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What Happens When Supermassive Black Holes Collide?

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As galaxies merge together, you might be wondering what happens with the supermassive black holes that lurk at their centres. Just imagine the forces unleashed as two black holes with hundreds of millions of times the mass of the Sun come together. The answer will surprise you. Fortunately, it’s an event that we should be able to detect from here on Earth, if we know what we’re looking for.

Most, if not all, galaxies in the Universe seem to contain supermassive blackholes. Some of the biggest can contain hundreds of millions, or even billions of times the mass of our own Sun. And the environments around them can only be called “extreme”. Researchers think that many could be spinning at the maximum rates predicted by Einstein’s theories of relativity – a significant fraction of the speed of light.

As two galaxies merge, their supermassive black holes have to eventually interact. Either through a direct collision, or by spiraling inward until they eventually merge as well.

And that’s when things get interesting.

According to simulations made by G.A. Shields from the University of Texas, Austin, and E.W. Bonning, from Yale University, the result is often a powerful recoil. Instead of coming together nicely, the forces are so extreme that one black holes is kicked away at a tremendous velocity.

The maximum kick happens with the two black holes are spinning in opposite directions, but they’re on the same orbital plane – imagine two spinning tops coming together. In a fraction of a second, one black hole is given enough of a kick to send it right out of the newly merged galaxy, never to return.

As one black hole is given a kick, the other receives a tremendous amount of energy, injected into the disk of gas and dust surrounding it. The accretion disk will blaze with a soft X-ray flare that should last thousands of years.

So even though mergers between supermassive black holes are extremely rare events, the afterglow lasts long enough that we should be able to detect a large number out there in space right now. The researchers estimate that there could be as many as 100 of these recent recoil events happening within 5 billion light-years of the Earth.

Their recently updated journal article, entitled Powerful Flares from Recoiling Black Holes in Quasars will be published in an upcoming issue of the Astrophysics Journal.

Original Source: Arxiv

About 

Fraser Cain is the publisher of Universe Today. He's also the co-host of Astronomy Cast with Dr. Pamela Gay.

Comments on this entry are closed.

  • Jon February 29, 2008, 3:10 PM

    That would be so cool to expereince.

  • Chris Paino February 29, 2008, 3:19 PM

    Could it be the black holes hold anti matter and not regular matter or maybe regular matter turns into anti matter when it is in a black hole? The reason I ask is this galaxy collision black hole thing sounds a lot like an atom when electricity passes from one to the next. Maybe the non black hole part of the galaxy is like the electrons and black hole is like the nucleas and much like atoms pass electrons along, galaxies pass matter along. I suspect the same is true at the universe level as well. Seems like same theme on different scales.

  • Dave February 29, 2008, 4:01 PM

    Hummm, so… Lets say that the black hole “kicked out” is sent flying at a very very high speed, and pulls a few stars along with it, and maybe the light from the glow of material around the kicked out black hole then would appear a lot more red-shifted than the nearby galaxy . . . And since this would occur in interacting colliding galaxies, they would, in the telescope, appear “peculiar” would then not? So there might be quasi-stellar objects, ejected from peculiar galaxies with discordant red-shifts perhaps??? Someone call Mr. Arp!

  • John B February 29, 2008, 5:15 PM

    I reckon that the gravity that drives towards the black hole centre will be weaken by the other, causing the black holes to reduce their hold on their matter and energy. One might exploded.
    Is this a “Small Bang”

  • Chris Paino February 29, 2008, 7:09 PM

    Dave,

    Are you suggesting the universe red shift doesnt mean it’s expanding? Please elaborate on your red shift comment. Thanks.

  • Colin B February 29, 2008, 11:59 PM

    So through this, 2 super-massive black holes can never merge into 1 ? In a galaxy merger the two will always interact in this manner? Cool!

  • Chuck Lam March 1, 2008, 3:54 PM

    Hmm . . . the merging of two black holes, including the accretion disks, could be a relatively silent unspectacular event. The reason could be as simple as absorbtion of one hole of another regardless of spin direction or mass. Assuming black hole theory is correct, nothing can escape a black hole. Why then would there necessarily have to be fireworks? Why would the merging black holes have to give up energy?

  • EverC1? March 1, 2008, 10:04 AM

    Thank guys. More “simulations” and no observations!

  • mipspc March 1, 2008, 6:09 PM

    Fusion is when two nuclei of particles merge together giving off tremendous amount of energy. Aren’t black holes void of electrons, protons, etc. Why wouldn’t two black hole be theoretically the same as fusion two nuclei but on an inconceivable scale?????

