After 2017 and 2019, Astrophysicists score a hat-trick with 2020 Physics
Nobel Prize for discovery of “a Super-massive Black Hole” in our Milky Way”
By (Dr) Surjit Singh Bhatti, Formerly Professor & Head (Deptt of Physics), and
Dean (Faculty of Sciences), Guru Nanak Dev University, Amritsar
The Nobel Prize Committee recently announced the 2020 – Physics Nobel Prize at the Royal Swedish Academy of Sciences in Stockholm, for researches that have improved our understanding of the Universe, including work on Black Holes, and for discovering such a supermassive object at the centre of the Milky Way.
Black Holes were predicted by Einstein’s General Theory of Relativity in 1915. The theory explains the effect of gravity on objects moving through the Universe. Their motions are influenced by the masses and energies of other heavy bodies. Too much matter and energy inside too small a space cause hugely abnormal increase in the gravity and a point of infinite density (called Singularity). Here, neither Einstein’s equations nor other physical laws apply anymore. These spaces are called “Black Holes” that devour forever everything that enters them. Once inside, objects need to travel faster than light to come out. This speed (3×108 metres per second), called Cosmic Limit, can not be attained, so that the objects can never escape.
What are Black Holes ?
The name Black Holes was given to dying stars at the end of their life or to the invisible residual matter after the collision of two stars, by an American scientist, John Wheeler, at New York in 1967. These represent un-imaginably huge vacant spaces inside all galaxies. However, they do not have vacuum inside them. Stars, planets, or any other matter entering these spaces, after crossing a certain region (called Event Horizon), get sucked in, and may extend to millions of miles from the centre of the Hole. These are called black because even rays of light crossing the Event Horizon cannot come out of it. Stephen Hawking, the British scientist, however, showed that they leak some energy, generated by their heating and spinning. This seepage is named Hawking Radiation in his honour.
How are Black Holes Created ?
Advanced X-ray and Radio telescopes have now established the presence of millions of Black Holes in all galaxies, including our own. The one in our Milky Way has mass about 4.3 million times that of our Sun and is at a distance of about 26,000 Light Years (1 LY is the distance travelled by light in one year). Normally the repulsive nuclear forces inside a star are countered by the attractive gravitational forces and a dynamic equilibrium exists. As the nuclear fuel is consumed with the passage of time, the enormous gravitational forces overpower and ultimately the aging star implodes into a very heavy dense mass. For such strong gravitational forces to exist it is necessary that mass of the star should be more than at least 20 Suns. Lighter stars can become Black Holes only after collisions. Stars having masses less than 10 Suns (called White Dwarfs) do not implode under gravity.
How to visualize a Black Hole ?
If the Earth were to become as compact as a Black Hole, it would have a diameter of about 2.5 cm only! To visualize how a Black Hole is formed, consider a tight trampoline held on all sides and a heavy metallic sphere rolled onto it. It will go to the centre where the net will dip deep down, making a curved cone. If another lighter sphere is now dropped on any side, it will roll over into the curved dip already made in the centre and will not be able to come out. Very strong gravitational pull of a gigantic star likewise bends the space into a curved cone-like space, with a wide top and a deep bottom narrowing downwards. Matter of any mass that falls into this conical trap has no chance of ever coming out. The adjective black is used for them perhaps to indicate that just as black colour has very high power to absorb incident radiations, Black Holes also absorb everything that gets into them.
What are the New Discoveries ?
The 2020 – Nobel Prize is awarded half to British astrophysicist Roger Penrose for showing convincingly how Black Holes could form and half to Reinhard Genzel, a German, and the American lady, Andrea Ghez for discovering a supermassive object at the Milky Way’s centre. (In 1971 , Martin Rees and Donald Lynden-Bell had suggested that a supermassive Black Hole existed in the Milky Way). Their decades long work proves that Black Holes do exist and Albert Einstein’s Theory of General Relativity is right. They have found that the Universe is full of such dark traps, lurking inside most galaxies, that are millions and billions of times as massive as our Sun. They have taken a picture of one in a galaxy some 55 million Light-Years away.
Dr. Sir Roger Penrose, FRS, born in 1931, is a Professor at the University of Oxford. He invented a new way of showing space and time relationship with Black Holes and the Universe. These are called Penrose diagrams, and being free of mathematical complexities of General Relativity, are now used widely in cosmology. He has published famous books on Artificial Intelligence, Computers, Mind and the Laws of Physics. With Stephen Hawking, he proved that since General Relativity was right, the Universe must also have had a beginning.
Dr. Andrea Mia Ghez , born in 1965, is a Professor at the University of California, Los Angeles. She is the fourth lady to win the Nobel Prize in Physics, after the French-Polish Marie Curie (in 1903), the German-American Maria Goeppert Mayer (in 1963) and the Canadian Donna Theo Strickland (in 2018).
Dr. Reinhard Genzel, FRS, born in 1952 is Director of the Max Planck Institute for Extraterrestrial Physics in Garching, a town near Munich in Germany, and also Professor at the University of California, Berkeley. She and Genzel have also shared the Holger Crafoord Prize (awarded in partnership with Royal Swedish Academy of Sciences) in 2012. They concluded that the masses at the galactic centre must be equivalent to at least four million Suns, in order to exert enough gravitational pull to keep in check the stars and gas that circle it .
In 2019, the Cosmologists were given this prize for work that transformed our ideas about the cosmos, while in 2017 the Swedish Committee honoured Rainer Weiss, Kip Thorne and Barry Barish for the discovery of gravitational waves from Black Holes. This year’s award only reinforces the great importance of research in Cosmology. Still, we do not understand completely what exactly is going on inside the Black Holes. Further, if space can be compressed into infinitesimally small regions, as in Black Holes, then time can be blown-out like a flame, and the laws of nature may also change.
Do these discoveries mean that the mysterious and monstrous Black Holes are the Gateways to the End of Time and ultimately to the End of the Universe, as the aging stars die or collide ?