Q&A with Andrea Ghez, who discovered the black hole Sagittarius A *

This week, the world got it his first ever look at Sagittarius A *, the supermassive black hole at the center of our galaxy. An image of a hazy golden ring of superheated gas and curved light was captured by the Event Horizon telescopea network of eight radio observatories around the world.

Ferial Ozela University of Arizona astronomer and founding member of the EHT consortium, said seeing the image of the black hole was like finally meeting in real life a person you only interacted with online.

for Andrea Ghezan astrophysicist from UCLA, the encounter was perhaps more like a biographer meeting his subject after decades of research.

In 2020 Ghez was awarded the Nobel Prize in Physics for its role in the discovery of a supermassive object at the center of the Milky Way. That object is now known to be Sagittarius A *, or Sgr A * for short.

Gez studies the center of our galaxy and the orbits of thousands of stars surrounding the dense object in its own heart. Although she was not involved in the EHT project, she claimed that her achievements were “impressive” about her, including her 2019 unveiling of the black hole anchoring a distant galaxy known as Messier 87 – offers intriguing new possibilities for the study of the cosmos.

The Los Angeles Times told her about black holes, cosmic surprises, and what Einstein has to do with the GPS app on your phone. The interview has been edited for length and clarity.

How does it feel to finally set your eyes on the thing you studied in your career?

It’s super exciting. We live in a truly interesting time where technology is advancing so rapidly in so many arenas and offering us new insights into these incredibly exotic objects.

Does it look different than you expected?

No, actually. It is strikingly similar. You should see a ring that has a radius that is about two and a half times the Schwarzschild radius [the radius of the event horizon, the boundary around a black hole beyond which no light or matter can escape]. This is the prediction of where gravity should bend, and that’s exactly where you see it. It is impressive.

A blurry image of a light ring.

This is the first image of Sagittarius A *, the supermassive black hole at the center of our galaxy.

(EHT collaboration)

How much have technological capabilities changed for researchers since you started studying black holes?

Huge, huge progress. I often say that we are surfing on the wave of technological development. Everything we do can be described as technology-enabled discovery.

One of the things I love about working in these areas where technology is evolving very rapidly is that it gives you the opportunity to see the universe in a way you’ve never been able to see before. It is so often that it reveals unexpected discoveries.

We are truly blessed to live in this time when technology is evolving so rapidly that you can really rewrite textbooks. The Event Horizon Telescope is a similar story.

What unanswered questions about the universe excite you the most?

I have a couple of favorites right now. What I’m super excited about is our ability to test how gravity works near the supermassive black hole using stellar orbits and also as a dark matter probe at the center of the galaxy. Both of these things should impress on the orbits.

Andrea Ghez, professor of physics and astronomy at UCLA.

UCLA astronomer Andrea Ghez won the 2020 Nobel Prize in Physics for her work on black holes.

(Aron Ranen / Associated Press)

One simple way I like to think about it is: first time, these orbits tell you the shape. And then after that you can probe more detailed questions because you somehow know where the star is in space.

For example, S0-2 (which is my favorite star in the galaxy and probably the universe) goes around every 16 years. We are now on the second step, and this gives us the opportunity to test Einstein’s theories in ways other than those that the Event Horizon Telescope is probing, as well as limiting the amount of dark matter that might be expected at the center of the galaxy. . There are things we don’t understand about early results and for me this is always the most exciting part of a measurement when things don’t make sense.

What is your approach in those moments?

You must have complete integrity with your process. Things may not make sense because you are making a mistake, which is the uninteresting result, or they may not make sense because there is something new to discover. That moment when you’re not sure is super interesting and exciting.

We have just discovered these objects in the center of the galaxy that seem to lengthen as they get closer to the black hole, and then become more compact. They are called tidal interactions. If you think of the movie “Interstellar” with that big giant tidal wave, this would be like a big tidal wave lifting off the planet. If we see stars that have one type of interaction, it means that the star must be, I don’t know, a hundred times larger than anything we predicted existed in this region. So this makes you scratch your head.

Yes, absolutely. Black holes represent the breakdown of our understanding of how gravity works. We don’t know how to make gravity and quantum mechanics work together. And you need these two things to work together to explain what a black hole is, because a black hole is strong gravity plus an infinitely small object.

Wait what? I thought black holes were huge.

No. The image is of the phenomena occurring around the black hole. The black hole doesn’t have a finite size, but there is this abstract dimension of the event horizon, which is the last point that light can escape. And then the gravitational interaction with local light is concentrated in this ring which is two and a half times larger than the event horizon.

Either way, we know that black holes represent the breakdown of our knowledge. That’s why everyone there keeps testing Einstein’s ideas about gravity, because at some point you expect to see what you might call the expanded version of gravity, in the same way that Einstein was the expanded version of Newton’s version.

It’s fair to say that Newton’s laws do a decent job of explaining how gravity works here on our little planet, but do we need Einstein once we make our way to the universe?

Yes, apart from what we take for granted today: our cell phones. The fact that we can find ourselves so well on Google or Waze or your favorite traffic app is because GPS systems position your phone relative to satellites circling the Earth. These systems must use Einstein’s version of gravity. yeah We could use Newton as long as we don’t care about things like this.