Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UW1Questions of the Day•What are the different ways that galaxies can be affected by interactions?•How can we study galaxies of different ages?•How do young galaxies appear to differ from the mature galaxies we see today?•What are the major methods of finding distances to nearby galaxies, why do they work, and over what range can we use them?Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UWAdministrative stuff•Final Exam will be cumulative (i.e. all material covered during the course)•No lecture one week from today! Possible review session instead....2Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UWLike nifty astronomy pictures?•http://antwrp.gsfc.nasa.gov/apod/3Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UWThe Rosette Nebula...4Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UWA white dwarf in the center of a planetary nebula...5Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UWMessier 886Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UW“Einstein Cross” gravitational lens7Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UWInteracting galaxies in a compact group8Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UW9If the dark matter acts like cold dark matter:1.Dark matter clumps into “halos”2.Little things merge to become bigger things“hierarchical merging”Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UW10“Merging” or “Galaxy Interactions”•Gravity pulls galaxies together!•They can orbit each other & eventually merge!Should be common if CDM is the right model for dark matter!Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UW11“The Antennae” (HST: Right)Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UW12Galaxy interactions happen…•All the time!•On all scales!– Big galaxies with big galaxies (“major merger”)– Big galaxies with little galaxies (“minor merger”)– Galaxy groups with galaxy groups!Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UW13Some interactions just “warp” galaxies.•Passed close enough to jiggle stars in the outskirts of the disk.Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UW14But some interactions are obviously more severe!Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UW15“Major Mergers”•Galaxies of comparable mass (within 50% or so).•Tends to make a single bigger galaxy ! ELLIPTICALS(?)•Messy. Lots of debris.Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UWXBrightest, inner parts look like ellipticals…Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UW16Multiple cores in some ellipticals in clusters of galaxies!Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UW17We can’t see this happening in real time. 1.Try to piece together snapshots of lots of different interacting galaxies…Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UW18Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UW19We can’t see this happening in real time2.Simulate the merger in a computer• Gravity has very simple rules.• Make some galaxies from millions of particles.• Teach them the rules and let them loose!Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UW20Simulations of Major MergersAstronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UWXEqual mass mergerAstronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UWXEqual mass mergerAstronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UW21“Minor Mergers”Satellite orbiting the Milky Way gradually disrupts, and leaves an orbiting trail.•Most common form of mergingAstronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UW22•Disrupts dwarf galaxies.•Good thing, because CDM predicts more dwarfs than are seen“Minor Mergers”Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UWXThese simulations can be used to “weigh” amount of dark matterReality!Light dark matter halo lets tails fling outwards.Heavy dark matter halo keeps tails close.Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UW23“Minor Mergers”We know this is currently happening…Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UW24Leaves “streams” of stars in the galaxy haloAstronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UW25Galaxies are evolving….Can we see this process in motion?• Directly, over our lifetime, no.We live for less than 100 years, or 0.000001% of the age of the universe, or 0.01% of the age of the shortest lived O-stars.Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UW26The Universe is a Time Machine!•Speed of light not infinite!•Distant = Younger!– The light we see from distant galaxies was emitted many, many years ago!Light takes longer to travel this distance……than this one.Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UW27If you know the distance, you know how long ago the light you’re receiving now was emitted….# of light-years (distance)# of years the light has been travelling (time)Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UW28Can detect light emitted when the Universe was very young:– Nearest Star: 3 light years– Center of Milky Way: 25,000 ly– Edge of Local Group: 3 million ly– Coma Cluster: 340 million ly– Most Distant Quasars: 10 billion lyUniverse is ~13.2 billion years oldAstronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UWXLooking back in time…•We see distant objects as they were many years ago!– Nearest Star: 3 years ago– Center of Milky Way: 25,000 yrs ago– Edge of Local Group: 3 million yrs ago– Coma Cluster: 340 million yrs ago– Most Distant Quasars: 10 billion yrs agoIf we know how far, we know how young the “snapshot” of the galaxy is Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UWXGalaxy Family Album" Big Bang Today!Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UW29We can piece together the history of the universe by observing it at different distances!•Can’t see the same galaxy at different distances.•Distant galaxies appear fainter, so harder to detect.•Distant galaxies appear smaller (angularly), so harder to resolve features.BUT…Astronomy 101, Winter 2010Copyright@2010
View Full Document
Unlocking...