Posted on by Jason Major

Our Galaxy’s Supermassive Black Hole is a Sloppy Eater

X-ray and infrared image of Sgr A*, the supermassive black hole in the center of the Milky Way

Like most galaxies, our Milky Way has a dark monster in its middle: an enormous black hole with the mass of 4 million Suns inexorably dragging in anything that comes near. But even at this scale, a supermassive black hole like Sgr A* doesn’t actually consume everything that it gets its gravitational claws on — thanks to the Chandra X-ray Observatory, we now know that our SMB is a sloppy eater and most of the material it pulls in gets spit right back out into space.

(Perhaps it should be called the Cookie Monster in the middle.*)

New Chandra images of supermassive black hole Sagittarius A*, located about 26,000 light-years from Earth, indicate that less than 1% of the gas initially within its gravitational grasp ever reaches the event horizon. Instead, much of the gas is ejected before it gets near the event horizon and has a chance to brighten in x-ray emissions.

The new findings are the result of one of the longest campaigns ever performed with Chandra, with observations made over 5 weeks’ time in 2012.

Read more: Chandra Stares Deep into the Heart of Sagittarius A*

“This new Chandra image is one of the coolest I’ve ever seen,” said study co-author Sera Markoff of the University of Amsterdam in the Netherlands. “We’re watching Sgr A* capture hot gas ejected by nearby stars, and funnel it in towards its event horizon.”

As it turns out, the wholesale ejection of gas is necessary for our resident supermassive black hole to capture any at all. It’s a physics trade-off.

“Most of the gas must be thrown out so that a small amount can reach the black hole”, said co-author Feng Yuan of Shanghai Astronomical Observatory in China. “Contrary to what some people think, black holes do not actually devour everything that’s pulled towards them. Sgr A* is apparently finding much of its food hard to swallow.”

X-ray image of Sgr A*
X-ray image of Sgr A*

If it seems odd that such a massive black hole would have problems slurping up gas, there are a couple of reasons for this.

One is pure Newtonian physics: to plunge over the event horizon, material captured — and subsequently accelerated — by a black hole must first lose heat and momentum. The ejection of the majority of matter allows this to occur.

The other is the nature of the environment in the black hole’s vicinity. The gas available to Sgr A* is very diffuse and super-hot, so it is hard for the black hole to capture and swallow it. Other more x-ray-bright black holes that power quasars and produce huge amounts of radiation have much cooler and denser gas reservoirs.

Illustration of gas cloud G2 approaching Sgr A* (ESO/MPE/M.Schartmann/J.Major)
Illustration of gas cloud G2 approaching Sgr A* (ESO/MPE/M.Schartmann/J.Major)

Located relatively nearby, Sgr A* offers scientists an unprecedented view of the feeding behaviors of such an exotic astronomical object. Currently a gas cloud several times the mass of Earth, first spotted in 2011, is moving closer and closer to Sgr A* and is expected to be ripped apart and partially consumed in the coming weeks. Astronomers are eagerly awaiting the results.

“Sgr A* is one of very few black holes close enough for us to actually witness this process,” said Q. Daniel Wang of the University of Massachusetts at Amherst, who led the study.

Watch Black Holes: Monsters of the Cosmos

Source: Chandra press release. Read the team’s paper here.

Image credits: X-ray: NASA/UMass/D.Wang et al., IR: NASA/STScI

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*Any resemblance of Sgr A* to an actual Muppet, real or fictitious, is purely coincidental.

Posted on by Shannon Hall

When do Black Holes Become Active? The Case of the Strangely-Shaped Galaxy Mrk 273

Mrk 273 as seen by the Hubble Space Telescope.

The Hubble image above shows a strange galaxy, known as Mrk 273.  The odd shape – including the infrared bright center and the long tail extending into space for 130 thousand light-years – is strongly indicative of a merger between galaxies.

Near-infrared observations have revealed a nucleus with multiple components, but for years the details of such a sight have remained obscured by dust. With further data from the Keck Telescope, based in Hawaii, astronomers have verified that this object is the result of a merger between galaxies, with the infrared bright center consisting of two active galactic nuclei – intensely luminous cores powered by supermassive black holes.

