How often do giant black holes become hyperactive?

Dec 20, 2010
The galaxy on the left, Abell 644, is in the center of a cluster of galaxies. The right panel contains SDSS J1021+131, a so-called field galaxy because it is isolated. Both images are composites with data from Chandra (blue) and the Sloan Digital Sky Survey (red, green, blue). A survey of these and hundreds of other galaxies tells scientists how often the biggest black holes in field galaxies like SDSS J1021+131 have been active over the last few billion years. This has important implications for how environment affects black hole growth. Credit: X-ray: NASA/CXC/Northwestern Univ/D.Haggard et al. Optical: SDSS

(PhysOrg.com) -- 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 "," 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 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."

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 -- 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 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.

Explore further: Astronomer confirms a new "Super-Earth" planet

More information: These results were published in the November 10th issue of the Astrophysical Journal.

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Tuxford
1 / 5 (5) Dec 20, 2010
Suppose the massive galactic cores are nucleating matter and energy (photon blue-shifting) in non-linear proportion to their mass. Nucleation and ejection of new star-forming material causes galaxies and clusters to grow over time, greatly accelerated in the most massive cores. Regions near the core star (of finite densities as they are generating energy therein faster than gravitational forces collapse) grow in proportion to the mass of the core star, not the reverse. Larger core stars are generating more matter and energy therein, yielding more outburst ejections, thus more massive AGN�s are more numerous. Stars are moving radially away from the center, not orbiting the galactic center. Does this sound familiar?

Our galaxy displays this conditions, and may pose a climate change danger for Earth one day (Fermi Bubbles?). See more on this cosmogenic model in comments here.

http://www.physor...ars.html
Tuxford
1 / 5 (5) Dec 20, 2010
Star material nucleated and ejected from galactic core.

http://www.physor...ays.html

Eventually forming a structure like this, in some cases of long-term AGN conditions.

http://www.physor...035.html
Tuxford
1 / 5 (5) Dec 20, 2010
Star forming regions absent in active AGN's. So how can they powered by accretion? More evidence that early shut-down of star formation is caused by matter expulsion from AGN's. Remember the Fermi bubbles.

http://www.physor...307.html

Not enough gas to fuel the AGN growth to final massive stages. And yet they grow. (Hint. Matter nucleation inside the core.)

http://www.physor...939.html
Tuxford
1.2 / 5 (5) Dec 20, 2010
Here is a Quasar (more massive galactic core) which is so massive, and therefore energetic, that it has blown all gas clouds out of the region. Through ejection, it has spawned another satellite galaxy, which has since grown into it's own massive core star which is ejecting new matter and spawning the formation of stars. The satellite is likely not yet massive enough (and thus less energetic) to completely disperse the star making gas clouds therein. Plus, the original quasar may be aligned to feed ejected material into the the adjacent satellite galaxy (or not). Still another example of a bare core which has destroyed it's host galaxy long ago.

http://www.physor...126.html
Tuxford
1 / 5 (5) Dec 20, 2010
And Fermi bubbles in M82 indicate these core ejections are common, and likely proportional to the galactic core total mass. Doradus 30 gamma ray emission likely the core region for the LMC, and is far less energetic.

The massive "young" stars in Doradus 30 – like near our galactic core – are actually old stars in this cosmogenic model, having time to develop increased metal content. Stars need substantial time to grow via nucleation. However, in a region of high mass density, this nucleation process is accelerated, such as near the galactic core.

http://www.physor...829.html
Tuxford
1 / 5 (5) Dec 20, 2010
And Fermi bubbles in M82 indicate these core ejections are common, and likely proportional to the galactic core total mass. Doradus 30 gamma ray emission likely the core region for the LMC, and is far less energetic.

The massive "young" stars in Doradus 30 - like near our galactic core - are actually old stars in this cosmogenic model, having time to develop increased metal content. Stars need substantial time to grow via nucleation. However, in a region of high mass density, this nucleation process is accelerated, such as near the galactic core. Likely, the blue stars near our galactic core grow more quickly than in Doradus 30.

http://www.physor...829.html
Graeme
4 / 5 (1) Dec 20, 2010
If there had been heavy radiation bathing the solar system in the past, there may be isotope effects still remaining on the surface of asteroids or pristine meteorites. The crystal structure in surface minerals may also be damaged by radiation in such a way to indicate the amount. The moon may also show this, but with so much dust it may obscure the surface.
zevkirsh
1 / 5 (2) Dec 20, 2010
what if there is a galazy out there that is composed only of black holes spiraling around each other....no non-collapsed starts, only black holes and neutron stars.

wierd.
DamienS
5 / 5 (4) Dec 20, 2010
Six posts in a row and not one with anything of value. Is that a record? Alas, I think the answer is probably no...
Tuxford
1 / 5 (4) Dec 21, 2010
Surely your post adds nothing to how AGN likelyhood is linked to the size of the galaxy? Can you add another explanation? I promise to consider your viewpoint.
DamienS
5 / 5 (1) Dec 21, 2010
Surely your post adds nothing to how AGN likelyhood is linked to the size of the galaxy?

