Astronomers using the NASA/ESA Hubble Space Telescope have found an unexpected thin disk of material furiously whirling around a supermassive black hole in the center of NGC 3147, a low-luminosity spiral galaxy located approximately 130 million light-years away.
An artist’s impression of the peculiar thin disk of material circling a supermassive black hole at the heart of NGC 3147. Image credit: M. Kornmesser / ESA / Hubble.
Dr. Stefano Bianchi from the Università degli Studi Roma Tre and colleagues initially selected NGC 3147 to validate accepted models about lower-luminosity active galaxies: those with malnourished black holes.
“The type of disk we see is a scaled-down quasar that we did not expect to exist,” Dr. Bianchi said.
“It’s the same type of disk we see in objects that are 1,000 or even 100,000 times more luminous. The predictions of current models for very faint active galaxies clearly failed.”
Black holes in certain types of galaxies such as NGC 3147 are considered to be starving as there is insufficient gravitationally captured material to feed them regularly.
It is therefore puzzling that there is a thin disk encircling a starving black hole that mimics the much larger disks found in extremely active galaxies.
Of particular interest, this disk of material circling the black hole offers a unique opportunity to test Albert Einstein’s theories of relativity.
The disk in is so deeply embedded in the black hole’s intense gravitational field that the light from the gas disk is altered, according to these theories, giving astronomers a unique peek at the dynamic processes close to a black hole.
“We’ve never seen the effects of both general and special relativity in visible light with this much clarity,” said Dr. Marco Chiaberge, of AURA for ESA, STScI and Johns Hopkins Univeristy.
NGC 3147 is relatively close by, at a distance of roughly 130 million light-years, and can be found in the constellation of Draco. Image credit: NASA / ESA / Hubble / A. Riess et al.
The disk’s material was measured by Hubble to be whirling around the black hole at more than 10% of the speed of light.
At such extreme velocities, the gas appears to brighten as it travels toward Earth on one side, and dims as it speeds away from our planet on the other. This effect is known as relativistic beaming.
The Hubble observations also show that the gas is embedded so deep in a gravitational well that light is struggling to escape, and therefore appears stretched to redder wavelengths. The black hole’s mass is around 250 million solar masses.
“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 we see the photons of light,” Dr. Bianchi said.
The findings were published in the Monthly Notices of the Royal Astronomical Society: Letters.
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Stefano Bianchi et al. 2019. HST unveils a compact mildly relativistic broad-line region in the candidate true type 2 NGC 3147. MNRASL 488 (1): L1-L5; doi: 10.1093/mnrasl/slz080