At the center of every single galaxy is a supermassive black hole. While the name sounds exciting, our supermassive black hole, Sgr A* is pretty quiescent.  But at the center of every early galaxy looms the opposite: an active galactic nuclei (AGN for short). There are plenty of AGN in the nearby Universe as well, but the question stands: how and when do these black holes become active?

In order to find the answer astronomers are looking at merging galaxies. When two galaxies collide, the supermassive black holes fall toward the center of the merged galaxy, resulting in a binary black hole system. At this stage they remain quiescent black holes, but are likely to become active soon.

“The accretion of material onto a quiescent black hole at the center of a galaxy will enable it to grow in size, leading to the event where the nucleus is “turned on” and becomes active,” Dr. Vivian U, lead author on the study, told Universe Today. “Since galaxy interaction provides means for gaseous material in the progenitor galaxies to lose angular momentum and funnels toward the center of the system, it is thought to play a role in triggering AGN.  However, it has been difficult to pinpoint exactly how and when in a merging system this triggering occurs.”

While it has been known that an AGN can “turn on” before the final coalescence of the two black holes, it is unknown as to when this will happen. Quite a few systems do not host dual AGN.  For those that do, we do not know whether synchronous ignition occurs or not.

Mrk 273 provides a powerful example to study. The team used near-infrared instruments on the Keck Telescope in order to probe past the dust.  Adaptive optics also removed the blurring affects caused by the Earth’s atmosphere, allowing for a much cleaner image – matching the Hubble Space Telescope, from the ground.

“The punch line is that Mrk 273, an advanced late-stage galaxy merger system, hosts two nuclei from the progenitor galaxies that have yet to fully coalesce,” explains Dr. U. The presence of two supermassive black holes can be easily discerned from the rapidly rotating gas disks that surround the two nuclei.

“Both nuclei have already been turned on as evidenced by collimated outflows (a typical AGN signature) that we observe” Dr. U told me. Such a high amount of energy released from both supermassive black holes suggests that Mrk 273 is a dual AGN system. These exciting results mark a crucial step in understanding how galaxy mergers may “turn on” a supermassive black hole.

The team has collected near-infrared data for a large sample of galaxy mergers at different merging states.  With the new data set, Dr. U aims “to understand how the nature of the nuclear star formation and AGN activity may change as a galaxy system progresses through the interaction.”

The results will be published in the Astrophysical Journal (preprint available here).

 

Posted on 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).

Posted on by Fraser Cain

What Is A Quasar?

What Is A Quasar?

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.
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/ESA
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/ESA
We 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.

An artist's impression of how quasars might be able to construct their own host galaxies. Image Credit: ESO/L. CalçadaWhen 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.

If you’d like more information on Quasars, check out NASA’s Discussion on Quasars, and here’s a link to NASA’s Ask an Astrophysicist Page about Quasars.

We’ve also recorded an entire episode of Astronomy Cast all about Quasars Listen here, Episode 98: Quasars.

Sources: UT-Knoxville, NASA, Wikipedia

Posted on by Tammy Plotner

Pulled Apart By Black Hole Heart

New observations from ESO’s Very Large Telescope show for the first time a gas cloud being ripped apart by the supermassive black hole at the centre of the galaxy. Shown here are VLT observations from 2006, 2010 and 2013, coloured blue, green and red respectively. Credit: ESO/S. Gillessen

If you thought all was reasonably quiet at the center of the Milky Way, you’d be wrong. Of course, you knew there was a black hole waiting… but did you know the ESO’s Very Large Telescope has seen a cloud of gas being ripped apart by its influence? Thanks to new observations, we’re able to see – in real time – a gaseous region so stretched that its leading edge has reached the event horizon and it’s retreating from the black hole at more than 10 million km/h while the trailing end is still falling inward!

Just two years ago, the VLT observed a gas cloud several times the mass of Earth making haste towards the Milky Way’s central black hole… an oblivion which dwarfs the cloud by about a trillion times. Right now the plucky cloud has reached its closest approach and “spaghettification” has began. The vaporous vagabond is being stretched out of proportion by the black hole’s gravitational field.

