James Peebles, Michel Mayor and Didier Queloz have won the 2019 Nobel Prize for Physics “for contributions to our understanding of the evolution of the universe and Earth’s place in the cosmos”.

Peebles bags half the prize for “theoretical discoveries in physical cosmology”.  Mayor and Queloz share the other half for “the discovery of an exoplanet orbiting a solar-type star”.

The prize is worth SEK 9m (about £740,000). Peebles will get one half of the prize money and Mayor and Queloz will share the other half. The new laureates will gather in Stockholm on 10 December, where they will receive their medals at a ceremony.

“They have painted a picture of a universe that is far stranger and more wonderful that we could ever have imagined,” said Nobel Committee member Ulf Danielsson of Uppsala University when the winners were announced. “Our view of the universe will never be the same again.”

In the 1960s, Peebles developed the Big Bang model of cosmology as a theoretical framework for describing the universe. Using the model, he predicted properties of the cosmic microwave background radiation (CMB), which was created 400,000 years after the Big Bang. His work has meant that measurements of the CMB have provided profound insights into how much matter was created in the Big Bang and how this matter then clumped to form galaxies and galaxy clusters.

In the early 1980s Peebles was a driving force behind the idea that the large-scale structure of the universe can be explained by the existence of an invisible substance called cold dark matter. In the 1980s he also helped revive the idea of Albert Einstein’s cosmological constant to account for the theoretical observation that about 69% of the mass–energy in the universe is missing. In 1998 the first measurement of the accelerating expansion of the universe confirmed the existence of this missing mass–energy in the form of dark energy. As a result Peebles played a crucial role in the development of the Standard Model of cosmology, which assumes the existence of cold dark matter and dark energy without describing the precise nature of either substance.

There are still many open questions – what is dark matter and Einstein’s cosmological constant?

James Peebles

“We have clear evidence that the universe expanded from a hot, dense state,” Peebles said on the telephone during the press conference that followed the prize announcement. “But we must admit that dark energy and dark matter are mysterious. There are still many open questions – what is dark matter and Einstein’s cosmological constant?”

Wobbling star

In October 1995, Mayor and Queloz made the first discovery of a planet orbiting a star other than the Sun (an exoplanet). Using custom-made instruments on the Haute-Provence Observatory in France, the pair detected the tiny wobbling motion of a star 50 light-years away. This wobble is caused by the close orbiting of a gas-giant planet called 51 Pegasi b, which is about half the mass of Jupiter.

As well as being the first-ever sighting of an exoplanet, the discovery signalled a major shift in our understanding of planet formation and evolution because the distance between 51 Pegasi b and its Sun-like star is just 5% of the distance between Earth and the Sun. This is unlike the much larger orbits of gas giants in the Solar System, yet many more large exoplanets with similar orbits have since been found. This has prompted planetary scientists to develop new theories that describe gas giants as “wandering Jupiters”, forming in relatively large orbits and then migrating inwards.

“It’s a great day for exoplanets,” planetary scientist Sara Seager from the Massachusetts Institute of Technology told Physics World. “To see a field go from obscure, fringe and laughable to Nobel-prize-worthy is a huge tribute to all the people around the world that make exoplanets real.”

Charming discovery

Commenting on the work of Mayor and Queloz, Peebles said: “It is so charming to me to think that we once had a good theory of how planets formed until we found the first [exoplanet] – it’s a good illustration of how science works”.

Since the 1995 discovery, new techniques and telescopes have been developed to make increasingly sophisticated observations of exoplanets. This includes spectroscopic measurements of the chemical compositions of the atmospheres of some exoplanets, which could reveal whether they are suitable for life.

As of 1 October 2019, 4118 exoplanets have been found in the Milky Way. These reside in 3063 exoplanetary systems, 669 of which are known to contain more than one exoplanet – illustrating how rich the study of exoplanets has become since the 1995 discovery.

Read more

Exoplanet researchers welcome ‘cataclysmic’ Nobel-prize announcement

Peebles was born in 1935 in Winnipeg, Manitoba, Canada. He completed a degree in physics at the University of Manitoba in 1958 before doing a PhD at Princeton University in 1962. He remained at Princeton ever since, where he is still active in research.

Learn more about cosmology and exoplanets:

• “Brave new worlds” by Alan Boss
• “Is life on Earth unique” by Ray Jayawardhana
• “Dark energy: how the paradigm shifted” by Lucy Calder and Ofer Lahav
• “How can we find life on distant planets?” – a short explainer video
• Peebles wins a share of the 2013 Dirac Medal
• “Searching for life on other planets” – audio interview with astronomer Sara Seager

Some of our reviews of books on these topics:

• “Commonly uncommon” – Hamish Johnston reviews One of Ten Billion Earths: How we Learn About our Planet’s Past and Future from Distant Exoplanets by Karel Schrijver
• “How to build a planet” – Louisa Preston reviews The Planet Factory: Exoplanets and the Search for a Second Earth by Elizabeth Tasker
• The dark-energy game – Robert P Crease reviews The 4% Universe: Dark Matter, Dark Energy, and the Race to Discover the Rest of Reality by Richard Panek

We have also created a collection of key papers by Peebles, Mayor and Queloz, which are free to read until 31 October 2019.