Friday Galaxy - 2 - NGC 720

This is a real hot off the press Friday Galaxy, the data for this was only taken last night, in Chile, by those very helpful people at the Gemini-South telescope. I'm using the 12 images they took (4 each of g',r' and i', that's blue, green and red to you and me) to pick out Globular Clusters for spectroscopic follow up.

The image below shows the image produced, there are a couple of odd things about this image. The first is that the galaxy itself is very blue, for an elliptical galaxy this is odd, these are usually known as being red and dead, because they don't form stars. At first I thought I had mixed up the blue and red channels, however in the top left corner you can see a very pretty background edge on spiral and this appears to be just the right colour for a spiral, hmm.

If we assume that the colours are correct and that we are seeing a blue elliptical galaxy, then their are two possibilities: Either some fraction of the galaxy is made up of hot young blue stars, which can't have been formed more than a few Gyrs ago (not that common for ellipticals), or else the galaxy must be very old and lacking in metals. This is one of the major drawbacks of using the colours of astronomical objects like galaxies to tell you about them, there is a degeneracy between the age of stellar populations and the amount of elements heavier than Helium that they contain (their metallicity). Basically things can appear blue for one of two reasons, they are either young, or they have a low metallicity (and are old).



To solve this conundrum will require spectroscopy, which hopefully we will be getting in the next few months. One other interesting thing that appears in this image can be seen in the top left, when you look at the spiral galaxy (shown enlarged below) you can just about make out what appears to be a stream of material trailing to the bottom right. This trail, if real, could be a trail of stars produced by a minor merger event, if I get the chance and have the space when I make up the mask for the spectroscopy I may well try and get a sly spectrum of this just to see whats going on.


That just shows you one of the cool things about astronomy, serendipity means you can find all sorts of interesting things in the unlikliest of places. There are loads of interesting things in the background of deep images like this one, if anyone finds anything interesting in the large version of the image, let me know, you never know I may try and get a spectrum of anything you find that looks interesting enough.

New Blog - ThreeSigmaResult

Myself and CMB have decided to set-up a new blog, this one will be a bit more focussed dealing only with science, so no politics or random distractions. The blog can be found at threesigmaresult.com. The first real post will appear some time tomorrow.

My intention is that any science posts by me will get mirrored here, but if you want to see the full effect of CMB in full flow you'll have to head over to the new blog. Apart from this announcements things should continue as before over here.

Milky Way Behaving Badly

Head over to Space.comfor a story about the dark side of our well behaved galaxy's nature, its being throwing its weight around and generally being a bad neighbour. The story is all about the streams of stars that are being found trailing around the Milky Way, these trails are thought to be the shredded remains of dwarf galaxies or globular clusters that wandered too close to the MW. Below you can see some of the streams uncovered by the Sloan Digital Sky Survey. The streams are detected by looking at the colours and positions of a huge number of stars over as large an area as possible, doing this it is possible to pick out groups of stars with the same sort of colour, implying that they probably formed at the same time from the same material.


Some of the streams have been associated with known GCs or dwarf galaxies, basically these objects lie right in the middle of the stream, in the pictorial representation at the top you can see the original dwarf with its tails of stars which spread out both in front and behind it in its orbit of the MW. Over time the streams will stretch further and further, getting progressively thinner and more tangled, until they form a diffuse halo of stars around the MW.

This kind of research is interesting because the current theories for the formation of galaxies predict that there should be many more dwarf galaxies around the MW than we see at present, one solution is that many of them have simply been torn apart by the MW and their stars spread into the halo of the galaxy. If enough of these streams are found this could help solve this so called "missing satellite problem".

Science At The Bleeding Edge

Two new and very interesting press releases to do with Physics have just been released, both of which I'm sure will end up on the ADiots anti-science webpage.

The first is explained much better than I ever could over at the Cosmic Variance blog, the gist of the story is that the MiniBooNE experiment has found some interesting results to do with Neutrinos, they are possibly weirder than we thought, don't look to me for an explanation though.

The second is the first results from the Gravity Probe B, this orbiting satellite is designed to test for the effects of General Relativity as it streaks round the Earth. The results so far are a stunning verification of General Relativity to much higher accuracy than has been possible with this type of experiment before.


To anyone keeping score, that a 0 for 2 for the Autodynamics crowd.

Science of Ugliness

The BBC has an interesting story about a potential explanation to a paradox of evolution. The paradox to be put bluntly is that there are still ugly people around, if females select their mates on the basis of looks then over time evolution should favour the genes that give rise to better looking people. Eventually everyone should be beautiful. Some of that noisy band of idiots that try to refute evolution like to use this argue that evolution is false.

