I’ve just got back from a tiring but enjoyable few days in Leiden, attending my first ever Virgo consortium meeting. Virgo was founded in the UK in 1994, but is now an international collaboration of scientists working on cosmological simulations. One of the founding members is now my primary supervisor, Peter Thomas.

A couple of other founding members were in attendance, two of which could be considered celebrities in the astrophysics community due to a mathematical profile they formalised that bears their name. Carlos Frenk and Simon White, working with Julio Navarro, penned the Navarro-Frenk-White (NFW) profile in the mid 90s, and it has since gone on to become a standard for describing the density distribution of dark matter in cosmological halos. The paper that introduced it has gone on to garner nearly 4000 citations, according to ADS.

Citation history for 'The Structure of Cold Dark Matter Halos', Navarro et al.

We can’t detect dark matter directly, so its presence must be inferred from its gravitational influence on baryonic matter. Inferring the exact distribution of dark matter in clusters of galaxies purely from the baryonic matter is challenging. The NFW profile was instead motivated and tuned to evidence from simulations of collisionless dark matter.

They argue that there is a ‘universal’ profile for dark matter halos that spans four orders of magnitude of halo mass, from galaxy halos to entire clusters. This assertion is still contentious; other authors either find different forms of the profile, or that it varies with environment.

The profile is also in tension with observations; the NFW profile suggests a central ‘cusp’ to the dark matter distribution, whereas observations suggest that dark matter haloes have shallower cores. This became known as the Cusp-Core controversy, and is still unresolved today.

At the end of the meeting we discussed some interesting projects, some of which I’m hoping to get involved in from the new year; will keep you posted, all 3 of you dear readers.