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Hubblecast 58: Caught in the cosmic web

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Astronomers have mapped a giant structure made of dark matter It extends almost 60 million light-years out from a huge galaxy cluster, and is our best glimpse so far of the scaffolding that gives the Universe its large-scale structure Hubblecast episode 58: Caught in the cosmic web Presented by Dr J, aka Dr Joe Liske Hello and welcome to the Hubblecast In its very early years, the Universe was extremely smooth and uniform There were no stars, and no galaxies, and all of the matter was distributed throughout the Universe very, very evenly – almost perfectly so But not quite. Even back then there were tiny variations in the density from place to place. And over time, these tiny fluctuations grew and condensed into a web-like pattern that pervades and gives structure to the Universe of today Formed of vast filaments and sheets of dark matter this structure is known to astronomers as the cosmic web Now the trouble is, because it’s made of dark matter you can’t actually see it when you look up into the sky You can model it using computer simulations, but until very recently it had only ever been observed indirectly Scientists know that less than a quarter of the matter in the Universe is actually visible, in the form of stars, nebulae, gas and so on The majority is dark matter, which cannot be seen directly Astronomers have had compelling evidence for the cosmic web for years thanks to galaxies clustering along it But directly observing the dark-matter web itself has been far more difficult. In fact, the very first successful observations of a filament of the web were only made earlier this year Now, a team of scientists has used Hubble to take this a step further making detailed observations of a dark matter filament measuring its length, shape and density Finding one of these filaments is no easy task First, you need to look where you are likely to find one Theories say galaxy clusters form where filaments of the cosmic web meet with the filaments gradually funneling galaxies and dark matter into the clusters So the team focused Hubble on the galaxy cluster MACS J0717 which is known to still be growing And then you need Albert Einstein As predicted by the theory of general relativity a beam of light is bent as it passes near an object with a large mass So although you can’t directly see a dark matter filament its mass should nevertheless bend the light coming from galaxies behind it, subtly distorting their shaopes Next, you have to combine Einstein and Hubble The space telescope can make very detailed observations of galaxy clusters, perfect for spotting these tiny distortions And if you map them all out, the hidden filament of dark matter is revealed And then finally, you take this two dimensional map and you extend it into three dimensions The astronomers used data from the Keck-II and Subaru telescopes in Hawaii among others to measure distances to the galaxies within the filament mapped by Hubble, and to trace their motions They used this to make the first ever three-dimensional reconstruction of a filament and of how it is funneling matter into a massive cluster of galaxies The filament extends across at least 60 million light-years of space From our perspective, we see it gently curving towards us then continuing almost along our line of sight before it plunges into the back of the galaxy cluster Measurements of hundreds of galaxies within the filament show them moving along the filament and into cluster MACS J0717 Observing and reconstructing the cosmic web is quite a big deal because it tells us about the underlying structure of the cosmos Now in the future we’ll be seeing more research like this The NASA/ESA/CSA James Webb Space Telescope scheduled to be launched later this decade will be an excellent tool for studying the cosmic web because of its greatly improved sensitivity compared to Hubble This is Dr J signing off for the Hubblecast Once again, nature has surprised us beyond our wildest imagination Hubblecast is produced by ESA/Hubble at the European Southern Observatory Transcribed by ESA/Hubble

Video Details

Duration: 6 minutes and 50 seconds
Country: Germany
Language: English
Producer: Lars Lindberg Christensen
Director: Oli Usher
Views: 214
Posted by: esahubble on Oct 16, 2012

In this episode of the Hubblecast, Joe Liske (aka Dr J) shows how a team of astronomers has used Hubble and a battery of other telescopes to discover the secrets of massive galaxy cluster MACS J0717. They have found that an invisible filament of dark matter extends out of the cluster. This is our first direct glimpse of the shape of the scaffolding that gives the Universe its structure.

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