Artist's View of M60-UCD1 Black
Hole
Image Credit:
NASA, ESA, STScI-PRC14-41a
Astronomers
using data from NASA’s Hubble Space Telescope and ground observation have found
an unlikely object in an improbable place -- a monster black hole lurking inside
one of the tiniest galaxies ever known.
The black hole is five times the mass of the one at the center of our Milky
Way galaxy. It is inside one of the densest galaxies known to date -- the
M60-UCD1 dwarf galaxy that crams 140 million stars within a diameter of about
300 light-years, which is only 1/500th of our galaxy’s diameter.
If you lived inside this dwarf galaxy, the night sky would dazzle with at
least 1 million stars visible to the naked eye. Our nighttime sky as seen from
Earth’s surface shows 4,000 stars.
The finding implies there are many other compact galaxies in the universe
that contain supermassive black holes. The observation also suggests dwarf
galaxies may actually be the stripped remnants of larger galaxies that were torn
apart during collisions with other galaxies rather than small islands of stars
born in isolation.
“We don’t know of any other way you could make a black hole so big in an
object this small,” said University of Utah astronomer Anil Seth, lead author of
an international study of the dwarf galaxy published in Thursday’s issue of the
journal Nature.
Seth’s team of astronomers used the Hubble Space Telescope and the Gemini
North 8-meter optical and infrared telescope on Hawaii’s Mauna Kea to observe
M60-UCD1 and measure the black hole’s mass. The sharp Hubble images provide
information about the galaxy’s diameter and stellar density. Gemini measures the
stellar motions as affected by the black hole’s pull. These data are used to
calculate the mass of the black hole.
Black holes are gravitationally collapsed, ultra-compact objects that have a
gravitational pull so strong that even light cannot escape. Supermassive black
holes -- those with the mass of at least one million stars like our sun -- are
thought to be at the centers of many galaxies.
The black hole at the center of our Milky Way galaxy has the mass of four
million suns. As heavy as that is, it is less than 0.01 percent of the Milky
Way’s total mass. By comparison, the supermassive black hole at the center of
M60-UCD1, which has the mass of 21 million suns, is a stunning 15 percent of the
small galaxy’s total mass.
“That is pretty amazing, given that the Milky Way is 500 times larger and
more than 1,000 times heavier than the dwarf galaxy M60-UCD1,” Seth said.
One explanation is that M60-UCD1 was once a large galaxy containing 10
billion stars, but then it passed very close to the center of an even larger
galaxy, M60, and in that process all the stars and dark matter in the outer part
of the galaxy were torn away and became part of M60.
The team believes that M60-UCD1 may eventually be pulled to fully merge with
M60, which has its own monster black hole that weighs a whopping 4.5 billion
solar masses, or more than 1,000 times bigger than the black hole in our galaxy.
When that happens, the black holes in both galaxies also likely will merge. Both
galaxies are 50 million light-years away.
The Hubble Space Telescope is a project of international cooperation between
NASA and the European Space Agency. NASA's Goddard Space Flight Center in
Greenbelt, Maryland, manages the telescope. The Space Telescope Science
Institute (STScI) in Baltimore conducts Hubble science operations. STScI is
operated for NASA by the Association of Universities for Research in Astronomy,
Inc., in Washington.
For images and more information about Hubble, visit:
NASA
Guillermo Gonzalo Sánchez Achutegui
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