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Andromeda mon amour

The views expressed are those of the author and are not necessarily those of Scientific American.


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Andromeda (GALEX/NASA/JPL)

There is something beautiful yet ominous about our nearest large galactic neighbor.

The Andromeda galaxy is a trillion star behemoth that spans some six times the diameter of the full Moon when seen through a telescope. At only 2.5 million light years away from the Milky Way it’s barely an intergalactic stone’s throw from us, and the gravitational might of our two galaxies is pulling them together against the stretching expansion of the cosmos. Every year we get closer by about 2 billion miles. And, as I’ve written about before, in some 4 billion years or so we’ll begin a process of merger, a grand slow-motion galactic collision.

The outcome of this will most likely be a new system, our merged components perhaps dissolving into a giant elliptical galaxy, with stellar orbits thrown into a vast puff. No more Milky Way, no more Andromeda, just distant memories.

These observations were made by Herschel's spectral and photometric imaging receiver (SPIRE) instrument. The data were processed as part of a project to improve methods for assembling mosaics from SPIRE observations. Light with a wavelength of 250 microns is rendered as blue, 350-micron is green, and 500-micron light is red. Color saturation has been enhanced to bring out the small differences at these wavelengths. (ESA/NASA)

But until then we get to observe this beautiful spiral object. Andromeda seems to be producing stars at a slightly slower rate than the Milky Way, but this doesn’t mean it’s devoid of stellar birth. New images from the ESA/NASA space observatory Herschel allow us to map out the cooler interstellar dust and dense regions of star and planet formation by sensing far infrared and submillimeter wavelength radiation from this matter. At these wavebands photons are less attenuated by gas and dust and less confused with starlight, allowing astronomers to peer deep into Andromeda’s nurseries.

Andromeda - to the left in far infrared, to the right in visible light (ESA/Herschel/PACS & SPIRE Consortium, O. Krause, HSC, H. Linz)

They’re extraordinary images, and here I show a comparison with the visible light image of Andromeda. Stars are being born in rings, spokes, and spiral arm structures throughout our neighbor. Chances are that we look a lot like this for any hypothetical Andromedan astronomer peering back at us across the void.

Caleb A. Scharf About the Author: Caleb Scharf is the director of Columbia University's multidisciplinary Astrobiology Center. He has worked in the fields of observational cosmology, X-ray astronomy, and more recently exoplanetary science. His latest book is 'Gravity's Engines: How Bubble-Blowing Black Holes Rule Galaxies, Stars, and Life in the Cosmos', and he is working on 'The Copernicus Complex' (both from Scientific American / Farrar, Straus and Giroux.) Follow on Twitter @caleb_scharf.

The views expressed are those of the author and are not necessarily those of Scientific American.





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  1. 1. jgrosay 3:20 pm 01/29/2013

    According to research published in Annals of the New York Academy of Sciences, the shape of Galaxies, eliptical or bar, or any other, is not a fixed feature of that particular galaxy, but a dynamic image caused by the temporal coincidence of the stars orbiting the galactic core, the image of arms, or spirals, or bars, is just what we see in the time of our observation, if you give a time ample enough, sorry none of us can do this in the time frame when we are in the situation of having interest in these issues of Nature, you’ll see the image of a Galaxy changing from a bar to arms forming spirals, and viceversa, what we perceive as types of galaxies doesn’t reflect any inherent or fundamental feature of the galaxy, it’s just a temporal coincidence in the orbits of stars, the same as a planetary conjunction, but nothing more. Or not?

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  2. 2. Acoyauh2 3:36 pm 01/29/2013

    Nice article, great pics.
    But “spans some six times the diameter of the full Moon when seen through a telescope” is iffy. WHO’s telescope are you talkin’ about? Wouldn’t its apparent size in the sky, location etc. be a bit more useful, and precise than this? Just sayin’…

    Link to this
  3. 3. SteveO 6:24 pm 01/29/2013

    Actually, it is six time the apparent size of the moon looking through anything on planet Earth, including your eyeballs. Of course it is too dim for your eyeballs to see. What a sight it would be, though!

    “…when seen through a telescope” is an awkward way of saying it. Perhaps “The Andromeda galaxy is a trillion star behemoth that spans some six times the apparent diameter of the full Moon.” would be more clear?

    Link to this
  4. 4. SteveO 6:25 pm 01/29/2013

    Oh, and instructions to find it: http://www.wikihow.com/Find-the-Andromeda-Galaxy

    Link to this

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