A Star Is Born
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Transcript of A Star Is Born
A Star Is BornA Star Is Born
Looking at the Interstellar MediumLooking at the Interstellar Medium
The Stuff in SpaceThe Stuff in Space
Material exists between the stars and Material exists between the stars and planetsplanets
““Building Blocks” for more stars and Building Blocks” for more stars and planetsplanets
Interstellar MediumInterstellar MediumComposed of Gas and DustComposed of Gas and Dust
Interstellar MediumInterstellar Medium
Seen in telescopesSeen in telescopesLarge clouds of gas and dust are stellar Large clouds of gas and dust are stellar
“nurseries”“nurseries” ISM is clumpy!ISM is clumpy!Obscures objects beyond itObscures objects beyond it
Interstellar GasInterstellar Gas
Gas is mostly individual atomsGas is mostly individual atoms Individual neutral atoms and ionsIndividual neutral atoms and ionsMoleculesMoleculesElectronsElectrons
Hydrogen is main componentHydrogen is main componentVery tenuous, doesn’t block lightVery tenuous, doesn’t block lightSome parts cool, some parts hotSome parts cool, some parts hot
Interstellar DustInterstellar Dust
More complex compositionMore complex composition1% of ISM1% of ISMClumps of atoms and moleculesClumps of atoms and moleculesMuch larger than gas particles so…Much larger than gas particles so…Can block lightCan block lightComposition is not well knownComposition is not well known
Interstellar DustInterstellar Dust
Light passes through dust cloudLight passes through dust cloudExtinction-dimming of lightExtinction-dimming of light
Longer Wavelengths pass throughLonger Wavelengths pass throughShort Wavelengths get absorbedShort Wavelengths get absorbed
Reddening- scattering of blue lightReddening- scattering of blue lightRed light makes it throughRed light makes it throughChanges star’s apparent colorChanges star’s apparent color
Dust and GasDust and Gas
Dust is believed to come from mass loss Dust is believed to come from mass loss winds in stars (like solar wind)winds in stars (like solar wind)
Gas of wind can cool and solidifyGas of wind can cool and solidifyDust grains provide coagulation seeds for Dust grains provide coagulation seeds for
moleculesmolecules
Evidence of Gas and DustEvidence of Gas and Dust
Observed Nebulae (clouds)Observed Nebulae (clouds)Dust and Gas form different types of Dust and Gas form different types of
nebulaenebulae4 basic types4 basic types
Emission (Bright) nebulaEmission (Bright) nebulaDark nebulaDark nebulaReflection nebulaReflection nebulaMolecular CloudsMolecular Clouds
Emission NebulaEmission Nebula
Example: Orion NebulaExample: Orion NebulaSpectra has emission lines (hot gas)Spectra has emission lines (hot gas)Does notDoes not shine under it’s own light shine under it’s own lightPowered by hot starsPowered by hot starsH II region (ionized hydrogen)H II region (ionized hydrogen)
Emission NebulaEmission Nebula
OB associationsOB associationsForm H II region hot spot on molecular Form H II region hot spot on molecular
cloudcloudDrives new star formationDrives new star formationReddish hue is from HydrogenReddish hue is from HydrogenH II regions are star “nurseries”H II regions are star “nurseries”Very bright!Very bright!
