Meg Urry discusses growth of supermassive black holes in astronomy and physics lecture

Claudia Megan "Meg" Urry (A '77), director of the Yale Center for Physics and Astrophysics, presented parts of her personal research and discussed her experience as a woman in the field of physics last night for the sixth Kathryn A. McCarthy Lecture in Physics at the Collaborative Learning and Innovation Complex (CLIC). Urry spoke to an audience of approximately 50 people at the event, titled “Supermassive Black Hole Growth in the Past 12 Billion Years,” which was sponsored by the Departments of Physics and Astronomy.

Urry, who is currently President of the American Astronomical Society, also earned a 2008 honorary degree from Tufts, organized the first-ever national meeting on Women in Astronomy and became the first female tenured faculty member in Yale's Department of Physics. 

Professor of Physics and Astronomy Peggy Cebe welcomed the speaker, explaining that the lecture series began in 2001 and has subsequently been held every three years in honor of former Provost and Professor Kathryn A. McCarthy (J '45), for whom a memorial service was held preceding the lecture.

Urry began her presentation with the display of a dimly lit galaxy-shaped letters portraying the title of the lecture.

“We are not near the galactic centre, and that is a good thing,” the astrophysicist said about the location of the planet in the Milky Way.

“To talk about black holes, we have to talk about gravity, and to understand gravity we have to talk about Sir Isaac Newton,” she said.

Urry explained the concept of dark stars in the universe and said that their escape velocity — the minimum velocity needed to escape the earth’s gravitation — is greater than the speed of light. She said that the same principle applies to black holes, with the use of a slow-motion movie of the universe’s expansion over the course of 15 years.

“We can detect the existence of a black holes by watching other objects orbiting black holes,” she said. “As stars get closest to the center [of the galaxy], they move very quickly.”

Urry also discussed Newton’s Second Law — which states that an object's acceleration is dependent on its mass and net force — as it relates to black holes.

“We can find the mass of a black hole by finding the speed of the stars that orbit it, but unfortunately we can’t do that for other galaxies, since they are so far off — only for the Milk Way,” Urry said.

Urry described the universe as being a hub of countless galaxies with almost each of them including a black hole. While discussing gravitational forces, Urry said that theoretical physicist Albert Einstein did not agree with Newton’s concept of gravity.

“Einstein created a new theory which has nothing to do with the force between two masses, rather with any mass curbing the force around it,” she said.

Urry, in an attempt to explain the space-time and Karl Schwarzschild metric as a means to calculate black hole size, showed the audience a video clip from “The Wizard of Oz,” in which a character comedically reciting Pythagoras' Theorem.

“When I was a kid at Tufts University, that is from 1973 - 77, we sort of just started to know that there must be black holes,” Urry said. “Before that, people just thought that black holes were a theoretical part of Einstein’s Theory of Relativity.”

According to Urry, black holes are called “dark objects” because nothing can escape their intense gravitational pull.

“[However], black holes cause some of the brightest phenomenon in the universe in the form of [Active Galactic Nuclei],” Urry said. “So I take the liberty to call them 'bright objects,' meaning the area around them is bright.”

Urry, via a screen image, also exhibited the expansion of the universe over time.

“Our universe is 13.8 billion years old, since the Big Bang; since inflation began,” Urry said. “Dark energy is helping the expansion of the universe to accelerate.”

One reason black holes form galactic centers is that the most massive parts of the galaxies are where new stars form, she said.

“It’s funny; black holes are really tiny. They are only a small fraction of the size or mass of a galaxy,” Urry said. “But in terms of energy they win.”

While discussing the process of galaxy merging, she explained that the reason it is impossible to observe a merger is  because the time duration is almost 700 million years.

“That’s too long, even for a graduate student," Urry said.

Urry also spoke about the role that Tufts has played in her life.

“I’ll be honest, I attended Tufts reluctantly because my father was a professor here — not a popular chemistry professor I must add — he would terrify students,” Urry said. “However, Tufts gave me the environment of physics; I got the worst grade of my life in my first final here, after which I said it can’t be that hard and buckled up.”

Urry concluded the event by discussing her gratitude for the memorial service held prior to the lecture, and for being invited as this year's speaker.

“When I first came to Tufts, there were very few women in physics, and [in] faculty of course,” Urry said. “I did not at first think that women could face challenges in physics, but I saw that with time, and became an activist for women in physics. I got that light and energy from Kathryn McCarthy.”

Urry said that when McCarthy started her career in physics, there were no role models for her.

“For her, there was no one to look up to, except Marie Curie perhaps,” Urry said. “You can’t over-say how important it is to have role models; we need people who think differently, who challenge your ideas, challenge you.”