The astronomer’s stellar studies led to the first confirmed discovery of a “failed star” and played a critical role in getting the Kepler Space Telescope off the ground.
Could it be a brown dwarf?
The thought popped into Gibor Basri’s mind as he studied the data coming in from the Keck 10-meter telescope in Hawai‘i. It was 1994, and while astronomers had predicted the existence of brown dwarfs — starlike orbs often called “failed stars” because they can’t sustain nuclear fusion —previous claims of discovery had been proven wrong. Now, Basri was using the new mammoth telescope to see if he could see a brown dwarf signature in an object known as PPL 15.
As he hastily reduced his data, Basri saw it: a spectral line that he says, “sort of maybe looked like something was there.” Back at the University of California, Berkeley, where Basri was a faculty member, he checked the data for a specific lithium signature — considered a sign indicative of a brown dwarf detection. It was there. Basri and colleagues wrote up the discovery sent the paper off for publication.
“I made the terrible political mistake of not putting it into Nature,” Basri says. He didn’t send the paper there, he says, because it had already published two brown dwarf announcements that were wrong. He didn’t want to overhype his result, so he chose the Astrophysical Journal instead. The paper was accepted but publication was slow; before it was printed, two other papers on brown dwarfs came out in Nature. Coincidentally, around the same time Michel Mayor and Didier Queloz announced the discovery of the first exoplanet, and that announcement overshadowed the brown dwarf discoveries. Still, Basri considers the discovery of PPL 15’s brown dwarf nature the highlight of his career.
A Stellar Focus
Born May 3, 1951, in New York City, Basri was the child of Saul Basri, then a physics PhD student at Columbia University, and Phyllis Basri, a dancer. Both of Basri’s parents had been immigrants, his father from Iraq and his mother from Jamaica, and they met while in graduate school at Columbia. After Gibor was born, the family moved to Fort Collins, Colorado, where Saul began a physics professorship at Colorado State University. His father’s work, Basri says, influenced his own interest in physics, but his passion for space was fostered in grade school, when he read science fiction novels and started to attentively track the progress of NASA’s Apollo program.
As the years passed, Basri became increasingly aware of the fact that he was the only black student and one of only a few Jewish people in his high school, so he says he “never felt on the inside.” But he was smart, and the other kids took notice, coming to him when they needed help on their homework. Affirmative action was set into motion around that time, too, as universities began to make efforts to diversify their student bodies, and several began to recruit Basri to come to their campuses. Enamored with California, he applied to Caltech and Stanford and was accepted to both. He chose Stanford, he says, because of Caltech’s policy of denying admission to women.
At Stanford, Basri majored in physics and did some research on the Sun. He had always loved astronomy, but he wasn’t sure the field was large enough to make a career in it. Nevertheless, when he applied to the University of Colorado, Boulder, and got in, he took his chance.
In Boulder, Basri studied stellar magnetic activity, working with advisor Jeffrey Linsky, and used the newly launched International Ultraviolet Explorer for his work.
While in Boulder, Basri married Jessica Broitman, a psychologist. After Basri’s graduation, he had lots of projects that would have allowed him to stay on as a postdoc, and he and Broitman wanted to continue living in the area. But Linksy said no. “He said, you know, Gibor, I think you could actually be a faculty member at a significant institution. And in order for that to happen, you have to come out from under my shadow,” Basri recalls.
Basri and Broitman loved Boulder and wanted to stay. But heeding Linsky’s advice, the couple began to plan their next step. Broitman decided to visit the Wright Institute, a private graduate school in Berkeley that focused on psychology. She loved the institute and told Basri: “Okay, you need to get a job at Berkeley.” He joked: “Oh yeah, I’m just going to go in there and get a job.”
And then, he did.
Brown Dwarfs and Starspots
When Basri walked into the Space Sciences Laboratory of the University of California, Berkeley, he ended up chatting with Stuart Bowyer. Bowyer was impressed with Basri’s stellar research, especially since Bowyer had just decided he needed an expert in that area for a mission he was developing. At Bowyer’s suggestion, Basri applied for the Chancellor’s Postdoctoral Fellowship in 1979 to continue his work on stars at the lab. Part of the fellowship’s purpose was to attract minority scholars who might be faculty quality. Indeed, Basri joined the university as an assistant professor in 1982, first focusing his research on very young stars called T Tauri stars.
Basri and others’ studies of T Tauri stars have revealed important details about the development of stars and their planetary systems, giving clues to the formation of our own solar system. Specifically, Basri looked at the role of stars’ magnetic fields, which can help orbiting material plunge onto the stellar surface.
Basri later expanded his research to examine the relationship between a star’s magnetic activity, its rotation, and its starspots — cool regions where magnetic flux oozes out of the stellar surface. His observations of the coolest star then known showed that it made a single rotation roughly every three hours. Jupiter by comparison spins around in 10 hours. A cool star spinning so fast should show extremely strong magnetic activity but this one showed nothing. So, Basri thought, maybe these cool stars are “more like giant planets than they are like stars in these ways.”
At around the time he realized that lithium could be used to distinguish low-mass stars from (at that point hypothetical) brown dwarfs. Called the “lithium test,” the method relies on the fact that stars will burn through their lithium in roughly 100 million years, while brown dwarfs never become hot enough to burn theirs. Brown dwarfs, therefore, typically show lithium in their spectra — a signature Basri used to show PPL 15 was indeed a brown dwarf.
This work instigated a slew of brown dwarf discoveries, and eventually it led to the addition of two new spectral classes in stellar classification: L and T. Now, from hot stars to cool stars, astronomers use the classifications, O, B, A, F, G, K, M, L, and T. And, he says, the old acronym “oh be a fine guy/gal, kiss me” became a bit longer: “Now it's lightly tonight or lustily tonight.” (Though there are other acronym options, too!)
Policy and Advocacy
Along with making discoveries, Basri used his understanding of stars’ magnetic activity to help the Kepler planet-hunting mission get off the ground. Before NASA was fully onboard, some astronomers questioned whether starspots would mess with exoplanets’ transit signals, especially for those caused by Earth-size planets. Basri’s calculations showed the claim was false. “Star spots are not going to be your problem,” he recalls telling NASA officials. “Your problem is going to be finding so many planets that everybody's going to be claiming planets like crazy.”
He was right. The Kepler telescope launched in 2009 and found thousands of planets. Despite the planet craze, though, Basri kept his focus on starspots. From them, “we learn how stars rotate at different rates,” he says, “and also how long they live on different kinds of stars.”
Alongside his research, Basri also began advocating for greater participation of minorities in science. He was the sole black faculty member in the entire division of physical sciences at Berkeley for most of his career. Women, too, remain underrepresented. It is clear, he says, that science is not utilizing the full talent pool available to it.
After becoming a full professor, Basri became the campus’s first Vice Chancellor for Equity and Inclusion. In that role, he pushed for diversity and inclusion to become part of the university’s ethos, a shift that ultimately changed tenure and promotion practices throughout the University of California system to recognize faculty members’ efforts in that realm, rather than penalizing them for it.
Basri stepped down as VCEI chair in 2015 and became an emeritus professor a year later. But he continues to give talks to encourage minority students to become scientists, and he still scours Kepler data for more clues about starspots.
Read Gibor Basri in the pages of Sky & Telescope with his 2005 article, "A Decade of Brown Dwarfs."
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