A crucial element was the computer algorithm used to create the 3D map: due to the large amount of data, a naïve implementation of the map-making procedure would have required an inordinate amount of computing time. Their absorption measurements using 24 faint background galaxies provided sufficient coverage of a small patch of the sky to be combined into a 3D map of the foreground cosmic web. But judging by the data quality as it came off the telescope, it was already clear to me that the experiment was going to work," says Joseph Hennawi (MPIA), who was part of the observing team.Īlthough the astronomers only observed for 4 hours, the data they collected was completely unprecedented. ![]() "We were pretty disappointed as the weather was terrible and we only managed to collect a few hours of good data. ![]() Keck Observatory on Mauna Kea, Hawaii – but were plagued by a problem more terrestrial than cosmic. Lee and his colleagues obtained observing time on one of the largest telescopes in the world: the 10m-diameter Keck I telescope at the W. Still, this would provide an unprecedented view of the cosmic web which has never been mapped at such vast distances." Lee says: "I was surprised to find that existing large telescopes should already be able to collect sufficient light from these faint galaxies to map the foreground absorption, albeit at a lower resolution than would be feasible with future telescopes. The use of the combined starlight of background galaxies for this purpose had been thought to be impossible with current telescopes – until Lee carried out calculations that suggested otherwise. Similar to a medical CT scan, which reconstructs a three-dimensional image of the human body from the X-rays passing through a patient, Lee and his colleagues reconstructed their map from the light of distant background galaxies passing through the cosmic web's hydrogen gas. Now a team of astronomers led by Khee-Gan Lee, a post-doc at the Max Planck Institute for Astronomy, has managed to create a three-dimensional map of a large region of the far-flung cosmic web nearly 11 billion light years away, when the Universe was just a quarter of its current age. ![]() Galaxies like our own Milky Way are embedded inside this web, but fill only a tiny fraction of its volume. Dark matter, which emits no light, forms the backbone of this web, which is also suffused with primordial hydrogen gas left over from the Big Bang. On the largest scales, matter in the Universe is arranged in a vast network of filamentary structures known as the 'cosmic web', its tangled strands spanning hundreds of millions of light years. Quelle: Casey Stark (UC Berkeley) und Khee-Gan Lee (MPIA)
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