Physics Nobel rewards discoveries on cosmic evolution and exoplanets | Science News for Students

Physics Nobel rewards discoveries on cosmic evolution and exoplanets

The three scientists helped better reveal the universe — and found an exoplanet orbiting a sunlike star
Oct 8, 2019 — 2:24 pm EST
a photo of James Peebles, Michel Mayor, and Didier Queloz

Three scientists have won the Nobel Prize in physics for revealing hidden aspects of the cosmos. James Peebles of Princeton University (right) studied the structure and evolution of the universe. Michel Mayor of the University of Geneva in Switzerland (center) and Didier Queloz of the University of Geneva and the University of Cambridge in England (left) identified the first exoplanet orbiting a sunlike star.


Three scientists will share the 2019 Nobel Prize in physics for their role in two major cosmic discoveries. That prize includes a medal for each and a lump sum of 9 million Swedish kronor (just over $900,000) to be split among them.

Half of the prize goes to James Peebles at Princeton University in New Jersey. He discovered new mathematical tools to study the universe. His research has included studies of the cosmic microwave background, or CMB. As that name suggests, this is light (at microwave wavelengths). It was emitted early in the history of our universe. It can now be found throughout the heavens, hence the term “background.” Peebles’ work eventually helped to reveal two mysterious cosmic features — dark matter and dark energy.

The second half of the prize goes to Michel Mayor at the University of Geneva in Switzerland and Didier Queloz of the University of Geneva and the University of Cambridge in England. Together, they made the first discovery of a planet orbiting a star other than our sun. It would be just one of many thousands of such exoplanets found orbiting stars throughout the Milky Way. The work by Mayor and Queloz helped reshape an understanding of our cosmic neighborhood.

Both discoveries revealed fundamental aspects of the universe that cannot be seen with the human eye.

Half of the prize goes for . . .

Peebles’ work helped establish that only 5 percent of the contents of the universe is the ordinary matter that makes up planets and people. The rest is a mix of dark matter (about 27 percent) and dark energy (about 68 percent). That dark matter scarcely touches ordinary matter except through gravity. Dark energy is a form of energy that makes the universe expand ever faster.

The discovery of the CMB won a Nobel Prize in 1978. Dark energy’s discovery led to a Nobel Prize in 2011.

At a news conference today announcing his sharing the 2019 Nobel Prize, Peebles said, "Theory in any of the natural sciences is empty without observation.” Showing that our universe is evolving, he argued, “was meaningless without the evidence that it [expanded] from a hot dense state."

Nobel committee member and physicist Ulf Danielsson used a cup of coffee as a metaphor for the early universe. He likened ordinary matter to the bit of sugar sprinkled into the swirling liquid. That dark liquid, he said, was the dark matter and dark energy. And that small sprinkle of sugar, representing normal matter, he said, “is what science has been all about for thousands of years — up until now.”

Cosmology is the study of the universe. And through Peebles’ work, Danielsson said, “cosmology evolved into a science of precision.”

Physicists lauded Peebles after hearing of his win. “Jim is among the fathers of physical cosmology,” said physicist David Gross. He’s president of the American Physical Society. Peebles “laid the foundation,” he says, “for the now remarkably successful standard theory of the structure and history of the universe.”

a visualization of light that was emitted just 380,000 years after the Big Bang
The cosmic microwave background is light that was emitted just 380,000 years after the Big Bang. The study of that light (shown) by Peebles and others has led to many new discoveries about the universe.
ESA, The Planck Collaboration

Peebles “has his fingerprints all over” that standard theory, agrees cosmologist Michael Turner. He works in Illinois at the University of Chicago. He says Peebles has been involved “in every major development in cosmology over the past 50 years.”

Cosmologist Jo Dunkley, who works with Peebles at Princeton, sums up the reaction of cosmologists at their university: “Yes, of course, he got the Nobel Prize. He made this field.”

In a news conference held later in the day at Princeton, Peebles seemed overwhelmed by the appreciation of his colleagues. “Now I know how rock stars feel,” he quipped.  Plenty of questions remain in cosmology, he noted. These include the identity of dark matter and dark energy. And, he added, “We can be very sure that as we discover new aspects of the expanding and evolving universe we will be startled and amazed once again.”

After the Big Bang, 13.8 billion years ago, the infant universe was a nearly uniform slurry of energy and matter. And the density of its matter varied only a little bit from place to place. Peebles’ work explains how the universe transformed over eons. Due to the pull of gravity, in time that cosmos became filled with complex structures, such as galaxies.

