A family shaped by flight
Andrea Mia Ghez was born in New York City on June 16, 1965. Her father, Gilbert Ghez, was born in Rome in 1938 to a Jewish family with roots in Tunisia and in Frankfurt, Germany. His father, a Jew of Tunisian origin, left Italy for the United States after Mussolini’s Fascist government passed its anti-Jewish racial laws in 1938, and the family spent most of the Second World War in New York. Gilbert later studied economics at Yale and Columbia. Andrea’s mother, Susanne Gayton, came from an Irish Catholic family in North Attleborough, Massachusetts.
In 1969, when Gilbert finished his doctorate, he became a professor of economics at the University of Chicago, and the family moved there. As a faculty child, Andrea attended the university’s Laboratory School. Her father gave her and her two younger sisters logic puzzles to solve in the summers.
The girl who wanted to walk on the Moon
Ghez was four when Apollo 11 landed on the Moon, and the Apollo missions made her want to be the first woman astronaut. Her mother encouraged the dream by buying her a telescope. At school her most influential role model was her chemistry teacher, a woman, at a time when women scientists were still rare. She began college at the Massachusetts Institute of Technology as a mathematics major, switched to physics, and graduated in 1987.
She went on to the California Institute of Technology, where she earned her PhD in 1992 under the infrared astronomer Gerry Neugebauer, studying young stars and how often they form in pairs. That work taught her the craft that would define her career: squeezing the sharpest possible images out of telescopes that the Earth’s atmosphere keeps blurring. In 1994 she joined the faculty of the University of California, Los Angeles, where she has remained.
Seeing through the twinkle
The centre of our galaxy lies about 26,000 light years away, in the direction of the constellation Sagittarius, hidden behind clouds of gas and dust that block visible light. Infrared light gets through, but the stars there are packed so tightly that a normal telescope image turns them into a blur. The problem is the atmosphere: pockets of warmer and cooler air act like moving lenses, which is why stars twinkle. For astronomers, twinkling destroys detail.
Ghez attacked the problem with the twin ten-metre telescopes of the W. M. Keck Observatory on Mauna Kea in Hawaii. From 1995 she used speckle imaging, taking thousands of very short exposures that freeze the atmosphere’s distortions and combining them by computer. She then became one of the pioneers of adaptive optics in astronomy: a deformable mirror, adjusted hundreds of times a second, cancels the atmosphere’s distortion in real time, and an artificial guide star made with a laser lets the system work anywhere in the sky. Over the years her team helped improve the resolution of images of the galactic centre enormously.
Each Keck mirror is almost ten metres across and made of 36 hexagonal segments that are controlled separately, which made the telescopes ideal for this kind of work. Ghez and her colleagues spent nights on Mauna Kea year after year, adding new measurements to a record that eventually covered more than two decades. The Nobel committee noted that through better detectors and adaptive optics, the two competing teams improved the sharpness of their images of the galactic centre more than a thousandfold.
Stars around an invisible giant
With sharp images taken year after year, Ghez and her UCLA Galactic Center Group could measure how the stars near the centre move. In 1998 they showed that stars close to the radio source Sagittarius A* move so fast that an enormous mass must be packed into a tiny space. In 2000 they measured the stars’ accelerations, showing that they are curving around a single central point. Then they followed whole orbits. A star known as S0-2 or S2 circles the centre once every sixteen years, close enough that astronomers could watch it complete an entire orbit.
Using Kepler’s laws, the same physics that describes the planets circling the Sun, the team calculated that the central object has a mass of about four million Suns, crammed into a region no larger than our solar system. Only one known kind of object can be that heavy and that small: a supermassive black hole. A German team led by Reinhard Genzel, working with telescopes in Chile, reached the same conclusion independently, and the two groups’ measurements agreed closely. It became the best evidence ever found that supermassive black holes exist.
The scale is hard to imagine. Our Sun takes more than 200 million years to complete one orbit of the Milky Way’s centre. S0-2, much closer in, swings around the black hole in about sixteen years, at its fastest moving at several thousand kilometres per second. The team tracks dozens of such stars, swarming like bees within about a light-month of the centre.
