the ism and stellar birth
DESCRIPTION
The ISM and Stellar Birth. Extinction and Reddening. Rayleigh Scattering. Extinction and Reddening. Near the Sun, Extinction amounts to 2 magnitudes per 1000 parsecs. That is, a star 1000pc from Earth will look about 2 magnitudes fainter than if space were empty completely. - PowerPoint PPT PresentationTRANSCRIPT
![Page 1: The ISM and Stellar Birth](https://reader035.vdocument.in/reader035/viewer/2022070400/5681358b550346895d9cf1ee/html5/thumbnails/1.jpg)
The ISM and Stellar Birth
![Page 2: The ISM and Stellar Birth](https://reader035.vdocument.in/reader035/viewer/2022070400/5681358b550346895d9cf1ee/html5/thumbnails/2.jpg)
Extinction and ReddeningRayleigh Scattering
![Page 3: The ISM and Stellar Birth](https://reader035.vdocument.in/reader035/viewer/2022070400/5681358b550346895d9cf1ee/html5/thumbnails/3.jpg)
Extinction and Reddening
![Page 4: The ISM and Stellar Birth](https://reader035.vdocument.in/reader035/viewer/2022070400/5681358b550346895d9cf1ee/html5/thumbnails/4.jpg)
![Page 5: The ISM and Stellar Birth](https://reader035.vdocument.in/reader035/viewer/2022070400/5681358b550346895d9cf1ee/html5/thumbnails/5.jpg)
Near the Sun, Extinction amounts to 2 magnitudes per 1000 parsecs. That is, a star 1000pc from Earth will look about 2 magnitudes fainter than if space were empty completely
![Page 6: The ISM and Stellar Birth](https://reader035.vdocument.in/reader035/viewer/2022070400/5681358b550346895d9cf1ee/html5/thumbnails/6.jpg)
• Near the Sun, Extinction amounts to 2 magnitudes per 1000 parsecs. That is, a star 1000pc from Earth will look about 2 magnitudes fainter than if space were empty completely• Dust thought to come from stellar ‘winds’, blowing out molecules of hydrogen, carbon, oxygenand other elements which cool and coalesce into dust grains
IR Visible UV
Carbon
![Page 7: The ISM and Stellar Birth](https://reader035.vdocument.in/reader035/viewer/2022070400/5681358b550346895d9cf1ee/html5/thumbnails/7.jpg)
2. Nebulae
Emission Nebulae:• Light is from emission spectrum• Reminder: result of a low density gas excited to emit light. The light is emitted at specific wavelengths • The gas is excited by light from hot stars > 25,000K (B1). It does not shine under it’s own light.• Sometimes called HII regions, as they mostly contain hydrogen that has been ionised by the light from stars• Density: 100-1000 atoms per cubic cm• Pink due to red, blue and violet Balmeremission lines
![Page 8: The ISM and Stellar Birth](https://reader035.vdocument.in/reader035/viewer/2022070400/5681358b550346895d9cf1ee/html5/thumbnails/8.jpg)
Orion Nebula (M42)
Eagle Nebula
![Page 9: The ISM and Stellar Birth](https://reader035.vdocument.in/reader035/viewer/2022070400/5681358b550346895d9cf1ee/html5/thumbnails/9.jpg)
Reflection Nebulae:• Light reflected (scattered) by dust/gas much like the moonreflects the Sun’s light – so doesn’t generate its own light• Scatter light from cooler stars• Mostly scatters blue light (like our atmosphere) – so they appear blue.• Dust grains must have sizes ranging from 0.01mm down to 100 nm• See absorption spectrum of nebula in the star’s spectrum• Doppler broadening due to motion of gas molecules• Lines split into more than one component indicates light travelled through different gas/dust clouds with different radial velocities
![Page 10: The ISM and Stellar Birth](https://reader035.vdocument.in/reader035/viewer/2022070400/5681358b550346895d9cf1ee/html5/thumbnails/10.jpg)
Witch Head Nebula
Merope Nebula
![Page 11: The ISM and Stellar Birth](https://reader035.vdocument.in/reader035/viewer/2022070400/5681358b550346895d9cf1ee/html5/thumbnails/11.jpg)
Dark Nebulae:• More dense clouds of dust and gas obscure light from backgroundstars• Very cool (10 - 100 K)
![Page 12: The ISM and Stellar Birth](https://reader035.vdocument.in/reader035/viewer/2022070400/5681358b550346895d9cf1ee/html5/thumbnails/12.jpg)
Snake nebula
Horse’s head nebula
![Page 13: The ISM and Stellar Birth](https://reader035.vdocument.in/reader035/viewer/2022070400/5681358b550346895d9cf1ee/html5/thumbnails/13.jpg)
![Page 14: The ISM and Stellar Birth](https://reader035.vdocument.in/reader035/viewer/2022070400/5681358b550346895d9cf1ee/html5/thumbnails/14.jpg)
1. HI clouds• seen through interstellar absorption lines and 21 cm radio radiation• Neutral Hydrogen• 50 – 150pc diameter• Few hundred K• 10 – 100 molecules / cubic cm• Twisted into long filaments• Near Stars, it is ionized to formHII regions
The components of the Interstellar Medium (ISM):
![Page 15: The ISM and Stellar Birth](https://reader035.vdocument.in/reader035/viewer/2022070400/5681358b550346895d9cf1ee/html5/thumbnails/15.jpg)
2. Hot intercloud medium• Between HI clouds• Few thousand K• 0.1 molecule / cubic cm• Mostly hydrogen (HII) ionized by ultraviolet light from stars
The components of the Interstellar Medium (ISM):
![Page 16: The ISM and Stellar Birth](https://reader035.vdocument.in/reader035/viewer/2022070400/5681358b550346895d9cf1ee/html5/thumbnails/16.jpg)
3. Giant molecular clouds (GMCs)• Contain larger molecules, sometimes organic, althoughstill mostly hydrogen• 10K• 1000 – 100,000 molecules / cubic cm• 15 – 60pc across• Often seen as dark nebulae
The components of the Interstellar Medium (ISM):
![Page 17: The ISM and Stellar Birth](https://reader035.vdocument.in/reader035/viewer/2022070400/5681358b550346895d9cf1ee/html5/thumbnails/17.jpg)
![Page 18: The ISM and Stellar Birth](https://reader035.vdocument.in/reader035/viewer/2022070400/5681358b550346895d9cf1ee/html5/thumbnails/18.jpg)
.