Peebles “was one of the key people who developed the entire framework of structure formation,” says Priyamvada Natarajan. She works at Yale University, in New Haven, Conn. Dark matter particles still await detection. Despite that, Peebles showed that “dark matter was in the driver’s seat” — key to forming the structures of the cosmos visible today.

Those structures span a broad range of size scales. At the upper end are clusters of galaxies, which can contain thousands of galaxies within. And each of those galaxies may host billions of stars or more. At the smaller end are stars and their planets. Those planets included the one discovered by Mayor and Queloz. Honoring both these discoveries, Natarajan says, is “a celebration of human understanding of the largest scales and the smallest scales. Both are frontiers.”

On that smaller scale — exoplanets

Like dark matter and dark energy, Mayor and Queloz’s 1995 discovery also was not visible to the human eye. This Jupiter-mass exoplanet orbited a sunlike star known as 51 Pegasi. The scientists detected it by watching the way the planet’s gravity tugged on the star. That tug made the star wobble back and forth slightly. In the process, the star’s light shifted from slightly bluer to slightly redder as the star moved slightly toward and then away from Earth.

The planet they found, 51 Pegasi b, was unlike anything that exists in our solar system. It lies closer to its star than Mercury does to the sun. Scientists thought it was impossible for giant planets to form so close to their stars. Until, that is, they found this one.

an illustration of Jupiter-mass planet 51 Pegasi b
The Jupiter-mass planet 51 Pegasi b is shown here in an artist’s illustration. It is widely regarded as the first exoplanet discovered orbiting a sunlike star. The discoverers, astronomers Michel Mayor and Didier Queloz, share the 2019 Nobel Prize in physics.
M. Kornmesser/ESO, Nick Risinger/

Astronomers now think giant planets probably form far from their stars, then later migrate inward to become hot Jupiters. The idea that planets’ orbits can shuffle positions around their stars has since been used to explain some mysteries in our own solar system.

“It’s so charming for me to think … that we had a pretty good theory of how planets formed before the first extrasolar planet was discovered,” Peebles said during the news conference. “That’s a good illustration of the nature of science, isn’t it?”

Since the discovery of 51 Pegasi b, more than 4,000 exoplanets have been found orbiting distant stars. Astronomers can now study individual planetary systems and planet populations as a whole. It helps them understand how alien worlds form and evolve. Scientists also are planning how to search for signs of life in exoplanets’ atmospheres.

“There’s a reason [51 Pegasi b] was found first — it’s the easiest type of planet to find,” says David Charbonneau. He’s an exoplanet expert at Harvard University in Cambridge, Mass. After all, big, close-orbiting planets will influence their stars the most.

Since 51 Pegasi b, astronomers have been finding smaller planets and cooler planets — ones more like Earth, Charbonneau says. In fact, he points out, “There’s an enormous amount of enthusiasm in the field.” Many feel that “with the right telescopes, we really could … find out whether or not there’s life on other planets.”

Charbonneau says “it’s about time” for exoplanet science to be recognized with a Nobel. “The community has really agreed that the discovery of 51 Peg was the discovery that really ignited the field,” he says.

Other exoplanet scientists were more surprised. Sara Seager is an exoplanet pioneer at the Massachusetts Institute of Technology, also in Cambridge. She did not expect her field to win the top honor. “I was so floored,” she says.

The prize is a huge boost for exoplanet science, she maintains. Some still see it as “a frivolous, almost stamp-collecting endeavor,” she says. But she sees it as much more. In just 25 years, “we went from being an obscure and laughable fringe to mainstream science that’s Nobel-worthy.”

Scientists thought the first known exoplanet, a hot Jupiter orbiting close to its star, was impossible. Now there’s a whole field of research on how stars can build these bizarre exoplanets.
Science News/YouTube

Power Words

(more about Power Words)

alien     A non-native organism. (in astronomy) Life on or from a distant world.

astronomy     The area of science that deals with celestial objects, space and the physical universe. People who work in this field are called astronomers.

atmosphere     The envelope of gases surrounding Earth or another planet.

