Bengaluru: The 2020 Nobel Prize in Physics has been awarded jointly to mathematical-physicist Roger Penrose (British), and the duo of Reinhard Genzel (German) and Andrea Ghez (American), all for their work in the field of black holes.
Penrose of Oxford University was awarded the prize for his mathematical models that prove the existence of black holes as a prediction of Einstein’s theory of general relativity.
Genzel and Ghez shared the other half of the prize for their discovery of a ‘supermassive compact object’ — compact objects are stellar remnants — at the centre of the Milky Way. This is thought to be our galaxy’s central supermassive black hole, called Sagittarius A* , pronounced ‘Sagittarius A-star’ and abbreviated to Sgr A*.
Black holes are predicted by Albert Einstein’s theory of general relativity, but the celebrated physicist himself had doubts about their existence.
Supermassive black holes are the biggest of their kind, weighing millions to billions of times the mass of our sun. They are thought to exist in the centre of every galaxy, around which the entire galaxy orbits.
Black hole predictions
Black holes are objects in spacetime where gravity is so strong that not even light can escape. A black hole is a singularity. At singularities, all laws of physics, as we know them, break down.
Black holes are one of three compact objects, the other two being white dwarfs and neutron stars. They were first predicted as a part of Einstein’s theory of general relativity in 1915, following which many notable theoretical physicists and cosmologists worked on its equations, trying to understand black holes and singularities.
In 1965, 10 years after Einstein died, Roger Penrose and Stephen Hawking, the late theoretical physicist, proved mathematically that black holes can form. They also explained the singularity at the heart of a black hole, where gravity and density approach infinity and all known laws of nature cease to exist.
Penrose and Hawking’s work, called the Penrose-Hawking singularity theorems, is considered to be one of the most groundbreaking papers published in theoretical physics.
Hawking was not awarded the Nobel as the prize is not given posthumously.
Since the 1930s, it was known that there was a strong source of radio waves at the heart of the Milky Way, coming from the direction of the constellation Sagittarius. The radio source was called Sgr A* because it was “exciting”, and excited states of atoms are denoted with an asterisk. Sgr A* was thought to be around 4 million times the mass of the sun.
In 2002, Reinhard Genzel’s team at the Max Planck Institute for Extraterrestrial Physics, Germany, reported observations of the motion of a star called S2 near Sgr A* over 10 years. His findings ruled out alternative objects and strengthened the argument for Sgr A* being a supermassive black hole.
Genzel’s early pioneering work was performed in collaboration with noted physicists Rainer Schödel and Andreas Eckart, who made seminal contributions to the findings.
Meanwhile, Andrea Ghez of the University of California Los Angeles (UCLA), US, developed models for kinematics of stars near the centre of the Milky Way to investigate this region and also produce images.
In 2008, Genzel led the team that published first evidence for the supermassive black hole.
Another shared prize for woman laureate
Ghez is the fourth woman to win the physics Nobel. All four women winners have shared the prize with others. The prize has been awarded to 211 men, and has faced strong criticism for overlooking women contenders.
The scientific community has urged the Royal Swedish Academy of Sciences, which hands out the Nobel prizes for physics, chemistry and economic sciences, to recognise groundbreaking work done by women scientists such as the late Vera Rubin, on dark matter, and Jocelyn Bell Burnell, for the discovery of pulsars, a finding that earned her adviser Antony Hewish a Nobel in 1974.
The three previous women winners of the prize were Marie Curie for radiation (1903, shared with Pierre Curie and Antoine Henri Becquerel), Maria Goeppert Mayer for modelling the nuclear structure (1963, shared with J. Hans D. Jensen and Eugene Wigner), and Donna Strickland, for chirped pulse amplification in lasers (2018, shared with Gérard Mourou and Arthur Ashkin).
The prize has also courted criticism for primarily picking winners from the US and Europe, not recognising collaborative work, and for not handing out posthumous prizes, including to Hawking this year for his work with Penrose.
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