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May 6, 2013 - What’s the Matter with Dark Matter?

What’s the Matter with Dark Matter? Dark matter—the invisible substance that accounts for the majority of mass in the universe—can only be detected indirectly, by the gravitational effect it has on nearby objects. It acts as a sort of galactic glue, making spiral galaxies, for example, rotate as if they were solid disks rather than collections of individual stars orbiting at different speeds. (This is, in fact, how dark matter was discovered in the 1970s.) But astronomers recently discovered that the merging galaxy cluster Abell 520, 2.4 billion light-years away, has a core of dark matter and hot gas (blue and green) that should be attracting more of the nearby galaxies than it actually is. This discovery challenges theories that say dark matter should be anchoring these galaxies, preventing them from roaming away.

Image credit: NASA, ESA, CFHT, CXO, M.J. Jee (University of California, Davis), and A. Mahdavi (San Francisco State University)

Weekly Calendar

May 6-12, 2013

Holidays - Sky Events - Space History

Monday 6

Uranus 4° south of Moon
Eta Aquarid meteor shower

1968: Neil Armstrong ejects safely from Lunar Landing Research Vehicle before it crashes
1975: NASA announces that Canada will build the Shuttle robot arm

Tuesday 7

1992: STS-49 Endeavour launched

Wednesday 8

Thursday 9

New Moon 8:29 PM ET

2003: Hayabusa launched, first mission to retrieve a sample from an asteroid

Friday 10

Pallas in conjunction with Sun

1967: M2-F2 lifting body crash-lands; footage later becomes opening scene of “The Six Million Dollar Man”

Saturday 11

Mercury in superior conjunction

1974: SMS-1 launched, first geostationary weather satellite
2009: STS-125 Atlantis launched, fifth and final Hubble servicing mission

Sunday 12

Mother's Day

Jupiter 3° north of Moon

1930: Adler Planetarium opens, first planetarium in Western Hemisphere

Suggestions for new history dates or better links? Corrections for errors on this page? Please e-mail me.