Sure, we like observing M31. Through binoculars, its familiar shape is obvious. Dust lanes appear with any good scope, as do its little blobby companion galaxies. Wonderful stuff. But sadly, friends are not likely to agree. Andromeda is a familiar name, and they’ve seen glorious photos of it. Only if you prep them with mouth-watering stories will their excitement overcome the brutal fact that M31 looks smudgy and ill defined.
Start with its location in the sky near the Milky Way. Of course, it couldn’t possibly sit within the band of the Milky Way because our own galaxy blocks out everything lying beyond. That it appears so near the Milky Way means it was a close call whether we would get to see it at all. Our galaxy’s disk aims almost in Andromeda’s direction, and Andromeda just barely clears the foreground muck and crud.
In fact, as our galaxy rotates, we’ll eventually be carried to the far side of the carousel, where the big bulge at the Milky Way’s core will obscure Andromeda totally. Then, it’ll vanish for many millions of years. That no-M31 epoch will begin in roughly 100 million years. Andromeda is the only major galaxy that comes and goes depending on where we happen to be as our galaxy performs its grand 240-million-year pirouette.
With the naked eye, and especially through binoculars, it’s obvious that M31’s flat disk is oriented nearly sideways. A shame. Its orientation, 13° from edgewise, is what makes it a smudgy mess through backyard instruments.
Strangely enough, that’s the same orientation our Milky Way would display to any Andromedans using a nice telescope to look back at us. When you think about Andromeda’s location in the sky near the Milky Way, you realize, yes, they must see us nearly, but not exactly edgewise.
In fact, maybe Andromeda doesn’t exist at all and, instead, there’s a giant mirror out there and we’re merely looking at ourselves! This very theory was proposed by no less than Henry Neimark, a mental patient at Bellevue Hospital.
Andromeda also was where the unpleasant, but brilliant, Edwin Hubble first detected extragalactic stars, proving the universe to be far larger than previously known. Realizing this in the 1920s, he and others decided that instead of “Andromeda Nebula” — its popular name for centuries — M31 should be called an “island universe” — a fabulous term for a separate starry empire. Too bad it didn’t stick. Instead, it was decided that these entities would be termed “galaxies.”
Reason: Astronomers wanted to retain the creamy theme of our own Milky Way, describing the distant star-cities as galactic because “lactic” means “pertaining to milk.” So the entire universe was to be considered some sort of vast dairyland, and it all started with Andromeda.
Backyard scopes reveal the star-like glow of M31’s nucleus. The Hubble Space Telescope split this nucleus in two, with the brighter component offset from M31’s true center. At its heart lies the customary massive black hole that seems to occupy the center of all galaxies. Andromeda’s may have the mass of 100 million suns.
The rest of the universe may be flying apart, but we and Andromeda will hang out forever thanks to our mutual gravitational grasp. Andromeda, though, is hurtling toward us at 60 miles per second (96.6 kilometers per second). So there’s an excellent chance Andromeda, now 2.9 million light-years away, will collide with us when Earth is about twice its current age.
It’s an attractive notion.
A galaxy’s stars lie so far apart that none makes contact when galaxies slam into each other. Instead, one galaxy simply passes through the other. What a future sight in our sky! And there’s always the chance that Sol will be among the many stars that gets yanked from one galaxy to the other. Imagine — our return addresses may someday say “Andromeda” instead of “Milky Way.” Later on, both galaxies may combine into one super-sized, globular-shaped elliptical galaxy.
No matter what happens, our fates are entwined forever. That’s a story to share before passing around the binoculars.