The Algol Mystery • Algol is a double-lined eclipsing binary Binary Evolution system with a period of about 3 days (very Novae, Supernovae, short). The two stars are: Star A: B8, 3.4M main-sequence star and X-ray Sources o Star B: G5, 0.8Mo `subgiant star http://apod.nasa.gov/apod/ What is wrong with this picture? http://www.space.com/32150-farthest-galaxy-smashes-cosmic-distance-record.html (very short period is a clue) Algol Mass Transfer in Binaries • The more massive star (A) should have • In the case of Algol, Star B, which initially left the main sequence and started up the had a mass of 3.0 Mo transferred 2.2Mo of RGB before the less massive star (B). material to Star A, which initially was 1.2 • What is going on here? Mo, after it became a red giant. • The key is the short-period orbit and the evolved state of star B. Star A: 1.2Mo -> 3.4Mo (main sequence) Star B: 3.0Mo -> 0.8Mo (red giant) Binary Star Evolution surface of equal total potential energy – including rotation Roche Lobe Mass exchange can greatly alter stellar evolution. It can CLASSICAL NOVAE change the composition we see on the surface of a star and • Classical novae are thought to occur about 30 to can alter the lifetime and luminosity of both stars. Also … 60 times a year in the Milky Way, but only about • When a massive star becomes a red giant, it may spill 10 are discovered each year. its H-envelope onto its companion changing the evolution of both. E.g. • L ~ 1038 erg s-1 for several days to months. About 105 times the luminosity of the sun, but ~105 times Type Ib supernova less luminous than the brightest supernova, but 105 • After the (initially) more massive star has died, more luminous than the sun interesting systems can be created in which one star is a white dwarf, neutron star, or black hole, • Recur – in theory - but the recurrence time scale may with another more ordinary star spilling matter be very long - typically tens of thousands of years onto it. Classical novae • Some mass is ejected, but the amount is small -6 -4 Type Ia supernovae 10 - 10 solar masses. The velocities are slower than supernovae – 100s to perhaps 1000 km s-1 X-ray binaries • Show emission lines of H, He, C, N, O, Ne, and Mg Novae Discovery Aug 29, 1975 Magnitude 3.0 • Nova Vel 1998 (3rd magnitude) V1500 Cygni A fast nova Novae Novae • Nova Persei became • Nova Cyg (1992) one of the brightest illuminated a cloud stars in the sky in 1901. of nearby Hydrogen Look there now and see the expanding shell gas. from the explosion. The • The expanding shell velocity of the material of the nova could be -1 is ~2000km s seen a few years later with HST. Nova Cygni 1992 Visible magnitude at peak was 4.3. Photo at left is from HST in 1994. Discovered Feb. 19, 1992. Spectrum showed evidence for ejection of large amounts of neon, oxygen, and magnesium. “Naked eye” novae occur roughly once per decade. 2.5 light days across ejected mass ~2 x 10-4 solar masses The companion star is typically a low mass (K or M) main sequence star. The orbital period is short < 1 day. An earth mass or so is ejected at speeds of 100s to 1000s of km s-1. Years later the ejected shells are still visible. The next page Nova Persei (1901) Nova Hercules (1934) shows images from a ground-based optical GK Per Nova Pictoris (1927) DQ - Her RR Pic survey between 1993 and 1995 at the William Hershel Telescope and the Anglo-Australian Telescope. Nova Cygni (1975) Nova Serpentis (1970) V1500 Cygni FH Ser http://www.jb.man.ac.uk/~tob/novae/ MODEL FOR CLASSICAL NOVAE Binding energy per gm for a 1 M white dwarf • A carbon-oxygen white dwarf accretes at a slow rate GM ⎛ (6.67 ×10−8 )(2×1033 ⎞ of about 10-10 - 10-8 solar masses per year from a binary = R ⎜ 5×108 ⎟ companion. Hydrogen and helium accumulate on the ⎝ ⎠ surface (at higher accretion rates can get SN Ia). 3 1017 erg g-1 6.8 1018 erg g-1 = q ≈ × × H • This material is initially too cool for nuclear reactions, but as accretion continues, it is compressed and heated. • The hydrogen continues to burn for several months At about 104 g cm-3, hydrogen burning ignites (“hot” as the entire accreted layer is driven off the star CNO cycle; temperature over 100 Million K) in a powerful wind. None of the accreted material is left behind. • Inititially the material is degenerate. Burning is also unstable because it happens in a thin shell on the WD • Accretion then resumes and the cycle repeats surface. Hydrogen burns explosively. Not all of the hydrogen burns because the material is not very tightly bound to the white dwarf, but it all is ejected nb. Novae can repeat! About 5000 trillion Kercek et al (1999) megatons/sec accrete explode accrete explode . SN 1998dh SN 