DOC PREVIEW
UT AST 350L - LECTURE NOTES

This preview shows page 1-2-23-24 out of 24 pages.

Save
View full document
View full document
Premium Document
Do you want full access? Go Premium and unlock all 24 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 24 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 24 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 24 pages.
Access to all documents
Download any document
Ad free experience
Premium Document
Do you want full access? Go Premium and unlock all 24 pages.
Access to all documents
Download any document
Ad free experience

Unformatted text preview:

The History and Philosophyof Astronomy (Lecture 26: Modern Developments I:The Dark Side)Instructor: Volker BrommTA: Amanda BauerThe University of Texas at AustinAstronomy 350L (Spring 2005)The Dark Side of the Universe• Big Q: What is the universe made of?• consensus view ofearly 21stcentury (WMAP):- 4% normal matter (`baryons’) (stars, gas, people…)- 23% dark matter- 73% dark energy``Deep into the darkness peering, long I standthere wondering, fearing.’’ (E.A. Poe, The Raven)• We don’t know what > 90% of universe is made of !!!Fritz Zwicky: Astronomy’s Mad Genius• Swiss national1898 (Varna) – 1974 (Pasadena)•Professor at Caltech (1925+)• creative genius:- concept of supernova- neutron stars- dark matter (`missing mass’)• intense eccentricity(“spherical bastards”)1933: Zwicky and the `Missing Mass’• Coma cluster of galaxies- ~1,000 individual galaxies- 300 million lightyears away• Zwicky measures average(radial) velocities (fromDoppler shift)- Result: ~1,000 km/sec• comparison with sumof visible (stellar) mass• BIG surprise: There must be 10 times more matter !1933: Zwicky and the `Missing Mass’RV• measure: V and R• calculate required mass to hold cluster together:(Newton’s constant)• Result for Coma:- need 10 times more massthan is visible!• For more than 30 years,no one else took thisseriously!Vera Rubin: The Dark Side of Galaxies• Born 1928 (Philadelphia)• 1965: Carnegie Institution (DTM, Washington D.C.)• firmly established existenceof dark matter in individualgalaxies (with Kent Ford)- flat rotation curves• activist for women’s rightsin the sciencesVera Rubin: The Dark Side of Galaxies (1970s)• measure orbital velocity of stars (using Doppler shift)Vera Rubin: The Dark Side of Galaxies (1970s)• measure orbital velocity of stars (using Doppler shift)expectMeasure!• `flat’ rotation curves:- galaxies must contain10 times more non-visible matter!Through a Universe Darkly• BIG Q: What is the dark matter????• more than 70 years after it was first posulatedby Zwicky, this remains one of the great unsolvedproblems in science!• But, by trial and error, we ve gained important cluesYakov B. Zeldovich: Godfather of Soviet Physics• 1914 - 1987• `father’ of Soviet Bomb(Atomic and Hydrogen)• great astrophysicist:- supermassive black holes- no-hair theorem• `Zeldovich pancakes’:- top-down theory ofgalaxy formation- neutrinos make up dark matterThe Neutrino Universe• neutrinos: - very elusive (weakly interacting)- they are known to exist!The Neutrino Universe• neutrinos: - produced in Big Bang fireball- travel (almost) with speed of light1 cm3~115 neutrinos from Big Bang• If neutrinos had (tiny) mass:- total mass of neutrinos in universehuge:Total Mass = N x mass_nuThe Neutrino Universe- If mass_nu ~ 1/10,000 x mass_electron:• there would be sufficient mass to `close’ the universe• Thus: Neutrinos could be very important on cosmic scales!The Neutrino Universe• Briefly after Big Bang: Matter and energy is distributedvery smoothly• but not quite: there aretiny irregularities (`lumps’)• smallest lumps grow fastest under gravity• What is their fate?The Neutrino Universe- Q: How much mass is needed to confine (coral in)neutrinos? - Early on (first 10,000 years), neutrinos move (almost)with speed of light (thus: `Hot Dark Matter’)Small massneutrinoNormal particlesLarge mass~ 1015solar masses mass of a cluster of galaxies (e.g., Coma) Small structuresare `erased’ byneutrino free-streaming!The Neutrino Universe• Zeldovich pancakes: Galaxies form from the `top down’time• Prediction: clusters form before galaxies do!Super-clusters (`clusters of clusters’)Clusters of galaxiesGalaxiesThe Neutrino Universe- May 1980: `Neutrino Spring’- Soviet physicist V.A. Lubimov claims thatneutrinos have large enough mass to closethe universe (~1/10,000 mass_electron)• Was dark matter riddle solved?• Alas, no: - Lubimov experiment proved wrong- astronomers contradict top-downscenario of galaxy formationThe Neutrino Universe Undone- early 1980s:- dwarf galaxies have dark matter halos, too!- clusters of galaxies form late in history of universe,after the galaxies themselves!• The neutrino universe doesn’t work!• Again: What is the dark matter???The Cold Dark Matter Model• 1984-86: postulate some mysterious particlethat is massive, but only interacts weaklywith ordinary matter other than through gravity(Blumenthal, Faber, Primack & Rees; Peebles)• WIMPs = Weakly Interacting Massive ParticlesNormal particleWIMP• small lumps survive!• sub-galactic (million solar massobjects form first)!The Cold Dark Matter Model• Galaxies form from the `bottom up’ (hierarchical)time• Prediction: clusters form after galaxies do!Super-clusters (`clusters of clusters’)Clusters of galaxiesGalaxiesThe Cold Dark Matter Model• Structure forms from the `bottom up’ (hierarchical)• Computer simulations: galaxies form before clusters!galaxyclusterTime 4Time 3Time 2Time 1The Cold Dark Matter Model• But what is the WIMP really???• Has not yet been directly detected!• But there is a promising candidate:- the lightest supersymmetric particle (photino)The Cold Dark Matter Model• for every normal particle, there is a supersymmetric(`shadow’) partner• the lightest one (the photino) cannot decay, and wouldthus have survived from the very early universe!The Dark Side of the Universe• 1930s: Missing mass problem realized (Zwicky)- galaxies in Coma cluster move too fast- there must be 10 times as much mass as can be seen- Zwicky’s prediction largely ignored • Hot vs Cold Dark Matter- Hot Dark Matter = neutrinos: top-down scenario- Cold Dark Matter = WIMPs: bottom-up scenario• 1970s: Dark halos of galaxies inferred (Rubin & Ford)- stars in galaxies continue to rotate quickly, even beyondthe extent of luminous galaxy- again: 10 times as much mass needed- this time, the evidence was overwhelming, and dark matterwas universally


View Full Document

UT AST 350L - LECTURE NOTES

Download LECTURE NOTES
Our administrator received your request to download this document. We will send you the file to your email shortly.
Loading Unlocking...
Login

Join to view LECTURE NOTES and access 3M+ class-specific study document.

or
We will never post anything without your permission.
Don't have an account?
Sign Up

Join to view LECTURE NOTES 2 2 and access 3M+ class-specific study document.

or

By creating an account you agree to our Privacy Policy and Terms Of Use

Already a member?