This week, the world got its first look at Sagittarius A*, the supermassive black hole at the center of the Milky Way. The Event Horizon Telescope, a network of eight radio observatories spread across the globe, has captured images of hazy golden rings of superheated gas and bent light.
Feryal Özel, an astronomer at the University of Arizona and a founding member of the EHT Consortium, said seeing an image of a black hole is like finally meeting someone in real life that you only interact with online.
For UCLA astrophysicist Andrea Ghez, the encounter may have been more like a biographer who came across her subject after a decades-long pursuit.
In 2020, Gates won the Nobel Prize in Physics for his role in the discovery of the supermassive object at the heart of the Milky Way. The celestial body is now known as Sagittarius A*, or Sgr A* for short.
Ghez studies the center of our galaxy, and the orbits of thousands of stars orbiting the dense object at its center. Although she was not involved in the EHT project, she said its “impressive” achievements — including the 2019 reveal of the black hole anchoring the distant galaxy Messier 87 — offer interesting new possibilities for studying the universe.
The Los Angeles Times interviewed her about black holes, cosmic wonders, and Einstein’s relationship to the GPS app on your phone. Interview has been edited for length and clarity.
What’s it like to finally see what you’ve been working on for your career?
This is super exciting. We are living in a very interesting time when technology is advancing so rapidly in so many fields and giving us new insights into these incredibly bizarre objects.
Does it look different than you expected?
No, actually. It’s very similar.You should see the ring at about twice and a half Schwarzschild’s 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 where you see it. This is admirable.
How much has the technical capabilities of researchers changed since you started studying black holes?
Huge, huge improvement. I have often said that we are riding a wave of technological development. Everything we do can be described as a tech-enabled discovery.
One of the things I love about working in these areas where technology is developing very rapidly is that it gives you the opportunity to look at the universe in a way that you never had before. Unexpected discoveries are revealed so often.
We’re really lucky that we’re living in a moment where technology is moving so fast that you can literally rewrite textbooks. The Event Horizon Telescope is a similar story.
What unanswered questions about the universe excite you the most?
I have a few favorites right now. I’m very excited that we’ll be able to use stellar orbits to test how gravity works near supermassive black holes, and as detectors of dark matter at the center of the Milky Way. Both of these things should be printed on the track.
One simple way I like to think about is: For the first time, the tracks tell you the shape. After that, you can explore more detailed questions because you kind of know where the stars are in space.
For example, S0-2 (which is my favorite star in the Milky Way, and probably in the universe as well) runs every 16 years. Now we’re on to the second paragraph, which gives us the opportunity to test Einstein’s theory in a different way than what the Event Horizon Telescope detects, and to limit the amount of dark matter you might expect in the center of galaxies. There are things we don’t know about the early results, and for me, that’s always the most exciting part of measuring — when things don’t make sense.
What is your approach in those moments?
You must have complete integrity of your process. Things may not make sense because you made a mistake that is uninteresting results, or they may not make sense because there is something new to discover. It’s super fun and exciting when you’re not sure.
We just discovered these objects at the center of the Milky Way, and they seem to stretch as they get closer to the black hole and then become more compact. They are called tidal interactions. If you think about that giant wave in the movie “Interstellar,” it’s like a giant wave that just rose from Earth. If we see stars having this interaction, it means that the star must be, I don’t know, a hundred times bigger than anything we predict exists in that region. So this leaves you scratching your head.
Does the new image of Sagittarius A* reinforce your finding that, at the moment, Einstein’s theory of general relativity seems to do the best job of explaining how gravity works throughout the universe?
yes. Absolutely. Black holes kind of represent a breakdown in our understanding of how gravity works. We don’t know how to get gravity and quantum mechanics to work together. You need these two things together to explain what a black hole is, because a black hole is a powerful gravitational force coupled with an infinitely small object.
Wait, what? I thought black holes were huge.
No, the image is what happens around a black hole.Black holes don’t have a finite size, but have this Abstract The size of the event horizon, the last point at which light can escape. Gravitational interactions with the localized light are then concentrated in this ring, which is two and a half times larger than the event horizon.
Regardless, we know that black holes represent the collapse of our knowledge. That’s why everyone is out there constantly testing Einstein’s ideas about gravity, because at some point you want to see what you might call an expanded version of gravity, just like Einstein was an expanded version of Newton’s .
It’s fair to say Newton’s laws explain pretty well how gravity works on our little planet, but do we need Einstein once we’re in the universe?
Yes, except for 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 transportation app is because the GPS system locates your phone relative to the satellites orbiting the earth. These systems must use Einstein’s version of gravity. So yes. Before we care about such things, we can use Newtons.