This "paradox" seems to me to be inherently wrong anyway, it makes the assumption that women have always been free to choose who they marry, which of course is blatantly not the case. It also of course neglects the impact of women choosing to marry for reasons other than looks, money being the obvious example.

Regardless of this, the researchers Professor Marion Petrie and Dr Gilbert Roberts of Newcastle University believe they have found a mechanism that explains why we are not all models.

The scientists claim that since genetic mutations can occur anywhere in the genome, some will affect the DNA repair kit possessed by all cells.

As a result, some individuals have less efficient repair kits, resulting in greater variation in their DNA as damage goes unrepaired.

This variation leads naturally to a variation in looks, it probably has other effects which are more beneficial to the population, like providing a wide range of mutations some of which could be useful in fending off disease for example. In other words it looks like there is a balance in a population between everyone looking good and having a wide enough variation in the population to be able to resist changes in the environment. Exactly as natural selection would predict.

Friday Lunchtime Talks - MOdified Gravity

On Friday we had the latest of the Durham Astronomy groups Friday Lunchtime Talks, these usually consist of two members of the group (which consists of over 50 members including students) giving a half hour talk, either about their own work or a paper that has appeared recently in which they have some interest. Last Fridays was something different however, it was an hour long talk by Professor Emeritus John Moffat of the Perimeter Institute on the subject of his own version of modified gravity, MOG.

I always have a lot of respect to someone that comes to Durham to talk about modified gravity, it really can be like entering the Lions den. Tinkering with gravity is usually done in an attempt to explain astrophysical phenomena without the need to demand that most of the mass in the Universe is invisible and can only be detected through its gravitational influence (the so called Dark Matter). Durham is world renowned as a centre of research into Dark Matter, as such some members of the group could be expected to be particularly partisan on the issue. I think its a great credit to the people involved that things never seem to get too heated, in fact in this Fridays talk, most of the difficult questions were directed from the one Professor in the group who has never been too happy with the current Cosmological Paradigm. He's generally good value for entertainment, and important in keeping everything honest.

Anyway, onto the talk itself. John Moffat has been working on modifying the gravitational laws for many years and has produced several different models. These models differ from most of the work on MOND (MOdified Netwonian Dynamics) in that from the beginning they were specifically chosen to be relativistic, that is that they are modifications to Einsteins General Relativity and not Newtons law of gravity. Essentially in MOdified Gravity (or if you prefer, MOffat Gravity, MOG) the gravitational constant G (also called Newtons Constant) is not in fact a constant, but can vary both in time and in space, so that the G that relates the force between two masses separated by one distance R1 is not the same G that relates the force between the same masses if they are separated by distance R2, similarly for time T1 and T2. These changes in G have to be negligible for objects within the solar system otherwise we should be able to detect deviations from the GR predictions which so far have not been observed, but they can become significant over galactic scales.

The speaker showed several examples of where his proposed changes would allow us to fit astronomical observations without the need to invoke Dark Matter. In particular he mentioned fitting the rotation curves of dwarf galaxies, spiral galaxies and clusters of galaxies (for clusters its technically not a rotation curve but the principle is the same). This in particular interested me as rotation curves are something I have personal experience with, both in my MSci project and the first paper I have published. Below is an example of a spiral galaxy rotation curve, it simply measures the speed at which stars at different radii in the disk orbit the galaxy, the data is the black circles (with error bars) the various dashed lines show the amount of velocity provided by the mass of various components of the galaxy including a DM halo. MOG allows you to explain the observed rotation of the galaxy without this DM component, by assuming the influence of the other two components is stronger than you would naively expect using Newtonian (or GR) gravity.

For me the first and largest problem that appeared during the talk appeared when JM was talking about these fits to the rotation curves. It seems it is possible using his model to fit all spiral galaxies using the same values for two parameters, as far as I could tell these parameters deal with the scale over which G begins to diverge from a constant value and some sort of normalisation of the size of the divergence. The problem was that when he fit the rotation curves of dwarf galaxies, or of clusters of galaxies the values of these two free parameters were different, all dwarfs had the same values, all clusters had the same values but different from the dwarfs or the spirals. This would appear to mean that there has to be yet another effect going on, meaning we need more free parameters to explain everything in terms of one unified gravitational theory. If this is true it would seem to be a problem. I have to go and look at the actual papers and see if in fact this is the case, or if I simply misunderstood something, it could be that the values he was quoting were actually telling you something about the scales involved, i.e that dwarf galaxies are smaller than spirals which are smaller than clusters.

