Thanks very much Andromeda!
The Andromeda Galaxy (credit NASA)
Our large Galaxy, the Milky Way is on a collision course with destiny! The end of its existence as a spiral galaxy will come in about 4 billion years when it smashes into another galaxy, the similarly sized,"nearby" spiral, Andromeda (M31). Spiral galaxies are elegant, glittering, star-splattered pinwheels whirling around in Space. Andromeda is currently a very safe 2 million light-years away--at least for the time being. Alas, the relentless lure of gravitation is pulling Andromeda towards our doomed Milky Way at, approximately, 100 kilometers per second. One light-year is the distance that light can travel in a vacuum in one year--which is about 5,878,625 million miles.
Both the Milky Way and Andromeda are the two largest denizens of the so-called Local Group of galaxies, which also hosts about 20 smaller galaxies. The Local Group is a few million light-years across. However, this is small when compared to entire galaxy clusters. Immense clusters of galaxies dwell in our Universe, and some of them contain hundreds of constituent galaxies. Our Local Group resides close to the outer limits of the Virgo Cluster of galaxies, whose core is 50 million light-years away from us. The many groups of galaxies and clusters of galaxies are themselves smaller denizens of unimaginably enormous web-like filaments and thin, broad expanses. For example, the so-called Great Wall of galaxies is a sheet-like group of galaxies residing roughly 200 million light-years away from us, and a similar gigantic structure is termed the Great Attractor. The Great Attractor is pulling mercilessly, with its mighty gravitational grip, on the entire Virgo Cluster of galaxies. We go along for the ride, of course, together with the rest of the Local Group, at about several hundred kilometers per second.
When the great smash-up between our Milky Way and the Andromeda galaxy occurs in the distant future, the merged galaxies will undergo a sea change.
Into Something Rich And Strange
Researchers announced on May 31, 2012 that the collision between our Galaxy and Andromeda will create an entirely new Galaxy, one likely sporting an elliptical (football) shape instead of the elegant and lovely spirals of the two doomed galactic wanderers. This strange, new Galaxy, has been named the "Milkomeda" Galaxy by playful astronomers, in honor of the two former spirals that will collide and merge to give rise to it.
"We do know of other galaxies in the local Universe around us that are in the process of colliding and merging. However, what makes the future merger of the Andromeda galaxy and Milky Way so special is that it will happen to us," Dr. Roeland van der Marel commented to the press on May 31, 2012. Dr. van der Marel is at the Space Telescope Science Institute in Baltimore, Maryland.
The Milky Way and Andromeda galaxies are currently galloping towards each other at a breathtaking 250,000 miles per hour. Astronomers have long suspected that the two large galaxies are doomed to splat into each other mercilessly, and sloppily, some billions of years from now. However, such dire predictions were highly speculative, because astronomers had not yet managed to measure Andromeda's sideways motion through Space--a necessary measurement in order for scientists to calculate that galaxy's path through the Universe.
However, Dr. van der Marel and his team used NASA's venerable Hubble Space Telescope (HST) to carefully observe certain regions of Andromeda over a seven-year span of time. They were able to successfully calculate Andromeda's sideways (tangential) course through Space, and they discovered that Andromeda and our Milky Way will suffer a gigantic head-on collision in about 4 billion years!
"The Andromeda galaxy is heading straight in our direction. The galaxies will collide, and they will merge together to form one new Galaxy," Dr. van der Marel told the press in May 2012. The terrible crash will be over in about 6 billion years.
Galactic Train Wrecks
To understand what the future holds for our Galaxy, astronomers have compiled a photo database of sundry colliding galaxies in various stages of their hapless crash-ups.
"We've assembled an atlas of galactic 'train wrecks' from start to finish. This atlas is the first step in reading the story of how galaxies form, grow and evolve," commented Dr. Lauranne Lanz in the August 16, 2011 Space.com. Dr. Lanz is at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts. She presented a study on the research at a 2011 conference.
