NASA X-ray Observatory Reveals How Black Holes Swallow Stars
The joint NASA-Italian Space Agency Imaging X-ray Polarimetry Explorer (IXPE) has looked deep into the hot gas surrounding a black hole, in observations that help us learn how black holes both gobble up and spit out matter.
IXPE launched in December 2021 to study some of the most energetic objects in the universe, including black holes, neutron stars and pulsars. It does this by observing the polarization of the X-rays emitted by these extreme objects. Polarization is the principle by which sunglasses work – they block all light except what oscillates in a specific direction. Similarly, the polarized X-rays that IPXE detects are electromagnetic waves that usually vibrate in a certain direction.
The polarization “carries information about how the X-rays were emitted,” said lead researcher Henric Krawcynski of Washington University in St. Louis in a statement. pronunciation (opens in new tab). With regard to black holes, polarization also tells us “whether, and where, [the X-rays] scatter material close to the black hole,” Krawcynski added.
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IXPE observed Cygnus X-1, a double X-ray system consisting of a 21-solar black hole and a 41-solar companion star 7,200 light-years away in the constellation Cygnus the Swan. The black hole’s gravity tears matter from its stellar companion, and this matter forms a stream of gas that spirals around the black hole, forming an ‘accretion disk’. Friction in the gas raises the temperature to millions of degrees, hot enough to emit X-rays. However, with frictional, magnetic, and gravitational forces all at play within the disk, it’s never been entirely clear to astronomers how some of that matter then falls across the event horizon and into the black hole’s maw, and how a part of the matter is piped through. in bipolar outflows escaping the black hole.
IXPE’s observations, combined with secondary X-ray observations from NASA’s NuSTAR mission and the NICE experiment aboard the International Space Stationshed light on the shape and location of the material emitting the X-rays around the black hole in Cygnus X-1.
They discover that the X-rays are scattered by material in a coronal region 2,000 kilometers wide around the black hole. A black hole’s corona is formed by ultra-hot plasma and is thought to be involved in the production of beams of charged particles seen by radio telescopes running away from black holes such as Cygnus X-1. The polarization of the X-rays measured by IPXE suggests that Cygnus X-1’s corona extends away from the black hole parallel to the plane of the accretion disk and perpendicular to the jets. Hence, the corona either traps the in-spiral matter, or actually forms the innermost part of the accretion disk.
In addition, the corona and inner accretion disk appear misaligned with respect to the companion star’s orbital plane around the black hole and the orientation of the outer accretion disk. This misalignment may have been caused by the supernova that produced the black hole causing the black hole to rotate at an angle to the system. This sharp rotation, and the gravity exerted by the black hole, could then have introduced torques into the inner disk, causing it to twist and warp.
“These new insights will enable improved X-ray studies of how gravity warps space and time near black holes,” Krawczynski said.
The findings are: published (opens in new tab) in the Nov. 3 issue of the journal Science.
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