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Supermassive black hole trio discovered

Black hole trio

The discovery of a triple black hole system will help scientists studying galactic evolution and gravity waves(Source: K. Thorne (Caltech)/T.Carnahan (NASA GSFC)))


The trio of black holes is the tightest system known to date, reports an international team of astronomers in the journal Nature.

The discovery will help scientists understand how black holes merge and influence the evolution of galaxies.

Closely orbiting systems such as this are also prime sources of gravitational waves, if the theory of general relativity is correct.

Most, if not all, large galaxies are thought to contain a supermassive blackhole at their centre.

Current models of galaxy evolution suggest large galaxies form by smaller galaxies merging in collisions, so there should be a lot of big galaxies containing more than one supermassive black hole.

But only a handful of such systems have been found.

"Multiple supermassive black hole systems are rare," says one of the study's authors Dr Ian Heywood of the CSIRO Australia Telescope National Facility.

"The fact that we only searched six galaxies before we came up with the close pair binary in this one, suggests that they may be more common than previously thought."

The team, led by Dr Roger Dean from the University of Cape Town, discovered the new triple system using a network of four radio observatories across the world, linked together and operating as a single giant telescope.

Using a process called very long baseline interferometery, which allows astronomers to see details 50 times finer than possible with the Hubble Space Telescope, the team focused on a galaxy called SDSS J1502+1115 located almost a third of the way across the universe.

The galaxy is known to contain two very bright compact radio sources separated by 9780 light-years.

As the team examined one of the radio sources in greater detail, they discovered that it was actually two supermassive black holes separated by just 456 light-years.

The two nearby supermassive black holes orbit each other at 300 times the speed of sound on Earth, and their radio emissions have been twisted into a giant helical or corkscrew-like "S" shape.

Peering into the future

The scientists believe sensitive telescopes could home in on this unique signal to detect more black hole systems in the future.

"The fact that we can possibly identify these systems by their large scale radio emission means we'll probably detect them in the all sky surveys coming up with the Australian Square Kilometre Array Pathfinder radio telescope, and eventually the Square Kilometre Array," says Heywood.

The SKA will be able to measure gravitational waves from such systems as their orbits decrease and they merge.

"Typically triple systems are very dynamically unstable systems — for three to merge would be quite rare," says Heywood.

"What's more likely to happen is that one of the black holes will be kicked out of the system, and the other two will settle down into a more stable orbit and eventually merge. Any merger you can catch in the act is worth studying from a galactic evolutionary point of view."

Tags: blackholes, physics, galaxies