two million image classifications by citizen scientists
combined to reveal in exquisite detail the kinds of stars
the Andromeda Galaxy (M31) gives birth to. When a
nebula’s clouds of gas and dust condense into stars,
astronomers see them produce a few giant hot stars,
some medium Sun-like stars, and many tiny red dwarfs.
The exact breakdown of star size and number produced
in a stellar nursery is known as the “initial mass function”
(IMF), and scientists want a detailed census so they can
better understand star formation and galaxy evolution
even when they are too far away to measure individual
stellar populations. The only places where astronomers
can observe these individual star-forming regions well
enough to measure the IMF have been within our own
Milky Way Galaxy — until now.
New ultra-high-resolution images of M31 allowed
researchers to measure the IMF not just in our immediate
neighborhood, but 2.5 million light-years away. They compared
populations across Andromeda, but found the same
IMF everywhere, and though it matched previous measurements
closer to home, some of the brightest stars appeared
less abundant than expected. The biggest stars explode in
supernova events and contribute heavy elements to the
universe — the kind that make up most of our bodies — so
knowing how quickly the cosmos grew its metals is crucial
to understanding cosmic evolution. The research appeared
June 20 in The Astrophysical Journal. —
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