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I hope you've kept up your collision insurance because something wicked big this way comes.

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Hope to see on the other side of the nebulous collision.


Astronomers have long known that the Milky Way (our home, sweet home galaxy) was moving towards a neighboring spiral galaxy known as Andromeda, Messier 31 (M31), or NGC 224. It was not known, however, whether Andromeda would miss us, strike a glancing blow, or smack us head on. It was one of those known unknowns a certain Secretary of Defense told us about.

In truth, of course, the two galaxies are in a complicated dance, each moving around the other. Astronomers have long known the radial or the component of the velocity vectory moving towards us. They did not know, until recently, the sidewise or transverse component. Without knowing the true speed and direction (a vector) there was no way to know whether the two galaxies would eventually collide.

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GALEX: The Andromeda Galaxy
Credit:GALEX, JPL-Caltech, NASA

Explanation: A mere 2.5 million light-years away, the Andromeda Galaxy really is just next door as large galaxies go. So close, and spanning some 260,000 light-years, it took 11 different image fields from the Galaxy Evolution Explorer (GALEX) satellite's telescope to produce this gorgeous portrait of the spiral galaxy in ultraviolet light. While its spiral arms stand out in visible light images of Andromeda (also known as M31), the arms look more like rings in the GALEX ultraviolet view, dominated by hot, young, massive stars. As sites of intense star formation, the rings have been interpreted as evidence Andromeda collided with its smaller neighboring elliptical galaxy M32 more than 200 million years ago. The large Andromeda galaxy and our own Milky Way are the dominant members of the local galaxy group.APOD

A study of Hubble Space Telescope data by astronomers at the Space Telescope Science Institute (STScI) in Baltimore found that the Milky Way is, indeed, lined up for a collision with its giant twin. "Our findings are statistically consistent with a head-on collision between the Andromeda galaxy and our Milky Way galaxy," said Roeland van der Marel of STScI.

The STScI team poured over reams of Hubble data from 2002 to the present to determine the true paths of the two giants and in about 4 billion years or so the Milky Way and Andromeda will mix it up like the Jets and the Sharks ending in a huge elliptical galaxy in something on the order of 2 billion years after the initial interaction.

Andromeda weighs around 7.1x10¹¹ solar masses (M☉), is currently about 2.5 million light years away, and contains about 1 trillion stars. It is travelling towards us at a speed of about 120 kilometres per second (400 lightyears every million years)Wiki. Our home, the Milky Way, is estimated to be about 7.0x10¹¹M but may actually be more massive based on some recent studies contains only 200 to 400 billion stars.
Astronomers used these new images to measure the total infrared brightness of Andromeda. Because the amount of infrared light given off by stars depends on their masses, the brightness measurements provided a novel method for "weighing" the Andromeda galaxy. According to this method, the mass of the stars in Andromeda is about 110 billion times that of the sun, which is in agreement with past calculations. This means the galaxy contains about one trillion stars (because most stars are actually less massive than the sun). For comparison, the Milky Way is estimated to hold about 400 billion stars.JPL
Odds are real good (as in near certainty) that the solar system will be unharmed—basically undisturbed in the encounter. Its orbit about the center of the new mass distribution will certainly change.
Although the galaxies will plow into each other, stars inside each galaxy are so far apart that they will not collide with other stars during the encounter. However, the stars will be thrown into different orbits around the new galactic center. Simulations show that our solar system will probably be tossed much farther from the galactic core than it is today.DailyGalaxy
Our night skies will be quite different than they are today. The solar system's new position in the resulting galaxy will mean all our constellations will be gone. New stars and old will be visible but they'll be in jumbled up together and in different places in the sky.

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Here's an animation of the the change that we might see from earth as the merging of the two galaxies progresses.

Originally posted to SciTech on Sun Jun 03, 2012 at 06:03 PM PDT.

Also republished by J Town and Community Spotlight.

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