A joint NASA/Italian space mission has put its sunglasses on to observe polarized X-ray light from a corona of hot gas around the Cygnus X-1 black hole.
Deep studies made by the joint NASA-Italian Space Agency Imaging X-ray Polarimetry Explorer (IXPE) into the heated gas enveloping a black hole are assisting in our understanding of how black holes both swallow and spit out stuff.
In order to examine some of the universe's most energetic objects, including as pulsars, neutron stars, and accreting black holes, IXPE was launched in December 2021. It does this by looking at how these extremely polarized objects' X-rays are polarized.
Sunglasses operate on the concept of polarization; they obstruct all light except that which oscillates in a certain direction. Similar to polarized X-rays, which are electromagnetic waves oscillating mostly in one direction, IPXE detects polarized X-rays.
Lead researcher Henric Krawcynski from Washington University in St. Louis stated that the polarization "carries information about how the X-rays were emitted" in a statement. The polarization also reveals "whether, and where, [the X-rays] reflect off stuff close to the black hole]" in relation to black holes, continued Krawcynski.
IXPE detected Cygnus X-1, an X-ray binary system in the constellation Cygnus the Swan that consists of a 21 solar mass black hole and a 41 solar mass companion star 7,200 light years distant. The stellar companion is being torn apart by the black hole's gravity, and this torn apart stuff is generating a stream of gas that spirals around the black hole and creates a "accretion disc." The temperature of the gas is increased by friction within it to millions of degrees, which is hot enough to release X-rays.
The NICER experiment on board the International Space Station and secondary X-ray observations from NASA's NuSTAR mission and IXPE have provided information on the nature and location of the material that is generating X-rays surrounding Cygnus X-1's black hole.
They discover that the X-rays are being reflected off of objects in a 2,000 km wide coronal area surrounding the black hole. Radio telescopes racing away from black holes like Cygnus X-1 have observed jets of charged particles, which are thought to be produced by the corona of a black hole, which is made of extremely hot plasma.
Cygnus X-1's corona appears to spread away from the black hole perpendicular to the plane of the accretion disc and parallel to the jets, according to the polarization of the X-rays as detected by IPXE. Therefore, the corona either constitutes the interior of the accretion disk or is sandwiching the in-spiring matter.
Additionally, the orientation of the outer accretion disc and the orbital plane of the companion star surrounding the black hole appear to be out of alignment with the corona and inner accretion disc, respectively. The supernova that created the black hole may have caused it to spin at an angle to the system, which may have led to this misalignment. The black hole's strong gravity in combination with this abrupt spin may have caused torques to be introduced into the inner disc, twisting and warping it.
According to Krawczynski, "These new understandings will permit improved X-ray studies of how gravity twists space and time close to black holes."
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