A bright, long duration flare may be the first recorded event of a black
hole destroying a star in a dwarf galaxy. The evidence comes from two
independent studies using data from NASA’s Chandra X-ray Observatory and
other telescopes.
As part of an ongoing search of Chandra's archival data for events
signaling the disruption of stars by massive black holes, astronomers
found a prime candidate. Beginning in 1999, an unusually bright X-ray
source had appeared in a dwarf galaxy and then faded until it was no
longer detected after 2005.
“We can’t see the star being torn apart by the black hole,” Peter
Maksym of the University of Alabama in Tuscaloosa, Ala., who led one of
the studies, “but we can track what happens to the star’s remains, and
compare it with other, similar events. This one fits the profile of
'death by a black hole.'”
Scientists predict that a star that wanders too close to a giant, or
supermassive, black hole could be ripped apart by extreme tidal forces.
As the stellar debris falls toward the black hole, it would produce
intense X-radiation as it is heated to millions of degrees. The X-rays
would diminish in a characteristic manner as the hot gas spiraled
inward.
In the past few years, Chandra and other astronomical satellites have
identified several suspected cases of a supermassive black hole ripping
apart a nearby star. This newly discovered episode of cosmic,
black-hole-induced violence is different because it has been associated
with a much smaller galaxy than these other cases.
The so-called dwarf galaxy is located in the galaxy cluster Abell
1795, about 800 million light years from Earth. It contains about 700
million stars, far less than a typical galaxy like the Milky Way, which
has between 200 and 400 billion stars.
Moreover, the black hole in this dwarf galaxy may be only be a few
hundred thousand times as massive as the sun, making it ten times less
massive than the galaxy's supermassive black hole, and placing it in
what astronomers call an “intermediate mass black hole” category.
“Scientists have been searching for these intermediate mass black
holes for decades,” said Davide Donato of NASA’s Goddard Space Flight
Center (GSFC) in Greenbelt, Md., who led a separate team of researchers.
“We have lots of evidence for small black holes and very big ones, but
these medium-sized ones have been tough to pin down.”
Watch an animated tour of galaxy cluster Abell 1795.
No comments:
Post a Comment