Testing Einstein
The stars around Sagittarius A* are a natural laboratory for gravity in its most extreme form. In 2018, when S0-2 made its closest approach to the black hole, Ghez’s team and Genzel’s team both measured how its light was stretched by the black hole’s gravity, an effect predicted by Einstein’s general theory of relativity. Ghez’s group published its result in 2019, confirming Einstein’s prediction in the strongest gravitational field in which it had then been tested with a star.
Her group also found surprises, including young stars where theory said none should form so close to a black hole, and strange dusty objects orbiting the centre. In 2020 the Nobel Prize in Physics was shared between Roger Penrose, for showing that black holes follow from general relativity, and Ghez and Genzel “for the discovery of a supermassive compact object at the centre of our galaxy.” She was only the fourth woman to receive the physics prize, after Marie Curie, Maria Goeppert Mayer and Donna Strickland.
Her team’s 2003 measurement of the light of S0-2 also produced what they called a paradox of youth: the star appeared to be young and massive, although the black hole’s violent surroundings should make star formation there almost impossible. Puzzles like this keep the galactic centre one of the most closely watched places in the sky.
Why it matters
Ghez’s discovery changed how we understand galaxies, including our own. Astronomers now believe that nearly every large galaxy has a supermassive black hole at its heart, and that these black holes help shape how galaxies grow. The Milky Way’s black hole, a hundred times closer than the next nearest, is the one where the evidence is clearest, and it became the target of the Event Horizon Telescope, which published the first image of its shadow in 2022.
Her methods matter just as much. The adaptive optics techniques she helped bring to maturity on Keck are now standard on the world’s largest telescopes and are being built into the next generation of giant observatories, letting astronomers on the ground see almost as sharply as from space. The same principle of correcting a distorted image in real time is used to look inside the living human eye, in laser communications and in other fields.
Teacher and role model
Ghez holds the Lauren B. Leichtman and Arthur E. Levine Chair in Astrophysics at UCLA, where she teaches undergraduates and trains graduate students. She has made a point of encouraging young people, and especially girls, to consider science. In 2006 she co-wrote, with Judith Love Cohen, a children’s book, You Can Be a Woman Astronomer, and she has appeared in documentaries for the BBC, PBS’s Nova and other broadcasters. Her advice to students, as reported by UCLA, is to follow their passions and to find comfort with discomfort.
Her honours include a MacArthur Fellowship in 2008, the Crafoord Prize in 2012, election to the National Academy of Sciences in 2004 and to the American Philosophical Society in 2012, and the Royal Society’s Bakerian Medal in 2015.
She has also explained her work to general audiences, including a TED talk in 2009 on the hunt for a supermassive black hole and the George Gamow Memorial Lecture, on the journey from the possibility to the certainty of a supermassive black hole. In interviews after her Nobel Prize she spoke of hoping to inspire other young women to enter physics, a field in which women remain a small minority.
Jewish heritage
Ghez’s Jewish heritage comes through her father. His family’s story, from Tunisia and Frankfurt to Rome and then to New York as refugees from Fascist antisemitism, is a twentieth-century Jewish migration in miniature. Her mother came from an Irish Catholic family, and Ghez has not spoken publicly about practising a religion.
She is counted among Jewish Nobel laureates on the basis of her father’s family, and Jewish media in Israel and abroad reported her prize as such in October 2020.
Life and legacy
Ghez is married to Tom LaTourrette, a geologist, and they have two sons. She is a keen swimmer with the UCLA Masters Swim Club.
Her legacy is the proof of something once considered almost science fiction: that at the centre of our galaxy, around which the Sun and all its neighbours turn, sits a black hole four million times heavier than the Sun. She found it by refusing to accept a blurred view of the sky, and in doing so helped give astronomers on the ground the sharpest eyes they have ever had.
Sources & further reading
The Nobel Prize in Physics 2020, Popular information, NobelPrize.org · Andrea Ghez wins 2020 Nobel Prize in physics, UCLA · Two Jews win two Nobel prizes in two days, South African Jewish Report · Andrea M. Ghez, Wikipedia · Researched from the sources above and checked against them. Spotted an error? Tell us.
A life of tikkun olam. This is part of tikkun olam, the Jewish idea of repairing the world, and every one of us can add to it.