Two Black Holes Play a Little One on One

If black holes could communicate, there would likely be a lotta in your face trash talkin’ going on between these two merging black holes. This image of NGC 6240 contains new X-ray data from Chandra (shown in red, orange, and yellow) that has been combined with an optical image from the Hubble Space Telescope originally released in 2008. The two black holes are a mere 3,000 light years apart and are seen as the bright point-like sources in the middle of the image.

Scientists think these black holes are in such close proximity because they are in the midst of spiraling toward each other – a process that began about 30 million years ago. It is estimated that the two black holes will eventually drift together and merge into a larger black hole some tens or hundreds of millions of years from now.

Finding and studying merging black holes has become a very active field of research in astrophysics. Since 2002, there has been intense interest in follow-up observations of NGC 6240 by Chandra and other telescopes, as well as a search for similar systems. Understanding what happens when these exotic objects interact with one another remains an intriguing question for scientists.

The formation of multiple systems of supermassive black holes should be common in the Universe, since many galaxies undergo collisions and mergers with other galaxies, most of which contain supermassive black holes. It is thought that pairs of massive black holes can explain some of the unusual behavior seen by rapidly growing supermassive black holes, such as the distortion and bending seen in the powerful jets they produce. Also, pairs of massive black holes in the process of merging are expected to be the most powerful sources of gravitational waves in the Universe.

Click here for access to larger versions of this image.

Source: Marshall Space Flight Center

14 Replies to “Two Black Holes Play a Little One on One”

  1. What an awesome multispectral image clearly showing the two presumed SMBHs and at the same time highlighting the star clusters detected by the HST in the visible band of the electromagnetic spectrum!

  2. 3000 light years seems a large distance for gravity to act between two bodies to the degree of causing them to fall into each other eventually. Although, I do realize we’re talking about supermassive black holes, not stellar mass.

  3. @ billymac: I think it’s because they strongly interact with the galaxy, much heavier than any of them. A kind of 3-body system, similarly to the influence a planet can have on relatively faraway objects in its system.

  4. We need to catch the gravitational waves produced by the collsion of two giant black holes with LIGO.


  5. # billymac11 Says:
    October 6th, 2009 at 12:45 pm

    “3000 light years seems a large distance for gravity to act between two bodies to the degree of causing them to fall into each other eventually. Although, I do realize we’re talking about supermassive black holes, not stellar mass.”

    Indeed they are supermassive, but if they existed in isolation then it would take much longer for them to fall into each other, because the only way the system could lose energy would be through gravitational waves. Manu is right – the (partial) reason for such a swift merger will be due to a process called dynamical friction, whereby the angular momentum of the pair is dissipated through an effective multi-body interaction with surrounding matter in the galaxy.

  6. The gravitational waves from these black holes would be pretty weak, which ~ 10^3 ly wavelengths. I’ll have to maybe run some numbers, but I suspect the source of the mutual slowing down at this point is due to the two black hole running througn gas and dust. As they take up this mass they will decrease in their orbital energy per mass.


  7. They have a lovely, bright dance, but I would hate to get in any neighborhood close to that “discussion” !
    I have no training or mathematical mind to follow a lot of these folks deeper scientific discussions, but they have sometimes given me even more to hash-over in this old brain, such as size, separation currently, interaction method and such. To story and scientific reader followups, Kudos!

  8. The Chandra result is intriguing and I suspect the interpretation is supported by physics.

    However, I have a hard time imagining how supermassive black holes with masses 10^8 to 10^{10} times the mass of the sun are slowed down by the coalescence of galaxies. It is not too hard to see how dust and gas in such collisions will mutually exhibit friction. Indeed starburst activities in the resulting merged galaxy are a product of this. However, from the perspective of these super massive black holes this source of friction would be pretty negligible. I would then suspect that the two black holes would remain more or less on the original trajectories of the two galactic centers.

    So the question I have is how it is that these thundering huge black holes have their orbits attenuated or their mutual Hamiltonian-energy reduced. I can imagine this happening over billions of years, but given NGC 6240 is a starburst galaxy due to a recent merger (30 million years ago), I must confess I scratch my head over what it is that brakes the motion of two multi-billion solar mass black holes so they end up in a 3000 light year orbit. I should think these black holes would be on orbits which remain largely on their original trajectories before coalescence. The gravitational attraction to the resulting coalesced galaxy will of course adjust the motion or orbits of the BHs, but it seems odd that this would somehow act so as to put the BHs in a comparatively tight mutual orbit.


  9. LC: I don’t think the ‘dynamical friction’ Astrofiend mentioned has anything to do with ‘ordinary friction’.
    I looked it up in wikipedia, it’s more about what I was thinking of: “loss of momentum and kinetic energy of moving bodies through a _gravitational_ interaction with surrounding matter in space”…
    “When galaxies interact through collisions, dynamical friction between stars causes matter to sink toward the center of the galaxy and for the orbits of stars to be randomized. This process is called violent relaxation and can change two spiral galaxies into one larger elliptical galaxy.”
    The same mechanism is involved in giant (exo)planet inward migration through interaction with a stellar accretion disk.
    I have no idea of the figures in the case of two smbh, though.

  10. What if forgot to compare this to is the Bullet galaxy collision. There from gravitational lensing data dark matter from the two galaxies is continuing on their merry way, leaving the luminous stuff behind. I would tend to think the black holes would carry on with the dark matter of the two galaxies.


  11. @Lawrence Crowell, Manu: A paper recently posted on the servers concerning “Triplets of SMBHs” ( ) has some interesting details in the first couple pages on the dynamics and eventual merger of binary SMBHs in galaxy mergers. As Manu pointed out, dynamical friction seems to be a major mechanism in fashioning binary SMBHs, although some caveats and open questions on details of such systems are also discussed. BTW, the ‘Bullet galaxy collision’ mentioned by LBC I believe refers to the “Bullet cluster” of galaxies, aka 1E 0657-55.8. This system of two merging galaxy clusters is of course on a vastly different scale than the merger of two individual galaxies, but I think I understand where LBC is coming from 🙂

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