Astronomy 100Exploring the UniverseTuesday, Wednesday, ThursdayTom [email protected] 100Exploring the UniverseTuesday, Wednesday, ThursdayTom [email protected] Ratio•You can compare the measured mass to the luminosity of a galaxyLight RatioYou can compare the measured mass to theMilky Way•Milky Way contains 90 billion solar masses of material within the Sun’s orbit•Luminosity of Milky Way at this orbit is 15 •Luminosity of Milky Way at this orbit is 15 billion solar luminosities• Mass-to-Light ratio of our Galaxy at this orbit is 6 solar masses per solar luminositiesMilky WayMilky Way contains 90 billion solar masses of material within the Sun’s orbitLuminosity of Milky Way at this orbit is 15 Luminosity of Milky Way at this orbit is 15 billion solar luminositiesLight ratio of our Galaxy at this orbit is 6 solar masses per solar luminositiesThis tells us that …•The value of 6 solar masses per solar luminosity tells us that most of the matter is dimmer than the Sun out to the Sun’s orbitSun out to the Sun’s orbit• Mass-to-Light ratio of our Sun is 1 solar mass per solar luminosity•So most matter is dimmer than the SunThis tells us that …The value of 6 solar masses per solar luminosity tells us that most of the matter is dimmer than the Sun out to the Sun’s orbitSun out to the Sun’s orbitLight ratio of our Sun is 1 solar mass per So most matter is dimmer than the SunFor some ..•For some galaxies, they have massof 50 solar masses to solar luminosity•This is too high to be accounted for by stars alone•This is too high to be accounted for by stars aloneFor some ..For some galaxies, they have mass-to-light ratios of 50 solar masses to solar luminosityThis is too high to be accounted for by stars aloneThis is too high to be accounted for by stars aloneFritz Zwicky (1898•Was among the first to suggest that there is a relationship between supernovae and neutron stars•Suggested in the 1930s that dark matter was •Suggested in the 1930s that dark matter was found in Galactic ClustersFritz Zwicky (1898-1974)Was among the first to suggest that there is a relationship between supernovae and neutron starsSuggested in the 1930s that dark matter was Suggested in the 1930s that dark matter was found in Galactic ClustersCluster•Cluster is a collection of galaxies (that can number dozens to thousands) that are gravitationally boundgravitationally boundClusterCluster is a collection of galaxies (that can number dozens to thousands) that areZwicky•By calculating the speed of galaxies as the rotate around in a cluster•He found that galaxies in the clusters had huge •He found that galaxies in the clusters had huge mass-to-light ratiosZwickyBy calculating the speed of galaxies as the rotate He found that galaxies in the clusters had huge He found that galaxies in the clusters had hugeTypes of Dark Matter• MACHOs• WIMPSTypes of Dark MatterMACHOs•Massive Compact Halo Objects• Includes–Brown Dwarfs –failed stars –Brown Dwarfs –failed stars – Faint red stars– Jupiter-sized objectsMACHOsMassive Compact Halo Objectsfailed stars failed starsWIMPs•Weakly interacting massive particles– No electrical charge–Do not emit electromagnetic radiation–Do not emit electromagnetic radiation–Have mass so do interact some with matterWIMPsWeakly interacting massive particlesDo not emit electromagnetic radiationDo not emit electromagnetic radiationHave mass so do interact some with matterNeutrinos•Dark matter in galaxies can’t be neutrinos because neutrinos escape from galaxies with enormous speedsspeedsNeutrinosDark matter in galaxies can’t be neutrinos because neutrinos escape from galaxies with enormousWIMPS•Have to have masses larger than neutrinos•Have not been discovered yetWIMPSHave to have masses larger than neutrinosHave not been discovered yetDark Energy•Gravity should be slowing the expansion of the universe down•However the universe appears to be accelerating•However the universe appears to be accelerating•Dark Energy is the name for what is causing the expansion to accelerateDark EnergyGravity should be slowing the expansion of the However the universe appears to be acceleratingHowever the universe appears to be acceleratingDark Energy is the name for what is causing the•http://www.nasa.gov/centers/marshall/mov/100452main_accel_expanding_univ_sm.movhttp://www.nasa.gov/centers/marshall/mov/100452main_accel_expanding_univ_sm.mov•Two teams of astronomers were looking for distant type Ia supernovae in order to measure the expansion rate of the universe with time. •They expected that the expansion would be •They expected that the expansion would be slowing (due to gravity) which would be indicated by the supernovae being brighter than their redshifts would indicate. •Instead, they found the supernovae to be fainter than expected. •The universe appears to be expanding Two teams of astronomers were looking for distant type Ia supernovae in order to measure the expansion rate of the universe with time. They expected that the expansion would be They expected that the expansion would be slowing (due to gravity) which would be indicated by the supernovae being brighter than their redshifts would indicate. Instead, they found the supernovae to be fainter The universe appears to be expandingSupernova Ia•Are exploding white dwarfs•Have the same masses when they explode •Have the same peak luminosities•Have the same peak luminosities•These supernovas are bright enough to be seen in far-away galaxiesSupernova IaAre exploding white dwarfsHave the same masses when they explode Have the same peak luminositiesHave the same peak luminositiesThese supernovas are bright enough to be seen in•Measuring the brightness of Supernova Ia’s allows you to calculate the distance to the Supernova Supernova •Measuring the Doppler Shift of the spectral lines of the Supernova allows you to calculate the speed the object is moving awayMeasuring the brightness of Supernova Ia’s allows you to calculate the distance to the Measuring the Doppler Shift of the spectral lines of the Supernova allows you to calculate the speed the object is moving awaySupernova Ia•The ones with the highest redshifts were dimmer than expected•That means they were farther away than expected•That means they were farther away than expected•Something had caused the universe to expand