Narrator: In 2011, NASA's Swift satellite
caught an X-ray outburst from a small galaxy 
3.8 billion light-years away. Within a couple of days, researchers realized
they were witnessing the aftermath of a tidal disruption event--a star
ripped apart by the monster black hole at the galaxy's center.
Some of the stellar material fell toward the black hole, forming
an accretion disk and a jet pointed in our direction.
Erin Kara: Tidal disruption events offer us this rare view
at the most common kind of supermassive black hole in the universe, these so-called
dormant supermassive black holes. Ninety percent of black holes
in the universe don't have a lot of hot material orbiting around
them, they don't form these accretion disks, and so we can't observe
them. Tidal disruption events, where the stellar debris
causes the formation of a temporary accretion disk, offers
us a way to probe this probe this population of supermassive black holes.
Narrator: Swift monitored the outburst's progress and was joined
by the European Space Agency's XMM-Newton observatory, 
and the Japanese Suzaku satellite. Recently, 
astronomers introduced a new analysis technique that for the first time allows
them to peer deep into the gravitational well of a normally quiescent black hole.
Called X-ray reverberation mapping, the
method charts the region close to the black hole using light echoes from X-ray flashes,
similar to the way sonar uses sound to map the ocean floor.
Erin: X-ray reverberation mapping has been
very successful at probing the accretion flow in 
well-established accretion disk structures, but had never been used
to look at tidal disruption events. My collaborator at the 
University of Maryland and I were having lunch one day, and she says 
"Has anyone ever looked at tidal disruption events with X-ray
reverberation mapping?" That night I stayed late at the office and
just tried it out on this data from Swift J1644
and much to my surprise the result was
amazing and I could see that we were looking at
the structure of the inner accretion flow around a normally
dormant black hole for the first time. It's not like a normal accretion flow
in an active galaxy that's a flat disk, this is
something that is extremely puffy, very turbulent, and
we are measuring flashes of X-ray emission deep within this
newly formed accretion disk. Narrator: Stellar
material streamed into the developing disk, churning it into a thick, chaotic
whirlpool of X-ray emitting gas, funneling toward the central black hole. 
Deep inside this cavity, multiple X-ray flares 
erupted, providing a flash that echoed throughout the region.
Erin: Previously, astronomers had thought that the X-ray emission
is coming from far out in a jet, but we're finding
with these observations is that the X-ray emission is coming from
flares very close to the supermassive black hole.  And we can
use these observations to probe properties of the black hole 
itself. For instance, we found that the mass of the black hole is something 
on the order of a million times the mass of the sun.
Narrator: The first observations of X-ray reverberations from deep inside an 
accretion disk are providing new insights into a rarely observed class 
of black holes. They're also laying the groundwork for a better 
understanding of tidal disruption events, and the black holes they illuminate. 
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