  • mipspc March 1, 2008, 6:12 PM

    Perhaps gravitational waves would act to repel two black holes from merging.

  • Poodlhed March 1, 2008, 8:26 PM

    Can’t wait til they find an example…

  • alokmohan March 1, 2008, 10:03 PM

    Blak holes donot have matter ,pro and anti.

  • hd March 2, 2008, 11:50 AM

    If one black hole gets kicked out of the galaxy, I wonder why the other doesn’t fly out in the opposite direction…..

  • Astrofiend March 2, 2008, 6:19 PM

    “# Dave Says:
    February 29th, 2008 at 4:01 pm

    Hummm, so… Lets say that the black hole “kicked out” is sent flying at a very very high speed, and pulls a few stars along with it, and maybe the light from the glow of material around the kicked out black hole then would appear a lot more red-shifted than the nearby galaxy . . . And since this would occur in interacting colliding galaxies, they would, in the telescope, appear “peculiar” would then not? So there might be quasi-stellar objects, ejected from peculiar galaxies with discordant red-shifts perhaps??? Someone call Mr. Arp!”

    Except for the fact that the variability of QSO sources, the features of their emission spectrums (both broad and detailed) etc. etc. are not stellar in any way shape or form…

  • Astrofiend March 2, 2008, 6:25 PM

    “# Chuck Lam Says:
    March 1st, 2008 at 3:54 pm

    Hmm . . . the merging of two black holes, including the accretion disks, could be a relatively silent unspectacular event. The reason could be as simple as absorbtion of one hole of another regardless of spin direction or mass. Assuming black hole theory is correct, nothing can escape a black hole. Why then would there necessarily have to be fireworks? Why would the merging black holes have to give up energy?”

    Two black holes in the middle of nowhere could be seen to merge without ‘fireworks’, though there would be other indicators such as (most probably) gravitational waves. In reality though, all black holes would likely be surrounded by material which would be excited greatly by a merger event. It is this emission that would be able to be detected. It is pretty much inconceivable that a merger could take place without at least some degree of accretion disk emission.

  • Yeo March 3, 2008, 11:50 AM

    So this must be the explanation for the quasar/galacy mistery of GQ6 NGC_4319

  • Chuck Lam March 3, 2008, 9:23 PM

    Astrofriend is probably correct concerning emissions. Good thinking!

  • mipspc March 4, 2008, 5:55 AM

    Astrofriend makes sense for what we know, which may not be much. “Assuming black hole theory is correct, nothing can escape a black hole”. Yes for what theory says but that doesn’t quite hold up when you start applying it to the “Big Bang”. We are all still in nursery school when it comes to what is really going on.

  • Dave March 7, 2008, 7:13 AM

    Not sure if anyone is still following this but I was asked to elaborate.

    Mr. Arp’s research showed that QSO’s had a remarkable, and statistically amazing, tendancy to be located in the area near “peculiar” galaxies, which we are aware today are often two or more galaxies in the process of collision and integration. QSO’s with high red-shifts are assumed to be tremedously distant objects, and thus could not be physically associated with the nearby galaxies that Apr’s research showed them to be located near on photographic plates that he studied, at least that is the predominent thinking. Since the QSO red shift, and consequent calculation of the Hubble constant, all fit neatly into the idea of universal expansion, the great majority of Arps contemporaries (and still today) did not want to have the universal expansion bubble burst by Arps “silly” ideas Arp’s idea was that, given a nearly impossible to be cooincedence statistical correlation of QSO’s and peculiar galaxies in terms of location, and in in terms of what appear to be visible streams of stars connecting them, then at least some QSO’s were NOT at tremendous distances at all and that there was some other possible explanation for the red-shifts. Arp has been roundly labeled a lunatic by modern physicists, and his ideas summarily dismissed. As for the spectral analysis of QSO’s “the features of their emission spectrums (both broad and detailed) etc. etc. are not stellar in any way shape or form..” Correct me here if I am wrong but if one explanation for Arp’s QSO’s is that they may be highly accelerated ejected black holes, I would think their spectrum might be expected to by rather non-stellar appearing would it not?

  • david March 11, 2008, 10:24 AM

    well i have an idea….mabey if two supermassive black holes were to at least try to collide then mabey they would because if one is spinning one way and the other is spinnig the other way then mabey they would but no one can say they wouldnt because no one really knows !!!!!!!

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