‘Oddball galaxy’ is host to most massive black hole

University of Texas astronomers have discovered the most massive black hole to date.

The black hole weighs 17 million times the mass of our sun, making up 14 percent of its galaxy’s mass, rather than the normal 0.1 percent.  

“This is a really oddball galaxy,” says Karl Gebhardt part of the team who made the discovery using the Hobby-Eberly Telescope (HET) at Austin’s McDonald Observatory. “It’s almost all black hole. This could be the first object in a new class of galaxy-black hole systems.” 

The black hole is at the centre of the unusually compact, ‘lenticular’ (meaning flattened), galaxy known as NGC1277. Although this is the largest to date, other massive black holes have been found in compact galaxies and the authors believe that five other nearby compact galaxies may also contain over-sized black holes.

The massive black hole and its unusual galaxy, is just one of many black hole systems that the team are studying to try and understand the relationship between black holes and their galaxies: how they form and grow together. The team’s findings are published in a paper in Nature today.

Lead author Remco van den Bosch said: “At the moment there are three completely different mechanisms that all claim to explain the link between black hole mass and host galaxies’ properties. We do not understand yet which of these theories is best.”

Astronomers currently know the mass of fewer than 100 black holes but understanding a black hole’s mass is a key to understanding its relationship with the galaxy. The study, which is known as Hobby-Eberly Telescope Massive Galaxy Survey (MGS), is calculating the mass of black holes within galaxies, a complex and time-consuming job that is looking for unusual examples like the NGC1277 black hole. 

“When trying to understand anything, you always look at the extremes: the most massive and the least massive,” Gebhardt adds. “We chose a very large sample of the most massive galaxies in the nearby universe,” to learn more about the relationship between black holes and their host galaxies.