Astronomers Discover “Impossible” Disk Around Supermassive Black Hole

Hubble image of NGC 3147 (left) and an artist's impression of its central supermassive black hole. NASA, ESA, S. Bianchi (Università degli Studi Roma Tre University), A. Laor (Technion-Israel Institute of Technology), and M. Chiaberge (ESA, STScI, and JHU); A. Feild and L. Hustak (STScI)

There’s an old adage that states that the most exciting phrase in science is not “Eureka!” but “That’s funny!” And this is probably how astronomers felt when looking at the thin disk of material surrounding the supermassive black hole at the center of the galaxy NGC 3147. They were not expecting it to look the way it does.

The supermassive black hole in question is starved of fuel to gobble up, and it is believed that this class of objects should be surrounded by a puffy donut-shaped ring of material. Only the most luminous and active supermassive black holes have a thin disk around them.

As reported in the Monthly Notices of the Royal Astronomical Society, researchers were using the Hubble Space Telescope to show that this theory holds true in the real universe. And they got a surprise. Contrary to expectations, the supermassive black hole in NGC 3147 has a thin disk.

“We thought this was the best candidate to confirm that below certain luminosities, the accretion disk doesn't exist anymore,” co-author Ari Laor of the Technion-Israel Institute of Technology said in a statement. “What we saw was something completely unexpected. We found gas in motion producing features we can explain only as being produced by material rotating in a thin disk very close to the black hole.”

The type of disk seen here is expected to occur in supermassive black holes that have luminosities 1,000 if not 100,000 times higher than what is seen in NGC 3147. The models clearly need to be revised to include this new discovery.

And while this is a blow to our theories about how supermassive black holes should behave, it is also a fantastic opportunity to study both special and general relativity at the same time. The researchers note that since the thin disk is unobstructed by a puffy ring, they have been able to study both theories in visible light at once.

“This is an intriguing peek at a disk very close to a black hole, so close that the velocities and the intensity of the gravitational pull are affecting how the photons of light look,” added first author Stefano Bianchi of Università degli Studi Roma Tre. “We cannot understand the data unless we include the theories of relativity.”

The material is very close to the supermassive black hole, whose gravitational pull has warped space-time around itself. The disk is in this gravitational well and spins around the black hole at about 10 percent of the speed of light. This is enough for the visible light from the disk to be brighter in the portion of the disk moving towards Earth and dimmer in the part moving away.

NGC 3147 is located 130 million light-years away. It is a stunning spiral galaxy, larger than the Milky Way, that stretches 140,000 light-years across.

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