Discovering the Black Hole Corona: New Insights from Recent Research

During a total eclipse, observers see a bright halo of light around the Moon. This halo is called the corona, the outer atmosphere of the Sun. Although the corona is thin and close to a vacuum, its temperature reaches millions of degrees, making it visible.

Black holes are thought to have a corona similar to the Sun’s. Observing black hole coronas has been difficult. A recent study published in The Astrophysical Journal has shed light on this elusive area.

For active black holes, a donut-shaped ring of gas and dust surrounds them. This ring contains an accretion disk of heated material that aligns with the black hole’s rotation. Jets of ionized gas stream from the black hole’s poles, moving at nearly the speed of light.

The accretion disk region should be very hot, streaming into the black hole. This corona reaches temperatures in the billions of degrees. However, it is often too faint to see because of the bright light from the accretion disk.

The researchers used a method similar to how we observe the Sun’s corona during an eclipse. The position of a black hole can block our view of its accretion disk. In some cases, the black hole obscures itself, similar to an eclipsed Sun.

Even when obscured, the corona emits high-energy X-rays. These X-rays can scatter off surrounding material, allowing us to detect them. The team analyzed data from NASA’s Imaging X-ray Polarimetry Explorer (IPXE) on a dozen obscured black holes, including Cygnus X-1 and X-3 in the Milky Way.

The researchers observed scattered X-rays from these black hole coronas. They found that the corona surrounds black holes in a disk shape, unlike the spherical shape of the Sun’s corona.

This research helps astronomers improve models of black holes. It also enhances understanding of how black holes consume matter and power active galactic nuclei in distant galaxies.