Big Bang     The rapid expansion of dense matter that, according to current theory, marked the origin of the universe. It is supported by physics’ current understanding of the composition and structure of the universe..

cosmic     An adjective that refers to the cosmos — the universe and everything within it.

cosmic microwave background     A type of radiation that fills the universe with a faint glow. It seems to flow in all directions and with an equal intensity. It's the heat left over from the Big Bang and that should exist throughout the universe. It is estimated to be about 2.725 degrees above absolute zero.

cosmology     The science of the origin and development of the cosmos, or universe. People who work in this field are known as cosmologists.

cosmos     (adj. cosmic) A term that refers to the universe and everything within it.

dark energy     A theoretical force that counteracts gravity and causes the universe to expand at an accelerating rate.

dark matter     Physical objects or particles that emit no detectable radiation of their own. They are believed to exist because of unexplained gravitational forces that they appear to exert on other, visible astronomical objects.

density     The measure of how condensed some object is, found by dividing its mass by its volume.

evolve     (adj. evolving) To change gradually over a long period of time.

exoplanet     Short for extrasolar planet, it’s a planet that orbits a star outside our solar system.

field     An area of study, as in: Her field of research was biology. Also a term to describe a real-world environment in which some research is conducted, such as at sea, in a forest, on a mountaintop or on a city street. It is the opposite of an artificial setting, such as a research laboratory.

fundamental     Something that is basic or serves as the foundation for another thing or idea.

gravity     The force that attracts anything with mass, or bulk, toward any other thing with mass. The more mass that something has, the greater its gravity.

Jupiter     (in astronomy) The solar system’s largest planet, it has the shortest day length (10 hours). A gas giant, its low density indicates that this planet is composed of light elements, such as hydrogen and helium. This planet also releases more heat than it receives from the sun as gravity compresses its mass (and slowly shrinks the planet).

mass     A number that shows how much an object resists speeding up and slowing down — basically a measure of how much matter that object is made from.

matter     Something that occupies space and has mass. Anything on Earth with matter will have a property described as "weight."

Mercury      A rocky planet and the one whose orbit is closest to the sun. (in meteorology) A term sometimes used to refer to the temperature. It comes from the fact that old thermometers used to use how high mercury rose within a tube as a gauge for temperature.

migrate     To move long distances.

Milky Way     The galaxy in which Earth’s solar system resides.

Nobel prize     A prestigious award named after Alfred Nobel. Best known as the inventor of dynamite, Nobel was a wealthy man when he died on December 10, 1896. In his will, Nobel left much of his fortune to create prizes to those who have done their best for humanity in the fields of physics, chemistry, physiology or medicine, literature and peace. Winners receive a medal and large cash award.

orbit     The curved path of a celestial object or spacecraft around a star, planet or moon. One complete circuit around a celestial body.

particle     A minute amount of something.

physical     (adj.) A term for things that exist in the real world, as opposed to in memories or the imagination. It can also refer to properties of materials that are due to their size and non-chemical interactions (such as when one block slams with force into another).

physics     The scientific study of the nature and properties of matter and energy. A scientist who works in such areas is known as a physicist.

planet     A celestial object that orbits a star, is big enough for gravity to have squashed it into a roundish ball and has cleared other objects out of the way in its orbital neighborhood.

range     The full extent or distribution of something. For instance, a plant or animal’s range is the area over which it naturally exists.

solar system     The eight major planets and their moons in orbit around our sun, together with smaller bodies in the form of dwarf planets, asteroids, meteoroids and comets.

star     The basic building block from which galaxies are made. Stars develop when gravity compacts clouds of gas. When they become dense enough to sustain nuclear-fusion reactions, stars will emit light and sometimes other forms of electromagnetic radiation. The sun is our closest star.

sun     The star at the center of Earth’s solar system. It’s an average size star about 26,000 light-years from the center of the Milky Way galaxy. Also a term for any sunlike star.

telescope     Usually a light-collecting instrument that makes distant objects appear nearer through the use of lenses or a combination of curved mirrors and lenses. Some, however, collect radio emissions (energy from a different portion of the electromagnetic spectrum) through a network of antennas.

theory     (in science) A description of some aspect of the natural world based on extensive observations, tests and reason. A theory can also be a way of organizing a broad body of knowledge that applies in a broad range of circumstances to explain what will happen. Unlike the common definition of theory, a theory in science is not just a hunch. Ideas or conclusions that are based on a theory — and not yet on firm data or observations — are referred to as theoretical. Scientists who use mathematics and/or existing data to project what might happen in new situations are known as theorists.

universe     The entire cosmos: All things that exist throughout space and time. It has been expanding since its formation during an event known as the Big Bang, some 13.8 billion years ago (give or take a few hundred million years).

wavelength     The distance between one peak and the next in a series of waves, or the distance between one trough and the next. It’s also one of the “yardsticks” used to measure radiation. Visible light — which, like all electromagnetic radiation, travels in waves — includes wavelengths between about 380 nanometers (violet) and about 740 nanometers (red). Radiation with wavelengths shorter than visible light includes gamma rays, X-rays and ultraviolet light. Longer-wavelength radiation includes infrared light, microwaves and radio waves.