A105 Stars and Galaxies Today’s APOD This week’s units: just 80 Quiz online this week – Original Test and Survey Tool Projects due Nov. 30

DARK MATTER The universe is NOT what it seems…

DARK MATTER “Extraordinary claims require extraordinary evidence.” (Carl Sagan) “Extraordinary claims require extraordinary proof.” (Marcello Truzzi) “The weight of evidence for an extraordinary claim must be proportioned to its strangeness” (Laplace) “A wise man, therefore, proportions his belief to the evidence” (David Hume)

Evidence for Dark Matter Rotation of galaxies Velocities of stars in galaxies Gravitational lensing Velocities of galaxies in clusters

Mass within Sun’s orbit: 1.0 x 1011 MSun Total mass: ~1012 MSun

What’s the PROBLEM??? The orbits of stars suggest that galaxies contain several times more mass that we can find in stars, gas and dust MISSING MASS! Dark matter is the material believed to account for the discrepancy between the mass of a galaxy as found from the orbits of stars and the mass observed in the form of gas and dust

The visible portion of a galaxy lies deep in the heart of a large halo of dark matter

Galaxy interactions require more mass than we can see Computer simulation The real thing Antennae Galaxy (HST)

Evidence for dark matter in clusters of galaxies We can measure the velocities of galaxies in a cluster from their Doppler shifts The mass we find from galaxy motions in a cluster is about 50 times larger than the mass in stars!

Exploring the Dark Universe with Gravitational Lenses

85% dark matter 13% hot gas 2% stars Clusters contain large amounts of X-ray emitting hot gas Temperature of hot gas (particle motions) tells us cluster mass The mass is much more than gas and galaxies

All methods of measuring cluster mass indicate similar amounts of dark matter

1E 0657-56 – The Bullet Cluster Direct observation of Dark Matter

Proof that Dark Matter Exists 1E 0657-56 – A collision of galaxy clusters A cluster of galaxies consists of three components 1. Galaxies 2. Hot Gas 3. Dark Matter

What’s going on with 1E 0657-56? TWO clusters of galaxies collide

The gas interacts, the dark matter and galaxies don’t The galaxies and dark matter pass through unimpeded, but the hot gas is separated from the clusters

Animation of 1E 0657-56 link to animation: http://chandra.harvard.edu/photo/2006/1e0657/1e0657_bullett_anim_lg.mpg

Dark Matter The universe contains additional matter we cannot see Dark matter interacts with normal matter through gravity Dark matter does NOT interact with light the way the normal matter does The Universe contains 5 or 6 times MORE dark matter than normal matter All galaxies are embedded in clouds of dark matter We do not know what it is!

What is DARK MATTER? Can’t see it, taste it, touch it, smell it… We can only detect it by gravity We don’t know! Detecting Dark Matter is one of the most active areas of high energy physics, and a reason to build large accelerators.

Why is DARK MATTER important? The formation of structure and of galaxies requires the extra mass provided by dark matter. Without dark matter, the Universe would not exist as we know it

Final News Quiz on Tuesday! Project Due Nov 30 Happy Thanksgiving! Unit 81, 82, 83 Final News Quiz on Tuesday! Project Due Nov 30