supermassive black holes Archives

August 13, 2014December 23, 2015 by Shannon Hall

NASA’S NuSTAR Catches a Black Hole Bending Light, Space, and Time

This plot of data captured by NASA's Nuclear Spectroscopic Telescope Array, or NuSTAR, shows X-ray light streaming from regions near a supermassive black hole known as Markarian 335. Credit: NASA

NASA’s Nuclear Spectroscopic Telescope Array (NuSTAR) has captured a spectacular event: a supermassive black hole’s gravity tugging on nearby X-ray light.

In just a matter of days, the corona — a cloud of particles traveling near the speed of light — fell in toward the black hole. The observations are a powerful test of Einstein’s theory of general relativity, which says gravity can bend space-time, the fabric that shapes our universe, and the light that travels through it.

“The corona recently collapsed in toward the black hole, with the result that the black hole’s intense gravity pulled all the light down onto its surrounding disk, where material is spiraling inward,” said coauthor Michael Parker from the Institute of Astronomy in Cambridge, United Kingdom, in a press release.

The supermassive black hole, known as Markarian 335, is about 324 million light-years from Earth in the direction of the constellation Pegasus. Such an extreme system squeezes about 10 million times the mass of our Sun into a region only 30 times the diameter of the Sun. It spins so rapidly that space and time are dragged around with it.

NASA’s Swift satellite has monitored Mrk 335 for years, recently noting a dramatic change in its X-ray brightness. So NuSTAR was redirected to take a second look at the system.

NuSTAR has been collecting X-rays from black holes and dying stars for the past two years. Its specialty is analyzing high-energy X-rays in the range of 3 to 79 kiloelectron volts. Observations in lower-energy X-ray light show a black hole obscured by clouds of gas and dust. But NuSTAR can take a detailed look at what’s happening near the event horizon, the region around a black hole form which light can no longer escape gravity’s grasp.

Specifically, NuSTAR is able to see the corona’s direct light, and its reflected light off the accretion disk. But in this case, the light is blurred due to the combination of a few factors. First, the doppler shift is affecting the spinning disk. On the side spinning away from us, the light is shifted to redder wavelengths (and therefore lower energy), whereas on the side spinning toward us, the light is shifted to bluer wavelengths (and therefore higher energy). A second effect has to do with the enormous speeds of the spinning black hole. And a final effect is from the gravity of the black hole, which pulls on the light, causing it to lose energy.

All of these factors cause the light to smear.

Intriguingly, NuSTAR observations also revealed that the grip of the black hole’s gravity pulled the corona’s light onto the inner portion of the accretion disk, better illuminating it. NASA explains that as if somebody had shone a flashlight for the astronomers, the shifting corona lit up the precise region they wanted to study.

“We still don’t understand exactly how the corona is produced or why it changes its shape, but we see it lighting up material around the black hole, enabling us to study the regions so close in that effects described by Einstein’s theory of general relativity become prominent,” said NuSTAR Principal Investigator Fiona Harrison of the California Institute of Technology. “NuSTAR’s unprecedented capability for observing this and similar events allows us to study the most extreme light-bending effects of general relativity.”

The new data will likely shed light on these mysterious coronas, where the laws of physics are pushed to their limit.

The article has been published in the Monthly Notices of the Royal Astronomical Society and is available online.

July 9, 2014December 23, 2015 by Shannon Hall

Supermassive Black Hole Blasting Molecular Hydrogen Solves Outstanding Mystery

An artist's conception of a supermassive black hole's jets. Credit: NASA / Dana Berry / SkyWorks Digital

The supermassive black holes in the cores of most massive galaxies wreak havoc on their immediate surroundings. During their most active phases — when they ignite as luminous quasars — they launch extremely powerful and high-velocity outflows of gas.

These outflows can sweep up and heat material, playing a pivotal role in the formation and evolution of massive galaxies. Not only have astronomers observed them across the visible Universe, they also play a key ingredient in theoretical models.

But the physical nature of the outflows themselves has been a longstanding mystery. What physical mechanism causes gas to reach such high speeds, and in some cases be expelled from the galaxy?

A new study provides the first direct evidence that these outflows are accelerated by energetic jets produced by the supermassive black hole.