The second major part of the talk dealt with JM's attempts to explain the results from the Bullet Cluster without the need for Dark Matter. This cluster is so far unique and very exiting. Its unique because it is actually two clusters, one of which has passed through the other, during this interaction the hot gas that resides in the clusters hit each other and slowed down, the gas from the smaller cluster having shocked and formed a bullet like shape as seen as the red triangle on the right of the image below. In the image below you can see the hot intracluster gas as the red regions. This is interesting because the hot intracluster gas has been separated from the galaxies of the clusters (seen in the blue regions), normally there is around 10x as much mass in this hot gas as there is in the galaxies of a cluster. By crashing through each other the two clusters have managed to separate the collisional material (the gas) from the collision less material (the galaxies and any Dark Matter).


It is possible to use gravitational lensing of background galaxies by the clusters of galaxies to work out the mass that must be contained within the galaxy clusters. This cluster is so important because it can be convincingly shown that even though the vast majority of the visible mass (the intracluster gas) has been removed the effect of gravity is still very strong, considerably stronger than can possibly be explained by the visible mass contained in the galaxies in the cluster. The traditional explanation is therefore that there must be some invisible mass (DM), which from this cluster we can see must be collision less, otherwise it would have piled up where the intracluster gas is. In MOG the explanation for the extra lensing, above what is predicted by GR for just the normal mass is that the gravity from the galaxies is stronger at larger distances, and also I believe that there is some lensing caused by the gravity from the intracluster gas.

If this is the case then there is happily a way to test which approach is correct, MOG or DM, the intracluster gas is much more massive than the mass contained in the luminous matter of the galaxies, but it is also located on one side of the cluster. Therefore it would seem that if MOG is correct there should be an increase in lensing on the side of the cluster nearest to the gas, of course the size of the effect would depend on many factors, but may in principle be measurable. If MOG is incorrect and DM is really at work, then the lensing should be more symmetric around the cluster, both because the DM is by far the largest mass contribution but also because the gravity of the gas is much less at larger distances than predicted by MOG.

Whatever the result of work such as this, we are really going to learn something fundamental about the Universe. Either most of the mass of the Universe is in some really exotic form, or else the force of gravity is even stranger than we have ever dreamt.

Unfortunately time caught up with us and we didn't get to find out much on the implications of this modified gravity on Cosmology, for example whether it could explain the mysterious Dark Energy at the same time that does away with Dark Matter. Many other interesting questions were raised however, it appears that MOG doesn't allow for singularities, so no black holes, though objects observationally indistinguishable from them probably can exist. This led one prominent member of the group to spend the time to see if the Metric for MOG is compatible with these condensed objects having a "last stable orbit", apparently it doesn't seem like it can, and as these are thought to be observed around BHs this is probably a problem for the theory.

All in all a very interesting talk, a perfect example of the kind of research that is ongoing in Astronomy. I don't think anyone is going to be packing in the DM work anytime soon, but if the DM particles continue to remain so illusive, its good to see that there are concrete alternatives being formulated.

South Pole Telescope

High time for some real science I think, the South Pole Telescope has just seen first light.

This telescope, located as the name suggests at the south pole is designed to look for small changes in the Cosmic Microwave Background (CMB) caused by the influence of clusters of galaxies. The south pole was chosen to site the telescope because the cold, dry (little moisture in the air) conditions are perfect for astronomy at the sub-millimeter wavelengths being used by this telescope.

The telescope will make use of an effect known as the Sunyaev-Zel'dovich effect to search for large clusters of galaxies. The SZ effect occurs when photons from the CMB interact with energetic electrons found in clusters of galaxies, some of the CMB photons are boosted in energy by the electrons through the Compton effect. By accurately measuring the CMB you can see regions where the CMB appears to be slightly hotter than it should be, these regions generally correlate with the position of clusters of galaxies. It should be noted that the CMB (see pic below) naturally has fluctuations in its temperature, these were the "seeds" that led to the formation of structure in the Universe after the Big Bang, so to determine which fluctuations in temperature are due to SZ and which are due to inherent fluctuations is actually slightly tricky. There are also other effects that need to be taken into account but you get the picture, its pretty hard.


By mapping the distribution of clusters it is possible to learn something about the elusive Dark Energy, particularly it may be possible to determine between the two competing explanations of Dark Energy, the Cosmological Constant and Quintessence.

Hubble Heritage

Click for VERY Big.

Thanks to the BadAstronomer I have found out about a cool new HST image from the Hubble Heritage site, what's even better is that two of the people that worked on the project to get the data work along the corridor, hence I am actually better informed than the BadAstronomer for the first time. The picture released by Hubble Heritage shows a cluster of Galaxies called Abell S0740. There are two versions of the image one without annotations and one showing zoomed regions of interest. See them both here.

This data is of particular interest because of what was found in the inner regions of the large elliptical galaxy at the centre of the cluster, when examined carefully it was discovered (by Russell Smith, here's the paper to prove it) that there were 3 gravitational arcs within the galaxy, you can see them in the inset in the top right of the image above. These arcs are the result of the light from a background galaxy being bent by the gravity of the large foreground elliptical galaxy, this has the effect of making several images of the same galaxy which are brighter and larger than they would usually be, making it possible to see galaxies further away. The gravitational arcs in this galaxy are the closest known example of strong lensing by an individual galaxy, as opposed to lensing by a cluster of galaxies.

