Supernova Supernova And other Cataclysmic Events Introduction Whats

Supernova! Supernova (And other Cataclysmic Events!)

Introduction • • • What’s in a name Historical Supernovae Types of Supernova Where do they go? Really wild Explosions Can I see a Supernova?

Nova • Nova - Latin for New Star Faint star that suddenly brightens • Supernova! A bright star that explodes Can be as bright as an entire galaxy • Hypernova Appears to be as bright as the rest of the Universe

Early Supernova Reports • Supernovae can be visible in daylight • Many Chinese reports of “Guest Stars” • Rock Drawings?

Chaco Canyon - SN 1054? ?

Milky Way Supernovae Year 185 AD 393/396 1006 1054 1181 1572 1604 1667? Date Apr 30 Jul 4 Nov 6 Oct 9 Con RA Dec mag Comment Cen Sco Lup Tau Cas Oph Cas 14: 43. 1 17: 14 15: 02. 8 05: 34. 5 02: 05. 6 00: 25. 3 17: 30. 6 23: 23. 4 -62: 28 -39. 8 -41: 57 +22: 01 +64: 49 +64: 09 -21: 29 +58: 50 -2 -3 -9 -6 -1 -4 -3 6? -6 mag M 1 Tycho Kepler Cas A SN

SN 1987 A Before After

Supernova Types • Type 1 • Type 2 • There are various subclasses • Defined by their Spectra and Lightcurves

The Spectrum

Types of Spectrum

Spectra of Elements Hydrogen Helium Carbon

Solar Spectrum

Type 1 Supernova

Type II Supernova

Lightcurve Comparison

Supernova Mechanisms • Basic Stellar Structure • Type II Supernovae • Type I Supernovae

What is a Star? • A sphere of gas in hydrostatic equilibrium

What is a Star? • A sphere of gas in hydrostatic equilibrium • Nuclear Fusion within the sphere

What is a Star? • • A sphere of gas in hydrostatic equilibrium Nuclear Fusion within the sphere Emits energy as radiation and particles Varies in size and brightness over its lifetime

Helium Burning

Timescales

But…! • Iron won’t “burn” and release energy • No energy from the core holding up the outer layers • The core collapses to about 10 Km diameter • Protons and electrons are squeezed together to form neutrons and releasing neutrinos • Neutrinos escape speeding up the collapse

… And. . . • Infalling material rebounds off the core • Shockwave travels outwards compressing and heating surrounding gas • Remainder of the star blasted out • Energy released is about the same as the Sun will generate in its entire life! • Supernova!! (Type II)

Type II Supernova

Type 1 Supernova

Type I Supernova Mechanism • Form in Binary Systems • Gas falls from a Red Giant onto a White Dwarf

Type I Supernova Mechanism • Form in Binary Systems • Gas falls from a Red Giant onto a White Dwarf • Gas forms on the surface of the White Dwarf

Type I Supernova Mechanism • Form in Binary Systems • Gas falls from a Red Giant onto a White Dwarf • Gas forms on the surface of the White Dwarf • Mass Exceeds stability limit (Chandarasekar Limit - 1. 4 Msun)

Type I Supernova Mechanism • • • Core collapses Carbon Core ignites explosively Supernova! Always happens at the same Mass Limit Gives out (nearly!) the same amount of energy • Can be used as a “Standard Candle”

Type I Sn Standard Candle • Allows us to measure distance to very remote galaxies • Remote Galaxies are a long way back in time • Allows us to measure changes in the rate of Cosmic expansion • Expansion is speeding up!!

