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How Often do Giant Black Holes Become Hyperactive?

For Release: December 20, 2010


SN 1979C
Credit: X-ray: NASA/CXC/Northwestern Univ/D.Haggard et al, Optical: SDSS
Press Image and Caption

A new study from NASA's Chandra X-ray Observatory tells scientists how often the biggest black holes have been active over the last few billion years. This discovery clarifies how supermassive black holes grow and could have implications for how the giant black hole at the center of the Milky Way will behave in the future.

Most galaxies, including our own, are thought to contain supermassive black holes at their centers, with masses ranging from millions to billions of times the mass of the Sun. For reasons not entirely understood, astronomers have found that these black holes exhibit a wide variety of activity levels: from dormant to just lethargic to practically hyper.

The most lively supermassive black holes produce what are called "active galactic nuclei," or AGN, by pulling in large quantities of gas. This gas is heated as it falls in and glows brightly in X-ray light.

"We've found that only about one percent of galaxies with masses similar to the Milky Way contain supermassive black holes in their most active phase," said Daryl Haggard of the University of Washington in Seattle, WA, and Northwestern University in Evanston, IL, who led the study. "Trying to figure out how many of these black holes are active at any time is important for understanding how black holes grow within galaxies and how this growth is affected by their environment."

This study involves a survey called the Chandra Multiwavelength Project, or ChaMP, which covers 30 square degrees on the sky, the largest sky area of any Chandra survey to date. Combining Chandra's X-ray images with optical images from the Sloan Digital Sky Survey, about 100,000 galaxies were analyzed. Out of those, about 1,600 were X-ray bright, signaling possible AGN activity.

Only galaxies out to 1.6 billion light years from Earth could be meaningfully compared to the Milky Way, although galaxies as far away as 6.3 billion light years were also studied. Primarily isolated or "field" galaxies were included, not galaxies in clusters or groups.

"This is the first direct determination of the fraction of field galaxies in the local Universe that contain active supermassive black holes," said co-author Paul Green of the Harvard-Smithsonian Center for Astrophysics in Cambridge, MA. "We want to know how often these giant black holes flare up, since that's when they go through a major growth spurt."

A key goal of astronomers is to understand how AGN activity has affected the growth of galaxies. A striking correlation between the mass of the giant black holes and the mass of the central regions of their host galaxy suggests that the growth of supermassive black holes and their host galaxies are strongly linked. Determining the AGN fraction in the local Universe is crucial for helping to model this parallel growth.

One result from this study is that the fraction of galaxies containing AGN depends on the mass of the galaxy. The most massive galaxies are the most likely to host AGN, whereas galaxies that are only about a tenth as massive as the Milky Way have about a ten times smaller chance of containing an AGN.

Another result is that a gradual decrease in the AGN fraction is seen with cosmic time since the Big Bang, confirming work done by others. This implies that either the fuel supply or the fueling mechanism for the black holes is changing with time.

The study also has important implications for understanding how the neighborhoods of galaxies affects the growth of their black holes, because the AGN fraction for field galaxies was found to be indistinguishable from that for galaxies in dense clusters.

"It seems that really active black holes are rare but not antisocial," said Haggard. "This has been a surprise to some, but might provide important clues about how the environment affects black hole growth."

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It is possible that the AGN fraction has been evolving with cosmic time in both clusters and in the field, but at different rates. If the AGN fraction in clusters started out higher than for field galaxies -- as some results have hinted -- but then decreased more rapidly, at some point the cluster fraction would be about equal to the field fraction. This may explain what is being seen in the local Universe.

The Milky Way contains a supermassive black hole known as Sagittarius A* (Sgr A*, for short). Even though astronomers have witnessed some activity from Sgr A* using Chandra and other telescopes over the years, it has been at a very low level. If the Milky Way follows the trends seen in the ChaMP survey, Sgr A* should be about a billion times brighter in X-rays for roughly 1% of the remaining lifetime of the Sun. Such activity is likely to have been much more common in the distant past.

