11Interstellar Medium and Star BirthInterstellar Medium and Star Birthhttp://www.spitzer.caltech.edu/images/3420-ssc2010-09a-Extragalactic-Space-Balls2Learning goals (based on textbook coverage)Learning goals (based on textbook coverage)16.1 Stellar Nurseries16.1 Stellar Nurseries Where do stars form?—interstellar medium - how gas and dust clouds can look sodifferent—star-forming clouds - giant molecular clouds—interstellar dust Why do stars form?—gravity vs pressure - collision of molecular clouds, SN blast—preventing pressure build-up - radiation of 1/2 of energy—formation of clusters - video—fragmentation of molecular cloud316.2 Stages of star birth - How stars form What slows contraction?—trapping of thermal energy in a protostar—growth of protostar by gas infall - inside out growth What role does rotation play in star birth?—protostellar disks (accretion disk)—protostellar jets When does nuclear fusion start in a newborn star?—protostar to main sequence - luminosity from contraction—surface of protostar - constant temperature maintained—birth stages on a life track416.3 Masses of newborn stars What are the range of masses of stars?• Smallest and largest masses possible• Typical masses?5Where do stars form?6Where do stars form?27What our Milky Way probably looks likeWhat our Milky Way probably looks likeYou are here.Where do stars form?8Please turn the brightness DOWN on your laptops.9We look this way in the Galaxy during winter nights.We look this way in the Galaxy during summer nights.To galactic center10Rosette Nebula: emission nebula with new open cluster of ~2000starsHydrogen gas needsa source of ultravioletphotos in order toemit at visiblewavelengths (Hα, Hβ,Hγ, Hε, etc.)Why?1112Plane of the Milky Way31314Emission nebulae15Digital camera + filtersBased on digitized B&W imageshttp://apod.nasa.gov/apod/ap061130.html1617HH 555 is a bipolar jet emerging from the tip of an elephant trunk enteringthe Pelican Nebula from the adjacent molecular cloud. Both beams of HH555 are curved away from the center of the H II region. This indicates thatthey are being deflected by a sidewind probably coming from a starlocated inside the nebula or by the expansion of the nebula itself. HH 555is most likely an irradiated jet emerging from a highly embedded protostar,which has not yet been detected.18419Dark nebulaReflectionnebulaEmissionnebulaBlue due to dustreflecting lightfrom nearby hotstars.H atoms emittingenergy aselectrons jumpfrom n = 3 to n = 2Dust: carbon,silicon, complexmolecules20Close up of the Cone Nebula21Star Star birthbirthCreated using Sky6Where do stars form?2223Trifidnebula:ReflectionandemissionLagoonnebula:EmissionDarknebulae24525262728Focus on the Orion star forming regionFocus on the Orion star forming region29OrionOrionNebulaNebulaHST at visiblewavelengthsIR wavelengthsGiant molecularcloud harborsnewly born stars30http://www.haydenplanetarium.org/about631WHERE do stars form?WHERE do stars form? In giant molecular clouds Within clumps wheretemperature is low (~10K)and density is high Where gas and dust arecompressed by asupernova shock wave Where 2 molecularclouds collide In spiral arms of spiralgalaxies (density wave)Whirlpool Galaxy32WHY do stars form?WHY do stars form? Given enough time, gas (and dust) in interstellarmedium will gather together Any small region that is slightly cooler anddenser will start to collapse under gravity33http://ircamera.as.arizona.edu/NatSci102/NatSci102/lectures/spiralarms.htmSchematically a green molecular cloud passesthrough a red spiral arm (colors arbitrary). Thecloud is compressed and starts to form massiveblue stars, which quickly evolve into supernovaexplosions (yellow). (animation by G. Rieke)NGC 381034Collapseof a starwithin aninterstellargiantmolecularcloudWhy and how do stars form?Why and how do stars form?•Why and how do stars form?35How stars formHow stars form Gravity is compressing star Gas heats up due to compressionand conservation of energy Increase in temperature stallscontraction Heat radiated away, cooling star Pressure decreases Gravity compresses again Repeat36Star Cluster Star Cluster FormationFormationWhat are some of the processes occurring during formation?1) gpe 2) turbo 3)gravity4) ejections737Why more stars donWhy more stars don’’t formt formNext stage would beclearing out of a cavityby the OB stars•Why don’t more stars form?38Zoom inMassive Massive Stars; IonizationStars; Ionization Fronts Fronts; Triggered; Triggered Star StarFormationFormation3940“Young, massive stars can have a profound effect on thesurrounding interstellar medium. The triggering of starformation by an H II region expanding into nearbymolecular material is an example of this type ofinteraction. “The Astrophysical Journal, 595:900-912, 2003 October 14142843What slows contraction?What slows contraction? Interior of star continues to heat and grow moredense Radiation has increasing difficulty “getting out”as opacity of star increases Gravity never gives up and keeps trying tocompress the star Center of star gets extremely hot and theprotostar becomes fully convective Collapse stops when fusion begins in the core Equilibrium sets in44Conservation of Angular MomentumConservation of Angular Momentum Terrestrial examples (list): If protostellar cloud has some spin, what happenswhen it collapses? Where will some material find it the easiest to“settle down”?Size of whole solar systemInfalling material powers jets•What role does rotation play?45What’s this?•What role does rotation play?46•When does nuclear fusion start?A star is bornA star is born47Reading chart-questions and tutorial.48How Stars FormBrown dwarfcore fusion impossiblestar slowly coolsover billions of yrsMass < ~0.08times Sun's mass0.08 < Mass < 10 Msungravity forces starto contract and heatuntil core fusion starts10 < Mass < 100 Msungravity in total controlstar contracts rapidlycore fusion starts quicklyMass is greater than ~0.08times Sun's massSurface temperaturereaches ~3000KAtmosphere becomesopaque to radiationProtostar collapsesgravity bringsmaterial to centeressentially in freefallSummary and the path to different mass stars:Summary and the path to different mass
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