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Justin Read Profile picture
Justin Read
@ReadDark
Head of physics at the University of Surrey. Astrophysicist interested in modelling, dynamics, and the hunt for dark matter. All opinions are my own.
Jan 16, 2019 • 13 tweets • 7 min read
The "ultra-diffuse" dwarf NGC 1052-DF2 is back in the news with two new papers better-measuring the kinematics of its stars and GCs:

arxiv.org/pdf/1901.03711…
adsabs.harvard.edu/abs/2018arXiv1…

I couldn't help but notice how similar DF2 is to the nearby Sagittarius dwarf

[A thread; 1/N] The Sagittarius dwarf (Sag) is a nearby galaxy, first discovered by Ibata et al. in 1995, that we know is currently being torn apart by tidal forces from the Milky Way.

adsabs.harvard.edu/abs/1995MNRAS.…
adsabs.harvard.edu/abs/1997AJ....…

[2/N]
Oct 19, 2018 • 13 tweets • 6 min read
There is a growing consensus in the astro simulation community that, once we begin to resolve the interstellar medium (ISM), gas cooling and heating causes gravitational potential fluctuations that kinematically "heat up" dark matter [a thread 1/N] If we can get the gravitational potential to fluctuate "significantly" on a timescale comparable to the local dynamical time, then dark matter (DM) is "heated up":

adsabs.harvard.edu/abs/1996MNRAS.…
adsabs.harvard.edu/abs/2005MNRAS.…
adsabs.harvard.edu/abs/2012MNRAS.…
adsabs.harvard.edu/abs/2014Natur.…

[2/N]
Aug 22, 2018 • 18 tweets • 5 min read
We have found observational evidence that dark matter is “heated up” at the centres of dwarf galaxies:

arxiv.org/abs/1808.06634…

This solves the long-standing “cusp-core” problem in LCDM, and suggests that dark matter is a cold, collisionless, fluid.

[A thread] I gave a ~20 minutes talk at KITP about this paper which you can watch here:

online.kitp.ucsb.edu/online/cdm-c18…

For a Twitter summary of the results, please read on ... [1/N]
Jun 15, 2018 • 10 tweets • 2 min read
This recent press release on some of the latest galaxy formation simulations has reignited an old debate about dark matter versus modified theories of gravity. Sadly, many commentators seem to be missing the point. (A thread, 1/N.)

quantamagazine.org/coder-physicis… In mod. grav. theories, all the force comes from the visible stars & gas. Given good observations, we can accurately predict the gravitational force field without knowing the first thing about how galaxies form. Such theories are easy to test in disc galaxies & work well. (2/N.)