CXC: Chandra Catches Giant Black Hole Rejecting Material

[bystander]

Sgr A*: Chandra Catches Our Galaxy's Giant Black Hole Rejecting Food
NASA | Marshall | SAO | Chandra X-ray Observatory | 2013 Aug 29

Click to view full size image 1 or image 2

The center of the Milky Way galaxy, with the supermassive black hole Sagittarius A* (Sgr A*) located in the middle, is revealed in these images. As described in our press release, astronomers have used NASA's Chandra X-ray Observatory to take a major step in understanding why gas around Sgr A* is extraordinarily faint in X-rays.

The large image contains X-rays from Chandra in blue and infrared emission from the Hubble Space Telescope in red and yellow. The inset shows a close-up view of Sgr A* only in X-rays, covering a region half a light year wide. The diffuse X-ray emission is from hot gas captured by the black hole and being pulled inwards. This hot gas originates from winds produced by a disk-shaped distribution of young massive stars observed in infrared observations (mouse over the image for the distribution of these massive stars).

These new findings are the result of one of the biggest observing campaigns ever performed by Chandra. During 2012, Chandra collected about five weeks worth of observations to capture unprecedented X-ray images and energy signatures of multi-million degree gas swirling around Sgr A*, a black hole with about 4 million times the mass of the Sun. At just 26,000 light years from Earth, Sgr A* is one of very few black holes in the Universe where we can actually witness the flow of matter nearby.

The authors infer that less than 1% of the material initially within the black hole's gravitational influence reaches the event horizon, or point of no return, because much of it is ejected. Consequently, the X-ray emission from material near Sgr A* is remarkably faint, like that of most of the giant black holes in galaxies in the nearby Universe.

The captured material needs to lose heat and angular momentum before being able to plunge into the black hole. The ejection of matter allows this loss to occur.

This work should impact efforts using radio telescopes to observe and understand the "shadow" cast by the event horizon of Sgr A* against the background of surrounding, glowing matter. It will also be useful for understanding the impact that orbiting stars and gas clouds might make with the matter flowing towards and away from the black hole.

Credit: X-ray (NASA/CXC/Q.D.Wang (UMass) et al.); IR (NASA/STScI)

Dissecting X-ray-emitting Gas around the Center of our Galaxy - Q. D. Wang et al

• Science 341(6149) 981 (30 Aug 2013 DOI 10.1126/science.1240755
  arXiv.org > astro-ph > arXiv:1307.5845 > 22 Jul 2013

Why Supermassive Black Holes Consume Less Material than Expected
University of Massachusetts, Amherst | 2013 Aug 29

Our Galaxy’s Supermassive Black Hole is a Sloppy Eater
Universe Today | Jason Major | 2013 Aug 29

[bystander]

Milky Way's black hole is a picky eater
New Scientist | Astrophile | Maggie McKee | 2013 Aug 29

Object: the Milky Way's black hole
Food source: big, gassy stars

[i]Artist's impression of the feast at the centre of the Milky Way [b](Image: Mark Garlick/SPL)[/b][/i]

---

---

Our galaxy's central black hole is a fussbudget, refusing to eat most of what it pulls to its lips because the food is too hot. Spitting out its meals may not only stunt its growth – the finicky black hole may also be preventing new stars from being born nearby.

Most large galaxies like the Milky Way are thought to harbour black holes at their cores that have a mass equal to that of millions or billions of suns. Some of these behemoths are enthusiastic eaters, pulling in surrounding gas with abandon. As the gas falls towards the black holes, it heats up, producing blazing beacons known as quasars that can be seen across the universe.

The Milky Way's relatively dim black hole, known as Sagittarius A* (pronounced "a-star"), is decidedly not one of these gorgers. A crowded disc of massive stars spins around it, and researchers had previously calculated that these stars should spew out enough gas in stellar winds to provide the black hole with about four Earths' worth of meals over the course of a year. But it does not seem to be swallowing that much material – if it were, it would shine 100 million times brighter in X-rays.

Scalding soup

Some scientists noted, though, that the brightness estimate assumed the gas coming from the stars was relatively cool, and that it could easily slip down the black hole's gullet, says Daniel Wang of the University of Massachusetts in Amherst. To find out what's really going on, Wang and his colleagues used NASA's Chandra X-ray Observatory to measure the temperature and brightness of gas at different distances from the black hole.

They found that the gas gets hotter and less abundant the closer it is to the black hole. The researchers estimate that less than 1 per cent of the surrounding gas ultimately comes near enough to be eaten. Wang thinks the food is just too hot.

Quasars are champion eaters because they slurp up relatively cool gas, below 1 million °C. Such gas is dense and flows in an orderly fashion into a quasar's maw, like water swirling into a drain. But the gas around Sagittarius A* is much hotter – collisions between stellar winds in the starry disc heat the gas to 10 million °C before it even starts to fall towards the black hole. This hot gas is tenuous and its particles zip around randomly, making it hard to corral.

"It's very hard to get steam into the sink," says Wang. That means the black hole should not get the blame for apparently turning up its nose at hot gas on its plate. "The black hole wants to suck it in, but it cannot," says Wang. Bizarrely, the tiny fraction of gas our black hole does imbibe may get in because it has transferred some of its jitteriness to gas particles that are thrown outwards, possibly by the black hole's own magnetic field lines.

