HST measures Draco dwarf galaxy over 18 years in DM study

[pinball1970]

TL;DR

Computer simulations suggest dark matter should be in a galaxy's center, a density cusp, many previous telescopic observations have indicated that it is instead more evenly dispersed throughout a galaxy. The results are consistent with the inner cusp predicted in ΛCDM cosmology and lessen the tension around the "cusp–core" problem and give further credence to standard ΛCDM cosmology.

The paper here.

https://iopscience.iop.org/article/10.3847/1538-4357/ad571c

From the conclusions.

"The measured slope is in good agreement with ΛCDM predictions, 49 given that our measurements fall well within the break radius of the DM density profile predicted by cosmological simulations. Our best likelihood results corroborate the idea that DM is formed by some sort of cold particle. An asymptotic core is marginally inconsistent with the data at 89.5% confidence, when marginalized over all other quantities, arguing against modified DM scenarios such as warm DM or SIDM. Nonetheless, a small asymptotic core cannot be effectively ruled out."

From the abstract.

"Our results provide a new stringent test of the so-called "cusp–core" problem that can be readily extended to other dwarfs."

 

[ohwilleke]

TL;DR Summary: Computer simulations suggest dark matter should be in a galaxy's center, a density cusp, many previous telescopic observations have indicated that it is instead more evenly dispersed throughout a galaxy. The results are consistent with the inner cusp predicted in ΛCDM cosmology and lessen the tension around the "cusp–core" problem and give further credence to standard ΛCDM cosmology.

The paper here.

https://iopscience.iop.org/article/10.3847/1538-4357/ad571c

From the conclusions.

"The measured slope is in good agreement with ΛCDM predictions, 49 given that our measurements fall well within the break radius of the DM density profile predicted by cosmological simulations. Our best likelihood results corroborate the idea that DM is formed by some sort of cold particle. An asymptotic core is marginally inconsistent with the data at 89.5% confidence, when marginalized over all other quantities, arguing against modified DM scenarios such as warm DM or SIDM. Nonetheless, a small asymptotic core cannot be effectively ruled out."

From the abstract.

"Our results provide a new stringent test of the so-called "cusp–core" problem that can be readily extended to other dwarfs."

The biggest issue in the big picture with this result is that most galaxies that have been observed do not have cuspy cores, while ΛCDM predicts that almost all of them do.

Solutions to this problem for most dark matter candidates, like "feedback" aren't sufficient to solve the problem, although a very low mass dark matter candidate with a large effective wave-length, or some kinds of self-interacting dark matter candidates could.

Even if Draco does have a cuspy core (and this study makes a good case that it does), that doesn't solve the larger problem for ΛCDM. Indeed, Draco is also potentially a problem since any solution that gives most galaxies a non-cuspy core in ΛCDM also has to not apply some subset of dwarf galaxies that have something in common with Draco.