Main Sequence Lifetimes • Time on Main Sequence • How much fuel it has (Core H) • How fast it consumes the fuel (Luminosity)
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
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
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
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!!
Degenerate States of Matter • Normal Matter only one atom may exist in a particular energy state. This causes atoms to have some spatial separation. • Degenerate Matter many atoms may exist in the same energy state. This causes atoms to become quite close together.
Degenerate Matter • Super-Fluids • Super-Conductors • Bose-Einstein Condensates
Bose-Einstein Condensates http://math.nist.gov/mcsd/savg/vis/bec/3D.00007.jpg
Bose-Einstein Condensates • http://science.nasa.gov/headlines/y2002/images/neutronstars/magnetar_huge.jpg
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.
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
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!!
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)
Lagrange Points http://www.jwst.nasa.gov/orbit.html
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!!!
More Massive Star is Dimmer?? • Β Lyrae • More Massive Star is Dimmer • Solution – Accretian Disk blocks some of light!!
Stellar Evolution in a Globular Cluster In the old globular cluster M55, stars with masses less than about 0.8 M are still on the main sequence, converting hydrogen into helium in their cores. Slightly more massive stars have consumed their core hydrogen and are ascending the red-giant branch; even more massive stars have begun helium core fusion and are found on the horizontal branch. The most massive stars (which still have less than 4 M ) have consumed all the helium in their cores and are ascending the asymptotic giant branch.
Dredges • 1rst – After Core H ceases • Relative abundance of Carbon, Nitrogen and Oxygen changed at surface • 2nd – After Core He ceases • Again Relative abundance of C, N, and O changed • 3rd – After during AGB (if M > 2 M() ) • Prominent Carbon compounds. C2, CH, CN • Strong C absorption lines in spectra • Carbon Star!!
TT Cygni is an AGB star in the constellation Cygnus that ejects some of its carbon-rich outer layers into space. Some of the ejected carbon combines with oxygen to form molecules of carbon monoxide (CO), whose emissions can be detected with a radio telescope. This radio image shows the CO emissions from a shell of material that TT Cygni ejected some 7000 years ago. Over that time, the shell has expanded to a diameter of about ½ light-year.
Later Stage of Low Mass Stars • Helium Shell burning decreases as its fuel is used up • Dormant Helium Shell provides insufficient pressure to support Dormant Hydrogen Shell • Hydrogen Shell contracts, Heats up, Re-ignites! • Helium produced in Hydrogen Shell adds to Helium Shell Fuel • Hydrogen Burning re-heats Helium Shell, Small Helium Flash!! • Helium Shell Burning Pushes Star out again • Outer layers detach!! Planetary Nebula!!
Planetary Nebulae • Thermal Pulses happen in increasingly shorter intervals over time • 1 M() loses about 40% of its mass this way • As outer layers are ejected, hot core exposed • Core Temp ~ 100,000 K emits UV radiation • Radiation ionizes gas creating Fluorescence glows • Radiation also propels gas outward in increasingly larger rings • Non-symmetric radiation creates hour-glass shapes
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
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+
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
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
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.
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 *****
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
Type II, Ib, Ic are found near sites of new star formation. • Type Ia found in galaxies where there are no ongoing star formations
Supernova leftovers • Remnants • Gasses and elements • Core Relics • Neutron Stars • Black Holes
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
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
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!!
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