Milky Way to turn it into a quasar,” Schawinski explained. “It just doesn’t happen. But it could happen if one of those small clouds of gas ran into the black hole. Random motions and stirrings inside the galaxy would channel gas into the black hole. Ten billion years ago, those random motions were more common and there was more gas to go around. Small galaxies also were more abundant and were swallowed up by larger galaxies.”
Quasars are distant and brilliant galactic powerhouses. These far-off objects are powered by black holes that glut themselves on captured material; this in turn heats the matter to millions of degrees making it super luminous. The brightest quasars reside in galaxies pushed and pulled by mergers and interactions with other galaxies leaving a lot of material to be gobbled up by the super-massive black holes residing in the galactic cores.
Schawinski and his team studied 30 quasars with NASA’s orbiting telescopes Hubble and Spitzer. These quasars, glowing extremely bright in the infrared images (a telltale sign that resident black holes are actively scooping up gas and dust into their gravitational whirlpool) formed during a time of peak black-hole growth between eight and twelve billion years ago. They found 26 of the host galaxies, all about the size of our own Milky Way Galaxy, showed no signs of collisions, such as smashed arms, distorted shapes or long tidal tails. Only one galaxy in the study showed evidence of an interaction. This finding supports evidence that the creation of the most massive black holes in the early Universe was fueled not by dramatic bursts of major mergers but by smaller, long-term events.
“Quasars that are products of galaxy collisions are very bright,” Schawinski said. “The objects we looked at in this study are the more typical quasars. They’re a lot less luminous. The brilliant quasars born of galaxy mergers get all the attention because they are so bright and their host galaxies are so messed up. But the typical bread-and-butter quasars are actually where most of the black-hole growth is happening. They are the norm, and they don’t need the drama of a collision to shine.
“I think it’s a combination of processes, such as random stirring of gas, supernovae blasts, swallowing of small bodies, and streams of gas and stars feeding material into the nucleus,” Schawinski said.
Unfortunately, the process powering the quasars and their black holes lies below the detection of Hubble making them prime targets for the upcoming James Webb Space Telescope, a large infrared orbiting observatory scheduled for launch in 2018.
Image caption: These galaxies have so much dust enshrouding them that the brilliant light from their quasars cannot be seen in these images from the NASA/ESA Hubble Space Telescope.
The LABOCA camera on the ESO-operated 12-metre Atacama Pathfinder Experiment (APEX) telescope reveals distant galaxies undergoing the most intense type of star formation activity known, called a starburst. This image shows these distant galaxies, found in a region of sky known as the Extended Chandra Deep Field South, in the constellation of Fornax (The Furnace). The galaxies seen by LABOCA are shown in red, overlaid on an infrared view of the region as seen by the IRAC camera on the Spitzer Space Telescope. Credit: ESO, APEX (MPIfR/ESO/OSO), A. Weiss et al., NASA Spitzer Science Center
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Located on the Chajnantor plateau in the foothills of the Chilean Andes, ESO’s APEX telescope has been busy looking into deep, deep space. Recently a group of astronomers released their findings regarding massive galaxies in connection with extreme times of star formation in the early Universe. What they found was a sharp cut-off point in stellar creation, leaving “massive – but passive – galaxies” filled with mature stars. What could cause such a scenario? Try the materialization of a supermassive black hole…
By integrating data taken with the LABOCA camera on the ESO-operated 12-metre Atacama Pathfinder Experiment (APEX) telescope with measurements made with ESO’s Very Large Telescope, NASA’s Spitzer Space Telescope and other facilities, astronomers were able to observe the relationship of bright, distant galaxies where they form into clusters. They found that the density of the population plays a major role – the tighter the grouping, the more massive the dark matter halo. These findings are the considered the most accurate made so far for this galaxy type.
Located about 10 billion light years away, these submillimetre galaxies were once home to starburst events – a time of intense formation. By obtaining estimations of dark matter halos and combining that information with computer modeling, scientists are able to hypothesize how the halos expanding with time. Eventually these once active galaxies settled down to form giant ellipticals – the most massive type known.
