A black hole in the centre of the Milky Way galaxy?
The story of Andrea Ghez, winner of the Noble Prize in Physics 2020
Back when I was in school in 9th-10th grade, I used to watch all the possible shows on Astronomy and Space on all the TV cable channels — Discovery, National Geographic, Discovery Science — you name it, I would have mostly watched it!
Ahh, watching these after returning from school was a good day! In fact, I used to watch them with rapt attention and would make even my parents and sister watch these (in my defence, my mom liked the Nat Geo show Mars :P). It was due to this that in 2020 when I saw the Nobel Prize in Physics winners — I knew I could not have been mistaken that I had seen one of them — Andrea Ghez, on TV in multiple shows!
I still vividly remember her talking about her discovery of a black hole at the centre of our galaxy on one of the Discovery Channel shows— and how inspiring it was to see women in astronomy do something so unique! So on this occasion of International Women’s Day, let’s look a bit deeper into the life and work of Andrea Ghez.
Early Life
Andrea Ghez did her undergraduate Bachelor of Physics from MIT and then her PhD from Caltech. She is now a professor in the Department of Astrophysics and Astronomy at UCLA. As a woman, it is very inspiring to see her success in her career along with a family-career balance (she is married and has two sons).
She is only the 4th woman to receive a Nobel Prize in Physics, and this was shared with Reinhard Genzel (with the other half to Roger Penrose) for the discovery of a supermassive black hole in the center of the Milky Way galaxy.
How was the discovery made?
This article by Andrea’s colleague (How Andrea Ghez won a Nobel Prize for an experiment nobody thought would work) mentions how she would not take “no” for an answer, by setting out to perform an experiment — with devices that were built for a completely different direction of studies.
To know what lies at the centre of our galaxy, astronomers wanted to look at it through powerful telescopes. The only problem? The centre mainly comprises a thick cloud of dust, so we cannot see what's underneath the dust in the visible light wavelength.
By using the NIRC(Near Infrared Camera) in the W M Keck Observatory in Hawaii, Andrea and her colleagues tried to look at the galactic centre in the infrared wavelength.
Infrared wavelength is longer than visible light, so it has lower energy and it is scattered less, thus it can reach us on Earth even from very long distances and we can see it.
They found two stars moving in a highly elliptical orbit at the centre of the galactic centre. Over time, with the help of Adaptive Optics (a technology in which the deformation of the wavelength reaching the telescope can be reduced by introducing deformation on the surface of the mirror itself being used), they were able to find the details related to the orbits of these stars in very high resolution.
With this information and Kepler’s third law, they could predict the mass of the centre around which the stars were orbiting. It turned out to be much heavier than we ever thought was possible — 4.1 million solar masses, that is 4.1 million times the mass of our Sun!!
This led to the conclusion that a supermassive black hole is at the galactic centre- called Sagittarius A*. Wondering why we had to go this way of guessing instead of observing it directly.
Well, a black hole is an object so dense (with enormously high mass but significantly less volume) that even light cannot escape it. If light cannot come outside the black hole, no light from the black hole (or any light that falls on the black hole) can ever reach us, which is why we cannot see it.
The principle mentioned above is the exact same principle of how we see any object with our eyes!
That said, you might remember that an image of this same black hole was captured by the Event Horizon Telescope in 2019, which was shared by one of the female computer scientists who worked on the algorithm to create this image, Katie Bouman.
Even in this image, we can see that the black hole has a dark central region, and we can only see the ring of light from the dust around it.
The world of black holes is dark, deep and enticing, and there is always so much to know and understand once you start looking under the hood! Andrea loved this subject and this problem of what lies in the centre of our galaxy so much that she worked on this problem for around 25 years! I hope you enjoyed this tidbit on the work of this famous TV personality :), and you can find more such small reads in the Space Nuggets series.
STEM looks so much different and diverse now than it did 50 years ago, thanks to the efforts of people like Andrea and every other woman in STEM! But we all know that we still have a long way to go. I am just super glad to see that there are more and more role models in STEM — and astronomy — to look upto every day — who have shown us that it is possible to dream and achieve these dreams — and a community to support each other at every step of the way :)
