* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Stars: HR Diagaram Stellar Evolution Astronomy 1 — Elementary Astronomy LA Mission College
Perseus (constellation) wikipedia , lookup
Aquarius (constellation) wikipedia , lookup
Space Interferometry Mission wikipedia , lookup
International Ultraviolet Explorer wikipedia , lookup
Corvus (constellation) wikipedia , lookup
Star formation wikipedia , lookup
Type II supernova wikipedia , lookup
Archaeoastronomy wikipedia , lookup
Stellar evolution wikipedia , lookup
Patronage in astronomy wikipedia , lookup
Timeline of astronomy wikipedia , lookup
Chinese astronomy wikipedia , lookup
Constellation wikipedia , lookup
Hebrew astronomy wikipedia , lookup
Astronomy in the medieval Islamic world wikipedia , lookup
History of astronomy wikipedia , lookup
International Year of Astronomy wikipedia , lookup
Ancient Greek astronomy wikipedia , lookup
Stars: HR Diagaram Stellar Evolution Astronomy 1 — Elementary Astronomy LA Mission College Spring F2015 Quotes & Cartoon of the Day “Ancient stars in their death throes spat out atoms like iron which this universe had never known. ... Now the iron of old nova coughings vivifies the redness of our blood.” — Howard Bloom “In the vast cosmical changes, the universal life comes and goes in unknown quantities ... sowing an animalcule here, crumbling a star there, oscillating and winding, ... entangling, from the highest to the lowest, all activities in the obscurity of a dizzying mechanism, hanging the flight of an insect upon the movement of the earth...” — Victor Hugo Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Announcements • • SS Homework posted, due 11/19 • I will drop the lowest midterm grade Schedule has been revised, final midterm now 12/3, Thursday after thanksgiving • If you miss midterm 3, that will become your drop grade • • unless you have a VERY good reason Very, very good Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Last Class • • • • • Intro to Stars Temperature, Color & Size Stellar Classification Intro to the HR Diagram LT HR Diagram Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 This Class • • • Midterm Debrief Stellar Classification (review) Intro to the HR Diagram • • LT HR Diagram Stellar Evolution • • • Main Sequence Red Giants and Supergiants Endgame (time permitting) • • Low mass stars— planetary nebulae, white dwarfs High mass stars — supernovae, neutron stars, black holes Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Midterm Debrief Astronomy 1 — Elementary Astronomy LA Mission College Spring F2015 Results Letter Current Course Grade Midterm 2 A 11 3 B 15 6 C 17 14 D 1 12 F 5 13 Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Review of Classification Astronomy 1 — Elementary Astronomy LA Mission College Spring F2015 The Harvard Computers • The director of the Harvard Observatory from 1877 to 1919, Edward Charles Pickering hired women to process astronomical data. • • • They were cheaper than men earned less than a clerical worker Willamina Fleming had been his maid Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 The Harvard Computers • "Pickering's Harem" or “the Harvard Computers” included several now-famous astronomers • • • Annie Jump Cannon, Henrietta Swan Leavitt Antonia Maury Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Modern Classification • • • • Harvard spectral sequence Developed by Annie Jump Cannon Characteristic absorption lines determine stellar class Note: in Astronomy “metal” means anything “heavier” than He Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Modern Classification • Cecilia Payne (PayneGaposchkin) discovered this was actually a temperature sequence • More precise than BB peak or color Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Spectral Classification • • • From hot to cool: OBAFGKM Each spectral class is further divided into 10 ranges • • • according to temperature. 0 = hot, 9 = cool therefore O0 is the very hottest, and O9 is slightly hotter than B0 and M9 stars are very cool This is still a temperature-based classification Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Let’s Practice Star Rue is Type K, Star Peeta is Type B, Star Katniss is Type F and Star Primrose is Type M. Which star is cooler than Rue? A. Peeta B. Katniss C. Primrose D. None of them Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 You observe a very bright, bluish star. It’s spectral classification is most likely ____. A. B B. G C. M D. More information is needed to determine this Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 H-R DIAGRAM Spectral Class isn’t everything • Spectral Class is not sufficient to uniquely identify a type of star • The supergiant Arcturus and the red dwarf Proxima Centauri are both Type M & 3500 K • They are definitely not identical! Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Hertzsprung and Russell http://outreach.atnf.csiro.au/education/senior/astrophysics/stellarevolution_hrintro.html • In 1911 Danish astronomer, Ejnar Hertzsprung, plotted the absolute magnitude of stars against their color • Independently in 1913 American astronomer Henry Norris Russell plotted spectral class against absolute magnitude • showed that the relationship between temperature and luminosity of a star was not random Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 The H-R Diagram • H-R diagram plots Color and/or Temperature against Luminosity and/or Absolute magnitude • • Any data plotted like this is an H-R diagram, as is a theoretical version The H-R diagram is one of the most important tools in Astronomy Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 The Main Sequence • The long strip from upper left to lower right is called the “Main Sequence.” (MS) • Stars spend most of their existence on the MS • 91% of nearby stars are MS stars. • MS stars are fusing H into He in their cores. Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Giants and Dwarfs Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 WARM-UP QUESTION Star A has an absolute magnitude of -8.1 and belongs to spectral class B8. Star B has an absolute magnitude of 11.2 and also belongs to spectral class B8. Which star has the higher temperature? A. Star A B. Star B C. They have the same temperature. D. There is not enough information to determine which star is hotter. Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 LECTURE-TUTORIAL ON THE HR DIAGRAM Star A has an absolute magnitude of -8.1 and belongs to spectral class B8. Star B has an absolute magnitude of 11.2 and also belongs to spectral class B8. Which star has the higher temperature? A. Star A B. Star B C. They have the same temperature. D. There is not enough information to determine which star is hotter. Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Let’s Practice A red giant of spectral type K9 and a red main sequence star of the same spectral type have the same _____. A. luminosity B. temperature C. absolute magnitude Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 What Type of Star is Aldebaran? A. Red Giant B. Main Sequence C. Supergiant D. White dwarf Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 What Type of Star is Vega? A. Red Giant B. Main Sequence C. Red Supergiant D. White dwarf Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Stellar Lifecycles Astronomy 1 — Elementary Astronomy LA Mission College Spring F2015 The H-R Diagram Reflects Evolutionary Stages • Main Sequence is “prime of life” Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 The Main Sequence isn’t forever! MASS is what controls ultimate fate © NASA MASS is what controls MS lifetime Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Life on the Main Sequence Astronomy 1 — Elementary Astronomy LA Mission College Spring F2015 The Main Sequence • Stars spend most of their lives on the main sequence fusing H to He in their core • The pressure resulting from the energy released by the fusion balances gravity • • the star is stable Hydrostatic equilibrium Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 • Stars on the Main Sequence are in Hydrostatic Equilibrium • The radiation pressure (outward) is balanced by the (inwards) pull of gravity • Pressure tries to blow it apart, Gravity holds it together Astronomy 1 - Elementary Astronomy Copyrighted, 1998 - 2011 by Nick Strobel http://www.astronomynotes.com/ Life on the Main Sequence -- Hydrostatic Equilibrium LA Mission College Levine F2015 Energy Source Nuclear Fusion • • The Sun is a typical MS star Powered by Thermonuclear fusion • • Converts H to He and energy Requires extreme conditions • Occurs only in star’s core Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Nuclear Fusion • nuclei have protons & neutrons • • • protons + electric charge like charges repel closer they get, harder they push apart • Must force nuclei very close, then nuclear force binds together • Temp over 10,000,000 K required • Energy is released • Image: http://www.thecollapsedwavefunction.com/ 2013/02/nuclear-fusion-and-why-its-awesome.html (for nuclei lighter than iron) Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 The Proton-proton Chain • • Image: http://theamateurrealist.com/2014/10/02/from-the-suns-core-toearths-thermosphere/ (creative commons) 1 4 Net reaction 4 H → He + energy He has less mass than 4 H • • Mass is converted to energy • • about 0.7% “missing” 2 Einstein’s mass-energy relation E=mc In Sun, happens 10 38 Astronomy 1 - Elementary Astronomy times per second LA Mission College Levine F2015 Rate of Mass-Energy Conversion © 2015 by Sidney • 1038 reactions per second consumes 6 x1011 kg per second • • • 600,000,000 metric tons Sun’s mass is very large! (2x1030 kg) 0.00001% per million year Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Low Mass and High Mass Stars • Low mass: less than about 4x Sun’s mass • • • Sun is good model use the proton proton chain High mass: • use the CNO cycle rather than the p-p chain • • same net result 4H->1He different set of reactions Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Let’s Practice It takes extreme physical conditions to initiate nuclear fusion because _____. A. nuclei have positive electrical charge and repel each other. B. the nuclear forces that hold nuclei together are very short range C. Both of these D. Neither of these Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 If fusing H to He converts millions of tons of mass into energy every second, why aren’t we worried about using up the Sun? A. The energy turns back into mass. B. The proton-proton chain only operates for a few seconds. C. A million tons of mass is a tiny fraction of the total mass of the Sun. D. The Sun is constantly manufacturing new H to replace the fused H. Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 The condition that keeps a Main-Sequence star relatively stable in size and temperature is _____. A. nuclear fusion B. the Jeans Instability C. hydrostatic equilibrium Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 The Sun’s Luminosity comes primarily from_____. A. chemical burning B. gravitational contraction C. nuclear fusion D. nuclear fission Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Stellar Evolution and “Death” Astronomy 1 — Elementary Astronomy LA Mission College Spring F2015 The Main Sequence isn’t Forever! • • Stars on the MS are stable/stationary • Mass determines maximum core temperature & fate Stars leave main sequence to become red giants or supergiants Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 RED GIANTS & SUPERGIANTS The Main Sequence isn’t Forever! • Low & Moderate Mass Stars become red giants • • • Up to about 4x Sun’s mass Up to about type A Max core temp supports fusion to He→C,O Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Core H Runs Out • • • No more fusion in core. What do you think happens when the power plant shuts down? He “ash” core Hint: think about pressure & gravity Image from: http://www.atnf.csiro.au/outreach/education/ senior/astrophysics/stellarevolution_mainsequence.html Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Core H Runs Out • • pressure reduces • what happens when the star shrinks? • • • star begins to collapse He “ash” core It heats up! Area around core reaches 10,000 K H fusion starts again Astronomy 1 - Elementary Astronomy Image from: http://www.atnf.csiro.au/outreach/education/ senior/astrophysics/stellarevolution_mainsequence.html LA Mission College Levine F2015 A Red Giant Emerges • H fusion starts again— Shell • Causes outer layers to expand • When they expand, they….. • • • He He fusing “ash” core …cool Red Giant Core continues to heat • at 100,000,000K He begins fusing • C & O build up Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 A Red Giant Emerges • • • H fusing shell expands He fusing shell forms He fusing core Core stars to build up C,O “ash” Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Life as a Red Giant (Low Mass Stars) • Red Giant is • • • • MUCH larger • Not as stable as a MS star cooler more luminous short-lived: about 1/10 Main Sequence life Astronomy 1 - Elementary Astronomy Image from: http://www.fromquarkstoquasars.com/the-day-withno-tomorrow/ LA Mission College Levine F2015 The Main Sequence isn’t Forever! • High Mass Stars become red giants & Supergiants • • • Above 4x Sun’s mass: OB and most A stars Much less stable & predictable Max core temp supports fusion up to Fe Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 High Mass Stars • Starts like low mass stars • • • Red Giant/Supergiant Core temps continue to increase • at ~1 billion K, C fusion stars • • layers of fusion up to Si (silicon)→ Fe (iron) Once Fe fusion starts, death (supernova) is imminent Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Let’s Practice If the red giant phase lasts 10% of a stars life on the main sequence, we would expect to find there are A. more main sequence stars than red giants. B. more red giants than main sequence stars. C. the same number of red giants as main sequence stars. Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Why might we observe a larger fraction of red giants compared to main sequence stars than the ~10% you would expect from the previous question? A. They live longer then main sequence stars. B. They are larger and brighter than main sequence stars. C. They are closer to us on average than main sequence stars. Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 ENDGAME OF LOW MASS/AVERAGE STARS STARS From Red Giant to Planetary Nebula • Low Mass Stars stop core fusion with He • H,He fusion shells expand • “Push off” outer layers • planetary nebula Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Planetary Nebulae http://www.astro.washington.edu/users/balick/WFPC2/ Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Final Remnant — White Dwarf • • Core exhausts He Contracts & interior heats • • Contraction stopped by electron degeneracy pressure • • but not hot enough to fuse C to O resists putting 2 e in same place Core becomes white dwarf • • • a hot, dense naked core Artist’s concept Image ESA/NASA ~25,000K at surface up to 1.4 x Sun’s mass compressed to Earth size Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 White Dwarf • White dwarfs last a long time • • Held up by e- pressure • In isolation, very slowly cool and fade away Cannot shrink, cannot heat up, cannot increase pressure “Stuck” Astronomy 1 - Elementary Astronomy Artist’s concept Image ESA/NASA LA Mission College Levine F2015 Let’s Practice A white dwarf is hot and tiny. This implies it will have a _____ color and a _____ luminosity than its main sequence progenitor. A. redder, lower B. redder, higher C. bluer, lower D. bluer, higher Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 ENDGAME