Integral, ESAs powerful gamma-ray space telescope, has discovered what seems to be a new class of astronomical objects.
An artists impression of the mechanisms in an interacting binary system. The supermassive companion star (on the right-hand side) ejects a lot of gas in the form of stellar wind. The compact black hole orbits the star and, due to its strong gravitational attraction, collects a lot of the gas. Some of it is funnelled and accelerated into a hot disc. This releases a large amount of energy in all spectral bands, from gamma rays through to visible and infrared. However, the remaining gas surrounding the black hole forms a thick cloud which blocks most of the radiation. Only the very energetic gamma rays can escape and be detected by Integral.
These are binary systems, probably including a black hole or a neutron star, embedded in a thick cocoon of cold gas. They have remained invisible so far to all other telescopes. Integral was launched one year ago to study the most energetic phenomena in the universe.
Integral detected the first of these objects, called IGRJ16318-4848, on 29 January 2003. Although astronomers did not know its distance, they were sure it was in our Galaxy. Also, after some analysis, researchers concluded that the new object could be a binary system comprising a compact object, such as a neutron star or a black hole, and a very massive companion star.
When gas from the companion star is accelerated and swallowed by the more compact object, energy is released at all wavelengths, from the gamma rays through to visible and infrared light. About 300 binary systems like those are known to exist in our galactic neighbourhood and IGRJ16318-4848 could simply have been one more. But something did not fit: why this particular object had not been discovered so far?
Christoph Winkler | ESA
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