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Dark Matter

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Dark Matter. Inquiring Minds Want to Know Prof. David Toback Texas A&M University. Inquiring Minds Want to Know. I keep hearing about “Dark Matter” in newspapers, on TV, etc What are people talking about? Why is it called Dark Matter? What do we know about it? - PowerPoint PPT Presentation

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Dark MatterInquiring Minds Want to KnowProf. David TobackTexas A&M UniversityInquiring Minds Want to KnowI keep hearing about Dark Matter in newspapers, on TV, etcWhat are people talking about? Why is it called Dark Matter?What do we know about it? Whats the evidence for it?So what?Quick AnswerStuff out in space we cant see directlyWhat is Dark Matter and why do we call it Dark Matter?What do we see when we look at the Heavens?Easy to see light from things like starsCan see the light from stars AFTER it has left the star and interacted with whatever is between us and the star

Anything else out there? What is Matter? Lots of ways to understand the word matterExamples:RocksYou The EarthThe SunAtomsOur Sun and Earth are attracted to each other by gravityThey are attracted to each other because they are made of matterThey have mass6Dark MatterThere is evidence that there is stuff in space that we cant see directlyCall this stuff Dark MatterStuff that is like atoms in that has gravity7Evidence for Dark MatterThe Rotation of GalaxiesGravitational LensingColliding Galaxies 8Evidence 1Watch the way stars move around the center of a Galaxy

9The Planets and the SunGravity does a good job of predicting the planets path around the SunHow Quickly do the Planets go Around the Sun? Inner planets like Mercury, Venus and Earth go quickly around the SunPlanets move MUCH slower

As the Solar System Turns

12What about Stars and Galaxies?Can again use Gravity to predict the orbits of stars as they move around the center of the galaxy Should look like the planets as they go around the Sun

Is that what our galaxy, the Milky Way, looks like? Does it spin like our solar system? Closest stars go around quickest?0

14Data doesnt look anything like expectations!The DataDifference due to Dark Matter?How the Galaxy Turns 16Dark Matter?Data well explained by lots of Dark Matter we cant seeAbout five times as much Dark Matter as stars Forms a halo around the entire galaxy

17Evidence 2Look at the effect gravity has on light as it travels through the Universe towards us

18What happens to light as it goes past the Sun?Path doesnt curvePath does curveNewton: only things with real mass feel the force of gravity. Light has no mass!Einstein: Objects with Energy move according to the curve of space-time, regardless of whether they have mass or notMore Detail

Star looks like its hereCan see the star directlyNow the Sun curves the path of the starlightThe Great Experiment of 1915Look at a stars position behind the sun as it passes in between us and the starResult: The apparent position of a star is different when the sun is close to the path In other words, we observe that the gravity of the sun bent the path of the light coming from the star

Dark Matter and Lensing

Dark Matter Lenses the galaxies behind them like a prismEvidence that the light coming to us is passing through lots of matter we cant see directly22Looking at Light from the Universe

GalaxyLight from a GalaxyLooks like a GalaxyHydrogenCloudLooks like a Galaxy behind a cloud of hydrogenLooks like a Galaxy behind a cloud of heavy stuff that isnt just stars and hydrogenAnother Galaxy23More on LensingSometimes we can even see more than one image of the same galaxy!

24Evidence 3Colliding Clusters of Galaxies25Look at Colliding Clusters of GalaxiesAtomsDark MatterAtomsDark MatterAtoms in the Galaxies interact and slow down as they pass through each other Dark Matter doesnt interact much so it isnt slowed down much26Colliding Galaxy ClustersAtoms and Dark MatterAtoms andDark MatterThe atom part and the Dark Matter part of Galaxies interact differently as they pass through each other AtomsAtomsDark MatterDark Matter27Colliding Galaxy ClustersAtoms and Dark MatterAtoms andDark MatterAtomsAtomsDark MatterDark Matter

Light from a Galaxy

GalaxyGalaxyGalaxy28Evidence for This in Nature?Colliding Clusters of Galaxies

Blue is the part from lensing onlyFast Dark MatterRed part from observing the lightSlow Atoms29What IS Dark Matter?We dont know Still working on itIs that the whole story?

Whats the Matter in the Universe? No real understanding of what this stuff isConcluding RemarksThe case that there is lots of Dark Matter in the Universe is very compellingThe fate of our Universe depends on Dark MatterMight be able to discover it using the Large Hadron Collider (LHC)If scientists are right, might be able to tie together Astronomy, Particle Physics and Cosmology