Main Sequence Lifetimes

1. Main Sequence Lifetimes • Time on Main Sequence • How much fuel it has (Core H) • How fast it consumes the fuel (Luminosity)

2. Main Sequence Lifetimes

3. Main Sequence Lifetimes • Our Sun M = 1 M() and L = 1 L() • tMS-lifetime = 1010 years = 10 billion years • Large Mass Bright Star M = 10 M() and L = 105 L () • tMS-lifetime = 1010 • tMS-lifetime = 106 years = 1 Million years

4. Stages in the Evolution of a Star with More than 0.4 Solar Masses (a) During the star’s main-sequence lifetime, hydrogen is converted into helium in the star’s core. (b) When the core hydrogen is exhausted, hydrogen fusion continues in a shell, and the star expands to become a red giant. (c) When the temperature in the red giant’s core becomes high enough because of contraction, core helium fusion begins.

5. Nuclear Fusion and Forces of Repulsion • For Hydrogen repulsion of 2 (1+) charges • At 1 Atomic radius Frepulsion= 2.3 x 10-8 N • For Helium repulsion of 2 (2+) charges • At 1 Atomic radius Frepulsion= 9.2 x 10-8 N • Ratio of forces 9.2/2.3~4x • For Hydrogen, we had 2 pairs of H fused to make 1 Helium. • For Helium, we need 3 pairs of He to fuse to make 1 Carbon  so ratio 3/2(4) = 6x  6x as much force

6. Nuclear Fusion • Hydrogen Fusion requires temps ~ 7 Million K • Helium Fusion requires temps ~ 100 Million K • A bit more than 6x (~14x) • Energy from Helium fusion ~0.1 Energy released in Hydrogen fusion • All stars > 0.5 M() can create Helium burning Temps of 100 million K

7. Nuclear Fusion • High Mass Stars create 100 Million K by contracting Core a little. • Low Mass Stars create 100 Million K by contracting Core a lot! • If a Low Mass Star contracts Core a lot, Core can become Degenerate!!

8. Degenerate Core of a Star • Gas atoms so close act like Solid! • Heat a Gas, Changes in Both Volume and Pressure • Heat a Solid, Small Changes in both Volume and Pressure.

9. High Mass Star (Normal Gas Core) • Fusion releases Energy  Heats Gas • Heated Gas  Gas Expands due to increase Pressure • Expanded Gas  Cools Gas • Cooling Gas decreases Nuclear Fusion rate • Decreased Nuclear Fusion Rate  Pressure drops • Gas Contracts  Increased Temps  Increased Fusion • Gas properties regulate Nuclear Fusion

10. Low Mass Star (Degenerate Core) • Fusion releases Energy  Heats Gas (Solid) • Heated Solid  No Increase in Pressure • No Increase in Pressure  No Expansion • No Expansion  No Cooling • Increased Temperatures  Increased Nuclear Rate • Increase Nuclear Rate  Increased Release of Energy • Increased Temps etc…… • No Regulation of Nuclear Fusion  Helium Flash!!

11. Helium Flash • Explosive release of energy • Usually restores Degenerate Core back to normal Core • Helium Flash Ends First Red Giant Phase of Low Mass Stars and start Yellow Giant Phase • High Mass Stars do not have a helium flash • High Mass Stars go originally to Yellow Giant Phase and then expand into Red Giants • Onset of Helium Burning often cause stars to become unstable (Variable Stars)

12. https://en.wikipedia.org/wiki/Abundance_of_the_chemical_elementshttps://en.wikipedia.org/wiki/Abundance_of_the_chemical_elements

13. The gravitational domain of a star in a close binary system is called its Roche lobe. The two Roche lobes meet at the inner Lagrangian point. The sizes of the stars relative to their Roche lobes determine whether the system is • A detached binary, (b) a semidetached binary, (c) a contact binary, or (d) an overcontact binary.

14. Close Binary Star Systems

15. Lagrange Points http://www.jwst.nasa.gov/orbit.html

16. Mass Mystery??? • Both stars in a binary form about same time • More massive stars evolve faster • Red Giant star (on left) is less massive than Main Sequence star (on right) • Solution Mass Transfer!!!