“The gas at the head of the cloud is now stretched over more than 160 billion kilometres around the closest point of the orbit to the black hole. And the closest approach is only a bit more than 25 billion kilometres from the black hole itself — barely escaping falling right in,” explains Stefan Gillessen (Max Planck Institute for Extraterrestrial Physics, Garching, Germany) who led the observing team. “The cloud is so stretched that the close approach is not a single event but rather a process that extends over a period of at least one year.”

At this point, the gas cloud is becoming so thin that its light is difficult to detect. However, by using the SINFONI instrument on the VLT, researchers took 20 hours of exposure time with the integral field spectrometer and were able to measure the velocity of various regions of the gas cloud as it blazes by the black hole.

“The most exciting thing we now see in the new observations is the head of the cloud coming back towards us at more than 10 million km/h along the orbit — about 1% of the speed of light,” adds Reinhard Genzel, leader of the research group that has been studied this region for nearly twenty years. “This means that the front end of the cloud has already made its closest approach to the black hole.”

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Where the gas cloud originated is anyone’s guess – but there are suggestions. Possibilities include jets from the galactic center, or stellar winds from orbiting stars. There may have once been a star in the center of the cloud, and the gas may have been a product of its winds or even a protoplanetary disk. In any circumstance, these new observations help to sort out the variety of possibilities.

“Like an unfortunate astronaut in a science fiction film, we see that the cloud is now being stretched so much that it resembles spaghetti. This means that it probably doesn’t have a star in it,” concludes Gillessen. “At the moment we think that the gas probably came from the stars we see orbiting the black hole.”

It’s an exciting time to be an astronomer. Through the “eyes” of the VLT, researchers the world over are able to watch a very unique event as it happens and not after the fact. ” This intense observing campaign will provide a wealth of data, not only revealing more about the gas cloud, but also probing the regions close to the black hole that have not been previously studied and the effects of super-strong gravity.”

As this drama at the heart of the Milky Way unfolds, astronomers are able to witness its many changes – “from purely gravitational and tidal to complex, turbulent hydrodynamics.”

Original Story Source: ESO News Release.

Posted on by Tammy Plotner

Dust In The Wind… Black Hole Style

This artist’s impression shows the surroundings of the supermassive black hole at the heart of the active galaxy NGC 3783 in the southern constellation of Centaurus (The Centaur). Credit: ESO/M. Kornmesser

Over the years, researchers have taken myriad observations of black holes and their environs, but now ESO’s Very Large Telescope Interferometer is giving us the most detailed look of the dust around a black hole at the center of an active galaxy ever obtained. Originally expected to be contained within the ring-shaped torus around the black hole, the observation held a surprise as astronomers discovered that a significant amount of the dust was located both above and below the torus. What can this mean? According to the latest findings and contrary to popular theory, it is possible the dust is being evacuated from the region as a cool wind.

For the last two decades, astronomers have discovered that nearly all galaxies harbor a black hole at their hearts. In many cases, these monsters increase in size by accreting matter from the immediate vicinity. This, in turn, is responsible for the creation of active galactic nuclei (AGN), one of the most energetic objects in the Universe. Surrounding the super-luminous giants are rings of cosmic dust which originate from space – drawn in like water swirling down a dark drain. According to theory, the intense infrared radiation exerted by AGN must have originated from these dusty eddies.

Thanks to the powerful eye of the Very Large Telescope Interferometer (VLTI) at ESO’s Paranal Observatory in Chile, astronomers have now seen something new in a nearby active galaxy cataloged as NGC 3783. While they observed the expected hot dust clocking in at some 700 to 1000 degrees Celsius, what they also observed confounded them… Huge amounts of cooler dust both above and below the main torus.

As Sebastian Hönig (University of California Santa Barbara, USA and Christian-Albrechts-Universität zu Kiel, Germany), lead author of the paper presenting the new results, explains, “This is the first time we’ve been able to combine detailed mid-infrared observations of the cool, room-temperature dust around an AGN with similarly detailed observations of the very hot dust. This also represents the largest set of infrared interferometry for an AGN published yet.”

Is this a black hole teething ring? From their observations, the researchers suspect the newly-discovered dust is flowing outward from the central black hole. This means the wind most likely plays a critical part in the tangled relationship of both the black hole and its surroundings. Apparently the black hole pulls immediate material into it, but the incredible amount of radiation this produces also seems to be pushing it away. Scientists are far from clear as to how these two processes work together, but the discovery of this dusty wind could lead to a better understanding of their evolution.

