# Black Holes in Intergalactic Space?

Physicists have recently theorized that the merger of two black holes would create gravitational waves that could eject the resultant object from its galaxy. Now such a black hole event has been observed for the first time. Theory predicted that the gravitational waves would be emitted primarily in one direction, pushing the newly enlarged black hole in the opposite, and that is what we seem to be looking at, according to scientists at the Max Planck Institute for Extraterrestrial Physics (MPE).

We can’t see black holes themselves, nor have we yet directly detected gravitational waves. But we can observe the interactions around black holes, in this case the broad emission lines of gases carried with the recoiling black hole as it exits its galaxy, which contrast with the narrow emission lines of the gases the object left behind. These data allowed the object’s speed — a scorching 2650 kilometers per second — to be measured. The recoil caused by the merger is pushing the black hole, which masses several hundred million times the mass of the Sun, completely out of the galaxy it once called home.

What would cause two enormous black holes to encounter each other? The most likely event is a collision between two galaxies. Early calculations and later simulations of such events predicted that such mergers could produce velocities of up to a few hundred kilometers per second, but working out the numbers for spinning black holes produced much higher velocities, up to the several thousand kilometers per second found by Stefanie Komossa’s team at MPE. With speeds like this, exceeding the escape velocity of even massive elliptical galaxies, we have to ponder the consequences for galaxy evolution absent the central black hole. The work also implies an intergalactic population of black holes.

Finding the first ever candidate for a recoiling black hole, thus verifying theory and simulation, is quite a catch. It’s also noteworthy given the distances involved. Komossa’s team first detected X-ray emissions from the black hole’s accretion disk from a gigantic ten billion light years away. The observation of gravitational waves through experiments like LIGO (Laser Interferometer Gravitational-Wave Observatory) and the space-based LISA (Laser Interferometer Space Antenna) may one day soon provide data that will help us refine our model of such events, as well as other black hole activity. We’ll also find out whether Einstein was right that gravitational waves and light waves travel at the same speed.

See this MPE news release for more. The paper is Komossa et al., “A Recoiling Supermassive Black Hole in the Quasar SDSS J092712.65+294344.0?” Astrophysical Journal 678 (May 10, 2008), pp. L81-L84 (abstract)

Comments on this entry are closed.

• djlactin May 3, 2008, 1:05

The idea that emission of a burst of gravitational waves could result in a recoil in the opposite direction seems very odd to me. (Doesn’t gravity always attract?) I know the concept is the same as any other kinematic interaction, but it just seems weird, especially given that this event accelerates an object massing “several hundred million times the mass of the sun” (which would be ~10^38 kg) to a velocity of 2650 km/s. The energy required boggles. Considering that gravitational waves (slah gravitons) are so weak that they have never been detected.

I suggest an alternative explanation. Instead of 2 interacting Black holes, perhaps there were 3 (or more), and their chaotic orbits resulted in one being ejected from the system (as explanation which has been evoked to circularize planetary objects).

Somehow, this hypothesis seems more parsimonious.

• Ron S May 3, 2008, 16:43

djlactin, are you really prepared to reject a hard calculation of the field equations in favor of a hypothesis that ‘seems’ better to you? You can of course read the paper (which I have not), since there is good reason to see the real possibility of the outcome they found. Consider:
– There is ample energy available. The mass is huge, which is also energy of course, and a large percentage of it (up to 29% IIRC) is in the black hole’s spin.
– To get propulsion you need asymmetry. You can get that easily enough with a difference in the two bodies’ masses. Black holes aggressively shake off any ‘hair’ (asymmetry) to rapidly reach the ‘no hair’ state as the horizons merge.
– Where does the energy of the ‘hair’ (asymmetry) go? There are limited avenues for it. Two are, gravitational radiation and net momentum of the merged body. The latter is where the propulsion is likely coming from.

• James M. Essig May 3, 2008, 19:03

Hi djlactin;

Somehow the net momentum of the initial state and the final state of the colliding blackholes and then the recoiling blackhole and the gravitational waves emmission must be the same as you implied in your comments about kinematic interaction.

The volumetric kinetic energy density of a several hundred million solar massed blackhole traveling at 2650 km/s staggers my mind also. This velocity is within an order of magnitude of many nuclear reaction fragments and simply boggles the mind.

It would be very interesting if the velocity of gravitational waves turned out to be greater than C, perhaps even dependent on the frequency and even the waveform shape of the wavepulse. I don’t think we have any reason to expect such radiation to travel as speed differing from C but any such discovered differences would be an awesome discovery.

