Astronomers discover why supermassive black holes consume less material than expected

Aug 29, 2013
A composite image of the region around Sagittarius A* (Sgr A*), the supermassive black hole in the center of the Milky Way. X-ray emission from NASA's Chandra X-ray Observatory is shown in blue, and infrared emission from the Hubble Space Telescope is shown in purple and yellow. The inset shows a close-up view of Sgr A* in X-rays only, covering a region half a light year wide. The diffuse emission is from hot gas captured by the black hole and being pulled inwards. Less than 1% of this material reaches the black hole's event horizon, or point of no return, because much of it is ejected. Credit: X-ray: NASA/UMass/Q.D. Wang et al.; IR: NASA/STScI

Using NASA's super-sensitive Chandra X-ray space telescope, a team of astronomers led by Q. Daniel Wang at the University of Massachusetts Amherst has solved a long-standing mystery about why most super massive black holes (SMBH) at the centers of galaxies have such a low accretion rate—that is, they swallow very little of the cosmic gases available and instead act as if they are on a severe diet.

"In principle, super massive suck in everything," Wang says, "but we found this is not correct." Astronomers once thought SMBHs with their intense indiscriminately devoured all sorts of stars, dust and other matter in epic amounts. But in recent years, using X-ray emissions as a measure of heat given off by powerful , they unexpectedly found that most SMBH accrete matter at very low levels.

In fact, SMBHs' signature X-ray emissions, which come from an area much larger than the black holes themselves, are often so surprisingly faint that the objects are difficult to distinguish from their galaxy centers. "There has been a big mystery about why most of these black hole signals are so faint," says Wang, an expert in deep space X-ray analysis.

Now, taking advantage of very long observation times with the Chandra instrument and their detailed knowledge of the nearest SMBH, Sagittarius A* (Sgt A*), about 26,000 away at the center of our own Milky Way galaxy, he and an international team of astronomers tested the leading models. For the first time, they were able to pinpoint and discriminate among X-ray sources near Sgt A* and identify exactly what the SMBH is feeding on. The advance is described in the current issue of Science.

To explain the faint X-ray signals, some astronomers had theorized that emissions from regions around SMBH had nothing to do with the black hole itself but rather with concentrations of low-mass stars associated with SMBHs. Wang adds, "There are also a huge number of young, massive stars as well as low-mass stars near these SMBHs, so it's very crowded in the downtown area of the galaxy. Hard to tell what was going on."

This artist's illustration shows the environment around Sgr A*, the supermassive black hole found some 26,000 light years away at the center of our Galaxy. The red disk depicts hot gas that has been captured by the black hole and is being pulled inwards. The source of the hot gas is young, massive stars, shown in blue, orbiting around Sgr A*. The illustration also shows a large amount of material being thrown outwards, a key factor in explaining why there is so little radiation from material near black holes. Credit: NASA/CXC/M. Weiss

"The massive stars have extremely high winds associated with them and the winds are colliding and swirling at very high speeds, which make the gases in this environment very hot. We found that first, the SMBH has difficulty in accreting such gases. Second, the gases are too hot for the black hole to swallow. Instead it rejects about 99 percent of this super hot material, only letting a small amount in. This makes sense because the hotter the gases, the more difficult it is for the black hole to pull them in."

A diet of cooler gases would accrete in a more orderly fashion, but the SMBH's sphere of influence and its ability to accrete or draw in new material both decrease with increasing gas temperatures, he points out.

Wang, who did this NASA-supported work while on four-month sabbatical as a Raymond and Beverly Sackler Distinguished Visiting astronomer at the University of Cambridge, U.K., points out, "Now we have physically resolved it and for the first time we've made the connection observationally between the moving around black holes and the X-ray emitting material. We can definitively rule out that these X-rays are coming from a concentration of low-mass stars. We don't see the expected energy signature predicted by that scenario."

The astronomers not only detected the X-ray source, he adds, but for the first time can describe its shape, which is elongated. "Now we know what kind of material is getting into the black hole, though exactly how it happens is still another question."

Others on the international team with Wang are from the University of Cambridge and University of Leicester, U.K.; Massachusetts Institute of Technology; University of Amsterdam; Chinese Academy of Sciences; Universidad Católica de Chile; University of California Berkeley; Université de Strasbourg; Centre National de la Recherche Scientifique, Paris; Northwestern University; Nanjing University; Boston University and the University of Maryland, College Park.

The center of our own galaxy offered the team an excellent lab for studying such questions because, as Wang says, "we know the kind of stars that are here in our own downtown." Another strength of this study, the Chandra instrument, provides improved spectral resolving power, he adds. In addition the researchers enjoyed unprecedented observation time of 3 megaseconds, almost five weeks, with the Chandra X-ray Observatory.

"We needed that long because the target is so faint, we need enough strength of signal to process the data to concentrate on such quiescent emissions and to get the signatures identified firmly."

