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Astronomy 350 Cosmology

Astronomy 350 Cosmology. Professor Lynn Cominsky Department of Physics and Astronomy Offices: Darwin 329A and NASA EPO (707) 664-2655 Best way to reach me: lynnc@charmian.sonoma.edu. Group 6. Justin Beck Tiffany Henning Pamela Riek Ryan Silva. Great job group 6!.

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Astronomy 350 Cosmology

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  1. Astronomy 350Cosmology Professor Lynn Cominsky Department of Physics and Astronomy Offices: Darwin 329A and NASA EPO (707) 664-2655 Best way to reach me: lynnc@charmian.sonoma.edu Lynn Cominsky - Cosmology A350

  2. Group 6 • Justin Beck • Tiffany Henning • Pamela Riek • Ryan Silva Great job group 6! Lynn Cominsky - Cosmology A350

  3. Stellar evolution made simple Puff! Bang! BANG! Stars like the Sun go gentle into that good night More massive stars rage, rage against the dying of the light Lynn Cominsky - Cosmology A350

  4. Exploding Stars • At the end of a star’s life, if it is large enough, it will end with a bang (and not a whimper!) Supernova 1987A in Large Magellanic Cloud HST/WFPC2 Lynn Cominsky - Cosmology A350

  5. Supernova Remnants • Radioactive decay of chemical elements created by the supernova explosion Vela Region CGRO/Comptel Lynn Cominsky - Cosmology A350

  6. Supernovae Chandra X-ray image of Eta Carinae, a potential supernova • Supergiant stars become (Type II) supernovae at the end of nuclear shell burning • Iron core often remains as outer layers are expelled • Neutrinos and heavy elements released • Core continues to collapse Lynn Cominsky - Cosmology A350

  7. Making a Neutron Star Lynn Cominsky - Cosmology A350

  8. Three views of a Supernova Lightcurve Spectrum Image Lynn Cominsky - Cosmology A350

  9. Crab nebula movie • Observed by Chinese astronomers in 1054 AD • Age determined by tracing back exploding filaments • Crab pulsar emits 30 pulses per second at all wavelengths from radio to TeV Lynn Cominsky - Cosmology A350

  10. Crab nebula Infrared/Keck Radio/VLA Lynn Cominsky - Cosmology A350

  11. Crab nebula Optical/Palomar Optical/HST WFPC2 Lynn Cominsky - Cosmology A350

  12. Crab nebula and pulsar X-ray/Chandra Lynn Cominsky - Cosmology A350

  13. Cas A neutron star X-ray/Chandra Radio/VLA • ~320 years old • 10 light years across • 50 million degree shell Lynn Cominsky - Cosmology A350

  14. Neutron Stars • Neutron stars are formed from collapsed iron cores • All neutron stars that have been measured have around 1.4 Mo (Chandrasekhar mass) • Neutron stars are supported by pressure from degenerate neutrons, formed from collapsed electrons and protons • A teaspoonful of neutron star would weigh 1 billion tons • Neutron stars with very strong magnetic fields - around 1012-13 Gauss - are usually pulsars due to offset magnetic poles Lynn Cominsky - Cosmology A350

  15. Neutron Stars: Dense cinders Mass: ~1.4 solar masses Radius: ~10 kilometers Density: 1014-15 g/cm3 Magnetic field: 108-14 gauss Spin rate: from 1000Hz to 0.08 Hz Lynn Cominsky - Cosmology A350

  16. Distances to Supernovae Supernova 1987A in LMC D = 47 kpc • Brightest SN in modern times, occurred at t0 • Measure angular diameter of ring, q • Measure times when top and bottom of ring light up, t2 and t1 • Ring radius is given by R = c(t1-t0 + t2-t0)/2 • Distance = R / q Lynn Cominsky - Cosmology A350

  17. Distances to Supernovae • Type Ia supernovae are “standard candles” • Occur in a binary system in which a white dwarf star accretes beyond the 1.4 Mo Chandrasekhar limit and collapses and explodes • Decay time of light curve is correlated to absolute luminosity • Luminosity comes from the radioactive decay of Cobalt and Nickel into Iron • Some Type Ia supernovae are in galaxies with Cepheid variables • Good to 20% as a distance measure Lynn Cominsky - Cosmology A350