If Sgr A* did become an AGN it wouldn't be a threat to life here on Earth, but it would give a spectacular show at X-ray and radio wavelengths. However, any planets that are much closer to the center of the Galaxy, or directly in the line of fire, would receive large and potentially damaging amounts of radiation.

These results were published in the November 10th issue of the Astrophysical Journal. Other co-authors on the paper were Scott Anderson of the University of Washington, Anca Constantin from James Madison University, Tom Aldcroft and Dong-Woo Kim from Harvard-Smithsonian Center for Astrophysics and Wayne Barkhouse from the University of North Dakota.

NASA's Marshall Space Flight Center in Huntsville, Ala., manages the Chandra program for NASA's Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory controls Chandra's science and flight operations from Cambridge, Mass.

More information, including images and other multimedia, can be found at: and

Media contacts:
Janet Anderson
NASA Marshall Space Flight Center, Ala.

Megan Watzke
Chandra X-ray Center, Cambridge, Mass.

Visitor Comments (10)

I understand elevated temperature enables particle detection by Chandra. Please explain how very hot gases can persist in the space. The same space just above our atmosphere is quite cold.

Posted by C A Young on Tuesday, 01.19.16 @ 18:56pm

Wow, that's amazing I didn't know that or even imagine that our Galaxy is embedded in an enormous halo of hot gas, that's so interesting, but can we get more information about the dark energy? because it represent I think more than the half of universe and it play an important role.

Posted by NASAFan on Saturday, 07.5.14 @ 08:42am

To Back who asked how the galaxy got so far away: The Big Bang theory as it presently exists is said to have included a period of "hyperinflation" of the (small--then suddenly large) universe very early in its history.

In addition, measurements made about a decade ago showed that even now the expansion of the universe is continuously accelerating.

Posted by Leonard on Wednesday, 08.22.12 @ 00:36am

Hi Bach,
Actually the age of the universe as I have read in many books is close to 14 billion years old.
Interesting question though and hope it gets answered by one of the Chandra team.
Marvin L. S.

Posted by Marvin L. S. on Tuesday, 01.11.11 @ 21:28pm

I have a simple question. With all the talk about the universe having started with a massive explosion and it being ONLY 12 Billion years old? can some please explain the following deduction.

Let's take this galaxy 1.1 LY away. Let's also assume the objects exploded at an average speed of 10M mph. In order for this galaxy to get that far away from us would take it 720B years. How then can the universe be only 12 B years old? Appreciate an explanation

Posted by Bach on Friday, 01.7.11 @ 12:59pm

The article shows the payoff from synergistic usage of two sets of instrumentation. Great work.

Posted by Chris on Thursday, 12.23.10 @ 01:55am

Thank you for the great shots, wow very interesting, will stay open for all information.

Posted by rick moll on Wednesday, 12.22.10 @ 02:54am

What is very interesting is the difference between a cluster galaxy and field galaxy but a middle supermassive black hole, it don't depend on the quantity and type of mater eated, what kind of star make a massive black hole, white dwarf, red magnestar, neutron star, this observation may show us that a super black hole isn't an evolution from a new black hole but depend of primaries state.

Posted by PECQUERY on Tuesday, 12.21.10 @ 21:21pm

Of utmost importance. If the AGN in our Milky Way is active, its radiation could destroy lifeformes on planets on a large scale. May be also on earth. This means destruction could be possible apart from destruction due to events in our planetary system and on earth.

Posted by H van Astenrode on Tuesday, 12.21.10 @ 10:57am

That is most interesting. So, has our galaxy been active like this in its past according to the above information?
There is so much to learn, how Astronomy and Astrophysics has grown over the past Century. A very complex subject.
Marvin L. S.

Posted by Marvin L. S. on Monday, 12.20.10 @ 21:04pm