Using the Very Large Telescope in Chile, a team of astronomers led by Clive Tadhunter from Sheffield University, observed the nearby active galaxy IC 5063. At locations in the galaxy where its jets are impacting regions of dense gas, the gas is moving at extraordinary speeds of over 600,000 miles per hour.

“Much of the gas in the outflows is in the form of molecular hydrogen, which is fragile in the sense that it is destroyed at relatively low energies,” said Tadhunter in a press release. “I find it extraordinary that the molecular gas can survive being accelerated by jets of highly energetic particles moving at close to the speed of light.

As the jets travel through the galactic matter, they disrupt the surrounding gas and generate shock waves. These shock waves not only accelerate the gas, but also heat it. The team estimates the shock waves heat the gas to temperatures high enough to ionize the gas and dissociate the molecules. Molecular hydrogen is only formed in the significantly cooler post-shock gas.

“We suspected that the molecules must have been able to reform after the gas had been completely upset by the interaction with a fast plasma jet,” said Raffaella Morganti from the Kapteyn Institute Groningen University. “Our direct observations of the phenomenon have confirmed that this extreme situation can indeed occur. Now we need to work at describing the exact physics of the interaction.”

In interstellar space, molecular hydrogen forms on the surface of dust grains. But in this scenario, the dust is likely to have been destroyed in the intense shock waves. While it is possible for molecular hydrogen to form without the aid of dust grains (as seen in the early Universe) the exact mechanism in this case is still unknown.

The research helps answer a longstanding question — providing the first direct evidence that jets accelerate the molecular outflows seen in active galaxies — and asks new ones.

The results were published in Nature and are available online.

June 16, 2014March 1, 2017 by Fraser Cain

How Much of the Universe is Black Holes?

We all fear black holes, but how many of them are there out there, really? Between the stellar mass black holes and the supermassive ones, just how much of our Universe is black holes?

There are two kinds of black holes in the Universe that we know of: There’s stellar mass black holes, formed from massive stars, and a supermassive black holes which lives at the hearts of galaxies.

About 1 in a 1000 stars have enough mass to become a black hole when they die. Our Milky Way has 100 billion stars, this means it could have up to 100 million stellar mass black holes. As there are hundreds of billions of galaxies in the observable Universe, there are lots, lots more out there. In fact, the math suggests there’s a new black hole forming every second or so. So just to recap, the entire Universe is about 1/1000th “regular flavor” stellar mass black holes.

Supermassive black holes are a slightly different story. Our central galactic black hole is about 26,000 light years away from us. Formally, it’s called Sagittarius A-star, but for our purposes I’m going to call it Kevin. Just so you know they don’t throw that term “supermassive” around for no reason, Kevin contains 4.1 million times the mass of the Sun.

Kevin is gigantic and horrible. We can only imagine what it’s like to be in the region of space near Kevin. What percentage of the galaxy do you think Kevin makes up, mass wise?

Kevin, whilst absolutely super-massive, is a tiny, tiny 1/10,000 of a percent of the Milky Way galaxy’s mass. So, to be precise, if we add Kevin’s mass to the mass of all the stellar mass black holes aka. “mini-Kevins”, we get a very minor 11/10000s of a %.

As it turns out this ratio holds up on a Universal scale and is approximately the same for all the mass in the Universe. So, 11 ten thousandths of a percent is the answer to the question. As far as we know.

Unless… dark matter is black holes. Dark matter accounts for more than ¾ of the mass of the Universe. It doesn’t absorb light or interact with matter in any way. We’re only aware of its presence through its gravitational influence.

Artistic view of a radiating black hole. Credit: NASA

As it turns out, Astronomers think that one explanation for dark matter might be primordial black holes. These microscopic black holes would have the mass of an asteroid or more and could only form in the high pressure, high temperature conditions after the Big Bang.

Experiments to search for primordial black holes have yet to turn up any evidence, and most scientists don’t think they’re a viable explanation. But if they were, then the Universe is almost entirely composed of the physics inspired nightmare that are black holes.

If it’s not the case now, in the far future, everything could be. Given enough time, all those stellar black holes and supermassive Kevins will scoop up all the available material in the Universe.

