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SUPERNOVAE. “A man is a small thing, and the night is very large and full of wonders” Lord Dunsany. CONTENTS. Introduction Classification of SNe Core-Collapse Mechanism Thermonuclear Mechanism. 1. Introduction.
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SUPERNOVAE “A man is a small thing, and the night is very large and full of wonders” Lord Dunsany
CONTENTS • Introduction • Classification of SNe • Core-Collapse Mechanism • Thermonuclear Mechanism
1. Introduction Supernovae are one of the most energetic explosive events in Nature. • RARE. About one per century in our galaxy Last recorded seen by naked-eye :1006 (Lupus), 1054 (Chinese), 1572 (Brahe), 1604(Kepler) SN1054 was as luminous as the moon for same days • LUMINOUS. 600 millions – 4 billions L A SN in 10 sec releases 100 times the energy that the sun realises in all its life • BRIEF. Luminosity falls by a factor of 100 during the course of 4 months
INTRODUCTION SN 1987 seen by naked-eye(23 February 1987, Large Magellanic Cloud) • The best studied SN of • all times: • Study of SN dynamics • Study of neutrino • masses For the first time, it was possible to look back in photographic archives at the location of the explosion and find the progenitor star of the Supernova
INTRODUCTION In Kamiokande II, the detection method consisted of: e + e e + e Nobel Prize 2002 Koshiba
Classification of SNe Basic SN types spectra Cappelaro&Turatto, Astro-ph,0012455
Cappelaro&Turatto, Astro-ph,0012455 Light Curves Classification of SNe • Type Ia SN • Similar luminosity • Similar spectral evolution • Distance indicators (cosmological parameters) • Type II SN • Dramatic differences • II-P (plateau)/ II-L (rapid declination)
3. Core - Collapse Mechanism • Life Cycle of a Massive Star • Hydrostatic equilibrium • gravity’s pull goes inward • Thermal pressure goes outward • Thermal equilibrium • heat and energy flow out from the core to be emitted as light • Fusion: hydrogen, helium, carbon, neon, oxygen, silicon • At the end of Silicon burming there is no more an energy source. • Any fusion or fission reactions in which iron participates absorb rather than release energy • At the end... • Layered Structure • Dense Iron Core • Progenitor Star (type II) with degenerate iron core • 107 g·cm-3 T 1010 K MCore 1.4M RCore 4000km “ The Final Catastrophe Of a Massive Star (8M < M < 60M)”
Stage 1- Core Collapse Core-Collapse Mechanism Once the star has finished its fuel the core cools because of two reasons: • Iron dissociation fusion of light nuclei the star continues emitting energy • Degenerate e- gas p + e-(2.25 MeV) n + e (neutronization) e escapes and remove energy b) Contraction turns into a free-fall collapse, vast amount of neutrinos are produced In less than a second the inner core radius goes from 4000 km to 10 km (matter from the rest of the core is falling inward)
Stage 2- Core Bounce Core-Collapse Mechanis Once the > 3·1014 g·cm-3, the very centre of the core (10 km) becomes incompressible and its collapse abruptly halts because of NUCLEON degeneration • The inner core violently rebounces (as a overcompressed rubber ball that suddemly is allowed to return to equilibrium), a layer of dense matter surges at 10.000 km/s (shock wave) • Matter from the outer layers is falling inward at 60.000 km/s • Shock wave loses energy and stops its rapid outward movement as it founds the infalling matter The region between the shock wave and the inner core is called the quasi-static layer .
Making Stars Explode Core-Collapse Mechanism Because the neutrinos free path is smaller than the radius of the quasi-static layer, the falling matter becames very hot, expands and surges outwards. Finally, ths star erupts in an explosion that ejects the star’s outer layers into space. This nebulae will form the planets, other stars... All that remains of the star is a very dense object called neutron star or a black hole PROBLEM: Turning the implosion into an explosion!!! There are several models explaining the explosion, but until now due to the enormous number of parameters involved and the great power of computing needed, simulations do not succeed in obtaining an explosion
4. Thermonuclear Mechanism “The Mortal Game in the Danse of a Stellar Couple” This mechanism concerns type Ia SNe It consists of a Binary System (white dwarf + companion) in which the WD accrettes matter for the companion star White dwarfs are formed from intermediate mass stars (M < 8M) and are composed of C and O with a strongly degenerate electrons By the pull of gravity, every object attracts every object in the Universe
Thermonuclear Mechanis Equipotencial contours in the equatorial plane of a binary system rotating about its center of mass( X) One unique surface intersects itself at the point L1, called the inner Lagrange point This surface defines two regions called Roche Lobes Mass accretion can occur if one of the stars fills its Roche Lobes.
Thermonuclear Mechanism For masses above 1.44M, there cannot be balance between electron degeneracy and the gravitational force. The collapse continues until is stopped by neutron degeneracy Animation of accrettion in an X-ray binary system (normal star + collapsed star) • In the thermonuclear mechanism: • The red giant fills its Roche Lobe, • The white dwarf accretes matter for the secondary star until reaches the Chandrasekhar limit • The sudden collapse of the star can cause runaway fusion of its • C ,O and the star becomes a huge nuclear bomb.
