luni, 21 octombrie 2013

About Einstein and Cosmos

A Cosmic Discovery That Would Surprise Even Einstein

A strange phenomenon of gravity, light and spacetime may force us to rethink our understanding of our galaxy
Albert Einstein had all sorts of crazy-sounding ideas—that objects should grow more massive and clocks should slow down as they approach the speed of light, for example, or that space and time are united in a single entity called “spacetime.” Some, like dark energy, were so crazy that even Einstein didn’t believe them (foolishly, as it turns out.)
But perhaps the craziest-sounding idea of all, at least for anyone without a physics degree, is that massive objects literally warp the space (OK, the spacetime) around them so that something in the relative foreground, like a star or a galaxy, can distort or even magnify something in the background—a phenomenon known as gravitational lensing. Astronomers saw the first example of gravitational lensing in 1979, when they observed what appeared to be a double quasar 8.7 billion light years from Earth, but that turned out to be a single one, visually warped by an intervening galaxy. Since then, researchers have  used these cosmic optical illusions as a way to map out dark matterdiscover rogue planets and find distant supernovas, among other things.
Now a team led by Arjen van der Wel of the Max Planck Institute for Astronomy in Heidelberg, Germany has announced what he understatedly calls a “weird and interesting discovery,” and what is more precisely described as the most distant gravitational lens ever seen. The lensing object is a galaxy some 9.4 billion light-years away—an enormous distance in a universe that burst into existence just 13.8 billion years ago.
The object being lensed—its image is split into four distinct spots of light—is obviously even more remote, although it’s so small and faint that it’s hard to assign its distance a hard number. What makes this discovery so weird, though, isn’t its distance but the nature of the thing being magnified. It’s a tiny dwarf galaxy whose weight in stars adds up to only about 100 million Suns’ worth—a piker compared with the Milky Way’s 100 billion or more. The overall color of the galaxy tells astronomers that it’s also very young—no more than 40 million years old—and forming stars at a furious rate.
Dwarf galaxies aren’t especially rare; astronomers keep finding them flitting around the Milky Way, and think many more are waiting to be found. But these tiny galaxies can’t sustain bursts of star formation for very long since they don’t have a lot of raw material to work with. That ought to have made this one very hard to spot, since it was at such a distance and it would have been bright enough to see only for a relatively small sliver of its lifespan. That, plus the inherent difficulty involved in  the lensing effect occurring at all—the foreground and background objects have to line up with exquisite precision—makes the fact that this lensed galaxy ever turned up in telescopes even more improbable, the result of just the right conditions and angles converging at just the right time.
Maybe that’s all it was—a cosmic coincidence. “[T]he discovery was completely by chance,” van der Wel said in a statement that accompanied the announcement of the discovery. But another case very similar to it occurred  just a few years ago. Nobody is quite sure how such a thing could happen, unless astronomers’ ideas about how stars form are wrong somehow. Maybe dwarf galaxies are brighter than we know, giving birth to stars for far longer than we believe. That could force us to rethink our most basic notions about the nature of dwarf galaxy behavior and formation. And since full-grown galaxies like the Milky Way were originally assembled out of much smaller ones that merged, that could alter the conventional wisdom about how our own galaxy came to be—something we never would have been in a position to contemplate at all if Einstein’s craziest idea hadn’t turned out to be  one more good one.

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