Black Hole Basics
This story originally appeared in the 2006 issue of Vassar Views in celebration of URSI’s 20th anniversary.
Unless you’re an astronomer or a physicist or a sci fi fan, it can be a challenge to wrap your mind around the idea of a supermassive black hole—an object “hiding” at the center of a large galaxy whose mass is more than a million times that of our sun and whose gravitational pull is so strong that nothing, not even light, can escape.
Olivia Johnson ’97, PPARC (Particle Physics and Astronomy Research Council) postdoctoral fellow at the University of Edinburgh, is doing research on black holes—specifically, how black holes affect galaxy evolution. “When you look at black holes and galaxies together, you see that there’s a perfect correlation—if you have a large galaxy, you have a large black hole, and if you have a small galaxy, you have a small black hole,” says Johnson. “What we think is that the black hole might tell the galaxy when to stop growing.”
According to Johnson, every galaxy has a supermassive black hole at its core—including our own Milky Way. “In about four percent of galaxies, these central objects are actively sucking up stars and gas, and we call them active galactic nuclei, or AGN. The most powerful AGN, called quasars, are very, very bright and can be seen a long way away,” Johnson explains. “What we’re finding out is that this active feeding phase isn’t something weird. It’s something they all do. It’s sort of like galaxy adolescence—it’s a very brief period, but it mars you for life.”
Although the supermassive black holes are, um, supermassive, they’re tiny in relation to the size of the galaxy itself, which might be 30,000 light years across. “Just to make it concrete, that’s like the difference between a single grain of sand and the planet earth,” says Johnson. “One thing I’m trying to look at is how something that tiny could play such a big role in a forming galaxy.”
When you talk to Johnson about her science, one thing that strikes you (in addition to the charming accent she’s acquired in her five years in Edinburgh) is how adept she is at describing it in terms that non-scientists can understand. “As most major astronomy projects are publicly funded, research councils like PPARC are increasingly aware of how vital good public communication is, and they’re actively encouraging scientists to have these skills,” says Johnson. She took media training courses at the Royal Society and at the University of Edinburgh and over the summer did an internship in science communications with the BBC through the British Association for the Advancement of Science. “The idea is to make us more media savvy,” she says. “This is an area where my broad studies at Vassar really do give me an edge.”
Pre-Vassar, Johnson saw herself as “a humanities person”—loved history and English and intended to major in film. “But I had gone to a really small Catholic school that didn’t have much in the way of science funding or equipment, and when I looked at the Vassar course catalogue, I thought, this is fantastic! It was like a shopping spree where everything is free. I decided I was going to take at least one course in each of the sciences before I left Vassar. It was sort of a Renaissance-woman thing.”
She started with astronomy because “it was the first letter of the alphabet” and took a course on the solar system with astronomy professor Fred Chromey. “He’s absolutely fantastic—an inspirational teacher. He described astronomy as factual storytelling, history on a larger scale, and that got my imagination going. At the end of the semester, I told him how much I enjoyed the class and asked if he would suggest a biology class, since ‘b’ is the second letter of the alphabet. And he said, ‘Oh, Olivia—I think what you ought to do is take some more astronomy.’ He was very open and deliberate about this. He saw my dad [dean emeritus and English professor Colton Johnson] on campus and said, ‘I’m going to turn your little girl into a scientist!’”
Chromey got her into the URSI program the following summer (1994), where she and Jeff Kern (from Colgate) studied hundreds of CCD images of spiral galaxy M81 to map and analyze the dust lanes near the center of the galaxy. “That’s really what won me over,” says Johnson. “I was stuck after that.”
The following summer, she did research at the National Radio Astronomy Observatory in Tucson, Arizona, under a National Science Foundation program for undergraduates, and the summer after that, at the VLA (Very Large Array) in New Mexico. During the year, she accompanied Chromey and astronomy professor Debra Elmegreen on observing trips to Kitt Peak National Observatory.
Johnson says the research experience was invaluable, not only from an educational standpoint, but in competing for jobs and admission to graduate school. “My URSI experience got me the next job, which in turn got me the next job, and so on. When I went to do my postdoc search, I had a long list of publications which I wouldn’t have had if I hadn’t participated in URSI.”
Johnson graduated from Vassar with a triple major—physics, astronomy, and an independent major in American modernism—and then worked at the Harvard-Smithsonian Center for Astrophysics, calibrating the Chandra X-ray Observatory, one of NASA’s four massive space observatories. After a few years, she was torn between going back to school and getting her doctorate in astronomy and making a major career change. She had almost made up her mind to leave astronomy and do graduate work in journalism—in fact, was registered for courses at Columbia—when her boss, who happened to be British, told her that the astronomy PhD in Britain only takes three years (as opposed to six in the U.S.) because there’s no coursework—just research. She got into three highly ranked schools and chose the University of Edinburgh.
And does she like it?
“Witness the fact I’m still here,” says Johnson. Her postdoc is through the British government, and she could have taken it anywhere in Britain. “I tried to think of other places because it’s better for your career to move about, but I couldn’t think of any place I’d rather live. I’m probably won over to Scotland.”