ASTR 001 Lecture Notes - Lecture 19: Baryon, Dark Matter, Weakly Interacting Massive Particles
Document Summary
The mass we find from galaxy motions in a cluster is about 50 times larger than the mass in stars! Our options: dark matter really exists, and we are observing the effects of its gravitational attraction, something is wrong with our understanding of gravity, causing us to mistakenly infer the existence of dark matter. However, some or all of dark matter could be made of particles which we have yet to discover: this (cid:449)ould fi(cid:374)d this to (cid:271)e (cid:862)e(cid:454)traordi(cid:374)ar(cid:455)(cid:863) (cid:373)atter. Physicists like to call ordinary matter baryonic matter: protons & neutrons are called baryons. An extraordinary matter candidate: we have already studied a nonbaryonic form of matter, the neutrinodetected coming from the sun, neutrinos interact with other particles through only two of the natural forces: Weak force (cid:894)he(cid:374)(cid:272)e (cid:449)e sa(cid:455) the(cid:455) are (cid:862)(cid:449)eakl(cid:455) i(cid:374)tera(cid:272)ti(cid:374)g(cid:863)(cid:895: their masses are so low & speeds so high, they will escape the gravitational pull of a galaxythey cannot account for the dark matter observed.