Emission NebulaEmission Nebula
Astronomy Picture of the Day
Heart and Soul Nebulae
Emission NebulaEmission Nebula
Astronomy Picture of the Day
The Eagle Nebula and a close up of a star forming region
Molecular CloudsMolecular Clouds
Composed mostly of HComposed mostly of H22 (hard to detect) (hard to detect)Use other molecules as tracersUse other molecules as tracers80 known ISM molecules80 known ISM moleculesMany are organic moleculesMany are organic moleculesAssociated with H II regionsAssociated with H II regionsMajority of ISM is hereMajority of ISM is here
Molecular CloudsMolecular Clouds
10’s of ly across (6 trillion miles= 1ly)10’s of ly across (6 trillion miles= 1ly)Cool clouds (Dark)Cool clouds (Dark)Occur in huge complexesOccur in huge complexesContain enough gas to make millions of Contain enough gas to make millions of
starsstars1000 + complexes in our Galaxy1000 + complexes in our Galaxy
Molecular CloudMolecular Cloud
APOD
Barnard 68
Molecular CloudMolecular Cloud
APOD
Horsehead Nebula
Note: there are several types of nebulae in this panorama
Dark NebulaDark Nebula
Example: Snake NebulaExample: Snake NebulaContain gas and dustContain gas and dustDust blocks lightDust blocks lightCool (10’s K)Cool (10’s K)Larger than our Solar SystemLarger than our Solar SystemAlso, dust lanes w/ H II regionsAlso, dust lanes w/ H II regions
Dark NebulaDark Nebula
APOD
Snake Nebula
Reflection NebulaReflection Nebula
Gas and DustGas and DustAbsorption line spectra (stars)Absorption line spectra (stars)Doesn’t generate own lightDoesn’t generate own lightScatters blue light from starlight passing Scatters blue light from starlight passing
throughthroughNebula appears blue (like sky)Nebula appears blue (like sky)Example: Pleiades NebulaExample: Pleiades Nebula
Reflection NebulaReflection Nebula
APOD
Witch Head Nebula
A Panorama in OrionA Panorama in Orion
APOD
Can you ID the different types of nebula here?
Neutral HydrogenNeutral Hydrogen
Presence was suspectedPresence was suspectedH II regions come from itH II regions come from itNot observed until 1951Not observed until 1951Need to observed from its own radiationNeed to observed from its own radiationLow-energy Low-energy RadioRadio emissions from the gas emissions from the gas
itselfitself
21-cm Radiation21-cm Radiation
From single electron orbiting nucleusFrom single electron orbiting nucleusNot from excitation, from Not from excitation, from spin of electronspin of electron2 possible configurations2 possible configurations
ParallelParallelAnti-parallelAnti-parallel
Lower energy one preferredLower energy one preferredSpin flipping emits 21-cm photonSpin flipping emits 21-cm photon
Coronal Interstellar GasCoronal Interstellar Gas
Very hot gasVery hot gasHighly IonizedHighly IonizedVery low densityVery low densityExists between cloudsExists between cloudsWhy?Why?
Star BirthStar Birth
Star’s life is a dance between gravity and Star’s life is a dance between gravity and radiation pressureradiation pressure
All stars have a similar originAll stars have a similar originCold, dark molecular cloudsCold, dark molecular cloudsCollapse to form starsCollapse to form stars
Cloud CollapseCloud Collapse
Giant molecular cloudGiant molecular cloudSomething to trigger collapse (shockwave)Something to trigger collapse (shockwave)Cloud begins to collapse under it’s own Cloud begins to collapse under it’s own
weightweightJean’s InstabilityJean’s InstabilityCloud will begin to heat up as it collapsesCloud will begin to heat up as it collapses
Cloud CollapseCloud Collapse
Heating causes outward pressureHeating causes outward pressureBalances out gravity pushing inwardBalances out gravity pushing inwardCollapse is “lumpy”, fragmentationCollapse is “lumpy”, fragmentationPockets collapse faster (denser)Pockets collapse faster (denser)Centrally dense region is where star will Centrally dense region is where star will
eventually formeventually form
Cloud CollapseCloud Collapse
Fragmentation occurs in several waysFragmentation occurs in several waysDozens of Massive StarsDozens of Massive StarsHundred or Thousands of Sun-like StarsHundred or Thousands of Sun-like Stars
No evidence for single star formationNo evidence for single star formationSingle stars must escape after formationSingle stars must escape after formation
Collapse can occur with or without rotationCollapse can occur with or without rotation
Cloud FragmentationCloud Fragmentation
Sun sized star comes from Sun sized star comes from 2 solar mass fragment2 solar mass fragment100 times radius of Solar System100 times radius of Solar SystemLess than 100KLess than 100K
