Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Protruding bullet heads indicating dark matter pull   A clump moving through the intracluster medium of a galaxy cluster can drive
a bow shock trailed by a bullet-like core. In some cases, such as in the
prototypical Bullet cluster, X-rays show a gas bullet with a protruding head
and pronounced shoulders. We point out that these features, while difficult to
explain without dark matter (DM), naturally arise as the head of the
slowed-down gas is gravitationally pulled forward toward its unhindered DM
counterpart. X-ray imaging thus provides a unique, robust probe of the offset,
collisionless DM, even without gravitational lensing or other auxiliary data.
Numerical simulations and a toy model suggest that the effect is common in
major mergers, is often associated with a small bullet-head radius of
curvature, and may lead to distinct bullet morphologies, consistent with
observations.

29
The categories of this paper are: funct-an
8
The categories of this paper are: hep-ex
10
The categories of this paper are: q-bio
11
The categories of this paper are: hep-lat
26
The categories of this paper are: bayes-an
5
The categories of this paper are: gr-qc
25
The categories of this paper are: patt-sol
36
The categories of this paper are: cmp-lg
33
The categories of this paper are: plasm-ph
16
The categories of this paper are: stat
2
The categories of this paper are: math
30
The categories of this paper are: q-alg
34
The categories of this paper are: chem-ph
0
The categories of this paper are: hep-ph
28
The categories of this paper are: alg-geom
12
The categories of this paper are: nucl-th