Meeting the neighbours
I wrote, just before my laptop left my life (incidentally, if you happen to be in Shepherd’s Bush with a newly acquired MacBookPro which, shall we say, fell into your hands, then I’m desperate enough to pay to have it back. Drop me an email?) a long piece about a fantastic paper released last week by some of my UCL colleagues.
They’ve produced what is being billed as the largest three-dimensional survey of galaxies across the entire sky ever to be produced. I’m a sucker for these kinds of things; there’s something special about being able to map our place in the Universe, and being able to identify exactly where in the many millions and billions of galaxies we are. The deepest survey to date – the Sloan digital sky survey – looks in detail at only a small fraction of the sky, whereas this more recent work uses galaxy positions from the 2MASS survey which covers the entire celestial sphere.
So what does our cosmic neighbourhood look like? The maps reach out 600 million light-years, and in all that space the largest supercluster is the Shapley supercluster, some 400 million light-years away. This structure is enormous, at least 20 million light-years across. Our local movements, though, are detemined primarily by the presence of the Great Attractor, around three times closer but pulling the Local Group, including our own Milky Way, toward it at the media-friendly velocity of a million miles an hour.
The maps are based on a technique which allows astronomers to infer the position of the dominant but invisible dark matter from the observed positions of the galaxies, and the next step will be to test this model by measuring the galaxies’ velocities directly. In the meantime, you can enjoy a spin around our local Universe here (large file).
Update : In response to a comment, stills are available via the RAS press release – scroll down for captions.
