突出的弹头表明暗物质的拉力
Protruding bullet heads indicating dark matter pull
摘要：
一个团块在星系团的团内介质中运动时，会产生一个弓形激波，后面跟着一个子弹状的核心。在某些情况下，例如在原型子弹集群中，X射线显示一个具有突出头部和突出肩部的气体子弹。我们指出，这些功能，虽然很难解释没有暗物质（DM），自然出现的头部的减速气体是引力向前拉向其不受阻碍的DM对应。因此，即使没有引力透镜或其他辅助数据，X射线成像也提供了偏移、无碰撞DM的独特的、鲁棒的探测。数值模拟和一个玩具模型表明，这种效应在主要的合并中很常见，通常与小的子弹头曲率半径有关，并可能导致不同的子弹形态，与观察结果一致。
英文摘要：
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.
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