Black holes, which have gravitational forces so intense that even light cannot escape, are often surrounded by accretion disks, swirling masses of gas. Some are also associated with relativistic jets - powerful outflows of matter. However, black holes also feature superheated coronae, much like the outer atmosphere of stars. Unlike the Sun's corona, which burns at around 1.8 million degrees Fahrenheit, a black hole's corona can reach temperatures of billions of degrees.
Astrophysicists have previously recognized coronae around both stellar-mass and supermassive black holes. Stellar-mass black holes are formed from collapsed stars, while supermassive black holes, like the one at the center of the Milky Way, have much larger masses.
"Scientists have long speculated on the makeup and geometry of the corona," said Lynne Saade, a postdoctoral researcher at NASA's Marshall Space Flight Center and lead author of the new findings. "Is it a sphere above and below the black hole, or an atmosphere generated by the accretion disk, or perhaps plasma located at the base of the jets?"
IXPE uses X-ray polarization, a characteristic of light that reveals the structure of highly energetic sources, to study the geometry of black hole accretion systems, including the corona. This data gives scientists a clearer picture of the corona's relationship with the black hole's accretion disk.
"X-ray polarization provides a new way to examine black hole accretion geometry," added Saade. "If the accretion geometry of black holes is similar regardless of mass, we expect the same to be true of their polarization properties."
The findings show that for all black holes where polarization data was available, the corona is extended in the same direction as the accretion disk, disproving the idea that the corona hovers above the disk like a lamppost.
IXPE examined 12 black holes, including stellar-mass black holes like Cygnus X-1 and Cygnus X-3, as well as supermassive black holes in distant galaxies such as NGC 1068 and NGC 4151. Despite the vast differences in the masses of stellar-mass and supermassive black holes, IXPE data indicates both types produce accretion disks with similar structures.
Marshall astrophysicist Philip Kaaret, principal investigator for the IXPE mission, noted, "Stellar-mass black holes rip mass from their companion stars, whereas supermassive black holes devour everything around them. Yet the accretion mechanism functions much the same way."
Saade is optimistic that further studies will yield even more insights. "IXPE has provided the first opportunity in a long time for X-ray astronomy to reveal the underlying processes of accretion and unlock new findings about black holes," she said.
Research Report:A Comparison of the X-Ray Polarimetric Properties of Stellar and Supermassive Black Holes
Related Links
Imaging X-ray Polarimetry Explorer IXPE
Understanding Time and Space
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