To get the resolution needed to study the core area of NGC 3783, astronomers needed to use the combined power of the Unit Telescopes of ESO’s Very Large Telescope. Through this union, an interferometer is created – one capable of “seeing” with the equivalent of a 130-meter telescope.

Another team member, Gerd Weigelt (Max-Planck-Institut für Radioastronomie, Bonn, Germany), explains, “By combining the world-class sensitivity of the large mirrors of the VLT with interferometry we are able to collect enough light to observe faint objects. This lets us study a region as small as the distance from our Sun to its closest neighbouring star, in a galaxy tens of millions of light-years away. No other optical or infrared system in the world is currently capable of this.”

What do these new observations mean to the world of astronomy? It might very well change the pattern of how we currently understand AGN. With proof that dust is being expelled by intense radiation, new models must be created – models which include this recent information of how dust can be distributed.

Hönig concludes, “I am now really looking forward to MATISSE, which will allow us to combine all four VLT Unit Telescopes at once and observe simultaneously in the near- and mid-infrared — giving us much more detailed data.” MATISSE, a second generation instrument for the VLTI, is currently under construction.

Original Story Source: ESO News Release.

Posted on by Elizabeth Howell

Black Hole Bonanza! Dozens (Potentially) Found In Andromeda As Another Study Probes X-Rays

A new analysis of data from the Chandra space telescope revealed 26 black hole candidates in the Andromeda Galaxy. This is the largest collection of possible black holes found in another galaxy besides that of the Milky Way, Earth's home galaxy. Credit: X-ray (NASA/CXC/SAO/R.Barnard, Z.Lee et al.), Optical (NOAO/AURA/NSF/REU Prog./B.Schoening, V.Harvey; Descubre Fndn./CAHA/OAUV/DSA/V.Peris)

More than two DOZEN potential black holes have been found in the nearest galaxy to our own. As if that find wasn’t enough, another research group is teaching us why extremely high-energy X-rays are present in black holes.

The Andromeda Galaxy (M31) is home to 26 newly found black hole candidates that were produced from the collapse of stars that are five to 10 times as massive as the sun.

Using 13 years of observations from NASA’s Chandra X-Ray Observatory, a research team pinpointed the locations. They also corroborated the information with X-ray spectra (distribution of X-rays with energy) from the European Space Agency’s XMM-Newton X-ray observatory.

“When it comes to finding black holes in the central region of a galaxy, it is indeed the case where bigger is better,” stated co-author Stephen Murray, an astronomer at Johns Hopkins University and the Harvard-Smithsonian Center for Astrophysics.

A close-up of the candidate black holes in Andromeda, as seen by the Chandra X-Ray Observatory. Credit: X-ray (NASA/CXC/SAO/R.Barnard, Z.Lee et al.), Optical (NOAO/AURA/NSF/REU Prog./B.Schoening, V.Harvey; Descubre Fndn./CAHA/OAUV/DSA/V.Peris
A close-up of the candidate black holes in Andromeda, as seen by the Chandra X-Ray Observatory. Credit: X-ray (NASA/CXC/SAO/R.Barnard, Z.Lee et al.), Optical (NOAO/AURA/NSF/REU Prog./B.Schoening, V.Harvey; Descubre Fndn./CAHA/OAUV/DSA/V.Peris

“In the case of Andromeda, we have a bigger bulge and a bigger supermassive black hole than in the Milky Way, so we expect more smaller black holes are made there as well,” Murray added.

The total number of candidates in M31 now stands at 35, since the researchers previously identified nine black holes in the area. All told, it’s the largest number of black hole candidates identified outside of the Milky Way.

Meanwhile, a study led by the NASA Goddard Space Flight Center examined the high-radiation environment inside a black hole — by simulation, of course. The researchers performed a supercomputer modelling of gas moving into a black hole, and found that their work helps explain some mysterious X-ray observations of recent decades.

Researchers distinguish between “soft” and “hard” X-rays, or those X-rays that have low and high energy. Both types have been observed around black holes, but the hard ones puzzled astronomers a bit.

