Multiple images of a distant quasar known as RX
J1131-1231 are visible in this combined view from Chandra (pink) and Hubble
(red, green, and blue).
Image Credit: NASA/CXC/Univ of Michigan/R.C.Reis et al; Optical:
NASA/STSc
Astronomers
have used NASA's Chandra X-ray Observatory and the European Space Agency's
(ESA's) XMM-Newton to show a supermassive black hole six billion light years
from Earth is spinning extremely rapidly. This first direct measurement of the
spin of such a distant black hole is an important advance for understanding how
black holes grow over time.
Black holes are defined by just two simple characteristics: mass and spin.
While astronomers have long been able to measure black hole masses very
effectively, determining their spins has been much more difficult.
In the past decade, astronomers have devised ways of estimating spins for
black holes at distances greater than several billion light-years away, meaning
we see the region around black holes as they were billions of years ago.
However, determining the spins of these remote black holes involves several
steps that rely on one another.
"We want to be able to cut out the middle man, so to speak, of determining
the spins of black holes across the universe," said Rubens Reis of the
University of Michigan in Ann Arbor, who led a paper describing this result that
was published online Wednesday in the journal Nature.
Reis and his colleagues determined the spin of the supermassive black hole
that is pulling in surrounding gas, producing an extremely luminous quasar known
as RX J1131-1231 (RX J1131 for short). Because of fortuitous alignment, the
distortion of space-time by the gravitational field of a giant elliptical galaxy
along the line of sight to the quasar acts as a gravitational lens that
magnifies the light from the quasar. Gravitational lensing, first predicted by
Einstein, offers a rare opportunity to study the innermost region in distant
quasars by acting as a natural telescope and magnifying the light from these
sources.
"Because of this gravitational lens, we were able to get very detailed
information on the X-ray spectrum – that is, the amount of X-rays seen at
different energies – from RX J1131," said co-author Mark Reynolds also of
Michigan. "This in turn allowed us to get a very accurate value for how fast the
black hole is spinning."
The X-rays are produced when a swirling accretion disk of gas and dust that
surrounds the black hole creates a multimillion-degree cloud, or corona near the
black hole. X-rays from this corona reflect off the inner edge of the accretion
disk. The strong gravitational forces near the black hole alter the reflected
X-ray spectrum. The larger the change in the spectrum, the closer the inner edge
of the disk must be to the black hole.
"We estimate that the X-rays are coming from a region in the disk located
only about three times the radius of the event horizon, the point of no return
for infalling matter," said Jon M. Miller of Michigan, another author on the
paper. "The black hole must be spinning extremely rapidly to allow a disk to
survive at such a small radius."
For example, a spinning black hole drags space around with it and allows
matter to orbit closer to the black hole than is possible for a non-spinning
black hole.
By measuring the spin of distant black holes researchers discover important
clues about how these objects grow over time. If black holes grow mainly from
collisions and mergers between galaxies, they should accumulate material in a
stable disk, and the steady supply of new material from the disk should lead to
rapidly spinning black holes. In contrast, if black holes grow through many
small accretion episodes, they will accumulate material from random directions.
Like a merry go round that is pushed both backwards and forwards, this would
make the black hole spin more slowly.
The discovery that the black hole in RX J1131 is spinning at over half the
speed of light suggests this black hole, observed at a distance of six billion
light years, corresponding to an age about 7.7 billion years after the Big Bang,
has grown via mergers, rather than pulling material in from different
directions.
The ability to measure black hole spin over a large range of cosmic time
should make it possible to directly study whether the black hole evolves at
about the same rate as its host galaxy. The measurement of the spin of the RX
J1131-1231 black hole is a major step along that path and demonstrates a
technique for assembling a sample of distant supermassive black holes with
current X-ray observatories.
Prior to the announcement of this work, the most distant black holes with
direct spin estimates were located 2.5 billion and 4.7 billion light-years
away.
NASA's Marshall Space Flight Center in Huntsville, Ala., manages the Chandra
program for NASA's Science Mission Directorate in Washington. The Smithsonian
Astrophysical Observatory in Cambridge, Mass., controls Chandra's science and
flight operations.
For an additional interactive image, podcast, and video on the finding,
visit:
For Chandra images, multimedia and related materials, visit:
NASA
Guillermo Gonzalo Sánchez Achutegui
No hay comentarios:
Publicar un comentario
Por favor deja tus opiniones, comentarios y/o sugerencias para que nosotros podamos mejorar cada día. Gracias !!!.