VLBI Network: Trio of Huge Black Holes in Distant Galaxy's Core

Two closely orbiting black holes in a galaxy about 4.2 billion light-years from Earth emit wavy jets while the third black hole in the trio is more distant, emitting linear jets. 

Research shows these kinds of systems are more common than originally believed. Image released June 25, 2014.

Credit: : © Roger Deane (large image); NASA Goddard (inset bottom left; modified from original)

Scientists have just discovered a distant galaxy with not one but three supermassive black holes at its core.

The new finding suggests that tight-knit groups of these giant black holes are far more common than previously thought, and it potentially reveals a new way to easily detect them, researchers say.

Supermassive black holes millions to billions of times the mass of the sun are thought to lurk at the hearts of virtually every large galaxy in the universe.

Most galaxies have just one supermassive black hole at their center. However, galaxies evolve through merging, and merged galaxies can sometimes possess multiple supermassive black holes.

Astronomers observed a galaxy with the alphabet soup name of SDSS J150243.09+111557.3, which they suspected might have a pair of supermassive black holes.

It lies about 4.2 billion light-years away from Earth, about "one-third of the way across the universe," said lead study author Roger Deane, a radio astronomer at the University of Cape Town in South Africa.

To investigate this galaxy, the scientists combined the signals from large radio antennas separated by up to 6,200 miles (10,000 kilometers), a technique called Very Long Baseline Interferometry (VLBI).

Using the European VLBI Network, the researchers could see details 50 times finer than is possible with the Hubble Space Telescope.

The astronomers unexpectedly discovered that the galaxy was actually not home to two supermassive black holes, but three.

Two of the black holes in this trio are very close together, which previously made them look like one black hole.



"All three of the black holes have masses around 100 million times that of the sun," Deane told reporters.

Scientists had previously known of four triple black-hole systems. However, the closest pairs of black holes in those triplets are about 7,825 light-years apart.

In this newfound trio of supermassive black holes, the closest pair of black holes is only about 455 light-years apart, "a very close pair of black holes," Deane said, the second-closest pair of supermassive black holes known.

The researchers found this "tight pair" of black holes after searching only six candidate galaxies. This suggests that tight pairs of supermassive black holes "are far more common than previous observations have found," Deane said.

Knowing how often supermassive black holes merge is key to discovering how they might influence their galaxies, the researchers noted. Supermassive black holes can shape the evolution of their galaxies with blasts of energy given off by turbulent matter, which gets sucked toward the black holes.

Although tight pairs of supermassive black holes might previously have been difficult to tell apart, the researchers discovered that the pair they saw left a helical or corkscrew-like pattern in the large jets of radio waves they emitted.

This suggests that twisted jets may serve as easy-to-find signals of tight pairs without the need for extremely high-resolution telescopic observations, such as those from the European VLBI Network.

"The twisted radio jets associated with close pairs may be a very efficient way to find more of these systems that are even closer together," Deane said.

Event Horizon Telescope: Seeing a Black Hole using VLBI

Theoretical calculations predict that the Milky Way's central black hole, called Sagittarius A*, will look like this when imaged by the Event Horizon Telescope. 

The false-colour image shows light radiated by gas swirling around and into a black hole. 

The dark region in the middle is the "black hole shadow," caused by the black hole bending light around it.

CREDIT: Dexter, J., Agol, E., Fragile, P. C., McKinney, J. C., 2010, The Astrophysical Journal, 717, 1092.

Black holes are essentially invisible, but astronomers are developing technology to image the immediate surroundings of these enigmas like never before.

Within a few years, experts say, scientists may have the first-ever picture of the environment around a black hole, and could even spot the theorized "shadow" of a black hole itself.

Black holes are hard to see in detail because the large ones are all far away. The closest supermassive black hole is the one that inhabits the centre of the Milky Way, called Sagittarius A* (pronounced "Sagittarius A-star"), which lies about 26,000 light-years away.

This is the first target for an ambitious international project to image a black hole in greater detail than ever before, called the Event Horizon Telescope (EHT).



The EHT will combine observations from telescopes all over the world, including facilities in the United States, Mexico, Chile, France, Greenland and the South Pole, into one virtual image with a resolution equal to what would be achieved by a single telescope the size of the distance between the separated facilities.

"This is really an unprecedented, unique experiment," said EHT team member Jason Dexter, an astrophysical theorist at the University of California, Berkeley.

"It's going to give us more direct information than we've ever had to understand what happens extremely close to black holes. It's very exciting, and this project is really going to come of age and start delivering amazing results in the next few years."

From Earth, Sagittarius A* looks about as big as a grapefruit would on the moon. When the Event Horizon Telescope is fully realized, it should be able to resolve details about the size of a golf ball on the moon.

That's close enough to see the light emitted by gas as it spirals in toward its doom inside the black hole. To accomplish such fine resolution, the project takes advantage of a technique called 'very long baseline interferometry (VLBI)'. In VLBI, a supercomputer acts as a giant telescope lens, in effect.

"If you have telescopes around the world you can make a virtual Earth-sized telescope," said Shep Doeleman, an astronomer at MIT's Haystack Observatory in Massachusetts who's leading the Event Horizon Telescope project.

"In a typical telescope, light bounces off a precisely curved surface and all the light gets focused into a focal plane. The way VLBI works is, we have to freeze the light, capture it, record it perfectly faithfully on the recording system, then shift the data back to a central supercomputer, which compares the light from California and Hawaii and the other locations, and synthesizes it. The lens becomes a supercomputer here at MIT."

A major improvement to the Event Horizon Telescope's imaging ability will come when the 64 radio dishes of the ALMA (Atacama Large Millimeter/submillimeter Array) observatory in Chile join the project in the next few years.

"It's going to increase the sensitivity of the Event Horizon Telescope by a factor of 10," Doeleman said. "Whenever you change something by an order of magnitude, wonderful things happen."

Read the full article here