Yup, we're even!
dan42day
not rated yet Dec 21, 2010
This may sound very simplistic, but it seems like the activity of a black hole would be dependent on the random event of a clump of gas, or small group of stars wandering too close and being drawn in. The bigger the galaxy and the more it has interacted with other galaxies, the better the chance of something wandering too close. I don't see the mystery.
lengould100
5 / 5 (2) Dec 21, 2010
AGN caused by galaxy collisions sounds like it might be about right, eg. 1.6% of galaxies.
Quantum_Conundrum
1 / 5 (3) Dec 21, 2010
dan42day:

Not to mention the galaxies are already moving through space.

I guess they didn't think about the fact that the AGN could just be passing through a "galaxy scale" nebula in intergalactic space, which is sucked up like a vaccuum cleaner picks up dust. With the galaxy moving trhough local space-time at up to thousands of kilometers per second, it could encounter hundreds of stellar masses worth of gas every year just as the galaxy itself "runs into" these nebula.

why they try to make amystery out of everything when there are such obvious explainatons, no clue...
Au-Pu
not rated yet Dec 26, 2010
Can mikong above be banned? This person is abusing their access to your site.

Now back to black holes.
The observations extend to 6.3 bly's but in the main they concentrate out to 1.6 bly's
So their observations of these events are observations of events that took place up to billions of years ago.
Could that not mean that these same events have already occured in our galaxy with a similar time frame, i.e. up to billions of years ado?
yyz
5 / 5 (3) Dec 26, 2010
"Could that not mean that these same events have already occured in our galaxy with a similar time frame, i.e. up to billions of years ado?"

That certainly seems to be the case. The recent discovery of a gamma ray 'bubble' by Fermi may indicate our galaxy's SMBH Sag A* dined on a dwarf galaxy or globular cluster in the recent past. Studies of x-ray reflection nebula near Sag A* also point to a smaller, stellar mass event 300-400 years ago.

These observations would be consistent with the bottom-up model of galaxy formation (smaller galaxies merging to form larger galaxies over cosmological time).
yyz
5 / 5 (2) Dec 26, 2010
"AGN caused by galaxy collisions sounds like it might be about right, eg. 1.6% of galaxies."

lengould100, you're spot on with that. In our local universe (~1 Gly) the number of AGN's closely matches the number of merging or gravitationally interacting galaxies. As we look back in time at more distant galaxies (~4-6 Gly), the number of AGNs AND galaxy mergers is seen to increase in lockstep. Future surveys of deeper space will look to see if this relationship holds up (it's hard to morphologically classify galaxies at cosmological distances, ie over ~5 Gly).

dan42day, QC, we know from studies along the sightlines to distant quasars that gas between galaxies is extremely diffuse and would not provide enough material to create and sustain AGNs. Perhaps during the reionization era this may have played a minor role, but you really need dwarf-galaxy mass objects (and larger) to sustain the AGNs in both the local and far universe.
Tuxford
1 / 5 (3) Dec 28, 2010
�As we look back in time at more distant galaxies (~4-6 Gly), the number of AGNs AND galaxy mergers is seen to increase in lockstep.�

Another reason why the AGN is likely instead the now giant remnant core star of a dispersed galaxy which has seeded the birth of the nearby interacting galaxies.

we know from studies along the sightlines to distant quasars that gas between galaxies is extremely diffuse and would not provide enough material to create and sustain AGNs. Perhaps during the reionization era this may have played a minor role, but you really need dwarf-galaxy mass objects (and larger) to sustain the AGNs in both the local and far universe.

Not likely all AGN's have galaxy-size objects somehow condensing onto an extremely active core star. Just illogical. Nucleation also takes place in intergalactic space, albeit extremely slowly, yielding the diffuse clouds observed.
TabulaMentis
1 / 5 (1) Dec 28, 2010
Maybe sometimes the hyperactivity is caused by black holes transmitting energy/information from one black hole to another via white holes?

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