In 10 quintillion years everything in the Universe will have either fallen into a black hole, or been flung out on an escape trajectory. And then those black holes will slowly evaporate over time, as predicted by Stephen Hawking.

In 10^66 years the smallest stellar black holes will have evaporated. The most massive supermassive black holes could take 10^100 years. And then, there won’t be any black holes at all.

What do you think? Is it mostly black holes or almost no black holes? Tell us what you suspect in the comments below.

May 2, 2014December 23, 2015 by Nancy Atkinson

Object “G2” Still Intact at Closest Approach to Galactic Center, Astronomers Report

This simulation shows the future behaviour of a gas cloud that has been observed approaching the black hole at the center of the Milky Way. Graphic by ESO/MPE/Marc Schartmann.

The latest observations by the Keck Observatory in Hawaii show that the gas cloud called “G2” was surprisingly still intact, even during its closest approach to the supermassive black hole at the center of our Milky Way galaxy. Astronomers from the UCLA Galactic Center Group reported today that observations obtained on March 19 and 20, 2014 show the object’s density was still “robust” enough to be detected. This means G2 is not just a gas cloud, but likely has a star inside.

“We conclude that G2, which is currently experiencing its closest approach, is still intact,” said the group in an Astronomer’s Telegram, “in contrast to predictions for a simple gas cloud hypothesis and therefore most likely hosts a central star. Keck LGSAO observations of G2 will continue in the coming months to monitor how this unusual object evolves as it emerges from periapse passage.”

We’ve been reporting on this object since its discovery was announced in 2012. G2 was first spotted in 2011 and was quickly deemed to be heading towards our galaxy’s supermassive black hole, called Sgr A*. G2 is not falling directly into the black hole, but it will pass Sgr A* at about 100 times the distance between Earth and the Sun. But that was close enough that astronomers predicted that G2 was likely doomed for destruction.

But it appears to still be hanging in there, at least in mid-March 2014.

Montage of simulation images showing G2 during its close approach to the black hole at the center of the Milky Way. Images by ESO/MPE/Marc Schartmann

Earlier this week, we explained how there were two ideas of what G2 is: one is a simple gas cloud, and the second opinion is that it is a star surrounded by gas. Some astronomers argue that they aren’t seeing the amount of stretching or “spaghettification” that would be expected if this was just a cloud of gas.

The latest word seems to confirm that G2 is more than just a cloud of gas.

This is exciting for astronomers, since they usually don’t get to see events like this take place “in real time.” In astrophysics, timescales of events taking place are usually very long — not over the course of several months. But it’s important to note that G2 actually met its demise around 25,000 years ago. Because of the amount of time it takes light to travel, we can only now observe this event which happened long ago.

We’ll keep you posted on any future news and observations.

January 28, 2014December 23, 2015 by Elizabeth Howell

What Fuels The Engine Of A Supermassive Black Hole?

Orbiting near a moving black hole doesn't seem like the safest mode of transportation, but time dilation might make it worth the risk. Credit: NAOJ

If you could get a good look at the environment around a supermassive black hole — which is a black hole often found in the center of the galaxy — what factors would make that black hole keep going?

A Japanese study revealed that at least one of these black holes stay “active and luminous” by gobbling up nearby material, but notes that only a few of the observed galaxies that are merging have these types of black holes. This must mean something unique arises in the environment near the black hole to get it going, the researchers say. What that is, though, is still poorly understood.

Supermassive black holes, defined as black holes that have a million times the mass of the sun or more, reside in galaxy centers. “The merger of gas-rich galaxies with SMBHs [supermassive black holes] in their centers not only causes active star formation, but also stimulates mass accretion onto the existing SMBHs,” stated a press release from the Subaru Telescope.

“When material accretes onto a SMBH, the accretion disk surrounding the black hole becomes very hot from the release of gravitational energy, and it becomes very luminous. This process is referred to as active galactic nucleus (AGN) activity; it is different from the energy generation activity by nuclear fusion reactions within stars.”

Figuring out how these types of activity vary would give a clue as to how galaxies come together, the researchers said, but it’s hard to see anything in action because of dust and gas blocking the view of optical telescopes. That’s why infrared observations come in so handy, because it makes it easier to peer through the debris. (You can see some examples from this research below.)