“This is the first time that we’ve been able to show this clear link between the most energetic starbursting galaxies in the early Universe, and the most massive galaxies in the present day,” says team leader Ryan Hickox of Dartmouth College, USA and Durham University, UK.
However, that’s not all the new observations have uncovered. Right now there’s speculation the starburst activity may have only lasted around 100 million years. While this is a very short period of cosmological time, this massive galactic function was once capable of producing double the amount of stars. Why it should end so suddenly is a puzzle that astronomers are eager to understand.
“We know that massive elliptical galaxies stopped producing stars rather suddenly a long time ago, and are now passive. And scientists are wondering what could possibly be powerful enough to shut down an entire galaxy’s starburst,” says team member Julie Wardlow of the University of California at Irvine, USA and Durham University, UK.
Right now the team’s findings are offering up a new solution. Perhaps at one point in cosmic history, starburst galaxies may have clustered together similar to quasars… locating themselves in the same dark matter halos. As one of the most kinetic forces in our Universe, quasars release intense radiation which is reasoned to be fostered by central black holes. This new evidence suggests intense starburst activity also empowers the quasar by supplying copious amounts of material to the black hole. In response, the quasar then releases a surge of energy which could eradicate the galaxy’s leftover gases. Without this elemental fuel, stars can no longer form and the galaxy growth comes to a halt.
“In short, the galaxies’ glory days of intense star formation also doom them by feeding the giant black hole at their centre, which then rapidly blows away or destroys the star-forming clouds,” explains team member David Alexander from Durham University, UK.
Artist's Concept of Water Vapor in Black Hole Disk - Credit: Leiden University
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A eye-opening discovery has been made by an international team of scientists led by astronomer Paul van der Werf (Leiden University, The Netherlands). They have discovered a black hole in the early Universe located about 12 billion light years away that’s surrounded by a nearly impenetrable disk of gas and dust. The halo isn’t the surprise, however… but the presence of star formation in dense water vapor is.
Using the sensitive radio telescopes of IRAM (Institut de Radioastronomie Millimétrique) at the Plateau de Bure in the French Alps, the team was searching for the signs of water vapor around a quasar – a distant galaxy which gathers its luminosity from the growth of a black hole which weighs in at hundreds of millions times more mass than Sol.
“Water in cosmic clouds is normally frozen to ice, but the ice can be evaporated by the strong radiation of the quasar or of young stars. Therefore we decided to search for water vapor in this object.” says van der Werf. “It is located so far away that we are looking back in time, to an era where the Universe was only 10% of its present age. This is one of the first searches ever conducted to find water in the early Universe.”
A shocking revelation? Not really. Water vapor has been discovered before. In this instance, however, the water amounted to about 1,000 trillion times the volume found on Earth. What’s more… it’s forming stars. It’s a dense disk, so thick that light barely escapes, and star propagation is rapid.
“Water molecules are sensitive to infrared radiation, so we could use the water vapor detected as a cosmic infrared light meter. With this method we found that essentially all radiation is locked up in the gas disk surrounding the black hole.” team member Marco Spaans (University of Groningen, The Netherlands) explains. “This trapped radiation is so intense that it will build up enormous pressure and eventually blow away the gas and dust clouds surrounding the black hole.”
These findings add a new complexity to our understanding of black holes and the galaxies which hold them. Team member Alicia Berciano Alba (ASTRON, The Netherlands) says: “There is a mysterious relation between the masses of black holes in the centers of galaxies and the masses of the galaxies themselves, as if the formation of both is regulated by the same process. Our results show that these opaque gas disks, which will be ultimately blown away by the intense pressure of the trapped radiation, probably play a key role in this process.” IRAM director Pierre Cox, co-author of the paper, adds: “This discovery opens new possibilities for studying galaxies in the early Universe, using water molecules that probe regions closest to the central black hole, that are otherwise difficult to explore.”
Keep on going, because the IRAM team is up to the task and continuing to look for other sources of water vapor in the early Universe!
[/caption]Astronomers have uncovered yet another clue in their quest to understand the Universe’s early life: the most distant quasar ever observed. At a redshift of 7.1, it is a relic from when the cosmos was just 770 million years old – just 5% of its age today.
