Biggest 3D galaxy map to probe dark energy's history

By Stephen Battersby Cosmic cartographers are starting work on the biggest 3D map of the universe so far. It should reveal an undulating landscape sculpted by the big bang, and might give us a clue to the underlying shape of space and the nature of the “dark energy” that is blowing the universe apart. The Sloan III project is the latest in a sequence of sky-surveys using a special wide-angle telescope sited in Sunspot, New Mexico. Since the completion of the Sloan I and II surveys, the telescope’s camera and optics have been updated, making it a more sensitive instrument. There has also been a shift in strategy, says Daniel Eisenstein, director of the new project at the University of Arizona in Tucson. While much of the effort in the earlier surveys was devoted to relatively nearby galaxies, the biggest objective of Sloan III will be to chart the positions of more luminous galaxies out to a distance of about 8 billion light years. With the locations of millions of these galaxies pinpointed on such a large-scale map, the team expects to see a subtle pattern emerging – the relic of a much more ancient pattern, seen in the cosmic microwave background radiation that was emitted 380,000 years after the big bang. That in turn was created by loud sound waves travelling through the dense, hot early universe. In this cosmic cacophony, one particular note was louder than the rest, and it survives to this day as a characteristic wavelength in the clustering of galaxies. “Galaxies are slightly more likely to be separated by 500 million light years than by 400 or 600 million light years,” Eisenstein told New Scientist. By plotting the positions of millions of galaxies, the Sloan team expects to see this pattern over a wide swath of the universe. They also hope to see it in the clustering of intergalactic gas, whose presence is revealed by their absorption of light from distant quasars. “It’s the first time anybody has tried to do this,” says Eisenstein. The standard length-scale can then be used to measure out the universe. Its apparent size tells astronomers exactly how far away they are looking, which is related to when in cosmic time they are looking. The distance (and time) can then be plotted against the galaxies’ redshift – the reddening of light caused by the expansion of the universe – to provide the history of cosmic expansion. That’s a step towards knowing what forces are at play in the universe. Seeing how the acceleration changes will reveal whether dark energy is getting stronger or weaker, or just staying the same. Combined with observations of supernovae and other astronomical data, the Sloan III survey should provide the best examination yet of this cosmic puzzle. This cosmic “ruler” could also show us the shape of spacetime. If spacetime is curved on large scales, it would magnify or shrink the apparent size of very distant objects – such as the length of the ruler itself. Such length changes could be distinguished from any caused by dark energy because the curvature of space would produce much stronger effects at high redshift than dark energy, astronomers say. Magnification would suggest that space is curved like the surface of a sphere – and it would mean we live in a finite universe. The Sloan III survey will also look closer to home, mapping the Milky Way galaxy and monitoring 10,000 stars for evidence that they host giant planets. Cosmology – Keep up with the latest ideas in our special report. More on these topics:
  • 首页
  • 游艇租赁
  • 电话
  • 关于我们