Hubble’s Clues to the Andromeda’s Stars

A collaboration between citizen scientists and astronomers has yielded clues to star births in the Milky Way’s celestial neighbor, the Andromeda galaxy.

Located 2.5 million light-years from Earth, the galaxy, also known as Messier 31 (M31), is larger than the Milky Way and contains more stars. However, the Milky Way is thought to have more mass due to a larger proportion of dark matter.

However, through Hubble Space Telescope’s images of 2,753 young, blue star clusters, scientists have determined the neighboring galaxies share a similar percentage of newborn stars based on mass.

The panoramic survey sought to find the neighboring galaxy’s initial mass function (IMF), which specifies the fractional distribution in mass of a newly formed stellar system. Close to 8,000 images of 117 million stars in Andromeda were obtained, including images in near-ultraviolet, visible and near-infrared wavelengths.



Results of the survey were published in The Astrophysical Journal.

Before the Hubble survey, astronomers only had IMF measurements completed in the local stellar neighborhood within the Milky Way. However, Hubble’s unique “bird’s-eye view” allowed for a massive sampling of star clusters, which are scattered across the galaxy. The star clusters vary in mass by factors of 10, and they range in age from four to 24 million years-old, according to NASA.

Researchers found the IMF was similar among all surveyed clusters. “Nature apparently cooks up stars like batches of cookies, with a consistent distribution from massive blue supergiant stars to small red dwarf stars,” according to NASA.

“It’s hard to imagine the IMF is so uniform across our neighboring galaxy given the complex physics of star formation,” said the study’s lead author Daniel Weisz, of the Univ. of Washington.

Star birth is anything but uniform. They form in interstellar clouds made of molecular hydrogen, dust and trace elements that are collapsing. “The cloud fragments into small knots of material that each precipitate a star,” according to NASA. Stars can range from one-twelfth to hundreds of times the mass of the sun.

The researchers found the most massive stars in the clusters were 25% less abundant than predicted, which suggests previous research underestimated of faint, low-mass stars forming alongside the massive ones.

Additionally, the findings suggest the early universe didn’t house many heavy elements necessary for planet formation. Planet building would require elements leftover from massive star supernovas.