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