[揽瓜阁精读] 250. Dark Matter

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250 Dark Matter
a cloud of dark matter been detected expanding like a smoke ring
DM don’t emit, absorb or reflect light. Reveal itself by the way gravity affects normal matter around it.
Discover DM from cosmic clash involving 2 clusters.
MJJ: detect the ring in HST 有地球到Pisces constellation（星座）5 b 光年那么远的距离.how cluster matter bends the light path. “gravitational lensing”
CC: ring-like structure found and been believed made of DM, because no visible matter concentration. Cluster ordinary matter thought to be hot gas form, mapped by CXO
CI0024+17 not a single galaxy cluster but pair clusters collided（碰撞）. simulations（模拟）show when collide, cluster’s DM explodes outwards and form a spherical shell.
Collision happened st 1&2 b years ago.
Modified gravity
The modifications of Newton’s law=evidence of dark matter(anomalies cited). but this possibility can be hardly to rule out because DM and Om are so well mixed
CI 0024 separate from any concentrations OM so it is difficult to explain without DM. Strongest DM existence evidence
Previous study revealed DM&OM separation but CI0024 is more complete
MB:if DM ring real , lb study properties（性质，特质）of DM
Instrumental effects
Because of ring’s characteristics. Gravitational lensing used for study is subtle an easy be confused by slight distortions arose by imperfect instruments
Team do careful analysis but be sceptical
Exotic particles
Ring were not an instrumental effect. DM do not interact strongly with one another. Because of the candidates A&N of DM. “mirror matter”(already interacts with itself) would collide more. If there is interaction between DM and particles, it can smear out(make, cause)shell-like structure

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