Black holes— The Strangest Objects in The Universe Are Finally Acknowledged By The Nobel Committee
By: Areeba Merriam
Tags: Astronomy, Nobel Prize, Black Holes, Space, Science

A Brief Explanation of Their Work

Roger Penrose wrote a ground-breaking paper with the late Stephen Hawking in 1970. They presented in that paper a new generalized theorem on spacetime singularities which revolutionized our understanding of spacetime. They proved that if our universe obeys Einstein’s general theory of relativity and Friedmann’s models about the universe, then there is essentially a singularity at the beginning. According to the Nobel Prize website:

“Penrose used ingenious mathematical methods in his proof that black holes are a direct consequence of Albert Einstein’s general theory of relativity.”

This time the Nobel prize is awarded for theoretical and observational discoveries. The theoretical work was being done in the 1970s by the legends Stephan Hawking and Roger Penrose, and it was observationally proved in the 21st century. They used Einstein’s general theory of relativity and proved the singularity theorems i.e the existence of a point in space-time where the gravitational pull is so strong that even light could not escape. These were just mathematical manipulations at that time but now it's a truth in front of us.

Now it’s an obvious question to ask why they both didn’t receive Nobel prize when we knew the black hole’s existence for so long. The answer to this is the Nobel community likes a theory to be experimentally or observationally verified. For example, Einstein predicted the existence of gravitational waves in 1916 and the Nobel community awarded them in 2017 upon their detection. This year it is awarded because we finally have received the incredible image of a supermassive black hole in the center of M-87 the previous year. It was brought to light by a huge collaborative team of the EHT (Event Horizon Telescope).

Now one can wonder why not the prize is shared between the EHT team and Roger Penrose. Well, it is hard to swallow but it's the policy of Nobel that the prize is only shared between three people and not the entire collaboration.

Professor Genzel and Andrea Ghez both have done an incredible job to answer the biggest mystery that lies inside our MilkyWay galaxy. They were observing stars near the galactic center using high-resolution infrared telescopes.

Infrared light has a long wavelength than visible light, which means it’s not blocked by tiny particles of interstellar dust in the space. We can’t see the center of our galaxy with visible light but with infrared light. Hence, in this way, one can measure the position and speed of stars locating near the center of the MilkyWay, then work out the orbits of those stars and the influence of gravity around them, after that one can calculate the mass of the central object to speculate the size of that object at the center.

In 1969, Donald Lynden-Bell and Martin Rees have put forward a suggestion that our home galaxy might contain a dense, compact supermassive black hole at its core. But there was no way to verify that because the core of the galaxy was always hidden behind gases and interstellar dust.

At that time Genzel was working as a post-doctoral fellow at UC Berkely with the late Charles Townes who was a Nobel laureate. His collaborator asserted that he presented a “remarkable technique, in which he can measure very accurately and determine quite precisely the mass and behavior of stars circulating around the galactic center.”

Together with this technique and the ground-based telescopes at ESO (European Southern Observatory) i.e NTT (New Technology Telescopes) located in Chile, they observed the motion and position of ten stars for about four years from 1992 to 1996. They collected data and modeled the orbits of those stars and derived the mass of a central object as about 2.45 million times the mass of the Sun. But that was just one result and hence can not be generalized at that time.

Observation by Genzel’s research group about the stars orbiting the galactic center also confirmed the predictions of Einstein's general theory of relativity; that the orbit of a star follows a flower-like pattern (perihelion shift) while orbiting a massive object.

Andrea Ghez has done that with much more precision with her team the galactic center group at UCLA. With more high-resolution W.M. Keck observatory’s telescopes in Hawaii, they observed the interstellar medium and dust around the supermassive black hole i.e Sagittarius A*.

They used adaptive spectroscopy, more precisely the laser technology to avoid turbulence which disrupts the light under observation in the atmosphere. They removed all kinds of turbulence and noise from their data. They observed more than 3000 stars for 12 years from 1995 to 2007. Finally, they obtained the result of the mass of a central object to be 4.5 million times the mass of the Sun. She also studied the dynamics and interactions between the stars. That observation again confirmed the previous result that a dense compact supermassive black hole resides in the galactic center.

The amazing work done by both independent teams has been recognized by royal Swedish academy of sciences. They said it “has given us the most convincing evidence yet of a supermassive black hole at the center of the Milky Way.” Keck Observatory Director Hilton Lewis admired Ghez as “one of our most passionate and tenacious Keck users.”

Andrea has been acknowledged by many people from MIT in very kind words. Nergis Mavalvala said,