The whole concept of using supercomputers to compute gravitational waveforms is an application that intreagues me perhaps because such computations open up a brand new area of applied theoretical physics and as such may be useful in our endeavers to travel to the stars. There is just something fresh and new about computational gravity wave astronomy.

Thanks;

Jim

• Zeroth May 4, 2008, 5:40

AWOL mass not exotic and an Olbers’ solution in one… excellent!

• djlactin May 4, 2008, 11:37

RonS. I do not reject the G-wave propulsion hypothesis outright. I simply propose an alternative hypothesis that is consistent with known phenomena in celestial dynamics: the three-body ‘problem’, in which interactions among 3 or more mutually-rotating objects can eject one of them from the system. My hypothesis makes a testable prediction: two (or more) black holes remain at the centre of said galaxy. The G-wave hypothesis predicts 0 remaining. Let’s wait and see.

• James M. Essig May 12, 2008, 16:29

Hi djlactin, Ron S, and Zeroth;

It occurred to me to mention the concept of producing small black holes, massive enough however to be stable against decay by Hawking Radiation for quite some time wherein the black holes would be accelerated electrodynamically to extremely high gamma factors, however that could be accomplished, by some distant future human R&D project.

The idea here is that the extremely relativistic massed black holes would be Lorentz contracted in the direction of travel to a great extent thus increasing their apparent forward facing surface area specific mass density.

One can imagine instilling lots of electrical charge within such black holes and then using the resulting electrodynamic fields emanating from the black holes to accelerate them and then colliding the black holes in an accelerator mechanism which would probably have to be of interstellar or galactic scale or perhaps even of the scale of the observable universe, a very distant future project indeed! I wonder if the gravity waves emitted by the collision would be so energy dense that the formation of a spattering of black holes would result, flying out in all directions. Thus such an experiment could result in new insight into gravitational wave mechanics.

Another concept occurred to me that involves Lorentz contracting black holes to a possible minimum thickness in the form of disk like or lamiconal structures that are bounded by a minimum thickness of the Planck Length of Lp= {[(h/(2 Pi)] G/(C EXP 3)} EXP 1/2 = 1.61625 x 10 EXP 35 meters. The idea here is borrowed from the new theory of Doubly Special Relativity that suggest a minimum possible Lorentz contraction factor based on the Planck length. However, if we could contract black holes to a smaller thickness than the Planck Length somehow, I wonder what we could discover or how we could apply the results.

Our only hope of achieving the relevant gamma factors for such experiments might be to somehow accelerate microscopically massed black holes so rapidly that time dilation effects permit the requisite Lorentz contraction before these black holes could decay; a daunting prospect in itself.

Thanks;

Jim

• ljk October 12, 2009, 1:21

Triplets of supermassive black holes: Astrophysics, Gravitational Waves and Detection

Authors: Pau Amaro-Seoane, Alberto Sesana, Loren Hoffman, Matthew Benacquista, Christoph Eichhorn, Junichiro Makino, Rainer Spurzem

(Submitted on 8 Oct 2009)

Abstract: Supermassive black holes (SMBHs) found in the centers of many galaxies have been recognized to play a fundamental active role in the cosmological structure formation process. In hierarchical formation scenarios, SMBHs are expected to form binaries following the merger of their host galaxies. If these binaries do not coalesce before the merger with a third galaxy, the formation of a black hole triple system is possible.

Numerical simulations of the dynamics of triples within galaxy cores exhibit phases of very high eccentricity (as high as $e \sim 0.99$). During these phases, intense bursts of gravitational radiation can be emitted at orbital periapsis. This produces a gravitational wave signal at frequencies substantially higher than the orbital frequency.

The likelihood of detection of these bursts with pulsar timing and the Laser Interferometer Space Antenna ({\it LISA}) is estimated using several population models of SMBHs with masses $\gtrsim 10^7 {\rm M_\odot}$. Assuming a fraction of binaries $\ge 0.1$ in triple system, we find that few to few dozens of these bursts will produce residuals $>1$ ns, within the sensitivity range of forthcoming pulsar timing arrays (PTAs). However, most of such bursts will be washed out in the underlying confusion noise produced by all the other ‘standard’ SMBH binaries emitting in the same frequency window.

A detailed data analysis study would be required to assess resolvability of such sources. Implementing a basic resolvability criterion, we find that the chance of catching a resolvable burst at a one nanosecond precision level is 2-50%, depending on the adopted SMBH evolution model. On the other hand, the probability of detecting bursts produced by massive binaries (masses $\gtrsim 10^7\msun$) with {\it LISA} is negligible.