1 / 32

The ISM and Stellar Birth

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.

hasad-horton
Télécharger la présentation

The ISM and Stellar Birth

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. The ISM and Stellar Birth

  2. Extinction and Reddening Rayleigh Scattering

  3. Extinction and Reddening

  4. 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

  5. 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, oxygen • and other elements which cool and coalesce into dust grains Carbon IR Visible UV

  6. 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 Balmer • emission lines

  7. Orion Nebula (M42) Eagle Nebula

  8. Reflection Nebulae: • Light reflected (scattered) by dust/gas much like the moon • reflects 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

  9. Witch Head Nebula Merope Nebula

  10. Dark Nebulae: • More dense clouds of dust and • gas obscure light from background • stars • Very cool (10 - 100 K)

  11. Horse’s head nebula Snake nebula

  12. The components of the Interstellar Medium (ISM): • 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 form • HII regions

  13. The components of the Interstellar Medium (ISM): • Hot intercloud medium • Between HI clouds • Few thousand K • 0.1 molecule / cubic cm • Mostly hydrogen (HII) ionized by ultraviolet light from • stars

  14. The components of the Interstellar Medium (ISM): • Giant molecular clouds (GMCs) • Contain larger molecules, sometimes organic, although • still mostly hydrogen • 10K • 1000 – 100,000 molecules / cubic cm • 15 – 60pc across • Often seen as dark nebulae

  15. Our solar system .

  16. The components of the Interstellar Medium (ISM): • 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!

  17. 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

  18. Stars are born when a small part of a giant molecular cloud collapses • Resistance to collapse: • Heat energy • 10K: average speed of hydrogen • Molecule is 800mph • Magnetic fields – act as springs • 3. Rotation • 4. Turbulence

  19. Need a triggering mechanism: shock waves

  20. Need a triggering mechanism: shock waves • Shock wave from: • Supernova explosions • Ignition of hot nearby stars • Collision of molecular clouds • Spiral pattern of galaxy

  21. NGC 1999 – Reflection nebula containing a small clump of a giant molecular cloud collapsing to form stars

  22. Protostars • Clumps of compressed gas resulting from • the shock wave passing through the gmc • start 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, on • average, the random motion of molecules is • So as the cloud collapses, its temperature • increases

  23. Protostars Protostar Dust Free Zone IR photon Outer Envelope cloaks protostar of Gas and Dust

  24. Protostars • As cloud collapses, it flattens out into a disk due to rotation

  25. Protostar continues contracting and heating up until the center becomes hot enough • to start fusing hydrogen into helium > the star is born! • Drive away their cocoon of dust and gas

  26. Birth line Hayashi track

More Related