Andromeda Unlocks Secrets of Galaxies

Remember that amazing high-def photo of M31, the Andromeda Galaxy, from Hubble a few months back? It was able to separate the light from the galaxy into the millions of visible stars that populate its spiral arms.  This image is used for far more than the wow factor of seeing another galaxy up close.  It allows us to study the entire galaxy and gain insights into the lives of spiral galaxies beyond our own, how they formed, how they evolve, and maybe even how they will eventually die.

Close-up of the Hubble M31 image showing young blue clusters. Credit: NASA, ESA, J. Dalcanton, B.F. Williams, and L.C. Johnson (University of Washington), the PHAT team, and R. Gendler

By looking at the spiral arms of M31, where the youngest and brightest stars are currently forming, astronomers have learned that the number of young stars forming is very similar to that of the Milky Way, in terms of mass.  In a sample of 2,753 young, blue clusters, astronomers were able to constrain the Initial Mass Function (IMF), which is a measure of the percentage of stars in a cluster that have a particular mass.  The idea is that young clusters across the universe should form in more or less the same way, given the material available in a galaxy.  Understanding the IMF can help astronomers interpret the light from more distant galaxies, and gain a better understanding from the data they obtain.

An amazing feature of this study is that it was a collaboration between professional astronomers and citizen scientists.  Daniel Weisz of the University of Washington in Seattle, lead author of the study, agrees. “Given the sheer volume of Hubble images, our study of the IMF would not have been possible without the help of citizen scientists,” Weisz said.

The measurement of the IMF was the main goal of the Panchromatic Hubble Andromeda Treasury (PHAT) program, responsible for the spectacular Hubble image of M31 that contains 8,000 images of 117 Million stars in multiple wavelengths. This is the first time the IMF has ever been measured outside of our own galaxy, and the first time so many clusters from different regions in a galaxy could be measured.  The surprising result so far is how similar the properties of young clusters are across the different regions of the galaxy.   “It’s hard to imagine that the IMF is so uniform across our neighboring galaxy given the complex physics of star formation,” Weisz said.

Another surprising result is that the most massive stars in the clusters are 25% less abundant than previous research has suggested.  This is likely because previous studies have underestimated the number of low mass stars in a cluster, instead mixing them together and counting them as high mass stars. This data suggests that the early universe was lacking in heavy elements, since there would be less high mass stars to explode as supernovae and populate the cosmos with planet forming material.

This is some fascinating and spectacular science coming from such a profound visual representation of our nearest neighboring galaxy.  I can’t wait to see what other science comes from the study of this data.

 

 

 

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