17. More Massive Star is Dimmer?? • Β Lyrae • More Massive Star is Dimmer • Solution – Accretian Disk blocks some of light!!

18. Neutrinos emanate from supernovae like SN 1987A More than 99% of the energy from such a supernova is emitted in the form of neutrinos from the collapsing core

19. 1980’s • Two “Neutrino Telescopes” went into operation • Kamiokande (U-Tokyo and U-Penn) detector in a zinc mine in Japan • IMB (U-Cal at Irvine, U-Michigan, and Brookhaven) detector in a salt mine in Ohio • Neutrinos interacts with a proton in the water creating a supersonic positron • Positron moves faster than the speed of light in water creating a shockwave effect known as Cerenkov radiation

21. http://ncas.sawco.com/condon/text/s6c06f1b.htm

22. http://www.pbs.org/wgbh/nova/barrier/boom/images/cone.jpeg

23. http://www.sonicbooms.org/T38/T38c3.jpg

24. http://www.simulationinformation.com/sonic%20boom.jpg

25. http://www.anomalies-unlimited.com/Odd%20Pics3/Images/shuttlesonic.jpghttp://www.anomalies-unlimited.com/Odd%20Pics3/Images/shuttlesonic.jpg

26. http://www.physlink.com/Education/AskExperts/ae219.cfm

27. http://dept.physics.upenn.edu/balloon/cerenkov_radiation.htmlhttp://dept.physics.upenn.edu/balloon/cerenkov_radiation.html

28. http://www.physlink.com/Education/AskExperts/ae219.cfm

29. Solar Neutrinos Vs Supernova Neutrinos?? • Energy • Solar Neutrinos ~<1 MeV • Supernova Neutrinos ~>20 MeV • Measuring Properties of Cerenkov radiation, the speed of the e+ which created the radiation can be found • Speed of e+ gives originally energy of neutrino which collided with proton that created the e+

30. February 23, 1987 • 12 second burst of neutrinos detected • Kamiokande detected 11 Neutrinos • IMB detected 8 Neutrinos • The Earth was subjected to a neutrino flux of approximately 1016 neutrinos • Supernova emitted 1058 neutrinos in about 10 seconds 160,000 years ago • Approximately 100x the Energy the Sun has emitted in its entire lifetime!! • About 100x the amount of light energy the Supernova emitted • Approximately 10x the total luminosity of the stars in the entire observable universe at the moment

31. February 23, 1987 • 3 hours later Light arrived from Supernova 1987 ???? • Neutrinos not blocked by gas layers of the star • Light created only after shockwave reached the outer-most layers of the star

32. Why was SN 1987A Unusual? • Peak Intensity about 0.1 of intensity of other observed Supernovas • Confusion over whether progenitor star was a Red Supergiant or a B3 I Blue Supergiant? • Pop I or Pop II star? • Possible Pop II meaning it oscillated between Red and Blue Supergiant.

33. Supernova 1987A • In Blue Supergiant phase, radius is about .1 of size than when in Red Supergiant phase • When explosion occurred more mass closer to core, more energy needed to push outer layers away, less available for creating brighter light • Type II Supernova

34. Types of Supernovas • Type II do have prominent Hydrogen Lines • Type I do not have prominent Hydrogen Lines in their spectra • Type I further subdivided into • Type Ia which has strong absorption lines of Si • Type Ib which does not have Si but does have absorption lines of He • Type Ic which has neither

35. http://csep10.phys.utk.edu/guidry/violence/sn87a-rings.html

36. http://apod.nasa.gov/apod/image/0402/sn1987a_acsHubble_full.jpghttp://apod.nasa.gov/apod/image/0402/sn1987a_acsHubble_full.jpg

37. http://physics.uoregon.edu/~courses/BrauImages/Chap21/FG21_08A.jpghttp://physics.uoregon.edu/~courses/BrauImages/Chap21/FG21_08A.jpg