Quasars are extremely old, outrageously luminous balls of radiation that were prevalent in the early Universe. Each is thought to have been fueled at its core by an incredibly powerful supermassive black hole. The most recent discovery (which carries the romantic name ULAS J1120+0641) is noteworthy for a couple of reasons. First of all, its supermassive black hole weighs approximately two billion solar masses – an impressive feat of gravity so soon after the Big Bang. It is also incredibly bright, given its great distance. “Objects that lie at such large distance are almost impossible to find in visible-light surveys because their light is stretched by the expansion of the universe,” said Dr. Simon Dye of the University of Nottingham, a member of the team that discovered the object. “This means that by the time their light gets to Earth, most of it ends up in the infrared part of the electromagnetic spectrum.” Due to these effects, only about 100 visible quasars exist in the sky at redshifts higher than 7.
Up until recently, the most distant quasar observed was at a redshift of 6.4; but thanks to this discovery, astronomers can probe 100 million years further into the history of the Universe than ever before. Careful study of ULAS J1120+0641 and its properties will enable scientists to learn more about galaxy formation and supermassive black hole growth in early epochs. The research was published in the June 30 issue of Nature.
The green "blob" is Hanny's Voorwerp. Credit: Dan Herbert, Peter Smith, Matt Jarvis, Galaxy Zoo Team, Isaac Newton Telescope
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Hanny’s Voorwerp is a popular topic of conversation due to its novel discovery by Hanny Van Arkel perusing images from the Galaxy Zoo project. The tale has become so well known, it was made into a comic book (view here as .pdf, 35MB). But another aspect of the story is how enigmatic the object is. Objects that are so green are rare and it lacked a direct power source to energize it. It was eventually realized a quasar in the neighboring galaxy, IC 2497 could supply the necessary energy. Yet images of the galaxy couldn’t confirm a sufficiently energetic quasar. A new paper discusses what may have happened to the source.
The evidence that a quasar must be involved comes from the green color of the voorwerp itself. Spectra of the object has shown that this coloration is due to a strong level of ionized oxygen, specifically the λ5007 line of O III. While other scenarios could account for this feature alone, the spectra also contained He II emission as well as Ne V and the lines were especially narrow. Should star formation or shockwaves energize the gas, the motions would cause Doppler broadening. An quasar powered Active Galactic Nucleus (AGN) was the best fit.
But when telescopes searched for this quasar in the galaxy, it proved elusive. Optical images from WIYN Observatory were unable to resolve the expected point source. Radio observations discovered an object emitting in this range, but far below the amount of energy necessary to power the luminous Voorwerp. Two solutions have been proposed:
“1) the quasar in IC 2497 features a novel geometry of obscuring material and is obscured at an unprecedented level only along our line of sight, while being virtually unobscured towards the Voorwerp; or 2) the quasar in IC 2497 has shut down within the last 70,000 years, while the Voorwerp remains lit up due to the light travel time from the nucleus.”
Recent observations from Suzaku have ruled out the first of these possibilities due to the lack of potassium absorption that would be expected if light from the galaxy were being absorbed in a significant amount. Thus, the conclusion is that the AGN has dropped in total output by at least two orders of magnitude, but more likely by four. In many ways, this is not entirely unexpected since quasars are plentiful in the distant universe where raw material on which to feed was more plentiful. In the present universe, quasars rarely have such material available and can’t maintain it indefinitely.
Analogs exist within our own galaxy. X-Ray Binaries (XRBs) are stellar mass black holes which form similar accretion disks and can shut down and excite on short timescales (~1 year). The authors of the new paper attempted to scale up a model XRB system to determine if the timescales would fit with the ~70,000 year upper limit imposed by the travel time. While they found a good agreement with the output from direct accretion itself (10,000–100,000 years) the team found a discrepancy in the disk. In XRBs, the material around the black hole is heated as well, and takes some time to cool down. In this case, the core of the galaxy should still retain a hot disc of material which isn’t present.
This oddity demonstrates that there is still a large amount of knowledge to be gained on the physics surrounding these objects. Fortunately, the relatively close proximity of IC 2497 allows for the potential for detailed followup studies.
