Cosmologist James Peebles (left) and exoplanet astronomers Michel Mayor and Didier Queloz (right) share the 2019 Nobel Prize in Physics.Credit: Torbjörn Zadig/University of Cambridge/ Inamori Foundation

Michel Mayor and Didier Queloz, who discovered the first extrasolar planet orbiting a Sun-like star, share award with theoretical cosmologist James Peebles.

Cosmologist James Peebles and astronomers Michel Mayor and Didier Queloz have won the 2019 Nobel Prize in Physics for discoveries about the evolution of the Universe and Earth’s place in it.

In 1995, Mayor, at the University of Geneva, and his then-student Queloz announced1 the first discovery of an exoplanet orbiting a Sun-like star — launching a field that has become one of astronomy’s hottest. They detected the planet through its tiny gravitational pull on the star 51 Pegasi, a technique that is now used to study some of the more than 4,000 exoplanets known to exist.

James Peebles, who is at Princeton University in New Jersey, developed a theoretical framework that the Nobel Committee said forms “the foundation of our modern understanding of the Universe’s history, from the Big Bang to the present day”.

Peebles helped to lay the theoretical foundations for the cosmic microwave background (CMB), the ‘afterglow’ of the Big Bang, and to establish the current ‘standard model’ of the evolution of the Universe. In this model, the mysterious substance known as dark matter plays a central part in assembling large-scale structures of the cosmos, such as galaxies and clusters of galaxies.

Mayor and Queloz, who are both Swiss and were born in 1942 and 1966, respectively, share one half of the prize, worth 9 million Swedish kronor (US$910,000). Peebles, who was born in Winnipeg, Canada, in 1935, will receive the other half.

Surprise world

Mayor and Queloz’s discovery “started modern exoplanet science”, says Guillem Anglada-Escudé, an astronomer at the Institute for Space Sciences-CSIC in Barcelona, Spain.

Researchers had previously discovered exoplanets around spinning cores of dead stars known as pulsars, but not around stars similar to our own — which astronomers hope may host habitable planets.

The pair’s discovery came as a surprise to the astronomy community. The planet they detected, called 51 Pegasi b, is a gas giant, a type that astronomers had expected would orbit a solar system’s outer reaches. But the pair found it orbiting around 10 times closer to its star than Mercury is to the Sun. The discovery was an early sign that other planetary systems might not follow the template of our own Solar System.

Several groups were making similar observations at the time, but Mayor and Queloz were first to make the detection because they cast a wider net, says exoplanet astronomer Francesco Pepe. “When they started their programme at the Observatoire de Haute-Provence — by which they found 51 Pegasi b — they didn’t focus on trying to discover planets like those in our Solar System,” says Pepe, who is the head of the astronomy department at the University of Geneva. In particular, their observations enabled them to see Jupiter-sized planets with very tight orbits. “This made the difference.”

The finding was remarkable for being almost completely unambiguous and quickly confirmed, says Anglada-Escudé. The team at the University of Geneva almost immediately began to survey the sky in earnest, he says, which kicked off a “cold war” in exoplanet hunting with a rival team at the University of California, Berkeley, that was using a similar technique to detect planets and who were the first to confirm the Swiss duo’s findings. The Berkeley team’s leader, Geoffrey Marcy, was previously also tipped as a Nobel contender. He stepped down from his position at Berkeley in 2015, after a university investigation ruled that he had violated sexual-harassment policies.

Both Mayor and Queloz, who splits his time between the University of Cambridge, UK, and the University of Geneva, are famed for their talent at building exquisitely precise instruments. They developed spectrographs able to observe the tiny shifts in frequency of light as a star wobbles under the influence of a planet. Known as the radial velocity technique, the method can detect exoplanets as well as estimate their mass. Today, it is just one of a number of methods that astronomers use to not only find exoplanets but to study their atmospheres and potential exomoons. Many Earth-like planets have been found, including the discovery in September of signs of water in the atmosphere of a planet twice the size of our own.

The pair are “superb scientists” who, together with an ever-growing community of researchers, paved the way for a completely new research area, says Christiane Helling, an exoplanet researcher at the University of St Andrews, UK. Queloz “has always worked to develop and support the community as a whole, rather than only for his own success”, she adds.

Probing first light

Meanwhile, Peebles’ theories have allowed cosmologists to understand the CMB, from which physicists draw most of their knowledge about the Universe’s beginnings.

“Were it not for the theoretical discoveries of James Peebles, the wonderful high-precision measurements of this radiation over the last 20 years would have told us almost nothing,” said Mats Larsson, a molecular physicist at Stockholm University and chair of the 2019 Nobel Committee for Physics, when he announced the prize.

“This is such a long-deserved recognition,” says François Bouchet, an astrophysicist at the Institute of Astrophysics in Paris, of Peebles’ prize. He says Peebles has left his mark on virtually all branches of cosmology, helping to put it on a sound basis with calculations rooted in physics. In particular, in 19702, Peebles was a pioneer in predicting the shape of the CMB. Bouchet was a leading researcher on the European Space Agency’s Planck mission, which in this decade has made the most precise mapping yet of the CMB sky.

Peebles helped to develop a model of the Universe’s evolution known as the ‘cold dark matter’ theory, which describes how cosmological structures formed as the Universe expanded and cooled from its hot, dense beginning. Together with the later addition of ideas about the enigmatic force known as dark energy, this has become the standard framework of modern cosmology.

Although the precise nature of dark matter has yet to be understood, several high-precision surveys of the Universe have lent support to this theory — these include studies of the CMB and the mapping of galaxies across large swaths of the sky. The hypothesis suggests that if dark matter consists of subatomic particles, these must be massive and relatively slow-moving; observations have now largely excluded models in which lighter but faster-moving particles would dominate dark matter.

Planck and other projects found features in the CMB that Peebles had predicted. “These are in the sky — they really exist, it’s not just theory,” says astrophysicist Rashid Sunyaev, who was among the Soviet astrophysicists who performed similar calculations in 1970 and is now at the Max Planck Institute for Astrophysics in Garching, Germany.

“The establishment that our Universe is evolving was in part a theoretical discovery but that was meaningless without the evidence — very firm evidence now — that it really did expand from a hot, dense state,” said Peebles, speaking by telephone to journalists after the announcement of the prize. “We depend on that interaction of theory and observation.”

It is unusual for extrasolar planets and cosmology to be paired up in the same prize, but both lines of work “give a fresh perspective of the place humans have in the cosmos”, Bouchet says.

https://www.nature.com/articles/

 

 

 

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