Cosmic Horizons

Things are crazily busy, with me finishing teaching this week. Some of you may know, that I am writing a book, which is progressing, but more slowly than I hoped. Up to just over 60,000 words, with a goal of about 80 to 90 thousand, so more than half way through. I know that I have to catch up with papers, and I have another article in  The Conversation  brewing, but I thought I would write about something interesting. The problem is that my limited brain has been occupied by so many other things that my clear thinking time has been reduced to snippets here and there. But one thing that has been on my mind is tests of cosmology. Nothing I post here will be new, but you might not know about it. But here goes. So,  the universe is expanding.  But how do we know? I've written a little about this previously, but we know that almost 100 years ago,  Edwin Hubble  discovered his " law ", that galaxies are moving away from us, and the further away they are, ...

Where did that month go? Winter is almost over and spring will be breaking, and my backlog of papers to comment on is getting longer and longer. So a quick post this morning on a recent cool paper by PhD student, Brendan McMonigal , called "Sailing under the Magellanic Clouds: A DECAm View of the Carina Dwarf". The title tells a lot of the story, but it all starts with a telescope with a big camera. The camera is DECam , the Dark Energy Camera located on the 4m CTIO telescope in Chile. This is what it looks like; It's not one CCD , but loads of them butted together allowing us to image a large chunk of sky. Over the next few years, this amazing camera will allow the Dark Energy Survey  which will hopefully reveal what is going on in the dark sector of the Universe , a place where Australia will play a key-role through OzDES . But one of the cool things is that we can use this superb facility to look at other things, and this is precisely what Bendan did...

We had a paper in  Nature  this week, and I think this paper is exciting and important. I've written an article for  The Conversation  which you can read it  here . Enjoy!

I am exhausted after a month of travel, but am now back in a sunny, but cool, Sydney. It's feels especially chilly as part of my trip included Death Valley, where the temperatures were pushing 50 degrees C. I face a couple of weeks of catch-up, especially with regards to some blog posts on my recent papers. Here, I am going to cheat and present two papers at once. Both papers are by soon-to-be-newly-minted Doctor,  Foivos Diakogiannis . I hope you won't mind, as these papers are Part I and II of the same piece of work. The fact that this work is spread over two papers tells you that it's a long and winding saga, but it's cool stuff as it does something that can really advance science - take an idea from one area and use it somewhere else. The question the paper looks at sounds, on the face of it, rather simple. Imagine you you have a ball of stars, something like this, a globular cluster: You can see where the stars are. Imagine that you can also measure the s...

I am still playing catch up on papers, and I've just woken up early here in San Francisco and have a small amount of time before I have to prepare for my talk today. So, this will be quick. The topic again is our nearest largest companion, the Andromeda Galaxy, especially working out the history of how stars have formed in the (relatively) inner regions of the galaxy. It might seem a little strange that we can work that out, because all we can see is stars, but with the magic of science, it is possible. That's the topic of this new paper by postdoctoral researcher,  Edouard Bernard . This beautiful science is done with the Hubble Space Telescope. The first thing you need to do is decide where to look. So, here's the fields we looked at One of the sad things is that the area Hubble can image (its field of view) is tiny compared to the extent of Andromeda, and so we are doing key-hole surgery in select areas on interesting bits of Andromeda, especially prominent bits ...

Well, I don't know where that month vanished, but I now find myself sitting in the very nice  Swan's Hotel  in Victoria, Canada, after doing some nice new work with  Alan McConnachie  at the  Herzberg Institute of Astrophysics . The week has gone fast, and I've given two talks, and have four more to give in California next week. But I realised that I have neglected the blog, and there has been quite a few papers of mine put on the arxiv I should talk about. I have quite a bit of catching up to do, so here's a first post, and I will try and post some more over the next couple of weeks. A few weeks ago, I posted an article about the fact that we now have  the final catalog  of the globular clusters found in the PAndAS survey. This has been a major undertaking, seeing out these balls of a few million stars in the outer reaches of Andromeda. But it's been very successful, and we can now start to ask the question "what have we learnt?" This is the topi...

Back from an exhausting week in Canberra allocating grants for the Australian Research Council.  Handing out a few tens of millions of dollars really takes it our of you. The sad part is not the excellent projects we funded, but the many excellent projects we could not as we ran out of cash. Anyway, the meetings are confidential, so I can't discuss them here. But time to catch up on some of my own science. There is something super exciting coming, so here I'll focus on a merely excellent piece of work by globular cluster finder extraordinaire,   Avon Huxor  (excuse his ever so happy face!). I've written many times about the  Pan-Andromeda Archaeological Survey , our superb survey of our nearest neighbour, the  Andromeda Galaxy.  As well as identifying lots of substructure, the shredded remains of small galaxies, we also see lots of globular clusters, balls of roughly a million stars living together. The Milky Way has about a hundred of these orbiting i...

We've had a pretty cool paper accepted for publication in the Monthly Notices of the Royal Astronomical Society  which tackles a big question in astronomy, namely what is the temperature of  dark matter . Huh, you might say "temperature", what do you mean by "temperature"? I will explain. The paper is by Hareth Mahdi , a PhD student at the  Sydney Institute for Astronomy.  Hareth's expertise is in  gravitational lensing , using the huge amounts of mass in  galaxy clusters  to magnify the view of the distant Universe. Gravitational lenses are amongst the most beautiful things in all of astronomy. For example: Working out how strong the lensing effect is reveals the amount of mass in the cluster, showing that there is a lot of dark matter present. Hareth's focus is not "real" clusters, but clusters in "synthetic" universes, universes we generate inside supercomputers. The synthetic universes look as nice as the real ones; here...