Hubble Survey Unlocks Clues to Star Birth in Neighbouring M31 Galaxy

After analysing images of 2,753 young, blue star clusters in the neighbouring Andromeda galaxy (M31), astronomers with the help from "citizen scientists" have found that M31 and our own Milky Way have a similar percentage of new-born stars based on mass.

By nailing down what percentage of stars have a particular mass within a cluster called Initial Mass Function (IMF), scientists can better interpret the light from distant galaxies and understand the formation history of stars in our universe.

The intensive survey, assembled from 414 mosaic photographs of M31 taken by Nasa's Hubble Space Telescope, was a unique collaboration between astronomers and "citizen scientists," volunteers who provided invaluable help in analyzing the mountain of data from Hubble.

"Given the sheer volume of Hubble images, our study would not have been possible without the help of citizen scientists," said Daniel Weisz from University of Washington in Seattle.

This evidence also implies that the early universe did not have as many heavy elements for making planets, because there would be fewer supernovae from massive stars to manufacture heavy elements for planet building.

It is critical to know the star-formation rate in the early universe - about 10 billion years ago - because that was the time when most of the universe's stars formed.

Stars are born when a giant cloud of molecular hydrogen, dust and trace elements collapses.

The cloud fragments into small knots of material that each precipitate hundreds of stars.

Hubble's bird's-eye view of M31 allowed astronomers to compare the IMF among a larger-than-ever sampling of star clusters that are all at approximately the same distance from Earth, 2.5 million light-years.

To the researchers' surprise, the IMF was very similar among all the clusters surveyed.

Nature apparently cooks up stars like batches of cookies, with a consistent distribution from massive blue supergiant stars to small red dwarf stars.

"It is hard to imagine that the IMF is so uniform across our neighbouring galaxy given the complex physics of star formation," Weisz noted.

The Andromeda Project is one of the many citizen science efforts hosted by the Zooniverse organization.

"The efforts of these citizen scientists opens the door to a variety of new and interesting scientific investigations, including this new measurement of the IMF," Weisz pointed out in a paper that appeared in the Astrophysical Journal.