This year the Nobel Prize in physics went to 3 people: One half of the prize went to **Roger Penrose**, for understanding black hole formation. The other half went to **Reinhard Genzel **and** Andrea Ghez** for their discovery of supermassive objects at the centre of Milky Way. Spotlight has been thrown on an Indian Physicist, **Amal Raychaudhuri** and his contributions as well. Let us delve deeper into each of their intriguing stories.

**Crux of the Matter**

**Early History Of Black Holes**

In the 18^{th} 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 19^{th} century, **Karl Schwarzschild **further found a feature of these ‘stars’, later called the event horizon.

**What Is A Black Hole’s Event Horizon?**

It is linked to the **object’s escape velocity** – the speed needed to exceed and 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. So the event horizon is the boundary around the black hole where the escape velocity surpasses the 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 the 2020 Nobel Prize in Physics, Penrose conceptualised the formation of black holes having different symmetries, via the **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 and forms the singularity. Penrose showed that if the **light becomes trapped inside** such a region and cannot escape, stars will collapse and form a black hole.

**Who Was The Indian Behind This?**

Kolkata-born physicist **Amal Kumar Raychaudhuri**. The Lev 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, and is confirmed by **General Relativity **and** Newton’s theory of gravitation.**

**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 The Milky Way**

The other two laureates, **Reinhard Genzel **and** Andrea Ghez** observed some thirty stars, for nearly three decades. They found that the stars move in perfect elliptical orbits, particularly one named S2. Given its calculated mass of about 4 million solar masses, and its invisibility, it was deduced that it is a** supermassive black hole**.

**Curiopedia**

**Kip Thorne**identifies the “**golden age of general relativity**” as the period roughly from 1960 to 1975 during which the study of general relativity entered the mainstream of theoretical physics. During this period, many of the concepts and terms which continue to inspire the imagination of gravitation researchers were introduced, including black holes and ‘gravitational singularity’.- The
**first image of a black hole**, the supermassive one at the center of galaxy Messier 87, was published by the Event Horizon Telescope Collaboration on**10 April 2019**. The image instantly went viral on the internet due to mass media and meme culture that followed it. **Karl Schwarzschild**was a German physicist and astronomer. Schwarzschild provided the**first exact solution**to the Einstein field equations of general relativity, for the limited case of a single spherical non-rotating mass, which he accomplished in 1915, the same year that Einstein first introduced general relativity.