Sky & Telescope - April 2022 - 35

M
arla Geha didn't want to get her hopes up. She
was poring over images of distant dwarf galaxies,
surrounding hosts similar to our own Milky Way,
when she realized that the dwarfs looked surprisingly different
from the ones in our backyard. It was the first hint
that the most-studied galaxy in the universe - our own -
might not be as typical as previously thought.
" Whenever I see a result, I basically try and figure out
what ways it could be wrong before getting excited, " says
Geha (Yale). " I think I've been hurt too many times. "
But it didn't take long before she realized that this was
no mistake. The dwarf galaxies imaged as part of the Satellites
Around Galactic Analogs (SAGA) Survey are studded
with young, brilliant, blue stars. That's a far cry from the
old, red stars in the faint satellites circling our galaxy.
Apart from the Magellanic Clouds (which are large,
recent arrivals), all 60-some known dwarfs around the
Milky Way are dead - and have been for at least 1 billion
years. The same story is true around Andromeda, where
only two of the galaxy's 30-odd satellites are currently
forming stars.
Such a stark contrast could be a problem. Much of our
knowledge about galaxy formation and even cosmology
is based on our understanding of the Milky Way's satellites.
Most of these small galaxies are also crowded with
dark matter, making them useful laboratories for studying
the mysterious substance. " There have been hundreds of
papers written about the Milky Way satellites and using
them to infer big things, " Geha says. But if the Milky Way's
satellites aren't the norm, then many of those conclusions
might need a rethink.
Enter SAGA, with the goal to observe satellites around
100 Milky Way analogs - galaxies comparable in brightness
and environment to our own home. To do so, the team
must reach beyond the Local Group, studying galaxies as
far as 100 million light-years away (well beyond the Virgo
Cluster) in order to provide the cosmological and statistical
comparison that would place the Milky Way in context.
sk yand tele scope .o r g * APRIL 2022 35

http://skyandtelescope.org

Sky & Telescope - April 2022

Table of Contents for the Digital Edition of Sky & Telescope - April 2022

Contents
Sky & Telescope - April 2022 - Cover1
Sky & Telescope - April 2022 - Cover2
Sky & Telescope - April 2022 - 1
Sky & Telescope - April 2022 - Contents
Sky & Telescope - April 2022 - 3
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Sky & Telescope - April 2022 - Cover3
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