EARLY HISTORY OF BLACK HOLES
In the 18th century, John Michell and Pierre-Simon Laplace speculated that dense, invisible, dark stars could have high gravity that did not let even light escape. In the 19th century, Karl Schwarzschild further found a feature of these ‘stars’, later called event horizon of these black holes.
SO WHAT IS AN EVENT HORIZON?
It is linked to the object's escape velocity - the speed needed to escape the black hole's gravitational pull. The closer something gets to a black hole, the greater speed is needed to escape that massive gravity. The event horizon is the boundary of the black hole where the escape velocity exceeds speed of light.
THEN WHAT HAPPENED?
In the 1930s, an Indian researcher, B. Datt, and separately, Robert Oppenheimer and Hartland Snyder, made the first calculations of the gravitational collapse of a star, with the assumption of spherical symmetry.
WHAT IS SPHERICAL SYMMETRY IN PHYSICS?
It means a uniform sphere rotated about its center will appear exactly as it did before the rotation. Thus, the axis of the sphere or in this case, a star, will preserve how it "looks".
WHAT DID ROGER PENROSE DISCOVER?
One of the three laureates of 2020, Penrose conceptualised the formation of black holes having different symmetries, via Penrose-Stephen Hawking singularity theorem, and can also be confirmed by Einstein’s General Theory of Relativity.
WHAT IS SINGULARITY?
At the center of a black hole the gravity is so strong that, space-time becomes distorted and the curvature becomes infinite, beyond which physics no longer exists - this is the singularity. Penrose showed that if light becomes trapped inside such a region and cannot escape, stars will collapse and form a black hole.
WHAT IS A SUPERMASSIVE BLACK HOLE?
It is the largest type of black hole, with mass on the order of millions to billions of times the mass of the Sun. Eg: Abell 85, that packs the mass of 40 billion Suns.
BLACK HOLE AT THE CENTER OF MILKY WAY
The other two laureates, Reinhard Genzel and Andrea Ghez observed 30 stars, for nearly 3 decades. They found that the stars move in perfect elliptical orbits around a point.
It was deduced that it is a supermassive black hole with a mass of about 4 million suns.
WHAT’S THE INDIAN CONNECTION?
Kolkata-born physicist Amal Kumar Raychaudhuri. The Landau–Raychaudhuri equation proves that gravitation is a universal attractive force between any two bits of mass-energy. This equation is a fundamental lemma for Penrose–Hawking singularity theorems.
DID YOU KNOW?
Kip Thorne identifies the Golden Age of General Relativity as the period roughly from 1960 to 1975. During this period, many of the concepts and terms which continue to inspire the imagination of gravitation researchers were introduced, including black holes.
