Supermassive black holes: hinting at the nature of dark matter?

Mar 22, 2010
Artist's schematic impression of the distortion of spacetime by a supermassive black hole at the centre of a galaxy. The black hole will swallow dark matter at a rate which depends on its mass and on the amount of dark matter around it. Image: Felipe Esquivel Reed

(PhysOrg.com) -- About 23% of the Universe is made up of mysterious ‘dark matter’, invisible material only detected through its gravitational influence on its surroundings. Now two astronomers based at the National Autonomous University of Mexico (UNAM) have found a hint of the way it behaves near black holes. Their results appear in a letter in the journal Monthly Notices of the Royal Astronomical Society.

In the early Universe clumps of dark matter are thought to have attracted gas, which then coalesced into stars that eventually assembled the we see today. In their efforts to understand and evolution, astronomers have spent a good deal of time attempting to simulate the build up of dark matter in these objects.

The UNAM astronomers, Dr. Xavier Hernandez and Dr. William Lee, calculated the way in which the found at the centre of galaxies absorb dark matter. These black holes have anything between millions and billions of times the mass of the Sun and draw in material at a high rate.

The researchers modelled the way in which the dark matter is absorbed by black holes and found that the rate at which this happens is very sensitive to the amount of dark matter found in the black holes’ vicinity. If this concentration were larger than a critical density of 7 Suns of matter spread over each cubic light year of space, the black hole mass would increase so rapidly, hence engulfing such large amounts of dark matter, that soon the entire galaxy would be altered beyond recognition.

Dr. Hernandez explains, “Over the billions of years since galaxies formed, such runaway absorption of dark matter in black holes would have altered the population of galaxies away from what we actually observe.”

Their work therefore suggests that the density of dark matter in the centres of galaxies tends to a constant value. By comparing their observations to what current models of the evolution of the Universe predict, Hernandez and Lee conclude that it is probably necessary to change some of the assumptions that underpin these models - dark matter may not behave in the way scientists thought it did.

Explore further: Astronomers release most detailed catalogue ever made of the visible Milky Way

More information: A preprint of the paper can be seen at arxiv.org/abs/1002.0553

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ebnv
2.8 / 5 (9) Mar 22, 2010
or -- there is no such thing as dark matter -- just saying
El_Nose
4 / 5 (4) Mar 22, 2010
-- this could explain the Great Void's http://en.wikiped...tes_void that exist. maybe there was a high concentration of dark matter near a large black hole... the size and gravity of the black hole increased significantlly effectively stripping a huge region of space of all matter and thus we now have the great void...
explaining Sloan's Wall http://en.wikiped...eat_Wall might be more difficult
LuckyBrandon
3 / 5 (2) Mar 22, 2010
in regards to the artists rendering...seems like space time would be distorted in such a way to rotate around the black hole, much as a galaxy rotates around its host black hole....
yyz
5 / 5 (1) Mar 22, 2010
El_Nose,

Maybe something along the lines of primordial black holes contributing to the formation of voids in the early universe? An interesting notion, but some (lonely) galaxies within nearby voids have been observed. That's not necessarily a significant problem, but would have to be taken into account.
yyz
5 / 5 (1) Mar 22, 2010
LuckyBrandon,

Check out some of the graphics and animations at "A Black Hole is a Waterfall of Space" ( http://jila.color...all.html ) to see what happens to matter near the event horizon of a black hole. (Actually, check out the 'hole' site for various types of black holes and their characteristics.)
antialias
5 / 5 (3) Mar 22, 2010
this could explain the Great Void....the size and gravity of the black hole increased significantlly effectively stripping a huge region of space of all matter


Unlikely. A black hole with a solar mass still has only the gravitational pull of one solar mass. Even supermassive black holes have a limited range beyond which their gravitational attraction becomes negligible (and stuff rather tends to orbit them than be swallowed up at those distances - much like the galaxy rotates but doesn't get eaten up by the central black hole(s).)

It is only near the event horizon where things get markedly different from a similar mass which is not a black hole. And the radius of the event horizon is 'relatively small'. Even for supermassive black holes is is on the order of only 10 AUs.

The Great Void is too large to have been sucked empty by an (or even many) supermassive black holes.
croghan27
not rated yet Mar 22, 2010
"It is only near the event horizon where things get markedly different from a similar mass which is not a black hole. "

If it has a similar mass .... why is it not a black hole too. Given what I have heard of the mass of the holes compaired to the size of the holes - it must be all sorts of huge.
Slotin
not rated yet Mar 22, 2010
In my opinion these large black holes virtually creating matter from vacuum fluctuations - we can see Big Bang in live broadcast there.

A Black Hole is a Waterfall of Space
It's rather observational illusion. The ripples at water surface are accellerating their speed from source, but it doesn't mean, true flow of matter occurs here - only dispersion of their energy into extradimensions, represented by underwater.
antialias_physorg
5 / 5 (3) Mar 22, 2010
If it has a similar mass .... why is it not a black hole too.


That was just an example to show that just because a body turns into a black hole it doesn't suddenly have more of a gravitational effect on nearby bodies than it did before it 'turned black'. The mass is the same and therefore so is the gravitational effect.

E.g. if our sun were to turn into a black hole (which it won't because it does not have enough mass) the earth would orbit around it exactly on the same path as it does now.

There are bodies that have masses greater than the Chandrasekar limit (1.44 masses of the sun for nonrotating bodies) which are not black holes (yet). This is because their internal radiation pressure still keeps them from collapsing. When that burns out these stellar bodies will collapse into black holes eventually.
croghan27
not rated yet Mar 22, 2010
Thanks for that, antialias .... they are like Scrooge's third ghost ... black holes yet to be.

Slotin .... I have always wondered .... we are in one dimension here - it appears that frequently thing zap off from our dimension into others ..... that brings up the question - do some things ever come TO us from other dimensions?

String theory posits 31 (last time I looked) dimensions ..... that sounds like there is a pretty good chance the occasional bit would make its' way here.

If observed by a physicist that frowns upon the string idea - it would leave him all sorts of dazzled!
CyberRat
2 / 5 (4) Mar 23, 2010
Dark mater, made up all due to the redshift calculations, some objects move faster then light IF redshift can be counted to movement and speed. Worse thing is 'mainstream' scientist just refuse to look at other theories. 99% of visible mater is plasma, plasma means: electric current. Electromagnetic is so much more powerful then gravity!