Explore further: Searching for alien worlds and gravitational lenses from the Arctic

More information: "Dissecting X-Ray–Emitting Gas Around the Center of Our Galaxy," by Q.D. Wang et al Science, 2013. On Arxiv: arxiv.org/abs/1307.5845

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User comments : 23

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Tuxford
1.3 / 5 (14) Aug 29, 2013
So then, the big question remains unstated; How do these supermassive core stars get so big? And if they aren't snacking on gas so much, how do they get so big in the early universe? Ah, but these questions are best left ignored....One would not like the inconvenient answer....
IMP-9
5 / 5 (8) Aug 29, 2013
these questions are best left ignored


Some aren't heavily accreting now but that doesn't mean it's always been so. AGN show rapid accretion does still happen today and in the past. Questions like this aren't ignored if you did your research, it's just not in this article. SMBH growth is a very hot topic of research.
Tuxford
1 / 5 (13) Aug 29, 2013

AGN show rapid accretion does still happen today and in the past.


I contend that your statement is simply a convenient assumption, adopted by lazy minded scientists, who lack technical imagination.
DruidDrudge
1 / 5 (6) Aug 30, 2013
"This makes sense because the hotter the gases, the more difficult it is for the black hole to pull them in."
why would this be?
alfie_null
5 / 5 (6) Aug 30, 2013
Hmph! Most of these comments are now crank stuff. Decreasing S/N ratio. Entropy is winning, I guess.
vlaaing peerd
3 / 5 (2) Aug 30, 2013
Instead it rejects about 99 percent of this super hot material, only letting a small amount in.


ok, sure...one might wonder why...

"This makes sense because the hotter the gases, the more difficult it is for the black hole to pull them in."


Of coouuuuurse, it all makes sense now.
IMP-9
5 / 5 (5) Aug 30, 2013
I contend that your statement is simply a convenient assumption, adopted by lazy minded scientists, who lack technical imagination.


Thankfully your opinion is irrelevant. It is a quantitative model, it doesn't have all the answers but it has a lot more than any competing model. To reject an idea because you think it isn't "imaginative" is just bias.
vlaaing peerd
4.2 / 5 (5) Aug 30, 2013
Luckily we have an expert on the matter:

In steady state Universe model of AWT the galaxies are condensing from dark matter clouds into very luminous but sparse objects, which condense and separate gradually like the mixture of oil and water into galaxies and central black holes, which evaporate gradually via their jets, until small remnants at the center mature galaxies remain. This process occurs everywhere around us.


Advanced theory mate!~ interesting how this oily/watery galaxy of stars always finds a central black hole to hang around with. How silly was I thinking gravity was doing all this stuff.

Do feel free to enlighten me about the steady state universe. I was probably heavily misinformed by those religious Hubble followers thinking we have a dynamic universe.
no fate
3.7 / 5 (6) Aug 30, 2013
This article seems to fly in the face of most of the black hole lore I have encountered. Where is the vacuum mechanic to explain about the giant electron at the center of the galaxy?
vlaaing peerd
3.7 / 5 (3) Aug 30, 2013
I repair vacuum cleaners, you could call me a vacuum mechanic if you wish, though I prefer the term "engineer".

There's a giant electron at the center of the galaxy. There, fixed it.

but seriously, anyone able to explain why "hotter" gas is more difficult to suck in by SMBH's? does it have to do with it's density/mass per m3 or what am I missing from the story?
cantdrive85
1 / 5 (11) Aug 30, 2013
That's an awesome "artists illustration" of the BH at the core, oddly the actual data doesn't look anything like that unicorn.
http://www.nrao.e...laments/
http://www.holosc...oarc.jpg

There actually is a spiral at the core, looks remarkably like a plasmoid instability.
http://www.holosc...iral.jpg
This is exactly what Plasma Cosmology expects to find, no scary monsters present.
cantdrive85
1.3 / 5 (11) Aug 30, 2013
I repair vacuum cleaners, you could call me a vacuum mechanic if you wish, though I prefer the term "engineer".

There's a giant electron at the center of the galaxy. There, fixed it.

but seriously, anyone able to explain why "hotter" gas is more difficult to suck in by SMBH's? does it have to do with it's density/mass per m3 or what am I missing from the story?

Does a unicorn fart?
Sometimes the answer to a question is pointless, like any question in re to fictional BH's.
IMP-9
5 / 5 (5) Aug 30, 2013
That's an awesome "artists illustration" of the BH at the core, oddly the actual data doesn't look anything like that unicorn.


That's completely expected. All of those images are on much larger scales than the accretion disk. It's like looking for atoms with a magnifying glass, you don't expect to resolve it. "Looks like" doesn't mean "can explain the data". It's completely subjective.
GSwift7
5 / 5 (7) Aug 30, 2013
but seriously, anyone able to explain why "hotter" gas is more difficult to suck in by SMBH's? does it have to do with it's density/mass per m3 or what am I missing from the story?


