Credit: European Space Agency, NASA and Felix Mirabel (the French Atomic Energy Commission & the Institute for Astronomy and Space Physics/Conicet of Argentina)
A Puzzling Change of State
Quasars are a type of "active galaxy" in which an accreting supermassive black hole at the galaxy's center powers an assortment of high energy radiation and, most notably, jets of radio-emitting charged particles stretching for thousands, or hundreds of thousands, of light years. Microquasars are accreting stellar-mass black hole or neutron star systems within our galaxy which behave like their more distant and much larger cousins, though on much smaller spatial and temporal scales. Microquasars offer nearby quasar analogues to help scientists study why compact objects are such messy eaters. The image above shows an artist's interpretation of a microquasar, consisting of a black hole and normal star in which a stream of gas from the normal star forms an accretion disk (in blue) around the black hole. As matter falls from the companion star towards the black hole, it gains gravitational energy from the black hole, generating high-energy X-rays and gamma rays and powering a jet of electrically-charged particles shooting off the disk into space. The black holes in microquasars can be finicky eaters too, with sporadic periods of gorging and starvation resulting in changes in the observed X-ray spectrum. An unusual case is the microquasar called GRS 1758-258. Using data from the INTEGRAL hard X-ray observatory, and the Rossi X-ray Timing Explorer, astronomers caught this system in a a peculiar faint state where the emission is dominated by low-energy X-rays, which eventually changes to a brighter, more energetic state. The detailed changes seen in the X-ray emission may suggest the presence of multiple accretion streams from the star to the black hole.
Published: June 23, 2025
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Page Author: Dr. Michael F. Corcoran
Last modified Monday, 30-Jun-2025 11:14:19 EDT