OF HIGH MASS STARS Supernova Destroyer/Creater Space.com Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 The biggah boomah Artist’s Concept of Supernova Credit: ESA • Type II Supernova • • • • • Huge cataclysmic explosion about 10 billion times as luminous as the Sun fade over months or years everything heavier than iron fused by explosion Leaves behind a neutron star or black hole Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Core-collapse • "Onion layers" of heavier and heavier elements in their interiors. • Fusion in stellar core wont go heavier than iron (Fe) • • Fusing Fe uses up energy Fe core reaches 1.4 M⊙◉☉. • • Chandrasekhar limit • takes seconds! electron degeneracy pressure can’t hold it up Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Core-collapse • The core collapses. • Protons and electrons are pushed together • • form neutrons and neutrinos exert a tremendous outward pressure. • • stops when neutrons getting packed too tightly • • • observe neutrino outburst neutron degeneracy outer layers fall inward • outer layers crash into the core and rebound • shock waves move outward Star explodes — Type II Supernova Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 End result is either a Neutron Star or Black Hole © NASA • Depending on the.....? Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 End result is either a Neutron Star or Black Hole © NASA • Depending on the.....? • • Remaining mass in the core! mass is (almost) everything if you are a star... Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 The Neutron Star Route • Collapsed core <2 or 3 M ⊙◉☉ • MS star about 8-20 M⊙◉☉ • made of degenerate neutrons • very intense magnetic fields • VERY Dense • • 1.4 to 3 M⊙◉☉ compressed into a radius of about 10 km. As something spinning collapses, it spins faster. • Artist’s Concept of a Neutron star undergoing a starquake. Credit: NASA neutron stars spin very fast Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Discovery of Neutron Stars/Pulsars • • • Predicted in 1930s discovered 1967 • A graduate student named Jocelyn Bell was monitoring radio emission from space • • • discovered a really regular signal. Unlikely anything natural could produce such a regular, repeating signal. The source of the radio signals was dubbed "LGM1". (Little Green Men) Several more were discovered. Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Pulsars • Astronomers finally deduced that they were observing very rapidly rotating neutron stars -pulsars. • Charged particles move around the magnetic fields • most intense around the magnetic poles. • As the pulsar rotates, acts like a ”light house." • When the radio emission is pointed at us, we see a "pulse." Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 The Black hole Route • Collapsed core >2 or 3 M⊙◉☉ • Progenitor star > about 20 M⊙◉☉ • for objects more massive than a neutron star, there is nothing that can stop the inward collapse due to gravity • The final result is a black hole, a very small, very dense “singularity” that warps spacetime sufficiently that not even light can escape. Astronomy 1 - Elementary Astronomy Artist’s Conceptof a Black Hole Credit: NASA LA Mission College Levine F2015 SO WHAT IS A BLACK HOLE? What is a black hole? Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Journey into a Black Hole Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 ANOTHER SCENARIO (INVOLVING MORE THAN 1 STAR) Type Ia Supernovae • Ingredients : a white dwarf with a post-mainsequence companion • Or 2 white dwarfs • companion dumps material onto the white dwarf • When the mass > 1.4 Msun, the degenerate gas cannot support the pressure • resulting supernova completely obliterates the white dwarf Astronomy 1 - Elementary Astronomy Artist’s Concept Image: NASA/CXC/M Weiss. LA Mission College Levine F2015 Importance of Type Ia SN • • • Standard Candle • Can assume the same peak brightness is always produced SNIa explosions happen under very consistent conditions The light output of a Type Ia SN is therefore very predictable Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Let’s Practice What is the fate of a 10-solar mass star? A. Type Ia supernova B. Type II supernova C. white dwarf Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 What is the fate of a 5 solar mass remnant core after a Type II supernova has occurred? A. neutron star B. black hole C. white dwarf D. planetary nebula Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 If your black hole research spaceship approached the site of very massive star that had gone supernova, what would happen? A. It would inevitably get sucked into the black hole with no possibility of escape. B. It would detect the gravitational pull of the black hole and be able to go into orbit around it. C. It would be unable to locate the black hole because it’s, well, black. D. It would be repelled by the black hole. Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 WRAP-UP Topic for Next Class • Galaxies & Our galaxy Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Reading Assignment • • Astro:10&11 Astropedia:15&16 Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Homework • HW SS Posted, Due 11/19 Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015