Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UW1Questions of the Day•Why do light beams bend due to gravity?•What is gravitational lensing?•What are the major components of the ISM, and what role do they play in star formation and evolution?•How does dust affect the appearance of galaxies, and why?•What is the initial mass function?Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UWAdministrative Stuff• Midterm: High score was 48, Median score was 36 (75% of 48).• New Coursepak available on-line and at the bookstore.• Next lab is hard to do if you don’t come to section!• I’m out of email contact until Wednesday AM.• Everybody is sick. No hugging.2Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UWCurved spaces:3Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UW4What about light???•Light must obey the same rules!•It must stay within the curved space!•Light travels on “straight” lines, but space itself is curved!Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UW5Due to the curvature of space, light paths are deflected by mass! Light must remain in the curved space“Gravitational Lensing”Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UWXDots show true position of stars, lines show positions of stars during eclipse.•Need eclipse so you can see stars right near the sun, otherwise too bright!Actual experiment in 1919Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UW6The curvature of space acts like a very weird magnifying glass.Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UW7Mass curves space, which distorts images of distant galaxies:Ringlike distortions of distant galaxies are frequently seen behind massive galaxy clustersAstronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UW8Any mass can magnify and warp images of more distant objectsNote: this is just an illusion! The distant galaxies are not actually shaped like arcs!Abell 2218Massive galaxies in the clusterDistant “background” galaxies, distorted by the curvature of space produced by the mass of the cluster!Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UWXFor clusters, the curvature of space is large, due to their high masses (1014M!)Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UW9“Einstein Rings”When alignment is perfect, the arcs can meet up and form a ring!Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UW10An “Einstein Cross”The mass in the very center of the galaxy ‘lenses’ a more distant quasar, making 4 images of a single object!Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UW11What happens to light leaving a massive object?•It takes energy for ANYTHING to escape from ANY gravitational field!•A ball thrown up loses kinetic energy.•LIGHT sent up loses energy too! (Note: In both these cases, total energy is conserved, because the “lost” energy is exchanged for gravitational potential energy.)Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UW12How can light lose energy?•Speed of light is constant!•But, energy of a photon is related to its wavelength E = h/! Less energy, longer wavelength!•The light gets redder as it climbs out of any mass!“REDSHIFT”Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UW13If you shine a flashlight from near the surface of a “black hole Sun”, we’d need a radio telescope to “see” it at Earth!Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UW14Redshifts: Not just for black holes!•Light we see from the Sun is slightly redder than it was where it was emitted! " 0.0002% •The wavelength increases by 20% from the surface of a neutron star. !detected = !emitted + 0.2 !emitted•From the surface of a BH, the redshift is Infinite!0.2 is the redshiftAstronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UWXWorks in the opposite direction!•If you look out from the surface of a black hole, all the light that’s falling in looks “blueshifted”.•You’d be bombarded by gamma-rays.Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UW15And now for something completely different….Where do stars come from?Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UW16Stars, gas, and dust are tightly coupled! 1.Stars form from cool gas…2.Evolving stars release gas, and heat the surrounding gas.3.Gas cools.4.See Step 1.Gas cycles between different “phases”…Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UWXThis star formation cycle fundamentally changes galaxies!•Steadily adds new stars.•Removes gas, overall.•Changes the state of the gas (molecular, atomic, or ionized).•Changes the metallicity of the gas and of subsequent generations of stars.Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UW17Stars form from the gravitational collapse of dense gas(Forms a disk because initial cloud rotates, and angular momentum is conserved!)This disk will probably form planets!Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UW18We actually see these “protostars”!•Why the jet? We don’t exactly know!Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UW19We can also see the disks!Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UW20“Protoplanetary” disksSeen in silhouette!These may eventually form planetary systems like our own!Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UW21Stars form from the collapse of dense gas within galaxies.Gas in galaxies = “Interstellar Medium”This gas has a range of densities and temperatures:Cold & Dense = Molecular! (H2)Warm = Atomic! (HI) Hot & Diffuse = Ionized! (HII)Stars form from the coldest densest gas " Molecular!Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UWXThe gas in between stars is the “Interstellar Medium” (or “ISM”)•Molecular (H2): –Cold, dense, tightly clumped.–Stars form within molecular clouds.•“Neutral” or Atomic (HI): –Cool, less dense, less tightly clumped.–Most common phase; the resevoir for forming the next generation of stars.•“Ionized” (HII): –Hot, more diffuse.–By-product of forming young stars.Note: “HI” reads as “H-one”, “HII” as “H-two”.Astronomy 101, Winter 2010Copyright@2010 Julianne Dalcanton, UW22Molecular gas in the Milky Way…(View of the outskirts, away
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