  18. Standard Candles • If you have two light sources that you know are the same brightness • The apparent brightness of the distant source will allow you to calculate its distance, compared to the nearby source • This is because the brightness decreases like 1/(distance)2 movie Lynn Cominsky - Cosmology A350

  19. Cosmological parameters W = density of the universe / critical density • < 1hyperbolic geometry W = 1flat or Euclidean W > 1spherical geometry Lynn Cominsky - Cosmology A350

  20. Cosmological parameters • In order to find the density of the Universe, you must measure its total amount of matter and energy, including: • All the matter we see • All the dark matter that we don’t see but we feel • All the energy from starlight, background radiation, etc. • The part of the total density/critical density that could be due to matter and/or energy =WM • Current measurements : WM< 0.3 Lynn Cominsky - Cosmology A350

  21. Supernovae & Cosmology 0.4 0 0.2 0.6 0.8 1 WM = matter WL = cosmological constant Redshift Lynn Cominsky - Cosmology A350

  22. Einstein meets Hubble WM = 8 p G r 3 Ho2 WL = L 3 Ho2 W(total) = WM +WL Perlmutter et al. 40 supernovae Lynn Cominsky - Cosmology A350

  23. Accelerating Universe • Results from Perlmutter et al. (and also by another group from Harvard, Kirshner et al.) strongly suggest that if WM = 0.3 : • WL = 0.7 • There is some type of dark energy which is causing the expansion of the Universe to accelerate • Other results indicate that Wtotal = 1 • This will be discussed later at much greater length Lynn Cominsky - Cosmology A350

  24. Distributions • If sources are located randomly in space, the distribution is called isotropic • If the sources are concentrated in a certain region or along the galactic plane, the distribution is anisotropic Lynn Cominsky - Cosmology A350

  25. Classifying Bursts • In this activity, you will be given twenty cards showing different types of bursts • Pay attention to the lightcurves, optical counterparts and other properties of the bursts given on the reverse of the cards • How many different types of bursts are there? Sort the bursts into different classes • Fill out the accompanying worksheet to explain the reasoningbehind yourclassification scheme Lynn Cominsky - Cosmology A350

  26. What makes Gamma-ray Bursts? • X-ray Bursts • Properties • Thermonuclear Flash Model • Soft Gamma Repeaters • Properties • Magnetar model • Gamma-ray Bursts • Properties • Models • Afterglows • Future Mission Studies Lynn Cominsky - Cosmology A350

  27. X-ray Bursts • Thermonuclear flashes on Neutron Star surface – hydrogen or helium fusion • Accreting material burns in shells, unstable burning leads to thermonuclear runaway • Bursts repeat every few hours to days • Bursts are never seen from black hole binaries (no surface for unstable nuclear burning) or from (almost all) pulsars (magnetic field quenches thermonuclear runaway) Lynn Cominsky - Cosmology A350

  28. X-ray Burst Sources bursters non-bursters Globular Clusters • Locations in Galactic Coordinates • Most bursters are • located in globular • clusters or near the • Galactic center • They are therefore relatively older systems Lynn Cominsky - Cosmology A350

  29. X-ray Burst Source Properties • Neutron Stars in binary systems • Weaker magnetic dipole: B~108 G • NS spin period seen in bursts ~0.003 sec. • Orbital periods : 0.19 - 398 h from X-ray dips & eclipses and/or optical modulation • > 15 well known bursting systems • Low mass companions • Lx = 1036 - 1038 erg/s Lynn Cominsky - Cosmology A350

  30. X-ray Emission • X-ray emission from accretion can be modulated by magnetic fields, unstable burning and spin • Modulation due to spin of neutron star can sometimes be seen within the burst Lynn Cominsky - Cosmology A350

  31. X-ray Burst Sources • Burst spectra are thermal black-body L(t) = 4 p R2s T(t)4 Temperature Radius Expansion c2 Lynn Cominsky - Cosmology A350 Cominsky PhD 1981

  32. Soft Gamma Repeaters SGR 1627-41 LMC • There are four of these objects known to date • One is in the LMC, the other 3 are in the Milky Way Lynn Cominsky - Cosmology A350

