20 Facts About Black hole

Black hole is a region of spacetime where gravity is so strong that nothing – no particles or even electromagnetic radiation such as light – can escape from it.

The first black hole known was Cygnus X-1, identified by several researchers independently in 1971.

Presence of a black hole can be inferred through its interaction with other matter and with electromagnetic radiation such as visible light.

Black hole correctly noted that such supermassive but non-radiating bodies might be detectable through their gravitational effects on nearby visible bodies.

Black hole's arguments were opposed by many of his contemporaries like Eddington and Lev Landau, who argued that some yet unknown mechanism would stop the collapse.

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At first, it was suspected that the strange features of the black hole solutions were pathological artifacts from the symmetry conditions imposed, and that the singularities would not appear in generic situations.

No-hair theorem postulates that, once it achieves a stable condition after formation, a black hole has only three independent physical properties: mass, electric charge, and angular momentum; the black hole is otherwise featureless.

Similarly, the total mass inside a sphere containing a black hole can be found by using the gravitational analog of Gauss's law, far away from the black hole.

The information that is lost includes every quantity that cannot be measured far away from the black hole horizon, including approximately conserved quantum numbers such as the total baryon number and lepton number.

The most general stationary black hole solution known is the Kerr–Newman metric, which describes a black hole with both charge and angular momentum.

Ergosphere of a black hole is a volume bounded by the black hole's event horizon and the ergosurface, which coincides with the event horizon at the poles but is at a much greater distance around the equator.

Once a black hole has formed, it can continue to grow by absorbing additional matter.

Such a black hole would have a diameter of less than a tenth of a millimeter.

Hawking radiation for an astrophysical black hole is predicted to be very weak and would thus be exceedingly difficult to detect from Earth.

Some most notable galaxies with supermassive black hole candidates include the Andromeda Galaxy, M32, M87, NGC 3115, NGC 3377, NGC 4258, NGC 4889, NGC 1277, OJ 287, APM 08279+5255 and the Sombrero Galaxy.

Consequently, the physics of matter forming a supermassive black hole is much better understood and the possible alternative explanations for supermassive black hole observations are much more mundane.

For example, a supermassive black hole could be modelled by a large cluster of very dark objects.

Therefore, Bekenstein proposed that a black hole should have an entropy, and that it should be proportional to its horizon area.

Link with the laws of thermodynamics was further strengthened by Hawking's discovery in 1974 that quantum field theory predicts that a black hole radiates blackbody radiation at a constant temperature.

In 2012, the "firewall paradox" was introduced with the goal of demonstrating that black hole complementarity fails to solve the information paradox.