Examples of infrared K-band images of luminous, gas-rich, merging galaxies. Credit: NAOJ

The team (led by the National Astronomical Observatory of Japan’s Masatoshi Imanishi) used NAOJ’s Subaru’s Infrared Camera and Spectrograph (IRCS) and the telescope’s adaptive optics system in two bands of infrared. Researchers looked at 29 luminous gas-rich merging galaxies in the infrared and found “at least” one active supermassive black hole in all but one of the ones studied. However, only four of these galaxies merging had multiple, active black holes.

“The team’s results mean that not all SMBHs in gas-rich merging galaxies are actively mass accreting, and that multiple SMBHs may have considerably different mass accretion rates onto SMBHs,” Subaru stated.

The implication is more about the environment around a supermassive black hole must be understood to figure out how mass accretes. Knowing more about this will improve computer simulations of galaxy mergers, the researchers said.

You can read the published study in the Astrophysical Journal or in prepublished form on Arxiv.

Source: Subaru Telescope

December 16, 2013March 14, 2017 by Fraser Cain

Can Stars Collide?

Imagine a really bad day. Perhaps you’re imagining a day where the Sun crashes into another star, destroying most of the Solar System.

No? Well then, even in your imagination things aren’t so bad… It’s all just matter of perspective.

Fortunately for us, we live in out the boring suburbs of the Milky Way. Out here, distances between stars are so vast that collisions are incredibly rare. There are places in the Milky Way where stars are crowded more densely, like globular clusters, and we get to see the aftermath of these collisions. These clusters are ancient spherical structures that can contain hundreds of thousands of stars, all of which formed together, shortly after the Big Bang.

Within one of these clusters, stars average about a light year apart, and at their core, they can get as close to one another as the radius of our Solar System. With all these stars buzzing around for billions of years, you can imagine they’ve gotten up to some serious mischief.

Within globular clusters there are these mysterious blue straggler stars. They’re large hot stars, and if they had formed with the rest of the cluster, they would have detonated as supernovae billions of years ago. So scientists figure that they must have formed recently.

How? Astronomers think they’re the result of a stellar collision. Perhaps a binary pair of stars merged, or maybe two stars smashed into one another.

Professor Mark Morris of the University of California at Los Angeles in the Department of Physics and Astronomy helps to explain this idea.

“When you see two stars colliding with each other, it depends on how fast they’re moving. If they’re moving at speeds like we see at the center of our galaxy, then the collision is extremely violent. If it’s a head-on collision, the stars get completely splashed to the far corners of the galaxy. If they’re merging at slower velocities than we see at our neck of the woods in our galaxy, then stars are more happy to merge with us and coalesce into one single, more massive object.”

There’s another place in the Milky Way where you’ve got a dense collection of stars, racing around at breakneck speeds… near the supermassive black hole at the center of the galaxy.

This monster black hole contains the mass of 4 million times the Sun, and dominates the region around the center of the Milky Way.

“The core of the Milky Way is one of those places where you find the extremes of nature. The density of stars there is higher than anywhere else in the galaxy,”Professor Morris continues. “Overall, in the center of our galaxy on scales of hundreds of light years, there is much more gas present than anywhere else in the galaxy. The magnetic field is stronger there than anywhere else in the galaxy, and it has it’s own geometry there. So it’s an unusual place, an energetic place, a violent place, because everything else is moving so much faster there than you see elsewhere.”

“We study the stars in the immediate vicinity of the black hole, and we find that there’s not as many stars as one might have expected, and one of the explanations for that is that stars collide with each other and either eliminate one another or merge, and two stars become one, and both of those processes are probably occurring.”

Stars whip around it, like comets dart around our Sun, and interactions are commonplace.

There’s another scenario that can crash stars together.

The Milky Way mostly has multiple star systems. Several stars can be orbiting a common center of gravity. Many are great distances, but some can have orbits tighter than the planets around our Sun.

When one star reaches the end of its life, expanding into a red giant, It can consume its binary partner. The consumed star then strips away 90% of the mass of the red giant, leaving behind a rapidly pulsating remnant.

