Wednesday, March 13, 2013

Overwhelming Notions, Staggering Numbers

Sometimes the studies from astronomers yield simply stupefying results and numbers.

Black holes that are as large as a billion solar masses can be found at the heart of most galaxies. Because they are created at the same time as their host galaxies, understanding how they formed could provide important information about galaxy formation and evolution. It is theorized that if the Black Hole sucks material from one specific direction it could develop a "spin". That spin could be measured by the X-rays emanating from material the inner edge of the disc which is affected by the black hole's gravity more when the black hole is spinning. Motion creates a "redshift", a "stretching" of the wavelength of characteristic X-rays emanating from iron and other elements in the accretion disc. By measuring the redshift--sort of a Doppler effect for light--, the spin of the black hole can be deduced. The problem, however, is that these X-rays must first travel through fast-moving clouds of gas that surround the accretion disc. The absorption of X-rays by the gas could mimic the effect of a spinning black hole.

Guido Risaliti of the Arcetri Observatory in Florence and astronomers in the US, Denmark and the UK have separated the redshift and cloud effects using data from NASA's NuSTAR space telescope. Risaliti looked a the "Supermassive Black Hole" (SMBH) at the centre of the galaxy NGC1365, which is about 56 million light-years away. This black hole, which is about 2 million times more massive than the Sun, is of particular interest because previous studies had suggested that it was rotating rapidly.

The study confirms that the SMBH is spinning at a rate close to the limit defined by the general theory of relativity. While the rotational properties of a spinning gravitational singularity are difficult to describe in a simple way, Risaliti explains that the rotational energy of the SMBH at the heart of NGC1365 is about the same as the energy that is given off by a billion stars burning for a billion years.

Is there anybody who can really grasp that?
Spinning black hole NGC1365:

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