A black hole is defined by only three parameters, its electric charge, mass, and spin. Even if it might have formed out of a complicated mix of energy and matter, all other details are erased when the black hole forms.
The black hole’s mighty gravitational field forms a surrounding surface, dubbed horizon, and anything that reaches that horizon (light, too) cannot escape. So, any details about the infalling material are digested and lost forever into the three established parameters. Recently, scientists came up with an intriguing technique of measuring a black hole’s spin. Here is what they found.
How Did Scientists Determine the Spins of Black Holes?
Scientists can estimate the masses of black holes in a relatively simple manner. They watch how matter passes in their proximity (other black holes, too) influenced by the gravitational field. The charges of black holes are believed to be unimportant since negative and positive infalling charges are usually equivalent in number.
The spins of black holes, on the other hand, are more challenging to determine. Both rely on understanding the X-ray eruption from the hot inner edge of the accretion disk around the black hole. One technique simulates the X-ray continuum pattern, and it is based on good evaluations of the mass, viewing angle, and length. The other simulates the X-ray spectrum, comprising detected atomic emission lines that are sometimes spotted in reflection from the hot gas. The two techniques have, in general, yielded similar results.
James Steiner, a CfA astronomer, and his team re-examined seven sets of spectra collected by the Rossi X-ray Timing Explorer of an explosion from a stellar-mass black hole in Milky Way, dubbed 4U1543-47. Other attempts to evaluate the spin of the object utilizing the continuum technique showed some disagreements. But, researchers utilized updated modeling algorithms and careful refitting of the spectra. They indicated a spin intermediate in dimension to the previous ones, moderate in magnitude, and settled at a 90 % confidence level. Since there have been just a few well approved black hole spins measured to date, the recent result is a significant addition.
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