What about when galaxies collide? That sounds like a recipe for mayhem.
Surprisingly, not so much.

“That’s actually a very interesting question, because if you imagine two galaxies colliding, you’d imagine that to be an exceptionally violent event,’ Professor Morris explains. “But in fact, the stars in those two galaxies are relatively unaffected. The number of stars that will collide when two galaxies collide is possibly counted on the fingers of one or two hands. Stars are so few and far between that they just aren’t going to meet each other with any significance in a field like that.”

Galaxy mergers, such as the Mice Galaxies will be part of Galaxy Zoo's newest project. Credit: Hubble Space Telescope — The Mice galaxies merging. Credit: Hubble Space Telescope

“What you see when you see two galaxies collide, however, on the large scale, is that the tidal forces of the two galaxies will rip each of the galaxies apart in terms of what it will look like. Streams of stars will be strewn out in various directions depending on the precise history of the interaction between the two galaxies. And so, eventually over time, the galaxies will merge, the whole configuration of stars will settle down into something that looks unlike either of the two initially colliding galaxies. Perhaps something more spheroidal or spherical, and it might look more like an elliptical galaxy than the spiral galaxy that these two galaxies now are.”

Currently, we’re on a collision course with the Andromeda Galaxy, and it’s expected we’ll smash into it in about 4 billion years. The gas and dust will collide and pile up, igniting an era of furious star formation. But the stars themselves? They’ll barely notice. The stars in the two galaxies will just streak past each other, like a swarm of angry bees.

Phew.

So, good news! When you’re imagining a worse day, you won’t have to worry about our Sun colliding with another star. We’re going to be safe and sound for billions of years. But if you live in a globular cluster or near the center of the galaxy, you might want to check out some property here in the burbs.

Thanks to Professor Mark Morris at UCLA – visit their Physics and Astronomy program homepage here.

August 13, 2013April 26, 2016 by Shannon Hall

How Do Black Holes Get Super Massive?

A binary black hole pair with an accretion disk inclined 45 degrees. Source: Nixon et al.

Since their discovery, supermassive black holes – the giants lurking in the center of every galaxy – have been mysterious in origin. Astronomers remain baffled as to how these supermassive black holes became so massive.

New research explains how a supermassive black hole might begin as a normal black hole, tens to hundreds of solar masses, and slowly accrete more matter, becoming more massive over time. The trick is in looking at a binary black hole system. When two galaxies collide the two supermassive black holes sink to the center of the merged galaxy and form a binary pair. The accretion disk surrounding the two black holes becomes misaligned with respect to the orbit of the binary pair. It tears and falls onto the black hole pair, allowing it to become more massive.

In a merging galaxy the gas flows are turbulent and chaotic. Because of this “any gas feeding the supermassive black hole binary is likely to have angular momentum that is uncorrelated with the binary orbit,” Dr. Chris Nixon, lead author on the paper, told Universe Today. “This makes any disc form at a random angle to the binary orbit.

Nixon et al. examined the evolution of a misaligned disk around a binary black hole system using computer simulations. For simplicity they analyzed a circular binary system of equal mass, acting under the effects of Newtonian gravity. The only variable in their models was the inclination of the disk, which they varied from 0 degrees (perfectly aligned) to 120 degrees.

After running multiple calculations, the results show that all misaligned disks tear. Watch tearing in action below:

In most cases this leads to direct accretion onto the binary.

“The gravitational torques from the binary are capable of overpowering the internal communication in the gas disc (by pressure and viscosity),” explains Nixon. “This allows gas rings to be torn off, which can then be accreted much faster.”

Such tearing can produce accretion rates that are 10,000 times faster than if the exact same disk were aligned.

In all cases the gas will dynamically interact with the binary. If it is not accreted directly onto the black hole, it will be kicked out to large radii. This will cause observable signatures in the form of shocks or star formation. Future observing campaigns will look for these signatures.

In the meantime, Nixon et al. plan to continue their simulations by studying the effects of different mass ratios and eccentricities. By slowly making their models more complicated, the team will be able to better mimic reality.

Quick interjection: I love the simplicity of this analysis. These results provide an understandable mechanism as to how some supermassive black holes may have formed.