To observe distant galactic smash-ups, the astronomers used images from NASA's infrared eye in the sky, the Spitzer Space Telescope, as well as NASA's Galaxy Evolution Explorer (GALEX), which has ultraviolet vision. The differing wavelength bands enabled the astronomers to attain more important details about the collisions than would be possible using one type of light alone.
Galactic train-wrecks are not as violent as sometimes supposed. Although galaxies do crash into one another, it's improbable that any two stars will actually splat together creating a big stellar mess. This is because the Space between stars that dwell within galaxies is usually quite vast. However, the floating clouds of gas and dust, that roam around within galaxies, will probably merge in a smash-up--and that sort of thing can result in Cosmic violence. This is because such an event will set off a writhing, churning atmosphere where new baby stars can be born in a dramatic, furious starburst.
Galactic smash-ups occur over millions to billions of years, and are not quickly over for the suffering parties. This is why the atlas is such a valuable tool for astronomers--it can capture galaxy systems at sundry stages of collision in order to put together a more complete picture of the long, drawn-out, merciless process.
Such a dramatic smash-up has never before occurred in our very old Galaxy's entire history. The Milky Way probably started taking shape 13.5 billion years ago, "shortly" (by cosmological standards) after the Big Bang birth of the Universe itself about 13.75 billion years ago! "The Milky Way has had, probably, quite a lot of small, minor mergers. But this major merger will be unprecedented," explained Dr. Rosemary Wyse to the press in May 2012. Dr. Wyse is at Johns Hopkins University in Baltimore, Maryland. She was not part of the study.
A Terrible Beauty Is Born
The coming collision will utterly change our night sky. If human beings are still around 3.75 billion years from now (an unlikely prospect), they will look up to see Andromeda fill the entire sky as it relentlessly approaches our Galaxy. For the next few billion years, what is possibly left of humanity, will gaze in shock at the merger, which will set off violent episodes of dazzling star-birth.
In about 7 billion years, the glowing core of the newborn elliptical Milkomeda Galaxy, now our own, will dominate the entire night sky. The prospect of human beings actually viewing this sight, however, is quite remote because the Sun will probably grow into a huge red giant star 5 or 6 billion years from now, and will likely cannibalize the inner planets--Mercury, Venus, and our own Earth.
Both the Milky Way and Andromeda are about the same age. Although the two sister galaxies are considered to be virtual twins, it is a little difficult to predict which one of the galaxies will suffer the most when the end comes. Dr. van der Marel told the press on May 31, 2012 that "This is pretty violent as things go in the Universe. It's like a bad car crash in galaxy-land."
I am a writer and astronomer whose articles have been published since 1981 in various magazines, newspapers, and journals. Although I have written on a variety of topics, I particularly love writing about astronomy because it gives me the opportunity to communicate to others the many wonders of my field. My first book, "Wisps, Ashes, and Smoke" will be published soon.
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The immense Andromeda galaxy, also known as Messier 31 or simply M31, is captured in full in this new image from NASA's Wide-field Infrared Survey Explorer, or WISE. The mosaic covers an area equivalent to more than 100 full moons, or five degrees across the sky. WISE used all four of its infrared detectors to capture this picture (3.4- and 4.6-micron light is colored blue; 12-micron light is green; and 22-micron light is red). Blue highlights mature stars, while yellow and red show dust heated by newborn, massive stars.
Andromeda is the closest large galaxy to our Milky Way galaxy, and is located 2.5 million light-years from our sun. It is close enough for telescopes to spy the details of its ringed arms of new stars and hazy blue backbone of older stars. Also seen in the mosaic are two satellite galaxies, known as M32, located just a bit above Andromeda to the left of center, and the fuzzy blue M110, located below the center of the great spiral arms. These satellites are the largest of several that are gravitationally bound to Andromeda.
The Andromeda galaxy is larger than our Milky Way and contains more stars, but the Milky Way is thought to perhaps have more mass due to its larger proportion of a mysterious substance called dark matter. Both galaxies belong to our so-called Local Group, a collection of more than 50 galaxies, most of which are tiny dwarf systems. In its quest to map the whole sky, WISE will capture the entire Local Group.