UNIVERSITY PARK, Pa. — “To understand how we prove the existence of a black hole, we first need to agree on what a black hole is,” said Andrea Ghez, professor of physics and astronomy and Lauren B. Leichtman & Arthur E. Levine Chair in Astrophysics at the University of California, Los Angeles (UCLA), and director of UCLA’s Galactic Center Group.
“The problem is today we don’t know how to make the description of things that are very small — quantum mechanics — work together with the description of things that have a lot of gravity, which is general relativity," she said. "And black holes are both small and have lots of gravity, so presumably, when we know how to make these two fields work together, we’ll be able to understand how to describe the essentials of what a black hole actually is.”
“Fortunately, we can ignore that small little problem for the proof of a black hole,” Ghez went on to explain. “That’s because of a concept of a size that is associated with a black hole — not its physical size, but its abstract size. Why is this important? It’s known as the Schwarzschild radius, after the person who understood its meaning, and it’s the last point at which light can escape from a black hole.”
Ghez, who is only the fourth woman to be awarded the Nobel Prize in Physics, recently presented the 2026 Russell E. Marker Lecture in Astronomy and Astrophysics and Physics, titled “From the Possibility to the Certainty of a Supermassive Black Hole.” She explained new developments in the study of supermassive black holes, including her Nobel Prize-winning research using the capture and analysis of 20 years of high-resolution imaging, which has moved the case for a supermassive black hole at the center of our galaxy from a possibility to a certainty and provided the best evidence to date for its existence.
“We’ve advanced the evidence for a supermassive black hole by a factor of 10 million,” Ghez explained about the research.
She also touched on what it was like to be awarded the Nobel Prize during the COVID-19 pandemic, the importance of research collaboration and competition, and the technological and telescope-instrumentation advances that have made her research possible.
“That specific part of the work is what was recognized by the Nobel Prize, and I wanted to point out that there were two operational groups that had been doing this kind of work for 30 years, so in other words, there was a little competition, and I love that the Nobel Prize Foundation recognized both competing teams,” she said. “There’s definitely a lot of advantages to having two competing teams for 30 years. … The science that comes out of that is far better than if any individual team was trying this alone. There is nothing like a competing team for keeping you on your toes and finding your mistakes. It’s, in a sense, a very slow collaboration, because as you publish, you understand the different ways in which the two groups are thinking about things.”
Ghez also added: “What I love about this particular prize is that half of the award money went to a theorist and the other half went to observational teams, so really messaging that importance of the partnership between theory and observations.”
Ghez concluded her talk by looking ahead to the future of the research field.
“People used to ask which came first, the black hole or the galaxy. We had a lot of theories that could explain either case. It’s kind of like the question, ‘Which came first, the chicken or the egg?’” she said. “Today we recognize that is not even the right way to think about it. We’ve come to recognize that there is a really nice correlation between how massive a black hole is and how massive the central component of the galaxy is. … So, that suggests that whatever formed one formed the other, and there has to be a feedback loop that keeps that relationship going over the lifetime of the galaxy.”
Ghez explained that there is far more to learn.
“Our galaxy is the only place to look at that feedback, to look at that environment," she said. "Now we have this amazing laboratory — there is definitely a black hole in the center — so now we want to understand a number of other things. … It’s like being a kid in a candy shop in that there is so much more to be pursued.”
About the Marker Lectures
The Marker Lectures were established in 1984 through a gift from the late Russell Earl Marker, professor emeritus of organic chemistry at Penn State, whose pioneering synthetic methods revolutionized the steroid hormone industry and opened the door to the current era of hormone therapies, including the birth control pill.
The Marker endowment allows the Penn State Eberly College of Science to present annual Marker Lectures in astronomy and astrophysics, the chemical sciences, evolutionary biology, genetic engineering, the mathematical sciences and the physical sciences.