While these results are interesting alone – based on that sheer curiosity that drives the discipline of astronomy forward – they may also play a more prominent role in our local universe.

Before we know it (please read with a hint of sarcasm as this event will happen in 4 billion years) we will collide with the Andromeda galaxy. This rather boring event will lead to zero stellar collisions and a single black hole collision – as the two supermassive black holes will form a binary pair and then eventually merge.

Without waiting for this spectacular event to occur, we can estimate and model the black hole collision. In 4 billion years the video above may be a pretty good representation of our collision with the Andromeda galaxy.

The results have been published in the Astrophysical Journal Letters (preprint available here). (Link was corrected to correct paper on 8/15/2013).

February 27, 2013December 23, 2015 by Tammy Plotner

NuSTAR Puts New Spin On Supermassive Black Holes

A supermassive black hole has been found in an unusual spot: an isolated region of space where only small, dim galaxies reside. Image credit: NASA/JPL-Caltech — A team of astronomers from South Africa have noticed a series of supermassive black holes in distant galaxies that are all spinning in the same direction. Credit: NASA/JPL-Caltech

Checking out the spin rate on a supermassive black hole is a great way for astronomers to test Einstein’s theory under extreme conditions – and take a close look at how intense gravity distorts the fabric of space-time. Now, imagine a monster … one that has a mass of about 2 million times that of our Sun, measures 2 million miles in diameter and rotating so fast that it’s nearly breaking the speed of light.

A fantasy? Not hardly. It’s a supermassive black hole located at the center of spiral galaxy NGC 1365 – and it is about to teach us a whole lot more about how black holes and galaxies mature.

What makes researchers so confident they have finally taken definitive calculations of such an incredible spin rate in a distant galaxy? Thanks to data taken by the Nuclear Spectroscopic Telescope Array, or NuSTAR, and the European Space Agency’s XMM-Newton X-ray satellites, the team of scientists has peered into the heart of NGC 1365 with x-ray eyes – taking note of the location of the event horizon – the edge of the spinning hole where surrounding space begins to be dragged into the mouth of the beast.

“We can trace matter as it swirls into a black hole using X-rays emitted from regions very close to the black hole,” said the coauthor of a new study, NuSTAR principal investigator Fiona Harrison of the California Institute of Technology in Pasadena. “The radiation we see is warped and distorted by the motions of particles and the black hole’s incredibly strong gravity.”

However, the studies didn’t stop there, they advanced to the inner edge to encompass the location of the accretion disk. Here is the “Innermost Stable Circular Orbit” – the proverbial point of no return. This region is directly related to a black hole’s spin rate. Because space-time is distorted in this area, some of it can get even closer to the ISCO before being pulled in. What makes the current data so compelling is to see deeper into the black hole through a broader range of x-rays, allowing astronomers to see beyond veiling clouds of dust which only confused past readings. These new findings show us it isn’t the dust that distorts the x-rays – but the crushing gravity.

Scientists measure the spin rates of supermassive black holes by spreading the X-ray light into different colors. Image credit: NASA/JPL-Caltech

“This is the first time anyone has accurately measured the spin of a supermassive black hole,” said lead author Guido Risaliti of the Harvard-Smithsonian Center for Astrophysics (CfA) and INAF — Arcetri Observatory.

“If I could have added one instrument to XMM-Newton, it would have been a telescope like NuSTAR,” said Norbert Schartel, XMM-Newton Project Scientist at the European Space Astronomy Center in Madrid. “The high-energy X-rays provided an essential missing puzzle piece for solving this problem.”

Even though the central black hole in NGC 1365 is a monster now, it didn’t begin as one. Like all things, including the galaxy itself, it evolved with time. Over millions of years it gained in girth as it consumed stars and gas – possibly even merging with other black holes along the way.

“The black hole’s spin is a memory, a record, of the past history of the galaxy as a whole,” explained Risaliti.

“These monsters, with masses from millions to billions of times that of the sun, are formed as small seeds in the early universe and grow by swallowing stars and gas in their host galaxies, merging with other giant black holes when galaxies collide, or both,” said the study’s lead author, Guido Risaliti of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., and the Italian National Institute for Astrophysics.

