A Star Is Born Looking at the Interstellar Medium

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<ul><li> Slide 1 </li> <li> A Star Is Born Looking at the Interstellar Medium </li> <li> Slide 2 </li> <li> The Stuff in Space Material exists between the stars and planets Material exists between the stars and planets Building Blocks for more stars and planets Building Blocks for more stars and planets Interstellar Medium Interstellar Medium Composed of Gas and Dust Composed of Gas and Dust </li> <li> Slide 3 </li> <li> Interstellar Medium Seen in telescopes Seen in telescopes Large clouds of gas and dust are stellar nurseries Large clouds of gas and dust are stellar nurseries ISM is clumpy! ISM is clumpy! Obscures objects beyond it Obscures objects beyond it </li> <li> Slide 4 </li> <li> Interstellar Gas Gas is mostly individual atoms Gas is mostly individual atoms Individual neutral atoms and ions Individual neutral atoms and ions Molecules Molecules Electrons Electrons Hydrogen is main component Hydrogen is main component Very tenuous, doesnt block light Very tenuous, doesnt block light Some parts cool, some parts hot Some parts cool, some parts hot </li> <li> Slide 5 </li> <li> Interstellar Dust More complex composition More complex composition 1% of ISM 1% of ISM Clumps of atoms and molecules Clumps of atoms and molecules Much larger than gas particles so Much larger than gas particles so Can block light Can block light Composition is not well known Composition is not well known </li> <li> Slide 6 </li> <li> Interstellar Dust Light passes through dust cloud Light passes through dust cloud Extinction-dimming of light Extinction-dimming of light Longer Wavelengths pass through Longer Wavelengths pass through Short Wavelengths get absorbed Short Wavelengths get absorbed Reddening- scattering of blue light Reddening- scattering of blue light Red light makes it through Red light makes it through Changes stars apparent color Changes stars apparent color </li> <li> Slide 7 </li> <li> Dust and Gas Dust is believed to come from mass loss winds in stars (like solar wind) Dust is believed to come from mass loss winds in stars (like solar wind) Gas of wind can cool and solidify Gas of wind can cool and solidify Dust grains provide coagulation seeds for molecules Dust grains provide coagulation seeds for molecules </li> <li> Slide 8 </li> <li> Evidence of Gas and Dust Observed Nebulae (clouds) Observed Nebulae (clouds) Dust and Gas form different types of nebulae Dust and Gas form different types of nebulae 4 basic types 4 basic types Emission (Bright) nebula Emission (Bright) nebula Dark nebula Dark nebula Reflection nebula Reflection nebula Molecular Clouds Molecular Clouds </li> <li> Slide 9 </li> <li> Emission Nebula Example: Orion Nebula Example: Orion Nebula Spectra has emission lines (hot gas) Spectra has emission lines (hot gas) Does not shine under its own light Does not shine under its own light Powered by hot stars Powered by hot stars H II region (ionized hydrogen) H II region (ionized hydrogen) </li> <li> Slide 10 </li> <li> Emission Nebula OB associations OB associations Form H II region hot spot on molecular cloud Form H II region hot spot on molecular cloud Drives new star formation Drives new star formation Reddish hue is from Hydrogen Reddish hue is from Hydrogen H II regions are star nurseries H II regions are star nurseries Very bright! Very bright! </li> <li> Slide 11 </li> <li> Emission Nebula Astronomy Picture of the Day Heart and Soul Nebulae </li> <li> Slide 12 </li> <li> Emission Nebula Astronomy Picture of the Day The Eagle Nebula and a close up of a star forming region </li> <li> Slide 13 </li> <li> Molecular Clouds Composed mostly of H 2 (hard to detect) Composed mostly of H 2 (hard to detect) Use other molecules as tracers Use other molecules as tracers 80 known ISM molecules 80 known ISM molecules Many are organic molecules Many are organic molecules Associated with H II regions Associated with H II regions Majority of ISM is here Majority of ISM is here </li> <li> Slide 14 </li> <li> Molecular Clouds 10s of ly across (6 trillion miles= 1ly) 10s of ly across (6 trillion miles= 1ly) Cool clouds (Dark) Cool clouds (Dark) Occur in huge complexes Occur