Where Stars are Born: Astronomy Graduate Student Amanda Lee Contributes to Uncovering Mystery of Star Formation at Edge of Galaxies

UMass Amherst astronomy graduate student Amanda Lee is part of a team of astronomers, led by Stony Brook University’s Jin Koda, that has tackled one of the discipline’s persistent questions: where do stars come from, and more particularly, how and why do stars form at the far edges of galaxies?

Image

While astronomers have long known that that molecular clouds – huge agglomerations of dense molecular gasses – near the inner parts of galaxies are typically where new stars are born, a surprising number of very young stars are known to have been born at the far edges of many galaxies. “This is a nagging mystery since their discovery by the NASA’s GALEX satellite 18 years ago,” Koda says.

The team used the Atacama Large Millimeter/submillimeter Array (ALMA) to investigate the far edge of the spiral galaxy M83, 15 million light years away, and they discovered something new: 23 molecular clouds, which are evidence of the birthing region of stars.

Furthermore, these 23 molecular clouds appear different from their counterparts in the typical, internal star-forming sites in galaxies. The large bodies of these clouds were not visible like “normal” molecular clouds – only their star-forming dense cores, the "hearts" of the clouds, were observed.

Additionally, it appears that the clouds work differently at the edges of galaxies than at their centers: Normally, the diffuse clouds of atomic gas condenses into dense molecular clouds, where even denser cores develop and form stars. This conversion from atomic gas to molecular cloud does occur at the galaxy edges, but the conversion is much more inefficient.

Lee, who is studying with Rob Gutermuth, associate research professor of astronomy, and Grant Wilson, professor of astronomy, at UMass, says “we still do not understand why this atomic gas does not efficiently become dense molecular clouds and form stars. As often is the case in astronomy, pursuing answers to one mystery can often lead to another. That’s why research in astronomy is exciting.”

Lee, Koda and their colleagues came to their conclusion by using data collected using several instruments from the National Science Foundation’s National Radio Astronomy Observatory, including ALMA, the Karl G. Jansky Very Large Array, and the Green Bank Telescope, as well as with the National Astronomical Observatory of Japan’s Subaru Telescope and the NASA Galaxy Evolution Explorer.