This new spin on black holes has shown us that a monster can emerge from “ordered accretion” – and not simply random multiple events. The team will continue their studies to see how factors other than black hole spin changes over time and continue to observe several other supermassive black holes with NuSTAR and XMM-Newton.

“This is hugely important to the field of black hole science,” said Lou Kaluzienski, NuSTAR program scientist at NASA Headquarters in Washington, D.C. “NASA and ESA telescopes tackled this problem together. In tandem with the lower-energy X-ray observations carried out with XMM-Newton, NuSTAR’s unprecedented capabilities for measuring the higher energy X-rays provided an essential, missing puzzle piece for unraveling this problem.”

Original Story Source: JPL/NASA News Release.

May 22, 2012December 23, 2015 by Jon Voisey

A Planetary System That Never Was Teaches About Those That May Be

While Kepler and similar missions are turning up planets by the fist full, there’s long been many places that astronomers haven’t expected to find planetary systems. The main places include regions where gravitational forces conspire to make the region around potential host stars too unstable to form into planets. And there’s no place in the galaxy with a larger gravitational force than the galactic center where a black hole four and a half million times more massive than the Sun, lurks. But a new study shows evidence that a disk, potentially far enough along to begin forming planets, is in the process of being disrupted.

The new study investigates an ionized cloud of gas discovered earlier this year, plummeting in towards the black hole. The cloud has been formed into an elliptical ring with a maximum distance of 0.04 parsecs (1 parsec 3.24 light years) which is coincident with a ring of young stars that orbit the black hole. At such distances from us, astronomers have been unable to learn much about the population of stars that may exist since only the brightest, most massive stars are visible.

However, such massive stars are able to determine an age limit for the group, which has been set somewhere between 4-8 million years. This age is crucial since most low-mass stars retain gas disks and are held to form planets at an age around 3 million years young. But by an age of 5 million years, the stars have begun clearing out that disk system halting planetary formation and only one fifth of stars less than 1 solar mass retain their disks.

This entire process is even more precarious because the gravitational perturbations from the nearby black hole would begin eating away at the edge of a potential disk. Astronomers predict that this should limit the size to 12 AU in radius. For even less massive stars, this could be as small as 8 AU. Still, theory predicts that these truncated disks could form in the vicinity of the Milky Way’s black hole. But such small disks would be impossible to observe directly with present technology.

The new research suggests that one of these stars was knocked from its stable orbit in the ring in much the same way that comets in the Oort cloud are occasionally jostled into falling towards the inner solar system. There, the tidal forces from the black hole as well as heavily ionizing UV radiation created by the black hole’s accretion disk would strip the gas and dust from the parent star, which is too faint to see directly, leaving it in an elliptical orbit.

If this theory is correct, it would provide the first indirect evidence of the presence of planet forming disks near the galactic center. This comes on top of evidence from earlier this year suggesting stars may be able to form in situ near the galactic center making this region a far more dynamic place than previously expected.

Yet, even if planets do form, living near a supermassive black hole is still not a hospitable place for life. The extreme amounts of UV radiation emitted as the black hole devours gas and dust is likely to sterilize the region.

March 21, 2012April 26, 2016 by Tammy Plotner

Speca – An Intriguing Look Into The Beginning Of A Black Hole Jet

A unique galaxy, which holds clues to the evolution of galaxies billions of years ago, has now been discovered by an Indian-led international team of astronomers. The discovery, which will enable scientists to unearth new aspects about the formation of galaxies in the early universe, has been made using the Giant Meterwave Radio Telescope (GMRT) of the National Centre for Radio Astrophysics, Tata Institute of Fundamental Research (NCRA-TIFR). CREDIT: Hota et al., SDSS, NCRA-TIFR, NRAO/AUI/NSF.

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Its name is SPECA – a Spiral-host Episodic radio galaxy tracing Cluster Accretion. That’s certainly a mouthful of words for this unusual galaxy, but there’s a lot more going on here than just its name. “This is probably the most exotic galaxy with a black hole, ever seen. It is like a ‘missing-link’ between present day and past galaxies. It has the potential to teach us new lessons about how galaxies and clusters of galaxies formed in the early Universe,” said Ananda Hota, of the Academia Sinica Institute of Astronomy and Astrophysics (ASIAA), in Taiwan and who discovered this exotic galaxy.

