Researchers Have Managed to Measure the Spin of a Black Hole

A black hole can be simply described, according to our current understanding, by only three factors: its mass, its rotation, and its electric charge. Although it might have taken shape from an intricate combination of matter and energy, all the other details disappear when the cosmic object forms.  

Its insanely powerful gravitational field creates a surrounding surface, known as a ‘horizon,’ and anything that gets to that horizon, including light, cannot escape. Therefore, the singularity looks black, and any information about the infalling material is lost and consumed in the three knowable factors.  

Astronomers are able to calculate the masses of black holes in a relatively direct manner, namely, by observing the way matter moves in their vicinity, impacted by the gravitational field. The charges of black holes are believed to be minor since positive and negative infalling charges are usually equivalent in number.  

Calculating the Spin of a Black Hole  

Black holes’ spins are more challenging to determine, and both depend on reading the X-ray emission from the hot inner edge of the accretion disk surrounding the black hole. One way to assess them is to model the shape of the X-ray continuum, and it depends on good estimates of the mass, distance, and viewing angle.  

The other method, models the X-ray spectrum, including identified atomic emission lines that are usually seen in reflection from the hot gas. It doesn’t rely on knowing as many other parameters. The two techniques have, in general, dropped similar results.  

CfA astronomer James Steiner and his colleagues reimagined seven sets of spectra collected by the Rossi X-ray Timing Explorer of an explosion from a stellar-mass black hole in our galaxy called 4U1543-47. Earlier efforts to calculate the spin of the object using the continuum method resulted in differences between papers that were significantly larger than the formal uncertainties – the studies suggested a mass of 9.4 solar masses and a distance of 24.7 thousand light-years.  

Employing refitting of the spectra and updated modeling algorithms, the researchers report a spin average in size to the previous ones, moderate in magnitude, and set at a 90 percent confidence level. Because there have been only a few well-confirmed black hole spins calculated so far, the new result is a significant addition. 

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