Credit: Marie Novotná
The Shape of a New Crown
Since no light can escape from a black hole, we can't view black holes by the radiation they directly emit. Instead, we must rely on indirect radiation emitted from the region around the black hole to help us understand its basic properties. Emission may be produced by three regions of hot gas around a black: an
accretion disk of material that's spiraling down into the black hole's event horizon; a jet of charged particles blasting off perpendicularly from the accretion disk into space; and a region of hot gas, called a corona, which sits like a crown on top of the accretion disk. These regions are hot and energetic, and emit lots of X-rays, so X-ray studies have provided important understanding of these regions, and how black holes can feed off of material stripped from a nearby companion star.
NASA's Imaging X-ray Polarimeter Explorer, or IXPE, is a unique X-ray space telescope sensitive to the polarization of X-ray radiation from strange sources like black holes and neutron stars. Measurement of X-ray polarization from accreting black holes by IXPE can provide information on the shape of the material feeding the black hole, information that's impossible to directly obtain in other ways. IXPE observations of known accreting black holes have provided important constraints on the feeding of black holes and the shape of the corona. In 2023 a new accreting black hole binary system, called Swift J1727.8-1613, went into outburst and was discovered by the Burst Alert Telescope on the Neil Gehrels Swift space observatory. This outburst was unusually bright, and the source unusually close to us, so it rapidly drew the attention of astronomical observers. IXPE observations of this source were able to put constraints on the shape of the corona and monitor this shape as the outburst progressed, and showed that the corona is the hot plasma is extended in the accretion disk plane, and that, despite enormous changes in source brightness, the geometry of the corona did not change significantly between the beginning and the end of the outburst. The image above shows an artist's illustration of the accreting black hole Swift J1727.8-1613 as it pulls material from its companion star, and the accretion disk (orange), jet (white) and corona (blue). The polarization direction of the waves of radiation leaving the corona and heading towards IXPE is shown in a sketch in the lower part of the illustration.
Published: December 9, 2024
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Page Author: Dr. Michael F. Corcoran
Last modified Monday, 09-Dec-2024 12:54:09 EST