A rare crash at the Milky Way's core

January 9, 2014 by Nicole Casal Moore
The galactic center as imaged by the Swift X-ray Telescope. This image is a montage of all data obtained in the monitoring program from 2006-2013. Credit: Nathalie Degenaar

(Phys.org) —University of Michigan astronomers could be the first to witness a rare collision expected to happen at the center of the galaxy by spring.

With NASA's orbiting Swift telescope, the U-M team is taking daily images of a mysterious gas cloud about three times the mass of Earth that's spiraling toward the at the Milky Way's core. From our vantage point, the core lies more than 25,000 light years away in the southern summer sky near the constellations Sagittarius and Scorpius.

The , called G2, was discovered by in Germany in 2011. They expected it to hit the black hole, called Sagittarius A* (pronounced Sagittarius A-star by astronomers), late last year. That didn't happen, but the cloud continues to drift closer. Astronomers now predict that the impact will occur in the next few months.

Astronomers have never seen anything like this, much less with a front-row seat.

"Everyone wants to see the event happening because it's so rare," said Nathalie Degenaar, who leads this imaging effort as a Hubble research fellow in the Department of Astronomy at the College of Literature, Science, and the Arts.

Supermassive are believed to lurk at the centers of all elliptical and spiral galaxies. The Milky Way's, by comparison, is dim—about a hundred million times fainter than scientists might expect. But it's likely the more common variety, Degenaar said.

"We think that the fainter ones are the majority, but it's very difficult to study those," she said. "We just can't see them. Ours is the only one we can study to understand what their role is in the universe."

The collision will give astronomers a unique opportunity to see how faint supermassive black holes feed and perhaps why they don't consume matter in the same way as their brighter counterparts in other galaxies. While black holes themselves are invisible and don't permit light to escape, the material falling into them shines in X-rays.

Since 2006, Degenaar and her colleagues have been using Swift's X-ray instruments to observe not just Sagittarius A*, but also some smaller black holes and neutron stars that reside at the galaxy's center with it. Neutron stars are the smallest, most dense star remnants from those that aren't quite massive enough to collapse into black holes.

The Swift observatory is the only telescope providing daily updates at X-ray wavelengths where the crash will show up most profoundly, the researchers said. Those capabilities, coupled with a research tool developed by Mark Reynolds, an assistant research scientist in astronomy at U-M, will help provide the first evidence of the collision. This tool quickly analyzes changes in the X-ray brightness of images across days—a sudden increase could signal impact. It also immediately posts the images online.

While astronomers expect to see a change in brightness, they don't know how dramatic it will be because they aren't sure exactly what the gaseous G2 object is. If it's all gas, the region would glow in the X-ray band for years to come as the black hole slowly swallows the cloud. But another possibility is that G2 could be shrouding an old star. If that's the case, the display would be less spectacular as Sagittarius A* slurped from the cloud while the star slipped by, dense enough to fight its grasp.

"I would be delighted if Sagittarius A* suddenly became 10,000 times brighter. However it is possible that it will not react much—like a horse that won't drink when led to water," said Jon Miller, a U-M associate professor of astronomy who also works on the project. "If Sagittarius A* consumes some of G2, we can learn about black holes accreting at low levels—sneaking midnight snacks. It is potentially a unique window into how most black holes in the present-day universe accrete."

Black holes play a key role in the life cycles of galaxies.

"They eat matter from their surroundings and blow matter back. The way they do that influences the evolution of the entire galaxy—how stars are formed, how the galaxy grows, how it interacts with other galaxies," Degenaar said. "Even more broadly, the way galaxies evolved is important for the evolution of the whole universe, how it came into being and how it's changing."

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1 / 5 (3) Jan 09, 2014
So the matter escapes a black hole ? now this article tells me that it sucks in the matter and spits it out ?

Does it act like a recycling plant then ? i thought the matter going in makes the black hole grow or perhaps it is just not known what happens inside a black hole ?
2.3 / 5 (3) Jan 09, 2014
Most matter that touches the event horizon does get trapped. However, during pair production, it's possible for one member of the pair to escape the event horizon. What this observation hopes to show is 1) that there's any proof to that claim, 2) anything else we can glean, because we've never seen this before. Perhaps we will see a belch in the relativistic jets. If so, how long does it take to show up? This can tell us something about time around an event horizon. Does the input mass = output mass? Why or why not? I could go on and on. All kinds of interesting possibilities.

Oh, and yes, the size of the black hole increases as information is added to it. Curiously enough, it increases in surface area and not volume.
Jan 09, 2014
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5 / 5 (1) Jan 09, 2014
@HeloMenelo: I think that this matter is orbiting the black hole outside the event horizon, where we can observe it. It is likely to encounter the event horizon on this pass around the black hole.
2 / 5 (4) Jan 09, 2014
How does it do that arpotu Skippy? I can not picture what you mean by that no. But then a lot of this space stuffs is way over the Ira's head. What is this information that you put in there?

He is subscribing to the Singularity Hypothesis for black holes, which is to say the belief that all of the matter is concentrated in a single point which is infinitely dense. Since there is no way to verify that it will always be a hypothesis, never a theory.

Anyway, if all the matter were concentrated in an infinitely dense point, then adding material doesn't increase the volume of the "singularity".

Whether or not the singularity hypothesis is true, the Event Horizon does not necessarily equal the surface of whatever object might be there.
Jan 09, 2014
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5 / 5 (1) Jan 09, 2014
No, I'm referring to the work of Raphael Bousso, out of Berkeley.
3 / 5 (2) Jan 09, 2014
It has little to do with a singularity, and more about information density (planck volume) inside an event horizon with respect to a Holographic Universe.
5 / 5 (2) Jan 09, 2014
Also, from James Palmer and Jim Lochner (1997), "So while the "size" of a black hole is given by the radius of its event horizon, it's volume is not determined by the usual 4/3*pi*r3. ... The volume of a black hole, therefore, is its surface area times the length of time the hole exists."
5 / 5 (1) Jan 09, 2014
Smallest unit of information is Planck Unit. That is the "information" I'm referring to.
Whydening Gyre
5 / 5 (1) Jan 10, 2014
You're saying it just gets denser - More Planck units per square whatever... gravitational "packing" efficiency.
not rated yet Jan 10, 2014
You cannot compress Planck Units.
1 / 5 (1) Jan 10, 2014
Heh! Love the way this article is written in the present tense and it happened 25,000 years ago!
Whydening Gyre
5 / 5 (1) Jan 10, 2014
You cannot compress Planck Units.

So.. you are just saying more information per planck unit, then? Or that there would be more planck units filled with info?
Captain Stumpy
5 / 5 (1) Jan 10, 2014
You cannot compress Planck Units.

So.. you are just saying more information per planck unit, then? Or that there would be more planck units filled with info?

Whydening Gyre
try reading these links and see if it helps a little...



3 / 5 (2) Jan 10, 2014
No, surface area and volume both increase. You can't have one without the other. The black hole at the center of our galaxy is NOT the same volume as one of say 10 solar masses....
4.2 / 5 (5) Jan 11, 2014
Arpotu is referring to the apparent volume of the black hole as you fall into it. A distant observer at rest with respect to the black hole would assume the normal surface area to volume ratio.
1 / 5 (1) Jan 12, 2014
Volume of sphere: 4/3(pir^3).
Surface area of sphere: 4pir^2.
"Volume" of a black hole: 4pir^3 (solved from: (4pir^2)(r)).
1 / 5 (1) Jan 12, 2014
If you are interested, you can search for "Bekenstein Bound" to get a better explanation of black hole information content.
Jan 12, 2014
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