Showing posts from January, 2014

Grey is the new black hole: is Stephen Hawking right?

Quick post. I've taken a bit of a hiatus from publishing in The Conversation  for a while, for mildly political reasons that I will talk about some day. But I decided to get back on this horse and have written an article called  Grey is the new black hole: is Stephen Hawking right? I'll let you have a read and I'll be happy to answer questions below. But for now, here's "Colin"

Hydrodynamical simulations of coupled and uncoupled quintessence models I: Halo properties and the cosmic web

Slightly under the weather as a very nice man removed four of my wisdom teeth yesterday, so a quick post for today. But we've got a new and exciting paper accepted. Cosmology has come a long way, and we now have exquisite data which point us to the make up of the Universe, a curious mix of dark matter, dark energy, and a few baryons like ourselves. But there's a problem. It's a boring Universe. What, you say! Boring. Yes, we have dark matter and dark energy, things that we still really need to discover in terms of their "quantum properties" such as are they this particle or that, this field or that, but we know what their effects on the expansion of the Universe are; dark matter is is gravitationally attractive, just like everyday matter, and dark energy is repulsive, driving the expansion acceleration of the Universe. But as far as we can tell from the data, dark energy appears to be the same as  Einstein's Cosmological Constant.  And the completely b

Just how big is Andromeda?

A quick post as I wait for the first coat of paint in the kid's bedrooms to dry. There's been a picture floating around on the interwebs showing a composite of the full Moon and the Andromeda Galaxy. Here it is. There is a discussion of this image over at  Bad Astronomy , and it's a composite of an image taken by  Stephen Rahn (over on flikr)  and an image of Andromeda taken by  GALEX , made by  Tom BH. Anyway, as you know, the disk of Andromeda is not all there is to the galaxy, and as part of the  Pan-Andromeda Archaeological Survey (PAndAS)  we've been mapping out the substructure into the halo of Andromeda. What if we plonked that on the above image? Well, I've done that and made the following (and credit to Stephen Rahn for the original image). How cool is that? It's an optical image of Andromeda itself on the same scale as in the GALEX image, but now I've also included the debris that we find in PAndAS. Just outside the main disk, there&#