stellar-death - -nnouncements . is due Thurs. 7 I s on...

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Unformatted text preview: -nnouncements . is due Thurs. 7 I s on April 5, 2010 _ill be the same as the first exam entrate on the material since the last exam ‘ - the lectures on the Sun). NASA, NOAO, ESAand The Hubble Heritage Team (STScl/ Degeneracy Pressure Heisenberg uncertainty principle: AxAp > h p N h/Ax : Eng/3 Compress electrons, Ax : n;1/3 Pressure: P : nevmp Classical mechanics: 0 = p/me :> P ~ h2n2/3/m6 Relativity: v = c :> p N hcn4/3 . . _ EL Number denSIty. ne 7 Am AST 203 (Spring 2011) Degeneracy Pressure Detailed calculation: Z Non-relativistic: P : 9.9 x 1012 dyn cm_2 (A HSE: R o< M—l/3 Z A L 1 g (urn—3 >4”( )“3 HSE: maximum mass is 1.4 M(D (Chandrasekhar mass) Relativistic: P = 1.2 X 1015 dyn (:m_2 ( AST 203 (Spring 2011) Stellar Death (Kulner, Ch. 11; see also Shu, Ch. 7; Hester el al., Ch. 17; Carroll and Osllie, Ch. 15) AST 203 (Spring 2011) Stellar Death (Shu on. 7) There are several different outcomes of stellar evolution: Nothing: the star explodes, ejecting all of its matter into the interstellar medium White dwarf: degenerate core of the star remains, and slowly cools and fades Neutron star: extremely compact (nuclear densities) core is left behind. May be active for some time, but will eventually fade Black Hole: a singularity Already seen: low mass stars (e.g. Sun) end up as a white dwarf. AST 203 (Spring 2011) Supernovae Supernovae are exploding stars. Supernova are classified according to their spectra. Type I supernovae—show no hydrogen in their spectrum. Further divided into : Type la (strong Si lines) Type lb (no Si; strong He lines) Type lc (no Si; no He lines) Type II supernovae—strong hydrogen lines in their spectrum. Type lb, lo, and II all have similar origins—massive star explosion. Type la are different—we'll discuss them later. AST 203 (Spring 2011) l Thermonucleor Supernovae Supernovae Spectra — mug-n _ Sulfar 9mm Type In No Hydrogen Strong Silicon SN lb, lo, and II have similar Weak Hydragen Strong Helium origins 3: Core Collapse Supernovae SN la have a distinct E mechanism from others. 3 : NTpry: Ic ,:_ E Type lb Type II strong Hydrogen _ Dan Kasen , , http:/Ipanisse.lbl.govl~dnkasenlluloriallgraphicslsn_lypes.jpg a LLLLlJ—LLLLLLLLl-LLLLLLLLLl—LLLLLLLLLl—LLLLLLLLU-LLLLLLLLLI— 4-000 5000 6000 7000 8000 9000 AST 203 (Spring 2011) Wavelength (Mgslromsj Core-Collapse Su pernovae Lightcurve—the luminosity/magnitude 1 A vs. time. = I glitchlgzmw g Quick rise followed by decay in 1 g . g 0 brightness over ~ a month. § Type II SNe are further divided into ll- 5 I l . l . ‘ Si) 0 50 100 l50 200 250 300 350 400 P (plateau) and ll-L (linear): —1*—v—'—v—x-——v—r—y——-.————-l—— Difference in shape due to time it 0 takes for radiation to leak out. 1‘pr ILL supernovae blue light cum m,7 below maximum light 4 l A L . (l 50 100 150 lllll 250 300 350 400 Days nflaz mmimum light FIGURE 15.8 The Characteristic shape» unype Hermd'l'ypc ILLliglu curve». These are composite light Curves. based on the observations of many supernovae (Fjgurcs adaplcd from Doggen and BranchAA'mm. 1.. 90. 2303, 1985.) AST 203 (Spring 2011) Core-Collapse Supernovae When massive stars evolve, they burn successively heavier elements on their way up to the iron peak. Once iron group elements are made (56Fe, 56Ni), any further reactions (fusion or fission) require energy to proceed. H burning He burning C burning Ne burning O burning Si burning Fe core AST 203 (Spring 2011) Core-Collapse Supernovae U 235 1/ flu 239 (U0!SS!JlSB:l/B!P9d!>l!M) Average binding energy per nucleon (MeV) 4:. O 30 60 90 120 150 180 210 240 270 Number ofnucleons in nucleus AST 203 (Spring 2011) Evolution of High Mass Stars No more energy from fusion once core is Fe. Star begins to collapse. No white dwarf + planetary nebula left behind, but rather, a core collapse supernova will result. A U: P: c 3 ._ E o m V > 3: m o E E 2 30,000 10,000 6,000 3000 surface temperature (Kelvin) my” (“@2003 Pearson mm in: gums fem-i Wm My AST 203 (Spring 2011) (from Bennett et al.) Core-Collapse Supernovae (Kutner Ch. 11, Hester et al. Ch. 17) Since the star has run out of energy sources, it begins to cool. Core is degenerate, grows in mass (from ashes from the shell sources above)—approaches the Chandrasekhar limit (1.4 Me). > 1.4 MG, core collapses—relativistic electron degeneracy pressure insufficient. Core T reaches ~ 1010 K —> photons (remember blackbody spectrum) break apart heavy nuclei—photodistinegration. The most important reactions are: 32Fe+ *y—> 13§He+4n §He+*y—> 2p—l—2n AST 203 (Spring 2011) Core-Collapse Supernovae (Kutner Ch. 11, Hester et al. Ch. 17) Heavy elements in the core break down—become protons, electrons, and neutrons. This takes energy out of the core. Further contraction —> electrons and protons combine to neutrons p + e —> n —l— V The core becomes a proto-neutron star. Making neutrons cools the stars Escaping neutrinos also cool the star—it continues to collapse. This entire process takes about 1 second. When the density of the core becomes close to nuclear densities, the collapse of the innermost part of the core stops. AST 203 (Spring 2011) Core-Collapse Supernovae (Kutner Ch. 11, Hester et al. Ch. 17) Strong force resists the collapse. Outer layers of the core do not know that the inner core stopped. Outer layers of the core hit the compact inner core and bounce— shock wave moves outward through the star. Neutrinos are produced at high rates during collapse. Core is dense—neutrinos are trapped. They create a bubble of hot gas behind the shock, which pushes the shock outward—this is really not well understood. AST 203 (Spring 2011) Core-Collapse Supernovae This event is called a core-collapse supernovae. We won't differentiate between Type lb, lo, and II supernovae Mechanism for all of these is very similar—gravity bomb: gravitational potential energy released from core collapse powers the supernovae. Most of the energy is carried away by the neutrinos. About 1% is photons. AST 203 (Spring 2011) Core-Collapse Supernovae These events mark the end of life of massive stars. Rare—about 1 per century per galaxy our size. Extremely luminous (~109 L®)—seen in galaxies throughout the universe. Heavy elements are produced here which chemically enrich the interstellar medium. Neutron rich reactions produce elements heavier than iron via the r- and s-processes. AST 203 (Spring 2011) Eta Carinae: a > 100 M star, 7000 — 8000 Iy away. In the 1843 it was the second brightest star in the sky (despite its great distance away) Expected to supernovae real soon... Eta Carinae http:/Iantwrp.gsfc.nasa.govlapodlap060326.hlml HUbble Space Telescope ' AST 203 (Spring 2011) m PRC‘JGVZBB ‘ ST SCI 0P0 - June 10. 1996 - J. Morse [U CO). K. Davidson (U. MN) and NASA Core-Collapse Supernovae Comparing images taken some time apart, and looking for “new” stars, we can find the supernovae in distant galaxies. Follow-up spectra observations can tell us what type it is. A Type II supernovae in M51 (SN 2005cs) (R. Jay GaBany) AST 203 (Spring 2011) Core-Collapse Supernovae Most of what we know about core-collapse SNe comes from computer simulations. (exuer pue KelsooM) Exceptionally difficult simulations. Need to follow the matter, neutrinos, and interactions between them to get it right. To date, 3-D core-collapse supernova models are unsuccessful in producing ex p I I o n s ' Figure 2: Looking mm m hmn‘affl supdrnava (14;. mepmon gamma vl'gorou: bailing af m nmfino—heumd, cum;an region mmmd the nascent neutron slur. Buaynnrbulzble: offiarmtm- mou'vig auwardr appmr brt'gllrm andpellaw. These are bounded by a :hoclcwvz, which expands outwards, dfimpfi'ng rise :rar. Th: inmges,from mp lafiro bottom right, Show the mus-mm MEI, 0.2, 5.3, and DJJECDIIdJ after the shock is born. Ar Hummus, file Jlloclr has at: mmgs mdt‘iu (inbuilt 2W, 309, .500, QMAOOG hlomerers, r'aspecfi'vety. AST 203 (Spring 2011) Remnant The explosion leaves behind a remnant and a compact object (neutron star or black hole, depending on the progenitor mass). V IC 443, and the wake caused by the moving neutron star. (NASAICXCIB. Gaensler el al; NASA/ROSAT/Asaoka & Aschenbach; NRC/DRAOID.Leahy; NRAONLA; DSS) AST 203 (spring 2011) Neutron Star Kick The guitar nebula—a bow shock from a 1600 km/s neutron star moving through the interstellar medium. Shami Chatterjee AST 203 (Spring 2011) SN 1987A One of the most famous core- - collapse supernovae is 1987A ' Exploded in the Large Magellanic Cloud—a satellite galaxy of ours. = .1 m 5 m 8 'c 9; Closest supernova (only 51.4 kpc away) since Kepler's (1604) in our galaxy. _ Ar I" m _|| UL '1" .