The Hubble Space Telescope (HST) has detected a black hole that should not exist, sitting 130 million light years from Earth. Most large galaxies contain supermassive black holes (SMBH’s) like this specimen, but this particular body poses major conundrums for astronomers. Sitting near the center of the spiral galaxy NGC 3147, this SMBH, 250 million times more massive than our Sun, is surrounded by a thin disk of gas, a structure that astronomical predictions suggest should not be possible for this type of object.
Many galactic black holes, like the one at the center of our own Milky Way, are “malnourished” due to a lack of material close enough to the black hole to feed it regularly. Usually, this results in material surrounding an inactive black hole to puff up into the shape of a torus, like a doughnut. Within NGC 3147, this feature forms a thin disk, much like those found surrounding much more active supermassive black holes.
Models suggest that disks like the one seen in NGC 3147 gather material through the gravitational attraction of supermassive black holes, until they emit vast amounts of light, producing a quasar. But, these new observations do not fit with the accepted model.
“The type of disc we see is a scaled-down quasar that we did not expect to exist. It’s the same type of disc we see in objects that are 1000 or even 100,000 times more luminous. The predictions of current models for very faint active galaxies clearly failed,” Stefano Bianchi of Università degli Studi Roma Tre, in Rome stated.
Al Little Bit of Relativity
Astrophysicists may be able to utilize this unusual structure to test predictions made by Albert Einstein in his two-part masterpiece, the Special and General Theories of Relativity. In 1905, Einstein published his Special Theory of Relativity, describing the effects of space and time on objects undergoing acceleration and the relationships between space and time. General Relativity, released in 1915, governs the behavior of the objects subjected to gravitational fields.
“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. We cannot understand the data unless we include the theories of relativity,” Bianchi explained.
The material circling this SMBH orbits around the object at 10 percent of the speed of light. At these velocities, the side of the disk traveling toward Earth appears to glow from an effect known as relativistic beaming. The massive gravitational pull of the supermassive black hole also pulls on light escaping the disk, making the light redder than it would normally be seen.
Serendipity Doo Dah
“It’s a bizarre but wonderful feeling, to arrive dead center of a target you didn’t even know you were aiming for.”
― Author Lois McMaster Bujold
Ironically, researchers studied NGC 3147 in order to see how disks do not form in low-luminosity active galaxies. What they found came as a surprise.
“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,” explained Ari Laor of the Technion-Israel Institute of Technology in Haifa, Israel.
In order to study astronomical objects in space, astronomers often separate light from stars or galaxies into spectrums of light, similar to rainbows. By examining these spectra, it is possible to deduce the chemical makeup of distant bodies, as well as their velocities relative to the Earth.
“The target was observed with the Space Telescope Imaging Spectrograph (STIS) on board the Hubble Space Telescope on 2018 May 17… The pointing aimed at the host galaxy photocenter, and automatically re-centred to the location of the brightest visible source in the acquisition image,” researchers reported in Monthly Notices of the Royal Astronomical Society.
The extreme resolution of this instrument aboard Hubble allowed the team to isolate light coming from around the black hole, while blocking out signals from nearby stars.
The research team hopes to use Hubble to search for additional compact (thin) disks surrounding supermassive black holes in similar galaxies.
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