39. Type II, Ib, Ic are found near sites of new star formation. • Type Ia found in galaxies where there are no ongoing star formations

40. Supernova leftovers • Remnants • Gasses and elements • Core Relics • Neutron Stars • Black Holes

41. Why More Supernovas in other Galaxies?? • Ought to see about 5 per century based on what we see in other galaxies (~100 remnants seen with radio in other galaxies) • Last Supernova in our Galaxy 1604 – Kepler • 1572 Brahe • 1054 China • Interstellar dust blocks best star forming regions from our view

42. Most supernovae occurring in our Galaxy are hidden from our view by interstellar dust and gases but a supernova remnant can be detected at many wavelengths for centuries after the explosion

43. Neutrons form : • Supernova’s Create many reactions • Neutrons first discovered in 1932 Chadwick • Zwicky (Caltech) and Baade (Mt. Wilson Obs) Proposed parallel to White Dwarf, Neutron Star • White Dwarf uses Degenerate e- pressure to sustain outer layers weight • Neutron Star uses Degenerate n pressure • Neutrons can with stand more force, hence 1.4 M() limit no longer applies

44. Improbabilities for a Neutron Star • Thimbleful would weigh 100 million tons Density 1017 kg/m3 • Recall 1 teaspoon of White Dwarf weighs ~ 5.5 tons!! Density 109 kg/m3  1 M() White Dwarf would have a diameter of 10,000 – 12,000 km, Size of Earth!!  1 M() Neutron Star would have a diameter of 30 km (19 miles), Size of large city!!

45. http://www.astro.umd.edu/~miller/nstar.html

46. 1960’s Cambridge England • 1967 Anthony Hewish’s Research Group from Cambridge University finish 4 ½ acre radio telescope array • Jocelyn Bell, Graduate Student, discovers regular pulses of radio noise from one location in the sky. • Period of Pulses was 1.3373011 seconds

47. Sources of Pulsing • Little Green Men (aliens) • Several Sources found across sky Periods range from 0.25 s to 1.5 s • Variable stars (cepheids, etc) • Variation in intensity is on order of days, weeks, not seconds! • White Dwarf Pulses (Acretion disks, Hot Spots) • Would require rotations less than 1 second at their diameters, not likely • Eclipsing Binaries • Again too short a period, stars would literally have to be overlapping to create that kind of period

48. Bell Burnell was in charge of operating the telescope and analyzing the data, according to an article she wrote for Cosmic Search Magazine in the 1970s. Using this technique, Bell Burnell spotted an object that appeared to be flickering every 1.3 seconds; this pattern repeated for days on end. The object didn't match the profile of a quasar. The signal conflicted with the generally chaotic nature of most cosmic phenomenon, the researchers would later explain. In addition, the light was of a very specific radio frequency, whereas most natural sources typically radiate across a wider range. For those reasons, Bell Burnell, Hewish and some other members of the astronomy department had to acknowledge that they might have found an artificially created signal — something emitted by an intelligence species. Burnell even labeled the first pulsar LGM1, which stood for "little green men 1." https://www.space.com/38916-pulsar-discovery-little-green-men.html

49. Bell Burnell would later report that Hewitt called a meeting without her, in which he discussed with other members of the department how they should handle presenting their results to the world. While their fellow scientists might practice restraint and skepticism, it was likely that the possible detection of an intelligent alien civilization could create chaos among the public, the scientists said. The press would very likely blow the story out of proportion and descend on the Cambridge researchers. According to Hewitt, one person even suggested (perhaps only partly joking) that they burn their data and forget the whole thing.  https://www.space.com/38916-pulsar-discovery-little-green-men.html

50. Years later, Burnell wrote that she was rather annoyed at the appearance of the strange signal for another reason. As a graduate student, she was trying to get her thesis work done before her funding ran out, but work on the pulsar was taking away from her primary pursuit.  "Here I trying to get a Ph.D. out of a new technique, and some silly lot of little green men had to choose my aerial and my frequency to communicate with us," she wrote in the article for Cosmic Search Magazine. https://www.space.com/38916-pulsar-discovery-little-green-men.html