Extreme Power of Black Hole Revealed
Astronomers have used NASA's Chandra X-ray Observatory and a suite of other
telescopes to reveal one of the most powerful black holes known. The black hole
has created enormous structures in the hot gas surrounding it and prevented
trillions of stars from forming.
The black hole is in a galaxy cluster named RX J1532.9+3021 (RX J1532 for
short), located about 3.9 billion light years from Earth. The image here is a
composite of X-ray data from Chandra revealing hot gas in the cluster in purple
and optical data from the Hubble Space Telescope showing galaxies in yellow. The
cluster is very bright in X-rays implying that it is extremely massive, with a
mass about a quadrillion - a thousand trillion - times that of the sun. At the
center of the cluster is a large elliptical galaxy containing the supermassive
black hole.
The large amount of hot gas near the center of the cluster presents a puzzle.
Hot gas glowing with X-rays should cool, and the dense gas in the center of the
cluster should cool the fastest. The pressure in this cool central gas is then
expected to drop, causing gas further out to sink in towards the galaxy, forming
trillions of stars along the way. However, astronomers have found no such
evidence for this burst of stars forming at the center of this cluster.
This problem has been noted in many galaxy clusters but RX J1532 is an
extreme case, where the cooling of gas should be especially dramatic because of
the high density of gas near the center. Out of the thousands of clusters known
to date, less than a dozen are as extreme as RX J1532. The Phoenix Cluster is the
most extreme, where, conversely, large numbers of stars have been observed to be
forming.
What is stopping large numbers of stars from forming in RX J1532? Images from
the Chandra X-ray Observatory and the NSF's Karl G. Jansky Very Large Array
(VLA) have provided an answer to this question. The X-ray image shows two large
cavities in the hot gas on either side of the central galaxy. The Chandra image
has been specially processed to emphasize the cavities. Both cavities are
aligned with jets seen in radio images from the VLA. The location of the
supermassive black hole between the cavities is strong evidence that the
supersonic jets generated by the black hole have drilled into the hot gas and
pushed it aside, forming the cavities.
Shock fronts - akin to sonic booms - caused by the expanding cavities and the
release of energy by sound waves reverberating through the hot gas provide a
source of heat that prevents most of the gas from cooling and forming new
stars.
The cavities are each about 100,000 light years across, roughly equal to the
width of the Milky Way galaxy. The power needed to generate them is among the
largest known in galaxy clusters. For example, the power is almost 10 times
greater than required to create the well-known cavities in Perseus.
Although the energy to power the jets must have been generated by matter
falling toward the black hole, no X-ray emission has been detected from
infalling material. This result can be explained if the black hole is "ultramassive"
rather than supermassive, with a mass more than 10 billion times that of the
sun. Such a black hole should be able to produce powerful jets without consuming
large amounts of mass, resulting in very little radiation from material falling
inwards.
Another possible explanation is that the black hole has a mass only about a
billion times that of the sun but is spinning extremely rapidly. Such a black
hole can produce more powerful jets than a slowly spinning black hole when
consuming the same amount of matter. In both explanations the black hole is
extremely massive.
A more distant cavity is also seen at a different angle with respect to the
jets, along a north-south direction. This cavity is likely to have been produced
by a jet from a much older outburst from the black hole. This raises the
question of why this cavity is no longer aligned with the jets. There are two
possible explanations. Either large-scale motion of the gas in the cluster has
pushed it to the side or the black hole is precessing, that is, wobbling like a
spinning top.
A paper describing this work was published in the November 10th,
2013 issue of The Astrophysical Journal and is available online. The first author is
Julie Hlavacek-Larrondo from Stanford University. The Hubble data used in this
analysis were from the Cluster Lensing and
Supernova survey, led by Marc Postman from Space Telescope Science
Institute.
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.
Image credit: X-ray: NASA/CXC/Stanford/J.Hlavacek-Larrondo et al, Optical:
NASA/ESA/STScI/M.Postman & CLASH team
NASA
Guillermo Gonzalo Sánchez Achutegui
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