How dense are the densest dark matter haloes?

Chiamaka Okoli

Congratulations to my PhD student, Chiamaka Okoli, on her first paper being accepted for publication in Monthly Notice of Royal Astronomical Society.

Chiamaka has shown that you can use the simple idea of energy conservation, combined with knowing when an ellipsoid collapses, to predict how dense (and hot) a dark matter halo will be when it forms.  Previously, people had to rely on numerical simulations, and ad hoc extrapolations and fitting functions, which often led to contradictory conclusions for the densest dark matter haloes. However, her method is more robust, easy to use, and elegant (and I am in no way biased 🙂 ) ! You can also apply it to any cosmology or initial conditions.

Read more here. 


Concentration of dark matter haloes, across 20 orders of magnitude in mass



Mann Fest: Happy Birthday Robb Mann!!


This weekend at Mann Fest, we celebrated the contributions of our colleague Robb Mann, on the occasion of his 60th birthday. Robb is very prolific, both in producing innovative scientific research, but also in training excellent undergraduate and graduate students. I met several of them during Mann Fest, who have now scattered across the globe, many as successful professors, and are engaged in diverse and exciting research. Not surprisingly, Robb is also an extraordinary lecturer.

You can find my talk at Mann Fest here. 


How aether censors singularities (and the most beautiful penrose diagrams you’ll ever see)

Einstein’s General theory of Relativity predicts the occasions of its own demise. These are known as spacetime singularities, where Einstein’s equations fail to predict the future. However, in most typical situations, we have found that the singularities lie behind event horizons of black holes. Since nothing moves faster than speed of light in Relativity, and light cannot escape event horizons, then it appears that most common singularities are invisible to us. Penrose promoted this observation to the Cosmic Censorship conjecture, proposing that singularities are generically censored by event horizons, to outside observers.

But what if something can travel faster (even infinitely faster) than speed of light? Would that render singularities naked and exposed?! My students Mike Meiers and Mehdi Saravani have just posted a paper on arXiv showing that even if gravity has an incompressible aether (with infinitely fast signals), it can still manage to censor its own singularities in collapsing charged and spinning black holes.

Also, congratulations to Mike on his first paper (and Mehdi for his 9th!), and the most beautiful Penrose diagrams that I have ever seen 🙂 (The red regions are censored by aether).

Read more here.