Located about 1.7 billion light-years from Earth, Speca is a radio source that contains a central supermassive black hole. As we have learned, galaxies of this type produce relativistic “jets” which are responsible for being bright at the radio frequencies, but that’s not all they create. While radio galaxies are generally elliptical, Speca is a spiral – reason behind is really unclear. As the relativistic jets surge with time, they create lobes of sub-atomic material at the outer edges which fan out as the material slows down… and Speca is one of only two galaxies so far discovered to show this type of recurrent jet activity. Normally it occurs once – and rarely twice – but here it has happened three times! We are looking at a unique opportunity to unravel the mysteries of the beginning phase of a black hole jet.

“Both elliptical and spiral galaxies have black holes, but Speca and another galaxy have been seen to produce large jets. It is also one of only two galaxies to show that such activity occurred in three separate episodes.” explains Sandeep Sirothia of NCRA-TIFR. “The reason behind this on-off activity of the black hole to produce jets is unknown. Such activities have not been reported earlier in spiral galaxies, which makes this new galaxy unique. It will help us learn new theories or change existing ones. We are now following the object and trying to analyse the activities.”

Dr. Hota and an international team of scientists reached their first conclusions while studying combined data from the visible-light Sloan Digital Sky Survey (SDSS) and the FIRST survey done with the Very Large Array (VLA) radio telescope. Here they discovered an unusually high rate of star formation where there should be none and they then confirmed their findings with ultraviolet data from NASA’s GALEX space telescope. Then the team dug even deeper with radio information obtained from the NRAO VLA Sky Survey (NVSS). At several hundred million years old, these outer lobes should be beyond their reproductive years… Yet, that wasn’t all. GMRT images displayed yet another, tiny lobe located just outside the stars at the edge of Speca in plasma that is just a few million years old.

“We think these old, relic lobes have been ‘re-lighted’ by shock waves from rapidly-moving material falling into the cluster of galaxies as the cluster continues to accrete matter,” said Ananda. “All these phenomena combined in one galaxy make Speca and its neighbours a valuable laboratory for studying how galaxies and clusters evolved billions of years ago.”

As you watch the above galaxy merger simulation created by Tiziana Di Matteo, Volker Springel, and Lars Hernquist, you are taking part in a visualization of two galaxies combining which both have central supermassive black holes and the gas distribution only. As they merge, you time travel over two billion years where the brightest hues indicate density while color denotes temperature. Such explosive process for the loss of gas is needed to understand how two colliding star-forming spiral galaxies can create an elliptical galaxy… a galaxy left with no fuel for future star formation. Outflow from the supernovae and central monster blackholes are the prime drivers of this galaxy evolution.

“Similarly, superfast jets from black holes are supposed to remove a large fraction of gas from a galaxy and stop further star formation. If the galaxy is gas-rich in the central region, and as the jet direction changes with time, it can have an adverse effect on the star formation history of a galaxy. Speca may have once been part of such a scenario. Where multiple jets have kicked out spiral arms from the galaxy. To understand such a process Dr Hota’s team has recently investigated NGC 3801 which has very young jet in very early-phase of hitting the host galaxy. Dust/PAH, HI and CO emission shows an extremely warped gas disk. HST data clearly showa outflow of heated-gas. This gas loss, as visualised in the video, has possibly caused the decline of star formation. However, the biggest blow from the monster’s jets are about to give the knock-down punch the galaxy.

“It seems, we observe this galaxy at a rare stage of its evolutionary sequence where post-merger star formation has already declined and new powerful jet feedback is about to affect the gaseous star forming outer disk within the next 10 million years to further transform it into a red-and-dead early-type galaxy.” Dr. Hota says.

The causes behind why present day radio galaxies do not contain a young star forming disks are not clear. Speca and NGC 3801 are ideal laboratories to understand black hole galaxy co-evolution processes.

Original Research Paper: Caught in the act: A post-merger starforming early-type galaxy with AGN-jet feedback. For Further Reading: Various press releases and news on the discovery of Speca. This article has been changed slightly from its original publication to reflect more information from Dr. Hota.