Dark Matter

Rotation Curves Creative Commons

Jan Oort 1932 – Studied velocities of nearby stars within the Milky Way galaxy (our galaxy) Found higher than predicted values Luminous mass of the galaxy could not account for the high velocities Oort measured (only accounted for half of the mass that was required for those velocities)

Fritz Zwicky 1933 – Studied the velocities of galaxies in the Coma Galaxy Supercluster Velocities were too high for amount of matter visible; must be some invisible mass Called it “dunkle materie…” (“dark matter” in German) But both Oort and Zwicky are generally ignored… Coma Cluster (NASA)

Vera Rubin 1975 – Used newly improved spectroscope to study rotation curve of other galaxies Found luminous matter could not account for high velocities of stars outside of the disk There was some missing mass  dark matter Creative Commons Begeman 1989

Gravitational Lensing Gravitational lensing happens not only with objects we can see (like black holes and galaxies)… If we detect gravitational lensing, we can infer that there must be a large mass in between the lensed object and ourselves. NASA/ESA/Richard Massey

How much is there? We understand about 4% of the universe…

Could dark matter be… brown dwarfs? The Idea: Brown dwarfs (stars too small to fuse H  He) The Problem: Despite systematic searches, there are not enough Conclusion: Dark matter is not brown dwarfs R. Hurt/NASA

Could dark matter be… planets? The Idea: Planets are hard to detect, so we are missing many in our mass counts The Problem: Requires thousands per star Conclusion: Dark matter is not just planets NASA/JPL

Could dark matter be… WIMPs? W eakly I nteracting M assive P articles WIMPs?

Searching for Evidence of WIMPs At least 6 facilities looking for direct evidence of WIMPs via particle scattering (direct evidence) Others are looking for evidence of WIMP annihilation (indirect evidence) Zina Deretsky, National Science Foundation NASA / Goddard Space Flight Center

Dark Matter Activity