Here’s what happens inside a black hole, as best as we can figure:

– Gas falls towards the singularity, orbits the black hole, and gradually becomes a flattened disk;

– As gas piles up in the center of the disk, it compresses and heats up;

– At a temperature of about 20 million degrees Fahrenheit (12 million degrees Celsius), the gas emits “soft” X-rays.

So where did the hard X-rays — that with energy tens or even hundreds of times greater than soft X-rays — come from? The new study showed that magnetic fields are amplified in this environment that then “exerts additional influence” on the gas, NASA stated.

Artist's conception of the Chandra X-Ray Observatory. Credit: NASA
Artist’s conception of the Chandra X-Ray Observatory. Credit: NASA

“The result is a turbulent froth orbiting the black hole at speeds approaching the speed of light. The calculations simultaneously tracked the fluid, electrical and magnetic properties of the gas while also taking into account Einstein’s theory of relativity,” NASA stated.

One key limitation of the study was it modelled a non-rotating black hole. Future work aims to model one that is rotating, NASA added.

You can check out more information about these two studies below:

– Andromeda black holes: Chandra identification of 26 new black hole candidates in the central region of M31. (Also available in the June 20 edition of The Astrophysical Journal.)

– X-ray modelling of black holes: X-ray Spectra from MHD Simulations of Accreting Black Holes. (Also available in the June 1 edition of The Astrophysical Journal.)

Sources: Chandra X-Ray Observatory and NASA

Posted on by Nancy Atkinson

Space Observatories Watch a Black Hole Go Dormant

The Sculptor galaxy is seen in a new light, in this composite image from NASA's Nuclear Spectroscopic Telescope Array (NuSTAR) and the European Southern Observatory in Chile. Image credit: NASA/JPL-Caltech/JHU

The Chandra X-ray Observatory has been keeping an eye on a black hole actively munching away on gas at the middle of the nearby Sculptor galaxy. Now, with the added eyes of the Nuclear Spectroscopic Telescope Array (NuSTAR), which sees higher-energy X-ray light, the observatories have found the black hole has fallen asleep, even amid rampant star-formation going on around it.

“Our results imply that the black hole went dormant in the past 10 years,” said Bret Lehmer of the Johns Hopkins University, Baltimore, and NASA’s Goddard Space Flight Center. “Periodic observations with both Chandra and NuSTAR should tell us unambiguously if the black hole wakes up again. If this happens in the next few years, we hope to be watching.”

Lehmer is lead author of a new study detailing the findings in the Astrophysical Journal.

The now-latent black hole is about 5 million times the mass of our Sun. The Sculptor galaxy (NGC 253) is a so-called starburst galaxy, which is actively giving birth to new stars. At just 13 million light-years away, it is one of the closest starbursts galaxies to us.

Why did the black hole go dormant?

“Black holes feed off surrounding accretion disks of material. When they run out of this fuel, they go dormant,” said co-author Ann Hornschemeier of Goddard. “NGC 253 is somewhat unusual because the giant black hole is asleep in the midst of tremendous star-forming activity all around it.”

“Black hole growth and star formation often go hand-in-hand in distant galaxies,” added Daniel Stern, a co-author and NuSTAR project scientist at the Jet Propulsion Laborator. “It’s a bit surprising as to what’s going on here, but we’ve got two powerful complementary X-ray telescopes on the case.”

Chandra first observed signs of what appeared to be a feeding supermassive black hole at the heart of the Sculptor galaxy in 2003. Then, in September and November of 2012, Chandra and NuSTAR observed the same region simultaneously. NuSTAR, which launched in June of 2012, detected focused, high-energy X-ray light from the region, allowing the researchers to say conclusively that the black hole is not accreting material.

There are two possibilities: either the black hole has in fact gone dormant, or another possibility is that the black hole was not actually awake 10 years ago, and Chandra observed a different source of X-rays. Future observations with both telescopes may solve the puzzle.

The combination of coordinated Chandra and NuSTAR observations is extremely powerful for answering questions like this,” said Lou Kaluzienski, NuSTAR Program Scientist at NASA Headquarters in Washington. “Now, we can get all sides of the story.”

NuSTAR launched into space in June of 2012.

If and when the Sculptor’s slumbering giant does wake up in the next few years amidst all the commotion, NuSTAR and Chandra will monitor the situation. The team plans to check back on the system periodically.