When they're talking about gas "temperature" in space, they are actually talking about the average speed of each individual particle (whether that's plasma ions, gas molecules, atoms, electrons, etc.). When you have a very hot gas like what they're talking about here (it's actually plasma, but oh well) the particles are moving around really fast and bumping into each other a lot. That sends a lot of them flying away from the black hole with enough velocity to escape or at least enough velocity so that they don't just fall straight in. You can see this demonstrated in our sun, where the force of gravity is balanced against the heat pressure of the gas. This is a bit of over-simplification in both cases, but you get the idea. There's actually a lot more going on, and they know that.
DruidDrudge
1 / 5 (8) Aug 30, 2013
@GSwift7..
this is a well known physical observation (in a star).
are you saying this has been "overlooked" by our brightest minds for umm 100 years?
GSwift7
4.1 / 5 (9) Aug 30, 2013
this is a well known physical observation (in a star).
are you saying this has been "overlooked" by our brightest minds for umm 100 years?


Black holes are a relatively newly discovered object, so 100 years is a bit exagerated, and the concept of the accretion disk around them is even newer than the idea of the black hole. The observation that they don't consume all the gas around them quickly is a completely new observation, since we didn't have the power to see that until not too long ago. Since then, as the story above says, there have been multiple possible reasons, and we still don't know for sure what the area around a black hole actually looks like. This gas pressure idea isn't exactly something they've overlooked. As you correctly said, the idea isn't new. However, the area around a black hole has many forces acting together. The question of which forces are dominant and how they actually affect the material around the BH is still open. It's a complicated place.
DruidDrudge
1 / 5 (8) Aug 30, 2013
well, thats the first time ever I have exagerated to make a point..
I am somewhat stunned by this. it changes everything
GSwift7
5 / 5 (4) Aug 30, 2013
Yeah, but it wasn't really taken seriously till much later. I really don't see what your point is. It's like OMG, they just now figured this out? No, not really. End of discussion.

You're still exagerating, but I still don't see what point you were trying to make.

We've only seriously begun to think about what might be going on around a real black hole for the past couple decades. Nobody really has a telescope that can answer the questions, and we're still not even sure what questions we need to be asking. There's no way to experimentally derive these conditions, and we can't observe them yet. The above story isn't anything extraordinary; it's just an incremental step up in our observational quality. It does a good job of eliminating SOME of the possible conditions, but it's not like they are proposing anything radical or new. This is just narrowing down the value of some of the unknowns.

You're making too big a deal out of it.
DruidDrudge
1.4 / 5 (8) Aug 30, 2013
I think you have me confused with someone else.
I was asking a serious question, and got a serious answer. thank you.
of course 100 years is a gross exageration.
I do think it is a big deal tho.
Torbjorn_Larsson_OM
4.4 / 5 (7) Aug 31, 2013
Nice to see that a science discussion silenced the massive anti-science troll invasion in the beginning.

"we never observed any black hole directly".

Well, since there isn't any strict definition of "direct" observation, and you very well can't make one (it sounds like Plato's magical "perception of ideal forms"), this merely means the observations thus far doesn't satisfy you.

Luckily they satisfy the science community, and the existence and many properties of black holes are accepted rather than rejected. In your terms, we have seen them "directly".
indio007
1 / 5 (8) Aug 31, 2013
Nice to see that a science discussion silenced the massive anti-science troll invasion in the beginning.

"we never observed any black hole directly".

Well, since there isn't any strict definition of "direct" observation, and you very well can't make one (it sounds like Plato's magical "perception of ideal forms"), this merely means the observations thus far doesn't satisfy you.

Luckily they satisfy the science community, and the existence and many properties of black holes are accepted rather than rejected. In your terms, we have seen them "directly".


If the author of this paper posted Blackholes are on a diet in comments a week ago you would be calling them trolls. What is with this now? Are blackholes gravitationally selective now?

Blackhole theory is mathematically and logically unsound. It's good for hype and making silly movies though.

What was it 3 weeks ago? A blackhole went dormant.
It gets more and more idiotic.

roldor
not rated yet Sep 01, 2013
Hot? what means hot??
vlaaing peerd
not rated yet Sep 03, 2013
but seriously, anyone able to explain why "hotter" gas is more difficult to suck in by SMBH's? does it have to do with it's density/mass per m3 or what am I missing from the story?


When they're talking about gas "temperature" in space, they are actually talking about the average speed of each individual particle (whether that's plasma ions, gas molecules, atoms, electrons, etc.). When you have a very hot gas like what they're talking about here (it's actually plasma, but oh well) the particles are moving around really fast and bumping into each other a lot. ....*cut*.... , and they know that.


Many thanks, I was already thinking it should be something in those lines.

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