Featured Research

from universities, journals, and other organizations

Why super massive black holes consume less material than expected

Date:
August 29, 2013
Source:
University of Massachusetts at Amherst
Summary:
Astronomers have solved the mystery of why most super massive black holes have such a low accretion rate -- that is, they feed on very little of the available gases, instead acting as if they are on a severe diet.

SgrA* closeup: The blue fuzzy object at the center are X-rays from emitted Sgr A*, the super massive black hole at the center of our Milky Way galaxy.
Credit: Courtesy Q. Daniel Wang, UMass Amherst

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 black holes suck in everything," Wang says, "but we found this is not correct." Astronomers once thought SMBHs with their intense gravitational pull 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 gravitational forces, 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* (Sgr A*), about 26,000 light years away at the center of our own Milky Way galaxy, he and an international team of astronomers tested the leading accretion models. For the first time, they were able to pinpoint and discriminate among X-ray sources near Sgr 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."

"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 massive stars 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 Catσlica de Chile; University of California Berkeley; Universitι 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."


Story Source:

The above story is based on materials provided by University of Massachusetts at Amherst. Note: Materials may be edited for content and length.


Journal Reference:

  1. Q. D. Wang, M. A. Nowak, S. B. Markoff, F. K. Baganoff, S. Nayakshin, F. Yuan, J. Cuadra, J. Davis, J. Dexter, A. C. Fabian, N. Grosso, D. Haggard, J. Houck, L. Ji, Z. Li, J. Neilsen, D. Porquet, F. Ripple, R. V. Shcherbakov. Dissecting X-ray-Emitting Gas Around the Center of Our Galaxy. Science, 2013; 341 (6149): 981 DOI: 10.1126/science.1240755

Cite This Page:

University of Massachusetts at Amherst. "Why super massive black holes consume less material than expected." ScienceDaily. ScienceDaily, 29 August 2013. <www.sciencedaily.com/releases/2013/08/130829145131.htm>.
University of Massachusetts at Amherst. (2013, August 29). Why super massive black holes consume less material than expected. ScienceDaily. Retrieved July 29, 2014 from www.sciencedaily.com/releases/2013/08/130829145131.htm
University of Massachusetts at Amherst. "Why super massive black holes consume less material than expected." ScienceDaily. www.sciencedaily.com/releases/2013/08/130829145131.htm (accessed July 29, 2014).

Share This




More Space & Time News

Tuesday, July 29, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Russia Saves Gecko Sex Satellite, Media Has Some Fun With It

Russia Saves Gecko Sex Satellite, Media Has Some Fun With It

Newsy (July 27, 2014) — The satellite is back under ground control after a tense few days, but with a gecko sex experiment on board, the media just couldn't help themselves. Video provided by Newsy
Powered by NewsLook.com
NASA EDGE: OCO-2 Launch

NASA EDGE: OCO-2 Launch

NASA (July 25, 2014) — NASA EDGE webcasts live from Vandenberg AFB for the launch of the Oribiting Carbon Observatory-2 (OCO) launch. Video provided by NASA
Powered by NewsLook.com
This Week @ NASA, July 25, 2014

This Week @ NASA, July 25, 2014

NASA (July 25, 2014) — Apollo 11 celebration, Next Giant Leap anticipation, ISS astronauts appear in the House and more... Video provided by NASA
Powered by NewsLook.com
Space to Ground: Coming and Going

Space to Ground: Coming and Going

NASA (July 25, 2014) — One station cargo ship leaves, another arrives, aquatic research and commercial spinoffs. Questions or comments? Use #spacetoground to talk to us. Video provided by NASA
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
 
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:  

Breaking News:

More Coverage


NASA's Chandra Observatory Catches Giant Black Hole Rejecting Material

Aug. 29, 2013 — Astronomers using NASA's Chandra X-ray Observatory have taken a major step in explaining why material around the giant black hole at the center of the Milky Way Galaxy is extraordinarily faint ... read more
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:  

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile iPhone Android Web
Follow Facebook Twitter Google+
Subscribe RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins