Reaching for the stars
Astronomer uses stellar forensics to understand giant explosions in space
For millennia, people have navigated by the stars, using the North Star Polaris and other predictable features of the night sky to find their way home. Although constellations seem to travel across the sky as the Earth rotates, the stars don’t change position relative to each other within each figure; that’s why the Big Dipper always looks like a ladle. In fact, most things in astronomy change only very slowly, too slowly for humans to really notice.
Maryam Modjaz, an astronomer at New York University, studies one of the most noticeable exceptions: supernovae, the intensely bright explosions that mark the death of stars. She is drawn to supernovae because of two paradoxes. When stars blow to smithereens, their remnants also spur the creation of new stars. And while the blast of light and gases is very obvious — sometimes even bright enough to be seen by the naked eye — the chain of events causing it remains hidden.
Modjaz, who is quick to laugh, calls her research stellar forensics. Like forensic scientists examining a crime scene to determine how someone died, she and her colleagues study supernovae and the space around them for signs of how the star lived before the explosion.
What sets Modjaz’s work apart, according to her Ph.D. adviser Robert Kirshner of Harvard, is her work ethic, which he thinks developed during her childhood in Germany. “I think in a lot of ways, she has a lot of the characteristics you think of as German,” he said. “She’s very careful, she’s very thorough, she gets things right.”
Germany is also where Modjaz first looked through a telescope, when she was a teenager. “I remember looking at Saturn with the rings, and actually I was very disappointed,” she said with a laugh. Thanks to the thickness of the Earth’s atmosphere, telescopes on the ground offer only blurry visions, even of the second largest planet in the solar system. In her head, she had pictured images from the orbiting Hubble Space Telescope, which are much sharper.
Modjaz attended the University of California, Berkeley, as an undergraduate and was already doing research by the summer after her freshman year. Guided by astronomer Alex Filippenko, she worked at the Lick Observatory near San Jose, where she first identified a supernova. Her enthusiasm has yet to wear off. “The discovery potential is really cool to me,” she said.
When Modjaz began graduate school, most people were studying the supernovae caused by the deaths of small stars, said Saurabh Jha, whose doctoral work overlapped hers and who is now a professor at Rutgers University. But Modjaz eventually decided to study a different type of supernova, formed by very large stars. “She was pretty prescient about the problem to pick to work on,” Jha said.
Overall, astronomers are seeing supernovae at a rate that is doubling every two years. That’s changed how scientists interact with the objects they study. “Back in the day, people observed just one object, and they knew it, it was like their first-born,” Modjaz said. Today, scientists tend to focus on collections of supernovae.
Scientists will discover even more supernovae with a new telescope, due to go online during the 2020s, which may prove the most powerful tool for discovering supernovae to date. What makes the Large Synoptic Survey Telescope special is that it will look at huge swaths of the sky. “For the first time ever, we’ll make movies of the sky — of the whole sky, not just some patches as we’ve done before,” said Modjaz, who is looking forward to using the telescope’s data.
Looking at more of the sky more frequently means the LSST will see more supernovae. Until now, the first step for any scientist trying to study supernovae was to figure out how to actually observe them — where to point the telescope and when to look through it. But LSST will allow scientists to skip that step, said Michael Wood-Vasey, an astronomer at the University of Pittsburgh who sits on the LSST’s science advisory committee. “You can just focus on the next question of what should you do with them,” he said.
But there is a catch. Some of the LSST’s data won’t be as detailed as astronomers who study supernovae would like. The best way to study a supernova is to take its light, smear it across the spectrum of colors we can see, and measure how much light is emitted in each thin slice of the rainbow, as Kirshner explains. Nuances of these patterns allow astronomers to infer characteristics about the star that formed the supernova, like its size and chemical composition. But because LSST was designed for many types of astronomy research, it only makes spectra for some, but not all of the supernovae. For the rest, astronomers are hoping to find ways to learn more from less data.
Bridging this gap and managing the sheer amount of information that the telescope will produce are for Modjaz the most important challenges in supernova studies right now. She says tackling these challenges will require working in large diverse groups so individuals can bring different approaches to the problem. For example, she’s excited to work with people who can manage large amounts of data. “We can answer old questions in new ways by using new tools on larger databases,” she said.
“She’s always been a great collaborator,” said Josh Bloom, an astronomer who worked with Modjaz when she was a postdoc at the University of California, Berkeley. “She has this really good ability to work with people who know different things and have different talents.”
When she isn’t studying supernova data, Modjaz particularly enjoys watching science fiction films. Unlike some experts who go to movies about their specialties, she doesn’t usually mind those that get the astronomy wrong, although she says one of her favorites, Gravity, is pretty accurate. She incorporates movies into both her astronomy course for non-majors and her public talks. At one talk she gave in November at the Lower Eastside Girls Club community center, she referenced the opening lines of Star Wars, then paused and smiled while two boys in the front row led the audience in humming the movie’s theme song.
Part of Modjaz’s inspiration for speaking to non-astronomers comes from her interest in promoting women in science, which she has tried to integrate at each step of her career. Noting the lack of examples for women to look to, she gives talks in part to show “that yes, there are people who look like you who do science,” she said.
She also feels an obligation to show the public how their tax dollars are being used and to tap into the enthusiasm for astronomy that people, “from grandkids to grandparents,” have. But at the end of the day, “it’s also a great way to step back and think about the big picture and remind myself why these questions are interesting and fun.”
That’s particularly important given how much technology may shape the astronomy of the future. But Modjaz still has a soft spot for the way she first learned to do astronomy. “I still like going to the telescopes, I still like going to the mountains,” she said. “It’s really beautiful.”