in huge complexes Contain enough gas to make millions of stars Contain enough gas to make millions of stars 1000 + complexes in our Galaxy 1000 + complexes in our Galaxy </li> <li> Slide 15 </li> <li> Molecular Cloud APOD Barnard 68 </li> <li> Slide 16 </li> <li> Molecular Cloud APOD Horsehead Nebula Note: there are several types of nebulae in this panorama </li> <li> Slide 17 </li> <li> Dark Nebula Example: Snake Nebula Example: Snake Nebula Contain gas and dust Contain gas and dust Dust blocks light Dust blocks light Cool (10s K) Cool (10s K) Larger than our Solar System Larger than our Solar System Also, dust lanes w/ H II regions Also, dust lanes w/ H II regions </li> <li> Slide 18 </li> <li> Dark Nebula APOD Snake Nebula </li> <li> Slide 19 </li> <li> Reflection Nebula Gas and Dust Gas and Dust Absorption line spectra (stars) Absorption line spectra (stars) Doesnt generate own light Doesnt generate own light Scatters blue light from starlight passing through Scatters blue light from starlight passing through Nebula appears blue (like sky) Nebula appears blue (like sky) Example: Pleiades Nebula Example: Pleiades Nebula </li> <li> Slide 20 </li> <li> Reflection Nebula APOD Witch Head Nebula </li> <li> Slide 21 </li> <li> A Panorama in Orion APOD Can you ID the different types of nebula here? </li> <li> Slide 22 </li> <li> Neutral Hydrogen Presence was suspected Presence was suspected H II regions come from it H II regions come from it Not observed until 1951 Not observed until 1951 Need to observed from its own radiation Need to observed from its own radiation Low-energy Radio emissions from the gas itself Low-energy Radio emissions from the gas itself </li> <li> Slide 23 </li> <li> 21-cm Radiation From single electron orbiting nucleus From single electron orbiting nucleus Not from excitation, from spin of electron Not from excitation, from spin of electron 2 possible configurations 2 possible configurations Parallel Parallel Anti-parallel Anti-parallel Lower energy one preferred Lower energy one preferred Spin flipping emits 21-cm photon Spin flipping emits 21-cm photon </li> <li> Slide 24 </li> <li> Coronal Interstellar Gas Very hot gas Very hot gas Highly Ionized Highly Ionized Very low density Very low density Exists between clouds Exists between clouds Why? Why? </li> <li> Slide 25 </li> <li> Star Birth Stars life is a dance between gravity and radiation pressure Stars life is a dance between gravity and radiation pressure All stars have a similar origin All stars have a similar origin Cold, dark molecular clouds Cold, dark molecular clouds Collapse to form stars Collapse to form stars </li> <li> Slide 26 </li> <li> Cloud Collapse Giant molecular cloud Giant molecular cloud Something to trigger collapse (shockwave) Something to trigger collapse (shockwave) Cloud begins to collapse under its own weight Cloud begins to collapse under its own weight Jeans Instability Jeans Instability Cloud will begin to heat up as it collapses Cloud will begin to heat up as it collapses </li> <li> Slide 27 </li> <li> Cloud Collapse Heating causes outward pressure Heating causes outward pressure Balances out gravity pushing inward Balances out gravity pushing inward Collapse is lumpy, fragmentation Collapse is lumpy, fragmentation Pockets collapse faster (denser) Pockets collapse faster (denser) Centrally dense region is where star will eventually form Centrally dense region is where star will eventually form </li> <li> Slide 28 </li> <li> Cloud Collapse Fragmentation occurs in several ways Fragmentation occurs in several ways Dozens of Massive Stars Dozens of Massive Stars Hundred or Thousands of Sun-like Stars Hundred or Thousands of Sun-like Stars No evidence for single star formation No evidence for single star formation Single stars must escape after formation Single stars must escape after formation Collapse can occur with or without rotation Collapse can occur with or without rotation </li> <li> Slide 29 </li> <li> Cloud Fragmentation Sun sized star comes from Sun sized star comes from 2 solar mass fragment 2 solar mass fragment 100 times radius of Solar System 100 times radius of Solar System Less than 100K Less than 100K Fragmentation ceases as density of each fragment