The photo above is an image taken by the Hubble Space Telescope of a nearby spiral galaxy with a globular cluster marked and enlarged.
Jay Strader, ’02, was an economics and math major when he took an astrophysics course as a sophomore. The course, taught by former Duke professor John Kolena, captured his imagination in a way economics never had, and a summer research project related to old massive star clusters convinced him to drop the econ major and replace it with physics (he kept the math). Today, he has a Hubble Fellowship at the Harvard-Smithsonian Center for Astrophysics. . . and he’s still fascinated by old massive star clusters, called globular clusters.
All stars form in clusters, but most form in star clusters that have very few stars (tens to hundreds) and disperse “immediately” (about 10 million years). But some stars form in massive, dense clusters that contain a million or more stars and can be as old as the universe. These are known as globular clusters.
Strader studies globular clusters to help tease out the secrets of how galaxies form. Most of the stars in a globular cluster are essentially the same age—to within a few million years or so—and astrophysicists can date the entire cluster using spectroscopy. Because the stars in a cluster are representative of the rest of the stars in the galaxy, Strader says, “You can figure out a distribution of ages in a globular cluster and that tells you an age distribution of the stars in the galaxy.”
Strader says most globular clusters that have been dated are very old. “This tells you that a huge amount of star formation took place at the start of the universe,” Strader says. “In the Milky Way, we form a couple of stars every year, but most of the star formation took place a long time ago. The universe is winding down in terms of forming stars.”
Intriguingly, globular clusters fall into two main groups—one group that is poor in heavy metals and one group that is rich in heavy metals. In general the metal-poor clusters are older than the metal-rich clusters. “When people run computer simulations of globular clusters forming to try to reproduce the two populations, they find it very difficult to do so,” Strader says. “The bimodal aspect of it is very unusual.”
What’s the life of an astrophysicist like? “I’m on a computer eight to 10 hours a day,” he says. “I travel to telescopes to take data probably five or six times a year. I use the telescopes in Arizona, Hawaii, Chile, and I’ve also used the Hubble space telescope quite extensively. What’s amazing to me is none of this would have happened if I hadn’t taken that astrophysics course as sophomore.”