Cosmic Horizons

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...

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...

Time for another PAndAS papers (and yes, there are more to come!), but this one is from me :) As you know, the Pan-Andromeda Archaeological Survey (PAndAS) is a big program we've been doing on the  Canada-France-Hawaii Telescope , mapping out the locations of all the stars in the halo of Andromeda (M31) and Triangulum (M33) galaxies. It's taken a lot of work, but with all the data now in, it's time to squeeze out the science. There is actually a bit of a hurry about this, as in the next year, we are making all of the data public, and even you can write PAndAS papers. What's this current paper about? Well, let's start with the first picture in the paper. So, the dense bits are M31 in the topish-right, and M33 in the bottom-left. The grey-scale is the density of stars in the map, and the regions outlined are the various bits of substructure orbiting around. Basically, there is a lot of stuff there, lots of streams, chunks, bits and pieces. Clearly, there has ...

Sunday morning. I've got a busy week coming up, having to head to Canberra tomorrow for my induction into the  Australian Research Council (ARC) College , then a few board of examiners meetings, the allocation of supercomputer time, and then Christmas drinkies on the Botany Lawn. So a quick post on  peer review. There has been an awful lot written on this, and I will focus on academic peer review, especially when it comes to publications. I read  this  interesting article on peer review, which points out that the press does not seem to understand the difference between a published article, and things written in popular science magazines, on blogs, or simply chatted about down the pub. But before I start, let me remind you how a paper gets published in a journal.  It starts by you having your idea, doing your work, and deciding that the results are significant enough to be interesting to everyone else.  You need to decide where you ar...

I have been swamped recently, not only at work (I am teaching electromagnetism to first year students) but also at home where we are renovating (and I am not too geeky enough to wield a sledge hammer). So, apologies for the sparse posting. The renovating is slowly approaching its conclusions (although we have lived almost a month with no doors inside the house), and research is trundling, so I will try and get back on top of posting. I should have posted this a little while ago, but the first paper in a new survey of the Galactic Centre was accepted for publication. The ARGOS project, as it is known, was originally intended to be a large scale international survey of a large chunk of sky, but we were not awarded time for that, and now it is a program focused upon the Galactic Bulge. It might seem strange, but while we can plainly see the centre of the Galaxy from here in Australia, there is a lot we don't know about it. It was only in the last 10-20 years we have come to...

Well, this caps of a busy, but successful week, but Pim van Oirschot (PhD student in the Netherlands, was my MSc student here in Australia a couple of years ago) and I just had a paper accepted for publication. It's called  "How does the Hubble Sphere limit our view of the Universe?" and is basically a response to some other papers published over the last years. Let's start with the basics, as in what is the Hubble Sphere? For gory details, I recommend the classic paper by  Ed Harrison , but simply put, the Hubble Sphere is the distance from us which objects are moving (relative to us) at the speed of light. We know the Universe is expanding, and that expansion is measured in terms of the  Hubble Constant , which is about 72 km/s/Mpc. What this means is objects 1Mpc away are moving away from us at 72km/s, those at 10Mpc are moving at 720km/s, 100Mpc at  7200km/s etc etc. So, if you go far enough, objects will be traveling at the speed of light, and then even fur...

I am slowly recovering from the recent round of grant writing. The internal deadline for our Australian Research Council (ARC) Discovery Projects (DPs) was on Monday, and, as ever, it was late nights and early mornings to put together the 115 pages of science case, budgets, budget justifications, publication records, career histories etc etc etc. Now all I have to do is sit back until July (when the referees' reports come in) and then to November (when the results are announced). If I get my grant, I'll write and say how great the systems is. However, if I am the three in four who will not get funded, I'll have a rant. Anyway, even though the days have been lost to grant writing, science has advanced, and we recently had a paper accepted for publication in MNRAS, using the Hubble Space Telescope to look at clusters around our nearest big galactic neighbour, Andromeda. Many objects are globular clusters, just like the ones we orbiting our own Milky Way. With Hubble Spac...

You wait for a bus, and then two come along at once. Postdoctoral researcher, Edouard J. Bernard , working with Annette Ferguson at Edinburgh's Institute for Astronomy , and myself, has had his paper on the star formation history in a couple of fields observed with the Hubble Space Telescope. Before continuing, I want to say that the IfA has the best, thickest custard in the entire world! The focus of the paper is deep Hubble Space Telescope fields in the outer parts of the Andromeda galaxy. The absolutely wonderful thing about Hubble is that being above the atmosphere, we can accurately measure the brightness of faint stars, but the annoying thing about Hubble is that the field o view is tiny. Here's the fields we got The grey area is the sky that we've observed as part of the PAndAS program with Canada-France-Hawaii Telescope , whereas the tiny squares are the bit covered by Hubble; all telescope time is quite competitive, but getting lots of Hubble time is diff...