A Quick Look at V404 Cygni

Astronomers are observing an unusual black hole which is surrounded by enormous X-ray rings. Using the Chandra X-ray Observatory and the Neil Gehrels Swift Observatory, researchers have been investigating how this strange phenomenon came to be and what it can tell us about both black holes and cosmic dust.

The black hole is part of a binary system called V404 Cygni, meaning the black hole has a companion star from which it is siphoning off material. As the black hole’s gravity pulls gas away from the star and devours it, the material is forming into a disk around the black hole. This disk glows in the X-ray wavelength, meaning the system is of a type called an X-ray binary.

But this particular system doesn’t just have a disk of material — it is also does something special, giving off periodic bursts of X-rays. These bursts bounce off the clouds of dust which are located between there and Earth, creating rings called light echos, in a similar way to how sound waves bounce off a wall.

To study this phenomenon, researchers collected data in both the X-ray and visible light wavelengths, combining the two into the image below. It shows a series of concentric rings, with some gaps due to the limits of Chandra’s field of view. In total, eight separate rings were observed.

The black hole in V404 Cygni. — The black hole in V404 Cygni is actively pulling material away from a companion star — with about half the mass of the Sun — into a disk around the invisible object. A burst of X-rays from the black hole detected in 2015 created the high-energy rings from a phenomenon known as light echoes, where light bounces off of dust clouds in between the system and Earth. X-ray: NASA/CXC/U.Wisc-Madison/S. Heinz et al.; Optical/IR: Pan-STARRS

This discovery isn’t only of interest because it can tell us about this black hole. It can also tell us about the dust clouds which were involved, and about the space in between V404 Cygni and Earth.

“The rings tell astronomers not only about the black hole’s behavior but also about the landscape between V404 Cygni and Earth,” Chandra scientists wrote. “For example, the diameter of the rings in X-rays reveals the distances to the intervening dust clouds the light ricocheted off. If the cloud is closer to Earth, the ring appears to be larger, and vice versa. The light echoes appear as narrow rings rather than wide rings or haloes because the X-ray burst lasted only a relatively short period of time. “

This black hole is creating enormous glowing X-ray rings

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