BLACK HOLES

These weird, yet fascinating bodies are characterised by gravity so immense that not even light can escape

Black holes are regions of space where gravity is so strong that nothing, including light, can escape. Hence a black hole’s blackness. The modern picture of black holes is provided by Einstein’s General Theory of Relativity. The theory tells us that a mass like the Sun creates a valley in the spacetime around it, into which other bodies fall. In this picture, a black hole is a bottomless well from which light cannot escape without being sapped of every last shred of its energy.

For reasons we do not fully understand, nature appears to have created two main classes of black holes: ‘stellar-mass’ black holes and ‘supermassive’ black holes, ranging in mass from millions of times the mass of the Sun to almost 50 billion times its mass. There is some evidence of the existence of a class of black holes between stellar-mass and supermassive, but so far astronomers have found very few of these ‘intermediate mass’ black holes.

Stellar-mass black holes are the endpoint of the evolution of massive stars. However, nobody knows the origin of supermassive black holes, or why there appears to be one in the heart of pretty much every galaxy, including our very own Milky Way. It is a chicken-and - egg puzzle. Does a galaxy of stars form first, and then later a supermassive black hole in its heart? Or does a supermassive black hole predate a galaxy and form the seed about which a galaxy of stars congeals?

The heating of matter as it swirls down onto a supermassive black hole creates an ‘accretion disk’ so super-hot that it can pump out 100 times more energy than a galaxy of stars. This is the power source of active galaxies, the most energetic objects in the Universe.