Astronomers using the Hubble Space Telescope have discovered structures around a black hole that were thought to be impossible. A small, "malnourished" black hole was found to have a flat disk of material circling it – a feature thought unique to supermassive black holes. This disc is also so close to the black hole that it's distorting and stretching the light itself.
While black holes are notoriously … well, black, they do often appear to give off light. This usually happens as disks of dust and gas swirl around them like water going down a drain, heating up the material and causing it to shine bright. But this is thought to only occur with larger black holes that have huge discs of material feeding them.
Smaller black holes usually stay fairly shrimpy and malnourished because there isn't enough material falling in and feeding them. The accretion disk of material fades away, leaving these systems looking pretty dim through telescopes.
At a glance, the spiral galaxy NGC 3147 looked like a textbook example. Located about 130 million light-years away, the galaxy's central black hole is relatively small – "only" about 250 million times the mass of the Sun – and its low luminosity suggested there was no disk to be seen. But when researchers on the new study examined the system through the Hubble telescope, they were in for a surprise.
"We thought this was the best candidate to confirm that below certain luminosities, the accretion disk doesn't exist anymore," says Ari Laor, an author of the study. "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."
NGC 3147 turned out to basically be a miniature version of larger systems, the brightest and most active of which are called quasars. That calls into question some of the models that astronomers have long thought to be true.
"The type of disk we see is a scaled-down quasar that we did not expect to exist," says Stefano Bianchi, first author of the study. "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 gas dynamics in very faint active galaxies clearly failed."
The other interesting thing about NGC 3147 is that this disk is very close to the black hole, which produces a few strange quirks. The intense gravitational forces at that range are accelerating the material to over 10 percent of the speed of light. To us the light appears red, because it's having such a hard time escaping the region that the gravity is stretching out the wavelengths.
The team plans to use Hubble to search for more of these kinds of systems. That way, astronomers can begin to build new models that explain the weird new discovery.
The paper was published in the journal Monthly Notices of the Royal Astronomical Society.
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