X-rays spot spinning black holes across cosmic sea

[beecee]

https://phys.org/news/2019-07-x-rays-black-holes-cosmic-sea.html

Like whirlpools in the ocean, spinning black holes in space create a swirling torrent around them. However, black holes do not create eddies of wind or water. Rather, they generate disks of gas and dust heated to hundreds of millions of degrees that glow in X-ray light.

Using data from NASA's Chandra X-ray Observatory and chance alignments across billions of light-years, astronomers have deployed a new technique to measure the spin of five supermassive black holes. The matter in one of these cosmic vortices is swirling around its black hole at greater than about 70% of the speed of light.

The astronomers took advantage of a natural phenomenon called a gravitational lens. With just the right alignment, the bending of space-time by a massive object, such as a large galaxy, can magnify and produce multiple images of a distant object, as predicted by Einstein.

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the paper:

https://iopscience.iop.org/article/10.3847/1538-4357/ab1d56

Constraining Quasar Relativistic Reflection Regions and Spins with Microlensing:

Abstract:

We present an analysis of Chandra spectra of five gravitationally lensed active galactic nuclei. We confirm the previous detections of FeKα emission lines in most images of these objects with high significance. The line energies range from 5.8 to 6.8 keV, with widths from unresolved to 0.6 keV, consistent with emission close to spinning black holes viewed at different inclination angles. We also confirm the positive offset from the Iwasawa–Taniguchi effect, the inverse correlation between the FeKα equivalent width (EW) and the X-ray luminosity in active galactic nuclei, where our measured EWs are larger in lensed quasars. We attribute this effect to microlensing, and perform a microlensing likelihood analysis to constrain the emission size of the relativistic reflection region and the spin of supermassive black holes, assuming that the X-ray corona and the reflection region, responsible for the iron emission line, both follow power-law emissivity profiles. The microlensing analysis yields strong constraints on the spin and emissivity index of the reflection component for Q 2237+0305, with a > 0.92 and n > 5.4. For the remaining four targets, we jointly constrain the two parameters, yielding a = 0.8 ± 0.16 and an emissivity index of n = 4.0 ± 0.8, suggesting that the relativistic X-ray reflection region is ultracompact and very close to the innermost stable circular orbits of black holes, which are spinning at close to the maximal value. We successfully constrain the half-light radius of the emission region to <2.4 r g (r g  = GM/c 2) for Q 2237+0305 and in the range 5.9–7.4 r g for the joint sample.