1998aq Type Ia SN 1998bu Supernovae Type Ia supernovae are some of the biggest thermonuclear explosions in the universe (only pair-instability SN are bigger). Thirty billion, billion, billion megatons. For several weeks their luminosity rivals HST that of a large galaxy. SN 1994D Spectra are similar from event to event Si II • Very bright, regular events, peak L ~ 1043 erg s-1 • Associated with an old stellar population (found in ellipticals, no clear association with spiral arms when in spiral galaxies) • No hydrogen in spectra; strong lines SN 1994D of Si, Ca, Fe • Total kinetic energy ~1051 erg (nothing left behind) • Higher speed, less frequent than Type II Spectra of three Type Ia supernovae near peak light – courtesy Alex Filippenko (A) A Leading Model* Accretion and growth to the Chandrasekhar Mass (1.38 solar masses) Possible Type Ia Supernovae Degenerate thermonuclear explosion. (Hoyle and Fowler, 1960). in Our Galaxy Explains: SN D(kpc) mV • Lack of H in spectrum 185 1.2+-0.2 -8+-2 White • Association with old population 1006 1.4+-0.3 -9+-1 Dwarf 1572 2.5+-0.5 -4.0+-0.3 • Regularity 1604 4.2+-0.8 -4.3+-0.3 Mass Transfer • Large production of 56Ni and a light curve dominated by radioactivity. Expected rate in the Milky Way Galaxy about 1 every 200 years, but dozens are found in other galaxies every year. About one SN Ia occurs per decade closer than 5 Mpc. SN 2014J was at 3.5 Mpc and * there are 2 others a) merging white dwarfs and b) explosion is being extensively studied. well before the Chandrasekhar mass is reached. Evolutionary scenario Another Possibility Merging White Dwarfs -19 -17 -15 0.9 + 0.9 solar mass WD still make subluminous event 1.1 + 0.9 can make a more typical SN Ia like 2011fe (Roepke et al 2012, ApJL, 750, L19) Progenitor Ignition occurs carbon fusion in the center of the white dwarf begin to generate energy faster than convection and neutrino losses can carry it away. In order for the white dwarf to grow and reach As 2 x109 gm cm-3; T 3 x108 K the Chandrasekhar Mass the accretion rate must be ρ → ≈ relatively high (to avoid the nova instability). In the case of the “single degenerate model” this M ≈1.38M must be maintained for millions of years. −7 M ~10 M sun / yr * 9 Ignition at c ~ 3 x 10 because: 1) Neutrino loss rates decline at very high density 2) Carbon fusion reaction enhanced at high density by “electron screening” 3) Central regions compressed and heated by accretion of matter on surface. Once carbon ignites, the core begins to convect. P is independent of T, but Energy is generated too fast for conduction or 26 ⇒ BANG diffusion to get it to the surface fast enough. εnuc ∝ T for carbon burning Δρ The Explosion - Burning and Propagation ~ − 20% g ~ 109 cm s-2 ρ eff RT → Shear, turbulence Explosion preceded by about a century of Zingale et al. (2005) Roepke and Hillebrandt (2007) convection. The convection is asymmetric 56 0.7 M of Ni 0.94 M of 56Ni SN Ia probably make about 2/3– 3/4 of the iron group elements found in nature Qualitative Type Ia Supernova Light Curve Radioactivity 56Ni + 56Co decay Entirely due to radioactivity 56 - 56 Diffusion and expansion time Ni + e → Co + ν τ1/2 = 6.1 days scales approximately equal q = 3.0 x 1016 erg/gm 1043 Luminosity Optical light curve 56 - 56 Co + e → Fe + ν τ1/2 =77.1 days 16 . q = 6.4 x 10 erg/gm gamma-ray escape 0.6 solar masses of radioactive Ni and Co can thus provide 1.1 x 1050 erg at late times after adiabatic expansion is 1042 essentially over. 0 20 40 60 t (days since peak) Supernova (Death of a star) Type II Type Ia • No hydrogen • Hydrogen in spectrum • Thermonuclear explosion of • M > 8 solar masses a white dwarf star • Iron core collapses to • No bound remnant a neutron star or black hole 51 • ~1051 erg kinetic energy • ~10 erg kinetic energy -1 • v ~ 5,000 – 30,000 km s-1 • v ~ 2,000 – 30,000 km s 53 • No neutrino burst • Neutrino burst ~ 3 x 10 erg 49 • E ~ 1049 erg • Eoptical ~ 10 erg optical 43 -1 • L ~ 3 x 1042 erg s-1 for about • Lpeak ~ 10 erg s for 2 weeks peak • Radioactive peak and tail (56Ni, 56Co) 3 months (varies from event to event) 56 • 1/200 yr in our Galaxy • Radioactive tail ( Co) • Makes about 2/3 of the iron • 2/100 yr in our Galaxy in the Galaxy • Makes about 1/3 iron and all the oxygen plus many other elements There are also Type Ib and Ic supernovae that share many of the properties of Type II but have no hydrogen in their spectra The bright x-ray sky – mostly point sources (AGN, SNR, black holes and neutron stars) Binary X-Ray Sources A neutron star or black hole receiving mass from a companion star HEAO survey completed 1978 841 sources mostly binary systems containing a neutron star or a black hole.