Just like mega-corporations, a couple of the countless supermassive black holes scattered across the universe have a merger about once a year — but they’re incredibly secretive about it.
Okay, it’s not really a cosmic “inside trading” scandal. Scientists just don’t know how to track such activity because they don’t know what “signatures” to look for.
That said, scientists are pretty sure those signatures should be hidden in powerful bursts of light and the ripples in spacetime known as gravitational waves, both of which are theorized to be byproducts of the merger activity.
And now a team of astrophysicists from Rochester Institute of Technology and Johns Hopkins University think they may have come up with a detailed blueprint for finding and tracking merging black holes. The best news? They don’t need fancy new equipment to do it. Their method can use existing telescopes and patterns in ordinary visible light.
Just what happens, physics-wise, when black holes collide? It starts with merging galaxies, most of which are thought to contain supermassive black holes. Sooner or later, during that larger merger, the two black holes either collide, or slowly spiral inward for a more gradual merger over as much as 10 million years, climaxing in a sudden burst of x-ray radiation.
Other simulations have shown a potentially interesting “recoil” effect, wherein one black hole gets pushed out of the newly merged galaxy at very high velocities, while the other gets a massive dose of powerful electromagnetic radiation injected into its accretion disk, resulting in a burst of x-rays that could last for several thousand years. (Think what happens in Highlander — “There can be only one!” — whenever one of the “immortals” is killed.)
The relative sizes of the two black holes are likely to be a significant factor, too, according to a new simulation by another team of scientists at RIT that investigates the merger of two black holes with extreme mass ratios of 100:1 (pictured left).
Most simulations of black hole mergers assume objects of equal mass, but “When two black holes collide in realistic astrophysical scenarios, they don’t have the same size,” Carlos Lousto, co-author of a paper on this “David and Goliath” scenario, told my Discovery News colleague Larry O’Hanlon. (As one might expect, in the simulation, Goliath “wins.”)
The new techniques he developed with his co-authors — once thought to be technically impossible, or at least 10 years into the future — will help astronomers identify the telltale signatures of black hole mergers.
Regardless of which type of scenario plays out, there should be a telltale burst of intense light from the respective accretion disks as the two black holes start to merge, since the gas and dust that make up the disks will inevitably heat up. That’s an aspect most binary black hole simulations to date — which are already incredibly complex — have not included.
Once you add in the complicating factors of gas and electromagnetic fields, the data sets become dauntingly huge and require massive parallel supercomputing. But that’s just what the new computer simulations will do.
The RIT/JHU scientists think these telltale bursts of visible light could be detected by existing instruments like the Large Synoptic Survey Telescope. Their computer models simulate this process, with the hope that they will be able to identify the “signatures” associated with binary black hole mergers.
As a bonus, since the same merging process also produces gravitational waves, those simulations could aid in the discovery of that key prediction of general relativity theory.
It’s an impressively ambitious project, and highly interdisciplinary, requiring expertise in numerical relativity, magneto-hydrodynamical simulation, advanced computation, manipulating large data sets, scientific visualization, and plain old observational astronomy.
In fact, it’s something of a merger itself, since it will study merging black holes through two complementary “lenses”: gravitational waves and electromagnetic waves. Team leader Manuela Campanelli describes it as a new type of astronomy:
Image top: The complex pattern of gravitational waves predicted to be generated after a black hole merger (NASA/James Van Meter)