Our solar system
![Page 19: The ISM and Stellar Birth](https://reader035.vdocument.in/reader035/viewer/2022070400/5681358b550346895d9cf1ee/html5/thumbnails/19.jpg)
4. Coronal gas• 100,000 – 1,000,000 K• 0.001 – 0.0001 atoms / cubic cm• Ionized atoms• From supernovae or very hot stars• Emit X-Rays• Nothing to do with the Sun’s corona!
The components of the Interstellar Medium (ISM):
![Page 20: The ISM and Stellar Birth](https://reader035.vdocument.in/reader035/viewer/2022070400/5681358b550346895d9cf1ee/html5/thumbnails/20.jpg)
![Page 21: The ISM and Stellar Birth](https://reader035.vdocument.in/reader035/viewer/2022070400/5681358b550346895d9cf1ee/html5/thumbnails/21.jpg)
We see evidence for the interstellar medium through...• Extinction and reddening• Emission nebulae• Dark nebulae• Reflection nebulae• 21cm radiation• X-rays from hot gas between stars
...from which we can figure out the components of the ISM:• HI clouds• Hot Intercloud medium• Giant molecular clouds• Coronal gas
![Page 22: The ISM and Stellar Birth](https://reader035.vdocument.in/reader035/viewer/2022070400/5681358b550346895d9cf1ee/html5/thumbnails/22.jpg)
• Stars are born when a small part of a giant molecular cloud collapses
• Resistance to collapse:1. Heat energy
- 10K: average speed of hydrogen Molecule is 800mph
2. Magnetic fields – act as springs
3. Rotation
4. Turbulence
![Page 23: The ISM and Stellar Birth](https://reader035.vdocument.in/reader035/viewer/2022070400/5681358b550346895d9cf1ee/html5/thumbnails/23.jpg)
Need a triggering mechanism: shock waves
![Page 24: The ISM and Stellar Birth](https://reader035.vdocument.in/reader035/viewer/2022070400/5681358b550346895d9cf1ee/html5/thumbnails/24.jpg)
Need a triggering mechanism: shock waves
Shock wave from:• Supernova explosions• Ignition of hot nearby stars• Collision of molecular clouds• Spiral pattern of galaxy
![Page 25: The ISM and Stellar Birth](https://reader035.vdocument.in/reader035/viewer/2022070400/5681358b550346895d9cf1ee/html5/thumbnails/25.jpg)
NGC 1999 – Reflection nebula containing a small clump of a giant molecular cloudcollapsing to form stars
![Page 26: The ISM and Stellar Birth](https://reader035.vdocument.in/reader035/viewer/2022070400/5681358b550346895d9cf1ee/html5/thumbnails/26.jpg)
Clumps of compressed gas resulting fromthe shock wave passing through the gmcstart to collapse under their own gravity
• As gas molecules fall in, their speed increases• They collide with other molecules and randomize their speeds • Temperature is just a measure of how fast, onaverage, the random motion of molecules is• So as the cloud collapses, its temperature increases
Protostars
![Page 27: The ISM and Stellar Birth](https://reader035.vdocument.in/reader035/viewer/2022070400/5681358b550346895d9cf1ee/html5/thumbnails/27.jpg)
Protostar
Dust Free Zone
Outer Envelope cloaks protostar of Gas and Dust
IR photon
Protostars
![Page 28: The ISM and Stellar Birth](https://reader035.vdocument.in/reader035/viewer/2022070400/5681358b550346895d9cf1ee/html5/thumbnails/28.jpg)
Protostars
•As cloud collapses, it flattens out into a disk due to rotation
![Page 29: The ISM and Stellar Birth](https://reader035.vdocument.in/reader035/viewer/2022070400/5681358b550346895d9cf1ee/html5/thumbnails/29.jpg)
![Page 30: The ISM and Stellar Birth](https://reader035.vdocument.in/reader035/viewer/2022070400/5681358b550346895d9cf1ee/html5/thumbnails/30.jpg)
• Protostar continues contracting and heating up until the center becomes hot enoughto start fusing hydrogen into helium > the star is born!• Drive away their cocoon of dust and gas
![Page 31: The ISM and Stellar Birth](https://reader035.vdocument.in/reader035/viewer/2022070400/5681358b550346895d9cf1ee/html5/thumbnails/31.jpg)
![Page 32: The ISM and Stellar Birth](https://reader035.vdocument.in/reader035/viewer/2022070400/5681358b550346895d9cf1ee/html5/thumbnails/32.jpg)
Birth line
Hayashi track