Supermassive black hole discovered in surprising part of universe

Astronomers have discovered a near-record supermassive black hole – weighing in at 17 billion suns – in an area of the universe that was previously considered relatively empty.

The study, published today in Nature, shows that supermassive black holes – those with masses of 10 billion suns or more – are not restricted to the cores of very large galaxies in regions full with other large galaxies. The current record holder – weighing 21 billion suns – was discovered in a spectacular and rare galaxy cluster called the Coma Cluster.

Today’s discovery was in an average-size galaxy group in a galaxy called NGC 1600 on the opposite side of the night’s sky to the Coma Cluster. Because galaxies like NGC 1600 are far more common researchers believe that supermassive black holes may be lurking everywhere in the universe.

We spoke with the author of the study Chung-Pei Ma, professor of astronomy at UC Berkeley and head of the MASSIVE Survey, a study searching for massive galaxies and black holes.

Ma's co-authors are first-author Jens Thomas of the Max Planck Institute for Extraterrestrial Physics in Garching, Germany; former UC Berkeley doctoral student Nicholas McConnell and John Blakeslee of the Dominion Astrophysical Observatory in Victoria, British Columbia; former Miller Visiting Professor Jenny Greene of Princeton University; and Ryan Janish of UC Berkeley's Department of Physics.

ResearchGate: What did you guys discover? Can you help us comprehend the size of this thing?

Chung-Pei Ma: We discovered a hefty black hole, weighing 17 billion suns.

A few ways to comprehend the enormous size:

  1. The event horizon of the NGC 1600 black hole is 340 AU, about 8 times the size of Pluto’s (average) orbit.

  2. The sphere of influence of this black hole — the central region of the galaxy within which gravity is dominated by the hole over that of stars and dark matter — is about 3000 light years across. This is the region we needed to resolve spatially with telescopes to study the stars’ velocities

  3. For many smaller galaxies in the universe, this black hole outweighs their entire individual masses. Even the entire disk of our Milky Way galaxy is only about 3 times more massive than this black hole.

RG: Where was it? How did you find it?

Chung-Pei Ma: The black hole is in the center of a massive elliptical galaxy, NGC 1600, located in a cosmic backwater — an average group of galaxies in an average region of the universe.

We obtained the black hole’s mass by measuring the velocities of stars near it, whose motions are strongly influenced by the gravity of the black hole.

A sky survey image of the massive galaxy NGC 1600. ESA/Hubble image courtesy of STScI.
A sky survey image of the massive galaxy NGC 1600. ESA/Hubble image courtesy of STScI.

RG: What makes a black hole a supermassive black hole?

Chung-Pei Ma: They are called “supermassive” to be contrasted with the “puny" (if you allow me to call a black hole so) ones of up to 100 or so solar masses. The latter are graveyards of massive stars and form as the natural end stage of a star’s life cycle. An example is the 30-solar-mass black hole pair found by LIGO.

RG: Do we know how supermassive black holes form?

Chung-Pei Ma: We know much less about how supermassive black holes form. Gigantic black holes like the one we found probably once shined as a brilliant quasar in the young universe when galaxy collisions were more frequent and more gas was available for consumption.

During this voracious growth spur, the black hole devoured the gas funneled to the center of the collision aftermath, where it resides. Galaxy cannibalism also brings together the black holes in the original galaxies to form a binary of supermassive black holes. Their coalescence also makes the remnant black hole more supermassive.

RG: Why do you believe they are more common than previously thought? How many are there?

Chung-Pei Ma: There may be more black holes like the one we found in NGC 1600 because there are more average-size galaxy groups like the NGC 1600 group than spectacular and rare galaxy clusters like the Coma Clusters, by about a factor of 50.

RG: What does your discovery mean for your field more generally?

Chung-Pei Ma: NGC 1600 is a fairly typical galaxy in our going MASSIVE Survey, a systematic study of the 100 most massive galaxies and their central black holes in the local universe (out to about 300 million light years). We are studying the other galaxies in the survey and will soon find out if NGC 1600 is the tip of an iceberg or a rare find. Such information will also help astronomers better understand the ancestral lineages between blazing quasars in the young universe and sleeping giants like the quiescent black hole in NGC 1600.

Featured image courtesy of NASA's Marshall Space Flight Center.