UCSC astronomer wins Herzberg Memorial Prize

The National Research Council of Canada (NRC) has awarded the 2001 Herzberg Memorial Prize and Fellowship to Puragra GuhaThakurta, associate professor of astronomy and astrophysics at the University of California, Santa Cruz.

The honor recognizes GuhaThakurta's outstanding work in observational astrophysics. The award consists of a prize and a one-year fellowship. GuhaThakurta will spend his fellowship year at NRC's Herzberg Institute of Astrophysics in Victoria, British Columbia.

"I'm really happy and totally surprised," said GuhaThakurta, who was honored at NRC's annual awards dinner and ceremony on February 20 in Ottawa.

GuhaThakurta earned international renown in the field of astrophysics for his influential work on a wide range of subjects, including interstellar dust, dark matter, planets, supernovae, and globular star clusters. His current focus is understanding how galaxies formed. GuhaThakurta charts the history of our galaxy, the Milky Way, by observing its closest relative, the nearby Andromeda galaxy.

"There are no mirrors in astronomy to tell us what the Milky Way looks like from the outside," said GuhaThakurta. The next best thing to looking in a mirror, he said, is looking at a close relative. Andromeda is a bigger version of the spiral-shaped Milky Way and, at a distance of two million light-years, is also its cosmic neighbor.

GuhaThakurta tracks individual stars in the Andromeda galaxy using the Keck Telescope in Hawaii and the Hubble Space Telescope. An instrument called a spectrograph separates the light from each star into its basic colors, like a prism. These colors tell the story of the star: its temperature, how fast it's moving, and its chemical makeup.

"It's pretty remarkable that light from a star two million light-years away can tell us so much about the evolutionary state of the star," GuhaThakurta said.

Stars are mainly hydrogen and helium, the simplest elements in the universe. But they make small amounts of heavier elements, such as calcium, during their lifetimes via the nuclear fusion reactions that cause stars to shine. When massive stars finally die in a grand explosion called a supernova, they inject these elements into their surroundings.

"The next generation of stars is born with these pollutants," GuhaThakurta said. The process then perpetuates: When some of these baby stars grow up and explode, they transmit the traces of their ancestors, along with newly made chemicals, to the next generation. Like traits in a pedigree, the amounts of metals in a star tell us about its ancestry.

What's surprising is that when GuhaThakurta examined 100 stars in a small area of Andromeda, their chemical tags were so diverse that he concluded the stars must have formed in different places and at different times.

"Andromeda's halo of stars appears to be the result of the smooshing together of many small galaxies, and the same process probably formed the Milky Way's halo," GuhaThakurta said.

During his fellowship at the Herzberg Institute of Astrophysics, GuhaThakurta will use the Canada-France-Hawaii telescope to continue his detailed survey of Andromeda. This telescope will provide complementary data to the Keck and Hubble telescopes. GuhaThakurta will begin his fellowship in summer 2002.

GuhaThakurta previously received a Hubble Fellowship, widely considered to be the most prestigious postdoctoral fellowship in international astronomy, and was an Alfred P. Sloan Research Fellow through 2001.

The National Research Council of Canada (NRC) established the international Herzberg Memorial Prize and Fellowship Award in 1999 to commemorate the late Gerhard Herzberg, NRC scientist and Nobel laureate known worldwide as the "father of modern molecular spectroscopy." This prestigious honor is given annually to an active researcher who has distinguished himself or herself through many years of outstanding achievements in a field that is relevant to NRC's programs.


Editor's note: Reporters may contact GuhaThakurta at (831) 459-5169 or raja@ucolick.org.