In work that will help scientists better understand the formation history of stars in the universe, researchers analyzed images from the nearby Andromeda galaxy and found that it contains roughly the same percentage of newborn stars based on mass as our own Milky Way galaxy.
As part of their research, which was published earlier this summer in the Astrophysical Journal, Daniel Weisz from the University of Washington and his colleagues reviewed more than 2,700 images of young blue star clusters in Andromeda that had been captured using the Hubble Space Telescope. The pictures were assembled from 414 mosaic photographs of the galaxy.
The project, which NASA described as “a unique collaboration between astronomers and ‘citizen scientists,’” determined what percentage of stars has a specific mass within a cluster – also called the Initial Mass Function (IMF). This was the main reason for Hubble’s recent panoramic survey of Andromeda, called the Panchromatic Hubble Andromeda Treasury (PHAT) program.
As part of the PHAT program, nearly 8,000 images of 117 million stars in the galaxy’s disk were taken in near-ultraviolet, visible, and near-infrared wavelengths, the US space agency said. These observations provided scientists with the first IMF measurements from beyond our galaxy’s own local stellar neighborhood, and enabled them to compare the masses of the different groups.
Heavy elements likely limited in the early universe
By comparing data from a larger-than-ever sample size of star clusters, all of which were about the same distance from Earth (2.5 million light-years), Weisz and his co-authors found that each of the clusters surveyed had similar IMF readings. In addition, much to the researchers’ surprise, the distribution was consistent across types of stars, from blue supergiants to red dwarfs.
The survey also revealed that the brightest, most massive stars in these clusters were about 25 percent less abundant than previous research had predicted. The light from these stars are used by astronomers to weigh distant star clusters and galaxies, as well as to measure how rapidly the clusters are forming stars. The findings suggest that previous mass estimates incorrectly assumed that there were too few faint low-mass stars forming with the brighter, more massive ones.
“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,” NASA explained. “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.”
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