Most massive black hole fills strange galaxy

U. TEXAS-AUSTIN (US) — A black hole that is 17 billion times the mass of the sun could change theories about how black holes and galaxies form and evolve.

The unusual black hole—possibly the most massive yet—makes up 14 percent of the mass of galaxy NGC 1277, rather than the usual 0.1 percent and lies 220 million light-years away in the constellation Perseus. The galaxy is only 10 percent the size and mass of our Milky Way, but despite its diminutive size, the black hole at its heart is more than 11 times as wide as Neptune’s orbit around the sun.


This small flattened galaxy contains one of the most massive central black holes ever found. At 17 billion solar masses, it weighs an extraordinary 14 percent of the total galaxy mass. View larger. (Credit: David W. Hogg/Michael Blanton/SDSS Collaboration)

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“This is a really oddball galaxy,” says Karl Gebhardt of the University of Texas at Austin. “It’s almost all black hole. This could be the first object in a new class of galaxy-black hole systems.”

Furthermore, the most massive black holes have been seen in giant blobby galaxies called “ellipticals,” but this one is seen in a relatively small lens-shaped galaxy (in astronomical jargon, a “lenticular galaxy”).

Reported in the journal Nature, the find comes out of the Hobby-Eberly Telescope (HET) Massive Galaxy Survey (MGS). The study’s goal is to better understand how black holes and galaxies form and grow together, a process that isn’t well understood.

“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,” says lead author Remco van den Bosch, who began this work as a postdoctoral fellow at the University of Texas at Austin and is now at the Max Planck Institute for Astronomy in Heidelberg, Germany.

The problem is lack of data. Astronomers know the mass of fewer than 100 black holes in galaxies. But measuring black hole masses is difficult and time-consuming. So the team developed the HET Massive Galaxy Survey to winnow down the number of galaxies that would be interesting to study more closely.

“When trying to understand anything, you always look at the extremes: the most massive and the least massive,” Gebhardt says. “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.

Though still ongoing, the team has studied 700 of their 800 galaxies with HET. “This study is only possible with HET,” Gebhardt says. “The telescope works best when the galaxies are spread all across the sky. This is exactly what HET was designed for.”

In the current paper, the team zeroes in on the top six most massive galaxies. They found that one of those, NGC 1277, had already been photographed by the Hubble Space Telescope. This provided measurements of the galaxy’s brightness at different distances from its center. When combined with HET data and various models run via supercomputer, the result was a mass for the black hole of 17 billion suns (give or take 3 billion).

“The mass of this black hole is much higher than expected,” Gebhardt says. “It leads us to think that very massive galaxies have a different physical process in how their black holes grow.”


This diagram shows how the diamater of the 17-billion-solar-mass black hole in the heart of galaxy NGC 1277 compares with the orbit of Neptune around the Sun. The black hole is eleven times wider than Neptune’s orbit. Shown here in two dimensions, the “edge” of the black hole is actually a sphere. View larger. (Credit: D. Benningfield/K. Gebhardt/StarDate)

Source: University of Texas at Austin