Archive for clusters of galaxies

Is the Expansion of the Universe Isotropic?

Posted in Astrohype, The Universe and Stuff with tags , , , , , on April 9, 2020 by telescoper

There’s a new paper out that has been making a few waves in cosmology. Here’s the title and abstract:

It’s published in Astronomy & Astrophysics but you can find it on the arXiv here.

Here’s a gratuitous pretty picture showing the distribution of the X-ray clusters used in the analysis.

The discussion in the paper focuses on two possibilities: (i) that the clusters are participating in a large-scale correlated motion; and (ii) that the Expansion of the Universe is not occurring isotropically. The latter option is the one that has attracted the most media attention (presumably because it has the most far-reaching implications). This seems to me to be a very unlikely explanation, however, because anisotropic expansion of the magnitude implied would leave a ~10% signal in the Cosmic Microwave Background which is not observed.

There is, however, a third possibility (admittedly duller than the other two) which is that there is some unknown systematic error in the observations…

SDSS-III and the Cosmic Web

Posted in The Universe and Stuff with tags , , , , , on January 12, 2011 by telescoper

It’s typical, isn’t it? You wait weeks for an interesting astronomical result to blog about and then two come along together…

Another international conference I’m not at is the 217th Meeting of the American Astronomical Society in the fine city of Seattle, which yesterday saw the release of some wonderful things produced by SDSS-III, the third incarnation of the Sloan Digital Sky Survey. There’s a nice article about it in the Guardian, followed by the usual bizarre selection of comments from the public.

I particularly liked the following picture of the cosmic web of galaxies, clusters and filaments that pervades the Universe on scales of hundreds of millions of lightyears, although it looks to me like a poor quality imitation of a Jackson Pollock action painting:

The above image contains about 500 million galaxies, which represents an enormous advance in the quest to map the local structure of the Universe in as much detail as possible. It will also improve still further the precision with which cosmologists can analyse the statistical properties of the pattern of galaxy clustering.

The above represents only a part (about one third) of the overall survey; the following graphic shows how much of the sky has been mapped. It also represents only the imaging data, not the spectroscopic information and other information which is needed to analyse the galaxy distribution in full detail.

There’s also a short video zooming out from one galaxy to the whole Shebang.

The universe is a big place.


First Science from Planck

Posted in The Universe and Stuff with tags , , , , , , , , , on January 11, 2011 by telescoper

It’s been quite a long wait for results to emerge from the Planck satellite, which was launched in May 2009, but today the first science results have at last been released. These aren’t to do with the cosmological aspects of the mission – those will have to wait another two years – but things we cosmologists tend to think of as “foregrounds”, although they are of great astrophysical interest in themselves.

For an overview, with lots of pretty pictures,  see the European Space Agency’s Planck site and the UK Planck outreach site; you can also watch this morning’s press briefing in full here.

A repository of all 25 science papers can be found here and there’ll no doubt be a deluge of them on the arXiv tomorrow.

A few of my Cardiff colleagues are currently in Paris living it up at the junket working hard at the serious scientific conference at which these results are being discussed. I, on the other hand, not being one of the in-crowd, am back here in Cardiff, only have a short window in between meetings, project vivas and postgraduate lectures  to comment on the new data. I’m also sure there’ll be a huge amount of interest in the professional media and in the blogosphere for some time to come. I’ll therefore just mention a couple of things that struck me immediately as I went quickly through the papers while I was eating my sandwich; the following was cobbled together from the associated ESA press release.

The first concerns the so-called  ‘anomalous microwave emission’ (aka Foreground X) , which is a diffuse glow most strongly associated with the dense, dusty regions of our Galaxy. Its origin has been a puzzle for decades, but data collected by Planck seem to confirm the theory that it comes from rapidly spinning dust grains. Identifying the source of this emission will help Planck scientists remove foreground contamination which much greater precision, enabling them to construct much cleaner maps of the cosmic microwave background and thus, among other things, perhaps clarify the nature of the various apparent anomalies present in current cosmological data sets.

Here’s a nice composite image of a region of anomalous emission, alongside individual maps derived from low-frequency radio observations as well as two of the Planck channels (left).

Credits: ESA/Planck Collaboration

The colour composite of the Rho Ophiuchus molecular cloud highlights the correlation between the anomalous microwave emission, most likely due to miniature spinning dust grains observed at 30 GHz (shown here in red), and the thermal dust emission, observed at 857 GHz (shown here in green). The complex structure of knots and filaments, visible in this cloud of gas and dust, represents striking evidence for the ongoing processes of star formation. The composite image (right) is based on three individual maps (left) taken at 0.4 GHz from Haslam et al. (1982) and at 30 GHz and 857 GHz by Planck, respectively. The size of the image is about 5 degrees on a side, which is about 10 times the apparent diameter of the full Moon.

The second of the many other exciting results presented today that I wanted to mention is a release of new data on clusters of galaxies – the largest structures in the Universe, each containing hundreds or even thousands of galaxies. Owing to the Sunyaev-Zel’dovich Effect these show up in the Planck data as compact regions of lower temperature in the cosmic microwave background. By surveying the whole sky, Planck stands the best chance of finding the most massive examples of these clusters. They are rare and their number is a sensitive probe of the kind of Universe we live in, how fast it is expanding, and how much matter it contains.

Credits: ESA/Planck Collaboration; XMM-Newton image: ESA

This image shows one of the newly discovered superclusters of galaxies, PLCK G214.6+37.0, detected by Planck and confirmed by XMM-Newton. This is the first supercluster to be discovered through its Sunyaev-Zel’dovich effect. The effect is the name for the cluster’s silhouette against the cosmic microwave background radiation. Combined with other observations, the Sunyaev-Zel’dovich effect allows astronomers to measure properties such as the temperature and density of the cluster’s hot gas where the galaxies are embedded. The right panel shows the X-ray image of the supercluster obtained with XMM-Newton, which reveals that three galaxy clusters comprise this supercluster. The bright orange blob in the left panel shows the Sunyaev-Zel’dovich image of the supercluster, obtained by Planck. The X-ray contours are also superimposed on the Planck image.

UPDATES: For other early perspectives on the early release results, see the blogs of Andrew Jaffe and Stuart Lowe; as usual, Jonathan Amos has done a very quick and well-written news piece for the BBC.