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Astronomers Spot an Unusual Set of X-ray Light Echoes Around a Black Hole

Posted by Guy Pirro 08/06/2021 03:39PM

Astronomers Spot an Unusual Set of X-ray Light Echoes Around a Black Hole

V404 Cygni is a black hole binary system located about 7800 light years away from Earth. The black hole is actively pulling material away from a companion star (with about half the mass of the Sun) into a disk around the invisible object. This material glows in X-rays, so astronomers refer to these systems as "X-ray Binaries." In 2015, Swift discovered a burst of X-rays from V404 Cygni. The burst created high-energy rings from a phenomenon known as light echoes. Instead of sound waves bouncing off a canyon wall, the light echoes around V404 Cygni were produced when a burst of X-rays from the black hole system bounced off of dust clouds between V404 Cygni and Earth. A team of researchers at the University of Wisconsin recently analyzed Swift and Chandra observations of the system. The rings tell astronomers not only about the black hole's behavior, but also about the landscape between V404 Cygni and Earth. The observed 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.


Comments:

"The team determined that the dust most likely contains mixtures of graphite and silicate grains. In addition, by analyzing the inner rings with Chandra, they found that the densities of the dust clouds are not uniform in all directions. Previous studies have assumed that they did not."
That seems counterintuitive to me...why would you assume that the dust clouds would be uniform in all directions?
I too would not expect the densities of the dust clouds to be uniform in all directions.


"The team determined that the dust most likely contains mixtures of graphite and silicate grains. In addition, by analyzing the inner rings with Chandra, they found that the densities of the dust clouds are not uniform in all directions. Previous studies have assumed that they did not."
That seems counterintuitive to me...why would you assume that the dust clouds would be uniform in all directions?