Tuesday, October 26, 2010

Lifelines 1


While enjoying a variety of magazines in the Emma Clark Library in Setauket, I came across the June 2008 issue of Astronomy. What caught my eye was an article by Abraham Loeb and T. J. Cox. It concerns the future of our galaxy. We live near an outer arm of a pinwheel shaped galaxy called the Milky Way. On a clear night we see the cloudy concentration of stars in these arms overhead. Our galaxy has about 200 billion stars. There is a similar pinwheel galaxy we can see in the night sky as a fuzzy dot. It is called Andromeda. It is somewhat larger than the Milky Way. It would take two and half million years traveling at the speed of light to reach its outer arms. Unlike most of the billions of galaxies in the universe, Andromeda is moving toward us, not away from us. It is “blue-shifted” instead of “red-shifted” when its spectrograph is taken. It is hurtling toward us at a sped of 220,000 miles per hour. The Milky Way and Andromeda are the largest galaxies in a cluster of mostly much smaller galaxies collectively called the local group.

About 5 billion years from now the gravitational attraction of our two large galaxies will result in a collision. Nothing will explode, however, because the stars in each galaxy are one or more light years apart (a few trillions of miles apart at their closest). Instead, the two galaxies (and probably the smaller members of the local group) will merge into a single galaxy shaped like a blunted football. The gas and energy associated with that merger will lead to the birth of millions of new stars. The authors call this future galaxy “Milkomeda”.

Our own sun will then be about 10 billion years old, making it an old star, with most of its hydrogen having been used up making helium and heavier elements. Such old stars begin to expand and turn red. They are called red giants. Our earth, if it is engulfed or heated up will have its life sizzled away. But I expect that long before that merger takes place our descendants, whatever species they may be, if still intelligent to have scientists will have long colonized other planets in near-by stars and may have done so for millions of generations. But among those planets in newer stars there may be intelligent life emerging with 20th century capacities of understanding and knowledge of the universe. They would not know of the origin of Milkomeda from two pinwheel galaxies and they might consider this their original galaxy.

If that life out there continued for another ten or 20 billion years the expansion of the universe would cause all other galaxies to have receded so far away from us that none of these galaxies could have their light reach our Milkomeda galaxy. Astronomers in that futuristic world, who lack this history of the past, would then assume that Milkomeda is the entire universe.

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