dwarf galaxy NGC 4395
March 27, 2014

WISE Data Helps In Search For Seeds Of Supermassive Black Holes

redOrbit Staff & Wire Reports - Your Universe Online

While experts might not know exactly how supermassive black holes grow to sizes up to a billion times that of our sun, astronomers using NASA’s Wide-field Infrared Survey Explorer (WISE) believe they have discovered the so-called cosmic seeds that will ultimately become gravity-rich regions from which light cannot escape.

Black holes come in various sizes, with the smallest ones only a few times greater in mass than our sun and the largest ones being millions or billions of times larger than that, NASA officials explained in a statement on Wednesday. These latter entities, which are known as supermassive black holes, ultimately grow together with their host galaxies, but scientists are still attempting to solve the mystery of how this process actually works.

Shobita Satyapal of George Mason University and her colleagues set out to examine this puzzle by using WISE data to seek out black holes in smaller, “dwarf” galaxies. Those galaxies have not undergone much change, and as a result they are more pristine than their heavier counterparts.

In many ways, these dwarf galaxies resemble those that could have existed during the earliest days of the universe, and they could provide new insights into the evolutionary process that ultimately results in supermassive black holes. Their findings appear in the March issue of The Astrophysical Journal.

As part of their research, Satyapal and her associates used data of the entire sky that was taken by WISE in infrared light, and located up to hundreds of dwarf galaxies that may contain black holes. Since infrared light can see through dust, using instruments that collects it makes it easier for astronomers to find hidden black holes.

“Our findings suggest the original seeds of supermassive black holes are quite massive themselves,” Satyapal said. In fact, they discovered that the black holes in those dwarf galaxies could be approximately 1,000 to 10,000 times the mass of our sun – larger than the astronomers expected to find in these smaller galaxies.

According to Daniel Stern, an astronomer at NASA’s Jet Propulsion Laboratory in Pasadena, California who specializes in black holes, the results of the research show the value of an all-sky survey such as WISE when it comes to tracking down the rarest types of black holes.

“Though it will take more research to confirm whether the dwarf galaxies are indeed dominated by actively feeding black holes, this is exactly what WISE was designed to do: find interesting objects that stand out from the pack,” said Stern, who was not a member of the team behind The Astrophysical Journal paper.

The new study contradicts one commonly held theory of black hole growth, which claims that the objects grow in mass through galaxy collisions. Those events were more likely to take place when the universe was young, the US space agency said. Another possibility is that the black holes in those galaxies also merged and accumulated more mass – a scenario in which supermassive black holes would be the result of a series of galaxy mergers.

“The discovery of dwarf galaxy black holes that are bigger than expected suggests that galaxy mergers are not necessary to create big black holes. Dwarf galaxies don't have a history of galactic smash-ups, and yet their black holes are already relatively big,” NASA said. “Instead, supermassive black holes might form very early in the history of the universe. Or, they might grow harmoniously with their host galaxies, feeding off surrounding gas.”

“We still don't know how the monstrous black holes that reside in galaxy centers formed. But finding big black holes in tiny galaxies shows us that big black holes must somehow have been created in the early universe, before galaxies collided with other galaxies,” added Satyapal, who was joined on the project by co-authors from George Mason University, the University of Victoria in Canada, and the Naval Research Laboratory in Washington.