The first indication that something big was happening arrived in Maryam Modjaz’s inbox on January 10. The “circular” came from Princeton scientists who noticed a burst of X-rays while reviewing data from a NASA satellite. The event was labeled XRT 080109, and at first, all anyone knew for sure was that it was a transient—an object that quickly becomes luminous and then fades away (XRT stands for X-ray transient).
Modjaz, a Miller postdoctoral fellow in the astronomy department, explains that, in transient research, anytime someone spots something interesting and time-critical, they send an email circular to colleagues around the globe alerting them to take a look, and right away. “When these things are putting on their show,” says Joshua Bloom, an assistant professor of astronomy, “you either catch it or you miss it. It’s a limited engagement. They don’t repeat, they don’t hold over.” For that reason, he and his team are wired to immediately receive notices, like doctors who are permanently on call.
Modjaz, who had been engrossed in another research project, dropped everything to investigate the X-ray transient. She and Bloom discussed which large telescopes to train on the event. They decided to trigger the Gemini South telescope in Chile, where they had a standing agreement allowing them use of the telescope in just such cases as this. They also alerted colleagues who had access to other observatories. Modjaz called her doctoral advisor at Harvard to persuade him to view the object. She mobilized observations from the PAIRITEL telescope in Arizona, and Keck Observatory in Hawaii. Berkeley professor Alex Filippenko’s robotic telescope at Lick Observatory near San Jose observed the event as part of its nightly survey of a thousand nearby galaxies.
That first night, Modjaz stayed up late, watching the stream of data coming from Gemini South, as circulars from observers in Asia and Europe, who had a jump on nighttime observations, began trickling in. The X-rays had faded by then, but an optical counterpart to the X-ray burst had been detected, suggesting that it was not an isolated event but part of something bigger. “You really need the optical light to tell what kind of object it is,” says Modjaz. “Supernovae have a specific spectrum, which is like their fingerprint,” she explains. Working with Harvard researchers, she was able to make a positive match. XRT 080109 was soon reclassified as SN 2008D (SN as in supernova).
Modjaz and her fellow researchers had witnessed a star in the process of exploding in a galaxy 90 million light-years distant. The fleeting event had transpired 90 million years ago—in other words, when dinosaurs still roamed Earth. And perhaps best of all, the scientists had caught it early.
Supernovae are very rarely observed from the beginning. There was one in 1987, explains Filippenko, but it was “a peculiar sort,” not typical of any specific class or subclass. By contrast, the Berkeley team identified SN 2008D as a classic type Ib supernova, a massive star that had lost its outermost layer of hydrogen. When its core collapsed, the outer layers fell inward, collided with the core, and rebounded, creating a shockwave that ripped through the surface. This was the explosion that emitted the original burst of X-rays.
Modjaz describes studying supernovae as a kind of stellar forensics: “You see the death, you see the corpse, so you need to deduce how it looked beforehand.” Sitting in her fourth-floor office in Campbell Hall, overlooking the tiled roof of the building where she took undergraduate physics courses, she muses: “When you think of death, it sounds very morbid, very sad, the end of something. But the death of that massive star is really … a moment of creation for elements that are important for our own lives.” Indeed, as Carl Sagan liked to say, we are all “made of star stuff.”
The findings about SN 2008D will affect transient research going forward. Plans are afoot for new satellites to monitor more of the sky for X-rays, and researchers can use SN 2008D‚Äôs X-ray signature as a guide for detecting more supernovae early in their existence. “This one event,” said Bloom, “launches a thousand ships.”
Filippenko, who mentored Modjaz when she was an undergrad at Berkeley, is working with her again as a postdoc. He says, “It’s been gratifying to me to see how well she’s done, and to see she’s been given this excellent opportunity. Because in science, as in life, it’s not just skill and dedication and all that. You need some luck.”