University of Texas astronomers have discovered what might be the universe's largest black hole, a finding experts said could lead to a better picture of how galaxies and black holes are formed.
The so-called supermassive black hole has the mass of approximately 17 billion suns.
What makes it so unique is that it contains 14 per cent of its galaxy's mass. Most black holes have less than one per cent of their respective galaxies' mass.
UT astronomy professor Karl Gebhardt and postdoctoral fellow Jonelle Walsh are part of a team of researchers led by Remco van den Bosch that used the Hobby-Eberly Telescope at the McDonald Observatory to locate the black hole in galaxy NGC 1277, located 220 million light-years away from Earth in the Perseus constellation.
The team's discovery appeared in the journal Nature this week.
Gebhardt said the find challenges the main theory of black hole and galaxy formation, which says the galaxy comes first and a black hole afterward.
"We're trying to understand what comes first," Gebhardt said. "Is it the black hole or the galaxy? It's the chicken and the egg problem." A black hole has strong gravity that pulls in everything around it, growing larger with the material it consumes.
All galaxies are believed to have a black hole, Gebhardt said. Smaller black holes are generally believed to be formed by the death of large stars, he said, but there are three theories about the formation of supermassive black holes like the one UT researchers measured.
In the main theory, the galaxies are formed first and send material to their centre to grow black holes. Another theory says the black hole comes first and determines how big galaxies grow, while a third contends that black holes and galaxies grow together.
UT astronomy professor John Kormendy, who wasn't involved in the new study, is reviewing black-hole theories and was part of a team in 1997 that discovered a black hole that made up nine per cent of its galaxy's total mass.
"The general idea is that black holes grow gradually over time because they eat the things they live in," Kormendy said.
"That theory is somewhat disfavoured by this new discovery, or at least it's not the whole story." Gebhardt said the research team anticipates that there are at least five more galaxies with massive black holes, and they will attempt to examine those within the next year. Experts currently know the mass of fewer than 100 black holes, he said, and the team's project is to measure 800 of them.
Gebhardt and the team have worked on the project for about four years, he said.
"I want to know how a galaxy is made," said Gebhardt, who got a job after college analyzing black holes at the University of Michigan. "I want to know what role black holes play in galaxy formation and evolution, which [now] appears to be a pretty big role." Gebhardt said his team was attracted to this particular galaxy because the stars were moving so fast and they wanted to find out why.
The team used the Hobby-Eberly Telescope, a 15-year-old telescope at McDonald Observatory in Fort Davis, Texas, to measure the black hole.
The $13.5-million telescope measures the light emitted from the galaxies in a process called spectroscopy, which gathers information about the temperature and speed of objects in space. In August, the telescope detected the first evidence of a planet destroyed by a star.
"Finding the largest black hole was not what we were after," said Matthew Shetrone, a resident astronomer who made the observations for Gebhardt's team. It "required shifting through the diamonds in the rough."
