The other great spiral galaxy in the local group demonstrates why we’re #2, even in our own backyard.
The Milky Way is our cosmic home, containing hundreds of billions of stars across 100,000 light-years.
But 2.5 million light years away, our big sister, Andromeda, outclasses us in every way.
It’s double our diameter, with around a trillion stars.
It’s the Local Group’s biggest, most massive and luminous galaxy.
When we look at the stars within Andromeda, with space telescopes like Hubble, the biggest differences emerge.
Over 117 million stars in the disk were measured by PHAT: the Panchromatic Hubble Andromeda Treasury.
The stars near the central bulge are far richer in heavy elements than our Sun.
New, blue stars shine in a slew of open clusters.
The low-density, outer halo contains stars just as ancient as the Milky Way’s oldest: 13+ billion years of age.
Andromeda has stellar streams populating that halo, with a third of those stars just 6–8 billion years old.
This means a major act of galactic cannibalism recently occurred.
Ultraviolet images showcase the newest stars, tracing out spiral arms and peaking in the center.
Infrared imaging pinpoints the galactic fuel that will birth future generations of stars.
Thousands of background galaxies, seen through Andromeda’s halo, showcase our chaotic, evolving Universe.
Mostly Mute Monday tells the cosmic story of an astronomical object or phenomenon in images, visuals, and no more than 200 words. Talk less; smile more.Ethan Siegel is the author of Beyond the Galaxy and Treknology. You can pre-order his third book, currently in development: the Encyclopaedia Cosmologica.