Dr Surjit Singh Bhatti, ( Retired) Professor & Head Physics

Dean, Faculty of Sciences, Guru Nanak Dev University, Amritsar, India

   Three scientists, James Peebles, Michel Mayor and Didier Queloz have been awarded the 2019 Physics Nobel Prize ( £ 740,000 ) for “ground-breaking” discoveries about the Universe. Peebles has done fascinating work on the Evolution of the Universe and Earth’s place in it. Mayor and Queloz have made discovery of a new planet around a Sun-like star. As a result of the work of these three, we are in a better position now to answer the following two questions:

1. How did the Universe evolve and what is its structure now ?
2. Are we alone or is there life anywhere else in the Universe ?

  James Peebles, born in 1935 in Winnipeg, Canada, did his undergrad at the University of Manitoba. He went to Princeton University in USA for his Graduate School and earned his PhD in 1962. He has been there ever since. He was honored with FRSC and was awarded the Order of Manitoba by Canada. He is considered the greatest living cosmologist today. He gave the  Chemical Composition of the universe at its beginning and the way the galaxies were formed from the density fluctuations in its primordial state. We can now understand what happened in the early period after the universe was born and what happened next.

   Cosmic Microwave Background ( CMB ) radiation,  afterglow of  the Big Bang, whose existence was predicted in 1965 and was theoretically explained by James Peebles, is crucial to understand these phenomena. Study of CMB enabled Peebles to find  the age, shape, temperature and contents of the Universe.  He found that its structure today is different from what it was in the past, when it was much hotter and more compact, and it will be different in future.

Cosmic Microwave Background ( CMB ) Radiation

  Einstein’s General Theory of Relativity predicted that all galaxies are moving away from one another and the universe is growing. It took almost half a million years for this expansion to cool the universe ( from the initial temperature of 1.7 billion  degrees)  to less than a  thousand  degrees Celsius.  The first rays began to move through space barely 400,000 years after the Big Bang, when the universe became transparent and light rays were able to travel through space. They still fill the cosmos, 13.8 billion years later.  Expansion converted these visible light rays into the invisible microwave radiations,  detected first in 1964, by Arno Penzias and Robert Wilson.  This radiation was interpreted as the Cosmic Microwave Background.

  Peebles interpreted the CMB from the earliest epochs, to predict how its variations would affect the amount of matter and energy which ultimately formed the galaxies and galactic clusters.  Satellite images obtained since 1992 have shown these first rays of light in the universe and their variations with time. Their observed temperature variations agree with his theoretical calculations. CMB radiation studies led Peebles to another  important finding concerning the unknown forms of predominant mass and energy, called  dark mass  and dark energy and their distribution in the universe.

 Dark Matter and Dark Energy – Cosmological Mysteries.

  The very high rotational speeds of galaxies indicate that only gravity from some unknown invisible matter can hold them together, or they would fly apart. Theory of Relativity says space is curved by the mass and energy it contains but at a critical stage the universe does not curve. Measurements of CMB radiation show that the matter contained in the universe is enough only for one third of the critical value of mass required. Of this,  only about five per cent is ordinary matter and the rest is unknown (or dark) matter and most of it cannot be traced. Peebles suggested that this is the energy of empty space, (or dark energy) that fills about two thirds of the expanding universe.

  Peeble’s  calculations show that the dark mass constitutes about 26 %  of the total matter in the universe. It  pulls the galaxies towards one another and prevents them from flying apart. The dark energy forms about 69 % of the total ( of mass and energy ) and pushes the galaxies to provide them the increasingly rapid speed required for expansion. The visible mass in the universe is the remaining 5 % of matter, of which everything on the earth and our planetary system is made of.

 Michel Mayor, born at Lausanne, Switzerland in 1942, is Professor Emeritus at University of Geneva. His doctoral student and now colleague,

 Dr Didier Queloz (born in Switzerland in 1966), obtained his PhD in Astrophysics in 1995. At present he is a Professor at the University of Geneva and also at the University of Cambridge. Together they had discovered in 1995, the first extrasolar planet orbiting around a main sequence, Sun-like star , outside the Milky Way. For this discovery, the two shared one half of the 2019 Nobel Prize amount, with James Peeble, who was awarded the other half.

  The planet discovered by Mayor and Queloz has been named 51-Pegasi b. It is a hot gas ball orbiting around a star known as 51- Pegasi, in the constellation Pegasus. It is about 50 light years away from the Earth and completes its orbit around its Sun in four (Earth) days. This is because its distance from its Sun ( 51- Pegasi) is only a fraction (1/20) of the distance of the Earth from our Sun. That explains why its surface temperature is as high as 1000⁰ C. In 2017, it was confirmed that traces of water exist on this planet. Its mass is about half of the mass of Jupiter, the biggest planet in our own solar system, about 150 times that of the Earth. It has thus become the first planet known to us with certainty, orbiting around another Sun. This has opened the gates for new researches in Astrophysics and Astronomy, leading to the discovery of more than 4000 more exoplanets, out of which the existence of 1900 has been confirmed. As a result, we now know that our Sun is not alone in having a planetary system around it.  Most of the billions of  stars in the Milky Way may also have accompanying planets.

Methods employed for discovery of new planets+

  One method makes use of the fact that movement of a star is affected by the gravity of the planet moving around it. Hence, both move around their common center of gravity. The star appears to wobble back and forth in the line of sight. The speed of this movement can be measured using the Doppler effect. Light rays coming from the star, moving towards the Earth, have a higher frequency and lower wavelength (having blue color). If it is moving away from us, the result is reversed, and rays appear to be red. These changes in light, called blue-shift and red-shift, give velocity in the line of sight. This is called Radial Velocity measurement  method. Optical fibers  are used to carry the light to the telescopes or spectrographs in the observatories. Satellites are also being used for this purpose. Another method, called Transit Photometry, is used to measure changes in the intensity of the star’s light when a planet passes in front of it. Together, these two methods provide the size, mass and density of the planet which  help to determine its structure.