The reason these lenses are so interesting is that when the position and brightness of the lenses are combined with the distance to the actual background galaxy (which can be worked out from its redshift) it becomes possible to measure precisely the amount of mass in the lensing galaxy within the radius of the arcs, with little or no assumptions. By looking at the way brightness of the lensing galaxy it is then possible (assuming that brightness is related to the amount of stars) to work out fraction of the mass in the lensing galaxy that is from normal matter and the fraction from dark matter. But wait that's not all.

By using the mass determined with the observed brightness of the lensing galaxy and the measured motion of stars in the galaxy (measured from spectroscopy) it becomes possible to work out exactly how the stars in the galaxy move as well, allowing a determination of parameters that can be used to constrain models of how galaxies form. Essentially these lenses could allow determinations of all the physical parameters of the lensing galaxy at accuracies previously unheard of.

Great you say, lets do it, but this is where things get difficult, it turns out that the arcs are so narrow that with current technology is actually impossible to get enough signal from them to determine a redshift, bugger. Basically they are so narrow that you add much more lensing galaxy light then you do lensed galaxy light. If STIS on the HST is ever repaired it may be possible, but if not it could be 10 years before its feasible. Note: if you happen to be someone sitting on a TAC (telescope allocation committee) and I, R. Smith or J. Lucey have a proposal to do what I've just claimed is impossible, I was wrong, we can do it, please give us the time.

Another thing I like about this work is shown in the other inset, a whole bunch of globular clusters. I study globulars, and when observing them from the ground it becomes very difficult to observe them at distances probably around 30-50Mpc away, these ones are located at 142Mpc, makes me even more annoyed that ACS has broken down, there will be no more new data like this for at least two years.

La Lune

I've recently come across another cool website, this one is a click-able map of the moon. You can find it at inconstantmoon.com what makes this site better than say, Google moon, is simply the huge amount of data at your finger tips. As well as the usual, click-able and zoom-able maps, with overlays of craters and Apollo landing sites there are things like the map above, which shows the amount of TiO2 in the moons surface, others show the thickness of the crust or the gravitational anomalies. Unfortunately no magnetic data yet, so its not possible to search for any magnetic anomalies, especially in the Tycho region (note for non sci-fi buffs read 2001).

To have a play around click on atlas, then just press buttons on the side bar to the right.

Mega Science

The UKs latest large piece of Scientific hardware is now up and working. The Diamond synchroton will be used to probe the nature of materials on the smallest scales, allowing new insights into how materials behave on the atomic level, as well as probing the structures of biological samples. Hopefully leading to better smart materials and new pharmaceuticals. The BBC has a reasonably good story covering the main talking points over here.

A synchrotron works by accelerating electrons to near the speed of light, confining them with magnetic fields they are forced around and around a circular ring. As they travel round the synchrotron the electrons emit electro-magnetic radiation in the X-ray and gamma ray region of the spectrum. At speeds close to the speed of light strange things begin to happen, one of which is that the light emitted is affected by Special Relativity and is boosted in wavelength by relativistic effects, another is that the radiation pattern becomes highly collimated. Because of these two effects synchrotrons are the brightest known sources of X-rays. Just another real life example of how an abstract physical concept has real world application.

Oh and in case your wondering (in light of many recent posts), no, Autodynamics cannot explain the light given off by a synchrotron, in fact it can't even match the observed motion of electrons around the synchrotron, oops.

Cool Sky Map

I came across this cool bit of astronomy software the other day. There seems to be two versions about sky-map.org and wikisky.org. They seem to be identical. They allow you to slide around the night sky with or without constellations and to search for your favourite night sky objects (like NGC galaxies), so far, so like any other planetarium software. The cool thing with this software is that it also has the SDSS imaging survey built in. So you can switch to SDSS mode and look at the actual images produced by the Sloan survey. Unfortunately the SDSS doesn't cover the whole sky so many of my favourites aren't in it.

This is really only the start, we have been talking about software like this at work for awhile now, the ultimate (wet) dream for astronomers would be software like this that started in planetarium view but over layed survey areas from the various surveys, or even little symbols to show where the HST had been pointed at an object (The first steps have been made to do this in the Astro Photo section, check it out). You would then be able to click on the little links to take you directly to the data, it would make life much simpler than searching dozens of archives to find out if what you would like to do has already been done, saving time and money for eveyone, plus it would make a great toy for everyone to enjoy.

Give it a go, there's probably plenty of weird things to be seen in the SDSS images.