NASA X-ray Observatory Reveals How Black Holes Gobble Up Stars
The joint NASA-Italian space agency Imaging X-ray Polarimetry Explorer (IXPE) peered deep into the hot gas surrounding the black hole, in observations that help us learn how black holes swallow and eject matter.
IXPE launched in December 2021 to study some of the most energetic objects in the universe, including accreting 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 that which oscillates in a certain direction. Similarly, the polarized X-rays that IPXE detects are electromagnetic waves that vibrate mainly in a specific direction.
The polarization “carries information about how the X-rays were emitted,” said lead researcher Henric Krawcynski of Washington University in St. Louis in statement (opens in new tab). As for black holes, polarization also tells us “if, and where, [the X-rays] bulk material near the black hole,” Krawcynski added.
IXPE observed Cygnus X-1, which is an X-ray binary system consisting of a 21 solar mass black hole and a 41 solar mass companion star 7,200 light years from us in the constellation Swan Swan. The black hole’s gravity pulls matter away from its stellar companion, and this matter forms a jet of gas that spirals around the black hole and forms an ‘accretion disk’. Friction within the gas raises the temperature to millions of degrees, hot enough to emit X-rays. However, with the forces of friction, magnetism, and gravity all at play within the disk, astronomers have never fully understood how some of that matter then falls across the event horizon and into the black hole’s opening, and how some of the matter is directed. into bipolar outflows emanating from the black hole.
IXPE’s observations, combined with secondary X-ray observations from NASA’s NuSTAR mission i NICE an experiment on board International Space Stationshed light on the shape and location of the X-ray-emitting material around the black hole in Cygnus X-1.
They found that X-rays are scattered from material in the 2,000-kilometer-wide coronal region around the black hole. A black hole’s corona is formed from ultra-hot plasma and is suspected to be involved in producing the jets of charged particles seen by radio telescopes rushing from black holes like Cygnus X-1. X-ray polarization measured by IPXE suggests that the Cygnus X-1 corona extends from the black hole parallel to the plane of the accretion disk and perpendicular to the jets. Therefore, the corona either merges the inspiral matter, or actually forms the inner part of the accretion disk.
Furthermore, the corona and the inner accretion disk appear to be misaligned with respect to the orbital plane of the companion star around the black hole and the orientation of the outer accretion disk. This mismatch could be caused as a result supernova which produced the black hole by causing the black hole to rotate at an angle relative to the system. This acute spin, and the gravity that the black hole rules, could then introduce torques into the inner disk, twisting and bending it.
“These new insights will allow for improved X-ray studies of how gravity curves space and time near black holes,” Krawczynski said.
The findings are published (opens in new tab) in the Nov. 3 issue of Science.
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