Source: JPL

Posted on by Tammy Plotner

Black Hole Secrets: Revealing The S-Star

Sgr A Chandra Image Courtesy of NASA/CXC/MIT/F. Baganoff, R. Shcherbakov et al.

Deep in the heart of the Milky Way resides a black hole. However, that is not the mysterious object which scientists Fabio Antonini, of the Canadian Institute for Theoretical Astrophysics, and David Merritt, of the Rochester Institute of Technology, have been endeavoring to explain. The objects of their attention are the orbits of massive young stars which attend it. They are called “S-stars”.

No. That’s not a stutter. S-Stars are a legitimate phenomenon which enable researchers to even more closely examine black hole activity. Their very presence causes astronomers to question what they know. For example, how is it possible for these massive young stars to orbit so close to a region where it would be highly unlikely for them to form there? The sheer force of the strong gravity near a black hole means these stars had to have once been further away from their observed position. However, when theoreticians created models to depict how S-stars might have traveled to their current orbital positions, the numbers simply didn’t match up. How could their orbits be so radically removed from predictions?

Today, Dr. Antonini offered his best explanation of this enigma at the annual meeting of the Canadian Astronomical Society (CASCA). In “The Origin of the S-star Cluster at the Galactic Center,” he gave a unified theory for the origin and dynamics of the S-stars. It hasn’t been an easy task, but Antonini has been able to produce a very viable theory of how these stars were able to get in close proximity to a supermassive black hole in only tens of millions of years since their formation.

“Theories exist for how migration from larger distances has occurred, but have up until now been unable to convincingly explain why the S-stars orbit the galactic center the way they do,” Antonini said. “As main-sequence stars, the S-stars cannot be older than about 100 million years, yet their orbital distribution appears to be ‘relaxed’, contrary to the predictions of models for their origin.”

3-dimensional visualization of the stellar orbits in the Galactic center based on data obtained by the W. M. Keck Telescopes between 1995 and 2012. Stars with the best determined orbits are shown with full ellipses and trails behind each star span ~15-20 years. These stars are color-coded to represent their spectral type: Early-type (young) stars are shown in teal green, late-type (old) stars are shown in orange, and those with unknown spectral type are shown in magenta. Stars without ellipses are from a statistical sample and follow the observed radial distributions for the early (white) or late (yellow/orange) type stars. These stars are embedded in a model representation of the inner Milky Way provided by NCSA/AVL to provide context for the visualization.
3-dimensional visualization of the stellar orbits in the Galactic center based on data obtained by the W. M. Keck Telescopes between 1995 and 2012. Stars with the best determined orbits are shown with full ellipses and trails behind each star span ~15-20 years. These stars are color-coded to represent their spectral type: Early-type (young) stars are shown in teal green, late-type (old) stars are shown in orange, and those with unknown spectral type are shown in magenta. Stars without ellipses are from a statistical sample and follow the observed radial distributions for the early (white) or late (yellow/orange) type stars. These stars are embedded in a model representation of the inner Milky Way provided by NCSA/AVL to provide context for the visualization.

According to Antonini and Merritt’s model, S-stars began much further away from the galactic center. Normal? Yep. Normal mode. Then these seemingly normal orbiting stars encountered the black hole’s gravity and began their spiral inward. As they made the inexorable trek, they then encountered the gravity of other stars in the vicinity which then changed the S-stars orbital pattern. It’s a simple insight, and one that verifies how the galactic center evolves from the conjoined influence of a supermassive black holes relativistic effects and the handiwork of gravitational interactions.

“Theoretical modeling of S-star orbits is a means to constrain their origin, to probe the dynamical mechanisms of the region near the galactic center and,” says Merritt, “indirectly to learn about the density and number of unseen objects in this region.”

Although the presence of supermassive black holes at the center of nearly all massive galaxies isn’t a new concept, further research into how they take shape and evolve leads to a better understanding of what we see around them. These regions are deeply connected to the very formation of the galaxy where they exist. With the center of our own galaxy – Sagittarius A – so near to home, it has become the perfect laboratory to observe manifestations such as S-stars. Tracking their orbits over an extended period of time has validated the presence of a supermassive black hole and enlightened our thinking of our own galaxy’s many peculiarities.

Original Story Source: Canadian Astronomical Society Press Release