While we’re here. . • “Classical Nova” mechanism is very similar to Type I Supernova • Gas accretes in a binary system • Layer of hydrogen forms around the white dwarf (about 1/100, 000 Msun) • Hydrogen ignites as a shell around the White Dwarf

While we’re here. . • “Classical Nova” mechanism is very similar to Type I Supernova • Gas accretes in a binary system • Layer of hydrogen forms around the white dwarf (about 1/100, 000 Msun) • Hydrogen ignites as a shell around the White Dwarf … and ejects the surrounding Hydrogen as a Planetary Nebula

What Happens Next? • Type II Supernova core forms a Neutron Star • Surrounding material ejected by the shockwave

Neutron Stars • Type II Supernova core forms a Neutron Star ~ 10 Km in diameter • Incredibly dense - 200, 000 tons / cc • Spins very fast and has a very powerful magnetic field

Conservation of Angular Momentum

Conservation of Magnetic Flux • The star’s magnetic field collapses • Magnetic field density increases to about 1012 Gauss • Magnetic poles may not be aligned with rotational poles • Produces the Pulsar Lighthouse Effect

Pulsar Radiation • Detailed mechanism not really understood • Probably caused by the intensely curved fields around the magnetic poles • Electrons in a curved magnetic field emit radiation • Highly directed in two beams

Pulsar Discovery • First detected in Cambridge in 1967 by Jocelyn Bell Burnell and Anthony Hewish • Initial discoveries were called LGM

Fast and Slow Pulsars • Periods can range from a few seconds to milliseconds • They slow down over time but are highly accurate over normal timescales • Binary Pulsar has been used to prove theory of Relativity • Pulsars were used on the Voyager plaque to pinpoint the Earth

Crab Pulsar

Crab Pulsar

Crab Pulsar

Nucleosynthesis • Lighter elements are created by fusion

Nucleosynthesis • Lighter elements are created by fusion • Heavy elements are created by nuclear reactions – s-process (Slow Neutron Capture) – r-process (Rapid Neutron Capture) – p-process (Proton Capture)

Where do we come from? • All elements heavier than Helium were created in previous generations of Supernovae

Where do we come from? • All elements heavier than Helium were created in previous generations of Supernovae • “We are Stardust”

Some Very Big Explosions • Stars below about 8 Msun won’t go Supernova, including our sun • Very massive stars will blow off gas during their lifetime

Some Very Big Explosions • Stars below about 8 Msun won’t go Supernova, including our sun • Very massive stars will blow off gas during their lifetime • Core of a star > 25 Msun is too massive to be held up by Neutron degeneracy and will collapse to a Black Hole about 20 Km wide

Gamma Ray Bursters • GRBs • Found by spy satellites and thought to be nuclear tests in space! • Originally thought to be Milky Way objects • Now identified with very intense explosions in external galaxies • Hypernova

Hypernovae • Energy flux if isotropic would be immense, about the same as the rest of the universe for a few seconds • Likely to be a directed beam effect like Pulsars • No-one is sure but there a number of theories

Collapse of Magnetic Star ~ 40 Msun • Very massive star with strong magnetic field collapses to a Black Hole

Collapse of Magnetic Star ~ 40 Msun

Collapse of Magnetic Star ~ 40 Msun • Very massive star with strong magnetic field collapses to a Black Hole • Matter ejected at near the speed of light • Matter is constrained by magnetic field into jets at the poles • Relativistic effects include beaming of energy in the direction of travel

Neutron Star Merge

Hypernovae • There do appear to be 2 classes of GRBs so both theories may be right • About 1 GRB detected per day but we only see those where the beam is directed at us • Frequency much higher in the early universe than now • A local GRB pointed at Earth would essentially cook that hemisphere!

Observing a Supernova • One in the Milky Way every 250 years • Last one in 1667, so we’re overdue one! • Sn 1987 A in the LMC (our nearest neighbour galaxy) • Can be observed in external galaxies • Hundreds have been discovered by amateurs

SN 2002 ap

SN 2002 cs

Stop Press!

Summary • • • There are various types of exploding stars Novae, Supernovae (types I & II), GRBs Large to huge amounts of energy released Produce all heavy elements They are observable with amateur equipment

Some Resources • • http: //skyandtelescope. com http: //www. supernovae. net http: //www. theastronomer. org http: //www-astronomy. mps. ohiostate. edu/~dhw/Intro/current. html#lectures • http: //www. pas. rochester. edu/~afrank/A 105 /index. html