Cosmic Horizons

A very quick rant about some bad physics that has been annoying me. The tension between North Korea and the rest of the world is not a laughing matter, but has been all over the news recently. But when reporting, we often hear the that North Koreans are on the verge of producing a missile capable of carrying a nuclear warhead. But not only a missile! A ballistic missile . Maybe I am reading too much into it, but when a reporter says ballistic, it's often said as if it is synonymous with evil! I'm sure that it's because we like to say something is "going ballistic" when something crazy happens. But all ballistic means is that the missile is unpowered (after launch) and is moving only under the power of gravity. That's it. There are powered missiles. Modern anti-tank missiles are usually powered and guided onto target. Here's one - Here is a ballistic missile. See - not so scary!

Another week gone, and no time for too much deep thinking (although progress is being made, so hopefully will have some interesting things to report). Luckily, the smart students out there are squirreling away, and so today I can present the latest in the study of the galactic bulge by ANU student Melissa Ness . I've written before about this really cool study, using the AAOmega Spectrograph  on the might Anglo-Australian Telescope  to measure the speeds and chemical make-up of stars in the Galactic Bulge , the centre of our Milky Way galaxy. This is hard work, as there are a lot of stars spread over a large amount of sky, and so to get lots of spectra, you need to use the multi-fibres and large field of view of AAOmega. This has been a mammoth task over the last few years, with us taking 28,000 spectra, and in this study almost 17,5000 stellar velocities were used. But what is it we want to know? Well, the present day shape, velocities and chemistry of the Milky Way is...

A weekend at home with the kids, with yesterday being wiped out by huge downpours from sunrise to sunset. Unfortunately, work has been full on, with a thousand different things going on, so no time to muck around. But we have another paper accepted, so here's a little summary. This week's paper is by PhD student,  Jovan Veljanoski , working at Edinburgh's  Institute for Astronomy . This is another paper based upon our extensive Pan-Andromeda Archaeological Survey (PAndAS) of Andromeda. As I've noted before, this survey reveals a mass of substructure in the outskirts of Andromeda, as well as a growing population of  dwarf galaxies.  It also reveals lots of  globular clusters , balls of a million or so stars orbiting Andromeda. The key thing in this study is the velocities of the globular clusters. Why? Well, their velocity depends upon the mass they are orbiting, so if you get lot of velocities, then you can measure the mass. But, of course, it is never as si...

An astro-ph post today. I've written previously about some papers that I've published looking at a "new" cosmological model, which is claimed to be superior to the currently favoured model, the ΛCDM  cosmology. This model, known as the R h = ct universe, is supposedly simpler, but in truth, it is not. And what's more, it is not a good description of the Universe we observe. If you're interested, you can read about it  here. So, what's in my new paper. I take a look at a couple of claimed successes of the R h  = ct universe, namely that it explains the birth of quasars and does away with inflation. The crux of my argument is that the presence of matter in the universe actually destroys the claimed successes of this cosmology. What I did is consider four cosmological models, the standard ΛCDM, with a present day matter density of 27% of the total, and a dark energy component making up the rest. The important thing is that the dark energy has an  equatio...

Easter is here, and so a little weekend's diversion. I thought I would have a little fun with Planck maps of the CMB sky we looked at previously. As a reminder, here's what Planck saw and what the blue and red spots indicate are structures in the Universe when it was only 400,000 years old. Also remember that we describe these bumps and wiggles by the  power spectrum  which tells us how many blobs of particular sizes we should see in the image. Our theories tell us the power spectrum, but not the location of each individual blob in the image. As I mentioned last time, we describe the structure we see in terms of  spherical harmon ics, which are particularly useful functions to use on a sphere, and the power spectrum basically tells us how much of a particular function we need to add in to get the map above. But we have a freedom, called the "phase" of the spherical harmonics. Basically, while the power spectrum tells you much of a function you need to add, it...

I've been away for a few days at the Synthetic Universes for Future Survey  at the University of Western Australia (phew - Perth is a long way away!). It was an excellent meeting, presenting just what we need to do with regards to making synthetic universes so we can understand what is going on in our own. As well as coinciding with the  equinox , we also watched the press conference covering the latest results  from the  Planck Satellite . While this was a spectacular success, it also was a bit of a disappointment. You might wonder how this can be. Let me explain. The  Cosmic Microwave Background (CMB)  was discovered in 1964, and it was realised that this was the ever-cooling radiation left over from the Big Bang. I have to show ab obligatory history of the universe to explain how it has trundled through the universe. You can think that the CMB was born at the end of inflation, and for a few hundreds of thousands of years the universe was a plasma ...

Argh!! Another couple of weeks have flown by like a huge fast flying thing! So fast, I almost missed my birthday (which I share with  another random person ). And the pressure ain't off, so a quick post. This time, a great paper by  Michelle Collins . As you will have guessed by now, we've been doing a lot of work on the dwarf galaxy population that orbits around our nearest large cosmological neighbour, namely the  Andromeda Galaxy. We, and other groups, have been measuring lots of properties of these dwarfs, including their positions and distances. Over the last few years, we've also managed to get the spectra of many stars in the dwarfs which, for one thing, allows us to measure the velocities of stars (via the famous  Doppler effect ). Michelle's paper focuses upon the velocities found in 18 of the 28 dwarfs we know live near Andromeda, and basically tries to find out lots of the nature of the dwarf population - such as are they all the same, or different,...