Supernova Type 2 Supernova

Supernova

Type 2 Supernova

Produced during the death of a very massive star.

SupernovaTWO VERY DIFFERENT TYPES OF SUPERNOVAETWO VERY DIFFERENT TYPES OF SUPERNOVAE

Supernova TypeSupernova Type Type Ia*Type Ia* Type IIType II

Maximum LuminosityMaximum Luminosity 3 x 103 x 1099 Suns Suns 3 x 103 x 1088 Suns Suns

SpectrumSpectrum No hydrogen linesNo hydrogen linesLines of many heavy elementsLines of many heavy elements

Hydrogen linesHydrogen linesContinuumContinuum

Where foundWhere found Among old star systemsAmong old star systems(galactic bulge, elliptical (galactic bulge, elliptical galaxies)galaxies)

Among young star systemsAmong young star systems(star-forming regions in disk (star-forming regions in disk galaxies)galaxies)

Parent StarParent Star White dwarf in binary systemWhite dwarf in binary system Massive star (usually a red Massive star (usually a red supergiant)supergiant)

Trigger mechanismTrigger mechanism Mass transfer from companionMass transfer from companion Collapse of iron coreCollapse of iron core

Explosion mechanismExplosion mechanism Thermonuclear explosion of Thermonuclear explosion of carbon/oxygen core --> ironcarbon/oxygen core --> iron

Rebound shock from neutron Rebound shock from neutron star surface: neutrino star surface: neutrino pressurepressure

Left behindLeft behind NothingNothing Neutron starNeutron star

DebrisDebris Mostly ironMostly iron All kinds of elementsAll kinds of elements

*Types Ib and Ic supernovae are unusual supernovae that have most of the properties of type II *Types Ib and Ic supernovae are unusual supernovae that have most of the properties of type II supernovae, except that their spectra show no hydrogen lines.supernovae, except that their spectra show no hydrogen lines.

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Type 2 Supernova

Late in the life a a very massive star (10 or more times the mass of the sun) the tiny core of the star develops a layered structure much like an onion, with heavier and heavier elements in deeper layers, culminating with iron in the center

See Figure 21.5

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Type 2 SupernovaBurning rates for very massive star of mass about 20 solar masses

ElementElement Time to FuseTime to FuseHydrogen 10 million years

Helium 1 million years

Carbon 1 thousand years

Oxygen 1 year

Silicon one week

Iron core Forms in less than 1 day.

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Type 2 Supernova

In very massive stars this situation eventually becomes unstable and the core of the star collapses catastrophically in a time of only a few thousandths of a second. This collapse leads to an explosion called a Type II Supernova that blows off the outer layers of the star and produces a prodigious light show that can rival the luminosity of an entire galaxy (billions of normal stars). As spectacular as this is, most of the energy of the supernova is actually contained in ghostly particles called neutrinos that are very difficult (but not impossible) to detect. There are other types of supernovae that involve a somewhat different mechanism associated with mass accretion by a white dwarf in a binary system, but the final result is similar: a gigantic explosion that destroys an entire star.

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Type 2 Supernova

Iron Core

Gravity

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Type 2 SupernovaGravity

Iron Core – pressure loss from interior (no radiation pressure)

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Type 2 Supernova

The core collapses as a result of the collapse of the outer layers

Electron degeneracy pressure is not enough to stop the gravitational collapse of the outer shells.

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Neutron Degeneracy Pressure

Extreme pressures in the core will increase the temperature to fantastically high numbers (10 billion K). At this temperature, the energies of photons in the core will be high enough to break the iron into fundamental particles

Photodisintegration: The process by which the core is broken into fundamental particles by high energy photons.

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p + e n + ν

When the density of the core is high enough (1012 kg/m3), protons and electrons will be crushed together, forming neutrons in the core and releasing neutrinos.

Neutronization: The conversion of the core into neutrons by the combining of electrons and protons.

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The neutronization of the core results in an enormous outflow of neutrinos.

A “large” neutrino flux at the earth is a sign of a supernova event.

p + e n + ν

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Like electrons, two neutrons cannot be in the same state at the same time.

Neutron Degeneracy Pressure: Pressure produced when two neutron are squeezed into a small enough space.

Neutron Degeneracy Pressure is a parallel to electron degeneracy pressure.

p + e n + ν

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When the pressure is the core is dominated by neutron degeneracy pressure, the core collapse stops, and the resulting pressure acts a barrier which stops the further collapse of the outer shells.

The process happens very rapidly, however, and the outer shells cannot react immediately to the pressure exerted by the core.

p + e n + ν

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Neutron Core – degeneracy pressure

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The inner shell will “rebound” off of the degenerate core

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Pushing outward on the collapsing outer shells

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Pushing outward on the collapsing outer shells

Until….

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Kablooey

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Neutron Star: The neutron rich remnant of a Type II Supernova. It is in equilibrium due to neutron degeneracy pressure.

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Type 2 SupernovaLong after the initial supernova explosion, its aftermath can be seen in the expanding cloud of debris produced by the explosion. These are called Supernova Remnants. One of the most famous supernova remnants is the Crab Nebula (M1), which is the remains of the supernova of 1054 AD that is chronicled in the Chinese literature, and is the first entry in the Messier Catalog

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Type 2 Supernova In 1987 a supernova (designated SN1987A by astronomers) was observed in a nearby galaxy called the Large Magellanic Cloud. This was the first "nearby" supernova in the last 3 centuries, and for the first time astronomers not only observed the light show, but also detected 19 of the elusive neutrinos (the detectors observed electron anti-neutrinos, to be more precise) produced by the collapse of the star's core. The burst of neutrinos preceded the first sighting of the supernova's light by about 3 hours, in agreement with the expectations of current supernova theory. It is estimated that for an instant in 1987 on the earth the neutrino luminosity of SN1987A was as large as the visible-light luminosity of the entire universe. The adjacent figure is a 1994 Hubble Space Telescope image of the region surrounding SN1987A. The supernova is in the center. The two bright stars are just in the field of view and are not associated with the supernova. The bright yellow ring is thought to be gas and dust heated by the supernova (the expanding shell of the explosion itself that will produce the supernova remnant is still too small to be seen in this photograph). The two large rings are not yet completely understood, though they appear to be associated with the supernova.

The supermassive and violently unstable star Eta Carinae. The adjacent image shows a nebula larger than the Solar System that was ejected in a violent outburst in 1841. For a time, this outburst made Eta Carinae the second brightest star in the sky.

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Type 2 Supernova

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Supernova Type 2 Supernova