Fragmentation ceases as density of each Fragmentation ceases as density of each fragment increasesfragment increases
Interior becomes opaqueInterior becomes opaqueRadiation is trappedRadiation is trapped
Fragmentation to ProtostarFragmentation to Protostar
10,000 + years passed10,000 + years passedCentral part 10,000KCentral part 10,000KOuter part coolOuter part coolDense, opaque central region=ProtostarDense, opaque central region=ProtostarStill contracting, material raining down on Still contracting, material raining down on
itit
Protostar (Sun predecessor)Protostar (Sun predecessor)
1,000,000 years have passed1,000,000 years have passedNot hot enough for P-P chainNot hot enough for P-P chainStill about size of Mercury’s orbit Still about size of Mercury’s orbit More luminous than Sun (bigger)More luminous than Sun (bigger)Surrounded by a dusty shroudSurrounded by a dusty shroudVaporizes nearby dustVaporizes nearby dust
ProtostarProtostarProtostar
Dust Free Zone
Outer Envelope of Gas and Dust
IR photon
Protostar to StarProtostar to Star
Protostar first appears on HR diagramProtostar first appears on HR diagramProtostar loses shroudProtostar loses shroud
VaporizesVaporizesFalls onto StarFalls onto StarBlown away by windBlown away by wind
Contracts, Luminosity Contracts, Luminosity , Temp , Temp Hayashi track on HR DiagramHayashi track on HR Diagram
Violent Surface Wind (T Tauri Star)Violent Surface Wind (T Tauri Star)
T-Tauri StarsT-Tauri Stars
Exhibit strong windsExhibit strong windsBipolar flowsBipolar flowsClear gas and dust away from young star Clear gas and dust away from young star
so it is at last visibleso it is at last visibleWhere the outrushing gas impacts Where the outrushing gas impacts
stationary gas in the ISM a bright hot spot stationary gas in the ISM a bright hot spot appearsappears
Herbig-Haro objectHerbig-Haro object
T-Tauri StarsT-Tauri Stars
Also appear to vary in brightnessAlso appear to vary in brightnessLikely associated with star’s magnetic Likely associated with star’s magnetic
field, much like the active Sunfield, much like the active SunHave “star spots” like sun spotsHave “star spots” like sun spotsAre still collapsing to final size Are still collapsing to final size Larger in size and therefore brighter than Larger in size and therefore brighter than
they will be as main sequence starsthey will be as main sequence stars
T-Tauri StarT-Tauri Star
APOD
A false color image of the T-Tauri system
Note jet
T Tauri TantrumT Tauri Tantrum
HH objectHH object
APODHubble Heritage
Pre-Main Sequence StarPre-Main Sequence Star
10,000,000 Years10,000,000 YearsNow a “True Star”Now a “True Star”P-P Chain has begunP-P Chain has begun Larger and Cooler than Main Sequence Larger and Cooler than Main Sequence
StarStarStill slowly contractingStill slowly contracting
At last, the Sun!At last, the Sun!
Contraction continues Contraction continues Central Temp=15,000,000KCentral Temp=15,000,000KOutward pressure balances inward gravityOutward pressure balances inward gravityHydrostatic Equilibrium (HSE)Hydrostatic Equilibrium (HSE)Contraction Stops, Balance ReachedContraction Stops, Balance ReachedMain Sequence Star!Main Sequence Star!All main sequence stars are in HSEAll main sequence stars are in HSE
Massive StarsMassive Stars
Steps occur fasterSteps occur fasterCollapse of Cloud occurs in similar wayCollapse of Cloud occurs in similar wayCentral part still collapses fasterCentral part still collapses fasterFragments are largerFragments are largerNo T Tauri phaseNo T Tauri phaseChain Reaction from OB associationChain Reaction from OB association>100 M>100 M Gravity can’t hold together Gravity can’t hold together
Failed StarsFailed Stars
Some cloud fragments are too smallSome cloud fragments are too smallDon’t get hot enoughDon’t get hot enoughH-fusion never occurs H-fusion never occurs Warm due to collapsingWarm due to collapsingBrown dwarfsBrown dwarfsCooling objectsCooling objects<0.08M<0.08M (Jupiter)(Jupiter)
Collapse with RotationCollapse with Rotation
Rotation during collapse leads to orbiting Rotation during collapse leads to orbiting clumps around protostarclumps around protostar
These clumps can attract more material These clumps can attract more material via gravity and form planetismalsvia gravity and form planetismals
These could be a future solar systemThese could be a future solar system
SummarySummary
All stars have a “cloudy” beginningAll stars have a “cloudy” beginningDifferent types of nebulaDifferent types of nebulaStars collapse from cloudsStars collapse from clouds