Under the classical theory of general relativity, once a black hole is created, it will last forever since nothing can escape it. A charged, non-rotating black hole is known as a Reissner-Nordstrom black hole, a charged, rotating black hole is called a Kerr-Newman black hole. Charged Black Hole can be of two types.This is a rotating black hole with no electrical charge. Kerr Black Hole is a more realistic scenario.Schwarzschild Black Hole, otherwise known as a ‘static black hole’, does not rotate and has no electric charge.Supermassive Black Holes weigh between 10 5 and 10 10 solar masses and are found at the centres of most large galaxies.Īlternatively, black holes can be classified by their two other properties of rotation and charge:.The first good IMBH is the X-ray source HLX-1, seen in projection near the centre of the S0 galaxy ESO 243-49. Intermediate Mass Black Holes of 10 2 and 10 5 solar masses may also exist.Stellar Mass Black Holes have masses between about 4 and 100 solar masses and result from the core-collapse of a massive star at the end of its life.These purely hypothetical objects could have been formed through the gravitational collapse of regions of high density at the time of the Big Bang. Primordial Black Holes have masses comparable to or less than that of the Earth.There are now thought to be 4 main types of black holes if classified by mass: This states that every singularity must have an event horizon which hides it from view – exactly what we find for black holes.īlack holes are completely characterised by three parameters: mass, rotation (spin) and charge. To avoid the situation where we could actually see this breakdown of physics occur, the cosmic censorship conjecture was proposed. Yet there is nothing in the theory of general relativity that stops isolated, or ‘naked’, singularities from existing. However we don’t really know what form matter takes at these extreme densities and thus how big a black hole may be within its cloak of invisibility, the `event horizon’.Īn interesting dilemma for astrophysicists is that the physical conditions near a singularity result in the complete breakdown of the laws of physics. It was thought the matter making up the black hole would be compressed to an infinitely small size, giving an infinitely dense object. It was referred to as a ` singularity’ in the classical, pre-(quantum mechanic) days. Well inside the event horizon lies the heart of the black hole. Our Earth would need to be compressed to a size smaller than 1.77 cm across (diameter). For example, our Sun would become a black hole if its mass was contained within a sphere about 2.5 km across. The only requirement is that its physical size is less than the Schwarzschild radius. In theory, any mass can be compressed sufficiently to form a black hole. The limit of this region is called the `event horizon’, a name which signifies that it is impossible to observe any event taking place inside of it (since information is unable to get out).įor a non-rotating black hole, the radius of the event horizon is known as the Schwarzschild radius -with no recognition of Droste – and marks the point at which the escape velocity from the black hole equals the speed of light. Using Einstein’s theory of general relativity, they discovered that matter compressed to a point (possibly no bigger than the Planck length) would be enclosed by a spherical region of space from which nothing could escape. However, it was Karl Schwarzschild (1873-1916) and the little-known Johannes Droste, who independently developed the modern idea for a black hole. The existence of black holes was first suggested as far back as the late 1700s. Outside the event horizon, v esc < c and there is therefore some hope to escape – if you’re quick enough. Within the event horizon, the escape speed ( v esc ) exceeds the speed of light ( c ), and given that nothing can travel faster than the speed of light, anything inside this sphere is trapped forever. The basic structure of a black hole consists of an object hidden behind an ` event horizon’.

Center of a blackhole