Snack time

Superhot stellar gas ejected from the black hole might be heating up other gas clouds surrounding the galactic centre, which is bad news for star formation, because they form when gas is cool enough to condense into dense bundles. All the extra heat may be stopping star birth. "That will have an effect on the evolution of the galaxy," says Wang.

Lest anyone worry that Sagittarius A* will starve as it tries, and mostly fails, to sip up the scalding soup of stellar gas, it may soon get a cooler snack as massive as three Earths.

"In the next few months, a large cloud of gas is on course to collide with the black hole," says Jeremy Schnittman of NASA's Goddard Space Flight Center in Greenbelt, Maryland, in an article accompanying the new study. Astronomers will be watching intently to see if Sagittarius A* opens wide.

<< Previous Astrophile

[BDanielMayfield]

Sgr A*: Chandra Catches Our Galaxy's Giant Black Hole Rejecting Food
NASA | Marshall | SAO | Chandra X-ray Observatory | 2013 Aug 29

The authors infer that less than 1% of the material initially within the black hole's gravitational influence reaches the event horizon, or point of no return, because much of it is ejected. Consequently, the X-ray emission from material near Sgr A* is remarkably faint, like that of most of the giant black holes in galaxies in the nearby Universe.

The captured material needs to lose heat and angular momentum before being able to plunge into the black hole. The ejection of matter allows this loss to occur.

Our teeny tiny speck of the Universe seems to be very good at recycling things. Here on Earth we have numerous cycles going on all the time that keep things going. We have the hydrologic cycle which waters the land from evaporation that has come largely from the seas. Vital elements like carbon, oxygen and nitrogen are constantly being recycled through the soil, living things and the atmosphere. Even the place were much of the garbage collects, the bottom of the sea floor, gets recycled over geologic time as the moving continents override the sea bed.

So after learning about the above as a kid I wondered about black holes and if they might have some kind of role, via some as yet undiscovered physics (white holes on the other side, etc) to sort of recycle material on a galactic scale. Therefore I welcome this news, for it means that much (and sometimes more that 99%) of what gets drawn toward black holes never goes down the drain. Could the SMBHs at the cores of all large galaxies be acting like enormous recycling engines?

[geckzilla]

Vital elements like carbon, oxygen and nitrogen are constantly being recycled through the soil, living things and the atmosphere.

Our personal battle against entropy, which couldn't function without the sun, which will eventually exhaust its fuel and stop contributing energy to us. Then our tiny fight against entropy will be no more. The water cycle also only functions as a result of the sun's presence near us. What energy do you suppose a black hole could contribute to create such a cycle?

[neufer]

Our personal battle against entropy, which couldn't function without the sun, which will eventually exhaust its fuel and stop contributing energy to us. Then our tiny fight against entropy will be no more. The water cycle also only functions as a result of the sun's presence near us. What energy do you suppose a black hole could contribute to create such a cycle?

Our young sun is a low entropy source.

An old black hole is a high entropy source.

[geckzilla]

That doesn't seem very cyclic.

[BDanielMayfield]

Our personal battle against entropy, which couldn't function without the sun, which will eventually exhaust its fuel and stop contributing energy to us. Then our tiny fight against entropy will be no more. The water cycle also only functions as a result of the sun's presence near us.

Your first two links are excellent examples of the basic, although far from simple chemical cycles making life as we know it possible.

Yes, I acknowledge that the sun is a finite energy source. This, thinking ahead, is an excellent reason to develop interstellar travel.

What energy do you suppose a black hole could contribute to create such a cycle?

My suggestion has nothing to do with Hawking radiation. The above news stories report the ejection of ordinary baryonic matter from the vicinity of SMBHs.

What I’m highlighting is the new discovery that the accretion disks around these monsters aren’t very good at accreting much into their black holes. Before things can fall in they get torn apart by tides and ionized by the intense heat of friction and collisions. This ionized gas can get so hot it was likened to trying to pour steam down a sink drain. And since it’s ionized it is charged, and so it can be accelerated by the mega magnetic field around the SMBH. So I’m wondering if these objects can, in effect, recycle entire solar systems, shredding them and then ejecting much of the material far out into space where, given enough time, the gas can cool off and eventually form new stars and planets. That’s what I mean by likening SMBHs to recycling engines.

[Markus Schwarz]

So I’m wondering if these objects can, in effect, recycle entire solar systems, shredding them and then ejecting much of the material far out into space where, given enough time, the gas can cool off and eventually form new stars and planets. That’s what I mean by likening SMBHs to recycling engines.

The "life-cycle" of the interstellar medium (ISM) works as you described: stars form in the cold, dense clouds of the ISM. Through the stellar wind and, later, planetary nebulae and supernovae the ISM gets replenished and enriched with "metals". The sun and the solar system formed from such recycled "left overs".

In principle, a SMBH could contribute to such a process. But I don't know by how much. Since star formation happens all over the galaxy, and not only close to the SMBH, I don't think they play a significant role in the ISM "life-cycle".