Astrophysicists find solution to black hole merger detection

Mar 4, 2008 14:01 GMT  ·  By
Artistic impression of two sumermassive black holes during gravitational interactions
   Artistic impression of two sumermassive black holes during gravitational interactions

Behemoths up to a billion times the mass of our Sun lie in our universe, swallowing up matter to hide it forever from the eyes of any outside observers. Not even light can escape their massive gravitational pull, that's why they are called black holes; they do not emit any form of electromagnetic radiation, thus no light. This is the biggest problem in the study of black holes, we as humans depend in a great proportion on observations with the help of electromagnetic radiation; without our eyes we would be dead in the water.

However, this doesn't necessarily mean that there are no other methods to study these elusive objects. One of the alternative ways to study the characteristics of black holes - those of the universe, and space-time fabric - is by studying gravitational waves created during the merging of two such massive objects. On the other hand, gravitational waves are only hypothetical effects since all previous experiments failed in detecting any.

Now, John Hopkins University researchers propose that one of the effects generated during the collision of two massive black holes may be an infrared afterglow that could in theory last as long as 100,000 years, enough time to detect a signature all across the whole diameter of the Milky Way. Better still, the theory can be tested immediately, compared to previous attempts that required several decades before being put to the test.

Usually, massive black holes weighing billions of times the mass of the Sun - the record holder weighs an impressive 18 billion solar masses - form in regions of space with high densities of matter, such as the nuclei of galaxies comparable in size with the Milky Way, or larger. From time to time, supermassive black holes eventually meet and merge causing a release of energy larger than the output of power of all the stars in the universe at a given moment. Part of that energy is converted into gravitational distortions, namely gravitational waves which propagate through the whole fabric of space-time.

The new study, recently published and led by Jeremy Schnittman, suggests that a small amount of the massive release of energy could be converted into electromagnetic radiation in the infrared spectrum, which is slowly emitted over a long period of time by the accretion disk surrounding the merger. As black holes are brought closer and closer together by massive gravitational fields, their accretion disks would collide first determining particles to smash into one another at great velocities.

With the merging process of the black holes complete, matter from the original two accretion disks surrounding the black holes starts to pull together once again around the merger, but loses most of the energy through chaotic movement within itself. The energy produced does not disappear into empty space, but is transformed in X-ray and other forms of light that bounces around through the volume of the accretion disk. By the time it escapes into interstellar space, light would have lost enough energy to the accretion disk to be re-emitted in the form of infrared radiation.

As you can see, due to this high concentration of matter in the accretion disk, the electromagnetic radiation produced during the merging cannot be emitted all at once, but in certain time intervals - to give you a small example, the light emitted in the very core of the Sun takes about 50 million years to reach the surface before being emitted in space, on a distance that in void light travels in a couple of minutes; it should be noted that most of the photons produced in the core will never reach the surface, due to matter density.

However, accretion disk density cannot be compared to that of the Sun's core, thus after about 100,000 years, the infrared afterglow should terminate. The team argues that NASA's Spitzer Infrared Space Observatory should have no difficulty in observing these light emissions. They also suggest that X-ray and ultraviolet radiation would not be available for a newly-created merger.

Astrophysicist Kristen Menou, from Columbia University, says that indeed infrared emission could be generated soon after a merging of two supermassive black holes, but that data can be easily falsified due to the large number of infrared sources in the visible universe. It is estimated that in the visible universe there could be as much as 100,000 sources created by black hole mergers. On the other hand, gravitational waves cannot be detected, at least not now. The LIGO facility has provided with a massive amount of information, but without a signature to filter out gravitational waves, the data is useless. It is hoped that the new gravitational wave detector LISA will have better changes, and is expected to be launched somewhere around 2018.