Dark Matter Fisticuffs I: The Backdrop

The large scale structure of the Universe, as predicted in the Millennium simulations (V. Springel)

ResearchBlogging.orgOn Thursday, two giants of astronomy met in the sleepy German city of Bonn to debate one of the basic tenets of our current cosmological vision: the existence of dark matter. In the blue corner was Simon White aka. the Reigning Champion, Director at the Max Planck Insitute for Astrophysics (MPA) in Garching, and figurehead of the concordance cosmology model we all know and live by. In the red corner, Pavel Kroupa aka. the Challenger, Professor at the Argelander Institute in Bonn and well-known expert on stellar populations and dynamics.

Astronomers in Bonn live-blogged the event, and have given me permission to re-post their words on here – see Part II. But I thought I’d get you up to speed first.

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Puffing up elliptical galaxies


Elliptical galaxies are the boring uncles of the galaxy family: they’re amorphous blobby things, ubiquitous in the Universe, that contain a fairly uniform population of old, red stars. Without the interstellar gas and dust that is needed to harbour pretty sites of star formation, they are supremely unphotogenic. But they have far more going on beneath their featureless surface: the complex dynamics inside many ellipticals show evidence of a turbulent past and, with many of the most massive known galaxies in our local Universe being ellipticals, they clearly play an important role in galaxies’ evolution.


Studies seem to suggest that high-redshift elliptical galaxies are more compact than their present-day counterparts (figure from Glazebrook, 2009)

Observational surveys of elliptical galaxies at high redshift have in recent years revealed a further interesting fact: ellipticals at high redshift appear to be much smaller in size than those in our local Universe, but have about the same mass and density of stars. In a recent ApJ paper, Ivana Damjanov of the University of Toronto and collaborators describe how a sample of elliptical galaxies at redshifts 1 to 2 looked 2-3 times smaller than those in the local Universe. The first surprise lies in that they evolve at all between redshift 2 and 0. In our current understanding of galaxy formation and evolution, ellipticals are the “red and dead” endpoints of evolution.

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More dark chatter

While Mars and exoplanets stole most of the science headlines in 2008, papers reporting results from a number of cosmic ray detectors gathered a lot of attention in the (astro-)physics community. Excesses in the number of particles detected at high energies (~50 GeV) that could not be explained by theoretical predictions sparked speculations that cosmic ray satellite PAMELA may be picking up the signature of dark matter in the Galaxy. A commonly accepted scenario for the nature of dark matter are the so-called WIMPs, or weakly interacting massive particles, which don’t interact in “regular” processes but may annihilate each other to produce high energy cosmic radiation. A number of cosmic ray and gamma ray detectors have produced intriguing results, leaving scientists with an intricate puzzle of information to assemble into a coherent picture.

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An Early Universe 101

I’ve been learning a bit recently about dark matter, dark energy and the history of the Universe, which are all fascinating. Mark over on Cosmic Variance has writted this interesting post on preheating in the early Universe. This proposed phenomenon has important consequences for the formation theory of dark matter, amongst other things.

While I’m on the topic, one of the best books I read this year was The Inflationary Universe by Alan Guth. I admit I don’t read as many popular science books as I should, and I finish even fewer – but this one is a cracker. Guth builds an excellent story about how he arrived at the theory, in collaboration and in conflict with other scientists around the world. It’s a fascinating account of a great scientific discovery, told in such an anecdotal style that it’s super easy to read. It’s completely rekindled my interest in fundamental physics and cosmology, which explains some recent posts (here, or here) on the topic :-)

More cosmic ray excesses reported

The Milagro cosmic ray detector

The Milagro cosmic ray detector

In a busy week for cosmic ray science, yet another paper reports the detection of excesses in cosmic ray detections from galactic sources. Using 7 years of data from the Milagro detector, scientists of the University of Maryland and Los Alamos National Laboratory have found two hotspots of high-energy cosmic radiation.

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