- 1987A was so Close that we The left image shows the supernova about 10 detected 24 neutrinos coming days after explosion and the right image shows from the event the blue giant star before exploding. AST 203 (Spring 2011) SN 1987A AAVSO DATA FOR SN 1937A r WWW.AAVS0.0RG 2 1 I Mag m 10 12 14 2445820 2447094 2447353 2447642 Juiian Date Visual Validated o AST 203 (Spring 2011) SN 1987A After the explosion, a :7 _ . . : " ' remnantappears. - _'.‘ Circumstellar material ejected from the progenitor is ionized by the explosion shock, making rings. So far, no neutron star , has been discovered in the remnant. (NASA/ESA) AST 203 (Spring 2011) SN 1987A March 23, 2001 December 7, 2001 January 5,2003 August 12, 2003 November 28, 2003 Supernova 1987A - 1994-2003 Hubble Space Telescope o WFPC2 - ACS NASA and R. Kirshner (HarvardrSmithsonian Center for Astrophysics) STSCJ’PRC04709b AST 203 (Spring I SN 1987A Credit: The SuperMACHO Team, CTIo. NOAo. NSF http:/Iantwrp.gsfc.nasa.govlapodlap060125.html Light echos from SN 1987A. We can see light echos from older SN in the LMC as well—we can even take spectra of them! AST 203 (Spring 2011) Neutron Stars (Shu on. 7) What happens when we try to compress a star beyond white dwarf densities? If the mass is greater than 1.4 MG, then it will collapse. Electrons + protons make neutrons. Just as with electrons, quantum mechanics says that two neutrons cannot be in the same place at the same time. Compressed neutrons will exert neutron degeneracy pressure. This is not the whole story—the strong force comes into play too. Most books (including our own) neglect this. You book derives a M-R relationship for neutron stars, but it is not as simply as the book implies. AST 203 (Spring 2011) Neutron Stars Different equations of state would give different mass-radius relations. From some models, a 1.4 M(D neutron star has R ~ 10 km! We can compute the density of this: _ M p _ (4/3)7TR3 This is an enormous density. = 6.6 X 1014 g CHI—3 A neutron “radius” is ~10'13 cm and its mass is 1.67 x 10'24 g, so the density of a neutron is p * were: : 4 x 1014 g (am—3 As-r 203 (spring 2011) See also|.gov/askasci/phyOO/phy00306.htm 2.5 2.0 1.5 Moss (Me) 1.0 0.5 0.0— AST 203 (Spring 2011) AST 203 (Spring 2011) Neutron Stars 6 8 1O 12 14 . . . I . . . I . 'v 2.5 03'0-‘1 Us _— 0° , 2.0 — ,z’sous I sow/"PALS _ E— 1.5 :- 1.0 _ 0.5 0.0 5 8 1O 12 14 Radius (km) (Lattimer Ii Prakash. Science 304:536-542,2004) Neutron Stars Isolated Neutron Star RX .1185635-3754 P1189762 - ST Sc! GPO - September 25‘ 1951.7 F. Walter {State University of New York at Stony Brook"! and NASA HST - WFPCZ Neutron Stars In a neutron star, neutrons are essentially touching one another. The neutron star acts like a giant nucleus Nuclear forces that we considered when studying fusion should also play a role here The strong force is important, and a new expression for the pressure, taking these nuclear forces into account is needed. This is a field of active research. AST 203 (Spring 2011) Neutron Stars The gravitational acceleration on the surface of a neutron star is: _ GM _ 6.67 x 10-8 g—1 cm3 s-2 1.4-2 x 1033 g — — — = 1.9 1014 —2 g R2 (1.5 x 106 cm)2 X cm S 100 billion times Earth's surface gravitational acceleration (actually General Relativity changes this some) Escape velocity (to overcome the NS gravitational pull) is a significant fraction of the speed of light! Einstein's theory of relativity is important in determining the structure of neutron stars. AST 203 (Spring 2011) Neutron Stars Neutron stars have a maximum mass—we don't know what it is. Most theories of neutron star structure predict a maximum mass ds3M. 0 Above this, there is no other pressure that can kick in to halt the gravitational collapse of the star—a black hole is formed. This is so dense that not even light can escape the surface. AST 203 (Spring 2011) ...
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This note was uploaded on 05/04/2011 for the course AST 203 taught by Professor Simon,m during the Spring '08 term at SUNY Stony Brook.

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