Accretion disc around a black
hole and a jet emanating from the disc’s central part
previously reported findings, and the team have been devising theoretical models to explain the appearance of optical and infrared emissions in unexpected accretion regions. “We looked at how X-rays are produced
in the accretion disc, and we realised that something was missing from the existing theories,” explains Poutanen. “What about the non-thermal particles?” The term non-thermal in astrophysics relates to particles that produce emission through synchrotron radiation, which occurs when a charged relativistic particle is accelerated in a direction tangential to its velocity via a magnetic field. Poutanen’s team believe that this synchrotron radiation is the cause of the previously unexplained and unexpected radiation confirmed by their experimental research, and suggest that when charged electrons cross the magnetic field found in a black hole’s accretion disc they radiate in the optical and infrared region.
There are three principal hypotheses that
attempt to explain these observed super- bright X-ray sources. The first hypothesis suggests that intermediate-mass black holes are formed from the collision of more than one star, and the resultant collapse leads to the formation of a black hole much larger than those formed from the collapse of a single star, while the second postulates that these intermediate black holes could be primordial
remnants from the Big Bang,
where the high density and velocity of materials could have provided the right conditions. The third however, says that these super-bright X-ray sources could simply be stellar-mass black holes, but with a very massive stellar companion from which a large amount of matter is accreted, producing very strong X-ray emission. The first step that Poutanen’s team took
towards identifying the most accurate hypothesis was to accurately measure the positions of the ultra-luminous X-ray sources, with respect to optical sources in
“The existence of intermediate-mass black holes was first hypothesised when the X-ray telescope on NASA’s Einstein satellite began observing ultra-luminous X-ray sources in nearby star-forming galaxies in the 1970’s”
nothing new in the world of astronomy, but the discovery of long-wavelength radiation being emitted from apparently the same location as X-rays, when previous theories had put them at the outer, less hot regions of the accretion disc, caught the interest of Poutanen and his team and prompted them to investigate further. For the last four years the team have
been accruing data from the Hubble Space Telescope, along with X-ray emission data from the XMM-Newton Space Telescope, and aligning these data sets in order to observe X-rays and low-energy radiation being emitted from the same location. Their observations confirmed the
www.projectsmagazine.eu.com
Intermediate-mass black holes Unidentified emissions are not the sole uncertainty surrounding black holes; there are even black holes whose very existence is still debated known as intermediate- mass black holes. Similarly to stellar black holes, they are characterised by their size, between one thousand and one hundred thousand solar masses, but unlike the stellar type how they are formed, indeed whether they are formed at all, remains subject to dispute. The existence of intermediate-mass
black holes was first hypothesised when the X-ray telescope on NASA’s Einstein satellite began observing ultra-luminous X-ray sources in nearby star-forming galaxies in the 1970’s. The incredible brightness of these sources, hundreds of times brighter than anything seen in our own Galaxy, led people to believe that they were black holes, but hundreds of times bigger than the stellar type previously observed.
the same region, in a nearby star-forming Antennae galaxies. Archived data was taken from two different observatories, optical emission data from the Hubble Space Telescope and X-ray emission data from the Chandra X-ray Observatory, and the images from these two sources were aligned against a quasar, a strong source of radiation projected by chance within the galaxy image, in order to obtain relative positions. The aim of this process was to assert if the chosen super-bright X-ray source was close to the super-bright optical source, i.e. whether the position of concerned matched
that a massive
collection of stars known as stellar cluster. The team found that there was a good
relation between the positions of the X-ray and optical sources, with the X-ray sources being found close to stellar clusters. In discord with intermediate-mass black hole theory however, the team noticed that the X-ray sources were not found at the centre of these stellar clusters, as would be
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the black hole of
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