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Dr David Whitehouse

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The Nobel Prize at the End of the Universe

Posted: 05/10/11 01:00

For the second time in five years the Nobel Prize in Physics has gone to astronomy, to two teams, one in the United States and the other in Australia, that charted the outer reaches of the universe using distant stellar explosions as probes of its expansion, and whilst sifting through the light of long dead stars discovered the unexpected fate of all things.

Once there was a system of two stars in orbit around each other, a common occurrence in our universe. The two stars were different. One went through its life cycle quickly and became a white dwarf - a star with the mass of our sun but the size of the Earth. The other had a different path to take, and was a large red star. As it circled its leery red companion the white dwarf's gravity sucked tendrils of matter off it and onto itself, sealing its doom.

As you read this somewhere in the universe such a star is about to explode. It's been quivering for over a thousand years, teetering on the edge of instability. Suddenly the influx of new material pushes it over the edge. Oxygen and carbon atoms are forced together liberating the colossal energies latent in matter. The white dwarf explodes, and within seconds is shining with the light of billions of suns, outshining the galaxy of a hundred thousand million stars it lives in.

Such is their brightness that supernovae, as they are called, are visible from the other side of the universe. Suddenly in the outskirts of a dim and ordinary galaxy, small and insignificant in the scheme of things, there appears a point of light that gets brighter and gets the attention of astronomers.

Space Patrol

The importance of this type of supernovae, there are other kinds, is that the white dwarf star that explodes is always about the same mass producing an explosion of uniform brightness from supernova to supernova. This means that wherever they occur, near or far, we know their true brightness and by measuring their apparent brightness we can compute their distance. These exploding stars are therefore markers, the milestones of the cosmos.

Patrolling the sky the two Nobel-winning teams picked up about 50 of these explosions, and when they tabulated their brightness they noticed something incredible - they appeared fainter than was expected. It was a small effect that only showed itself in the statistics but both teams had spotted it. It implied what many astronomers regarded as unthinkable.

We have known that the universe was expanding since Edwin Hubble discovered the effect almost a century ago. It meant that the universe was created in a Big Bang some 14 billion years ago. But the question was; will the expansion continue forever. Will it stop and the universe collapse in a so-called Big Crunch? Will it go on forever?

What the Nobel supernova collectors discovered was the weirdest option. Not only will the cosmos go on expanding forever it is actually accelerating.

The implications are profound. In the distant future stars and galaxies will drift further and further apart. The galaxies will eventually disintegrate and the stars wither and die. The cosmos will become dark, the glory of the stars a dim memory. Over vast swathes of cosmic time the universe will reduce itself to particles, and then to energy becoming ever weaker and thinner, forever and forever, until time itself has no meaning.

This fate lies in the far future. At the moment the universe is full of stars that light its every corner. Some stars are stable like our sun. Many contribute only a feeble light. But some blaze their death throws across space and time allowing astronomers on a ball of rock orbiting a commonplace star to obtain a glimpse of a bleak eternity.


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