increases Fragmentation ceases as density of each fragment increases Interior becomes opaque Interior becomes opaque Radiation is trapped Radiation is trapped </li> <li> Slide 30 </li> <li> Fragmentation to Protostar 10,000 + years passed 10,000 + years passed Central part 10,000K Central part 10,000K Outer part cool Outer part cool Dense, opaque central region=Protostar Dense, opaque central region=Protostar Still contracting, material raining down on it Still contracting, material raining down on it </li> <li> Slide 31 </li> <li> Protostar (Sun predecessor) 1,000,000 years have passed 1,000,000 years have passed Not hot enough for P-P chain Not hot enough for P-P chain Still about size of Mercurys orbit Still about size of Mercurys orbit More luminous than Sun (bigger) More luminous than Sun (bigger) Surrounded by a dusty shroud Surrounded by a dusty shroud Vaporizes nearby dust Vaporizes nearby dust </li> <li> Slide 32 </li> <li> Protostar Protostar Dust Free Zone Outer Envelope of Gas and Dust IR photon </li> <li> Slide 33 </li> <li> Protostar to Star Protostar first appears on HR diagram Protostar first appears on HR diagram Protostar loses shroud Protostar loses shroud Vaporizes Vaporizes Falls onto Star Falls onto Star Blown away by wind Blown away by wind Contracts, Luminosity , Temp Contracts, Luminosity , Temp Hayashi track on HR Diagram Hayashi track on HR Diagram Violent Surface Wind (T Tauri Star) Violent Surface Wind (T Tauri Star) </li> <li> Slide 34 </li> <li> T-Tauri Stars Exhibit strong winds Exhibit strong winds Bipolar flows Bipolar flows Clear gas and dust away from young star so it is at last visible Clear gas and dust away from young star so it is at last visible Where the outrushing gas impacts stationary gas in the ISM a bright hot spot appears Where the outrushing gas impacts stationary gas in the ISM a bright hot spot appears Herbig-Haro object Herbig-Haro object </li> <li> Slide 35 </li> <li> T-Tauri Stars Also appear to vary in brightness Also appear to vary in brightness Likely associated with stars magnetic field, much like the active Sun Likely associated with stars magnetic field, much like the active Sun Have star spots like sun spots Have star spots like sun spots Are still collapsing to final size Are still collapsing to final size Larger in size and therefore brighter than they will be as main sequence stars Larger in size and therefore brighter than they will be as main sequence stars </li> <li> Slide 36 </li> <li> T-Tauri Star APOD A false color image of the T-Tauri system Note jet </li> <li> Slide 37 </li> <li> T Tauri Tantrum </li> <li> Slide 38 </li> <li> HH object APOD Hubble Heritage </li> <li> Slide 39 </li> <li> Pre-Main Sequence Star 10,000,000 Years 10,000,000 Years Now a True Star Now a True Star P-P Chain has begun P-P Chain has begun Larger and Cooler than Main Sequence Star Larger and Cooler than Main Sequence Star Still slowly contracting Still slowly contracting </li> <li> Slide 40 </li> <li> At last, the Sun! Contraction continues Contraction continues Central Temp=15,000,000K Central Temp=15,000,000K Outward pressure balances inward gravity Outward pressure balances inward gravity Hydrostatic Equilibrium (HSE) Hydrostatic Equilibrium (HSE) Contraction Stops, Balance Reached Contraction Stops, Balance Reached Main Sequence Star! Main Sequence Star! All main sequence stars are in HSE All main sequence stars are in HSE </li> <li> Slide 41 </li> <li> Massive Stars Steps occur faster Steps occur faster Collapse of Cloud occurs in similar way Collapse of Cloud occurs in similar way Central part still collapses faster Central part still collapses faster Fragments are larger Fragments are larger No T Tauri phase No T Tauri phase Chain Reaction from OB association Chain Reaction from OB association &gt;100 M Gravity cant hold together &gt;100 M Gravity cant hold together </li> <li> Slide 42 </li> <li> Failed Stars Some cloud fragments are too small Some cloud fragments are too small Dont get hot enough Dont get hot enough H-fusion never occurs H-fusion never occurs Warm due to collapsing Warm due to collapsing Brown dwarfs Brown dwarfs Cooling objects Cooling objects </li></ul>

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