  33. Soft Gamma Repeater Properties • Young Neutron Stars near SNRs • Superstrong magnetic dipole: B~1014-15 G • NS spin period seen in bursts ~5-10 sec, shows evidence of rapid spin down • No orbital periods – not in binaries! • 4 well studied systems + several other candidate systems • Several SGRs are located in or near SNRs • Soft gamma ray bursts are from magnetic reconnection/flaring like giant solar flares • Lx = 1042 - 1043 erg/s at peak of bursts Lynn Cominsky - Cosmology A350

  34. SGR 1900+14 • Strong burst showing ~5 sec pulses • Change in 5 s spin rate leads to measure of magnetic field • Source is a magnetar! Lynn Cominsky - Cosmology A350

  35. SGR burst affects Earth • On the night of August 27, 1998 Earth's upper atmosphere was bathed briefly by an invisible burst of gamma- and X-ray radiation. This pulse - the most powerful to strike Earth from beyond the solar system ever detected - had a significant effect on Earth's upper atmosphere, report Stanford researchers. It is the first time that a significant change in Earth's environment has been traced to energy from a distant star. (from the NASA press release) Lynn Cominsky - Cosmology A350

  36. Gamma Ray Burst Properties • A cataclysmic event of unknown origin • Unknown magnetic field • No repeatable periods seen in bursts • No orbital periods seen – not in binaries • Thousands of bursts seen to date – no repetitions from same location • Isotropic distribution • Afterglows have detectable redshifts which indicate GRBs are at cosmological distances (i.e., far outside our galaxy) • Lg= 1052 - 1053 erg/s at peak of bursts Lynn Cominsky - Cosmology A350

  37. The first Gamma-ray Burst • Discovered in 1967 while looking for nuclear test explosions - a 30+ year old mystery! Vela satellite Lynn Cominsky - Cosmology A350

  38. Compton Gamma Ray Observatory BATSE • Eight instruments on corners of spacecraft • NaI scintillators Lynn Cominsky - Cosmology A350

  39. CGRO/BATSE Gamma-ray Burst Sky • Once a day, somewhere in the Universe Lynn Cominsky - Cosmology A350

  40. The GRB Gallery When you’ve seen one gamma-ray burst, you’ve seen…. one gamma-ray burst!! Lynn Cominsky - Cosmology A350

  41. Near or Far? Isotropic distribution implications: Very close: within a few parsecs of the Sun Why no faint bursts? Very far: huge, cosmological distances What could produce such a vast amount of energy? Sort of close: out in the halo of the Milky Way A comet hitting a neutron star fits the bill Silly or not, the only way to be sure was to find the afterglow. Lynn Cominsky - Cosmology A350

  42. Breakthrough! In 1997, BeppoSAX detects X-rays from a GRB afterglow for the first time, 8 hours after burst Lynn Cominsky - Cosmology A350

  43. The View From Hubble/STIS 7 months later Lynn Cominsky - Cosmology A350

  44. On a clear night, you really can see forever! 990123 reached 9th magnitude for a few moments! First optical GRB afterglow detected simultaneously Lynn Cominsky - Cosmology A350

  45. The Supernova Connection GRB011121 Afterglow faded like supernova Data showed presence of gas like a stellar wind Indicates some sort of supernova and not a NS/NS merger Lynn Cominsky - Cosmology A350

  46. Hypernova • A billion trillion times the power from the Sun • The end of the life of a star that had 100 times the mass of our Sun movie Lynn Cominsky - Cosmology A350

  47. Iron lines in GRB 991216 • Chandra observations show link to hypernova model when hot iron-filled gas is detected from GRB 991216 Iron is a signature of a supernova, as it is made in the cores of stars, and released in supernova explosions Lynn Cominsky - Cosmology A350

  48. Catastrophic Mergers • Death spiral of 2 neutron stars or black holes Lynn Cominsky - Cosmology A350

  49. Which model is right? The data seem to indicate two kinds of GRBs • Those with burst durations less than 2 seconds • Those with burst durations more than 2 seconds Short bursts have no detectable afterglows so far as predicted by the NS/NS merger model Long bursts are sometimes associated with supernovae, and all the afterglows seen so far as predicted by the hypernova merger model Lynn Cominsky - Cosmology A350

  50. Gamma-ray Bursts • Either way you look at it – hypernova or merger model • GRBs signal the birth of a black hole! Lynn Cominsky - Cosmology A350

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