High mass endingsHigh mass endings

Answers from you folks on Answers from you folks on yesterday’s quiz.yesterday’s quiz.

Differences between a dying low mass vs. a dying high mass star:

No He flash in a high mass star death. Low mass stars end in white dwarfs, high mass

stars end in supernovae. Heavy elements formed in death sequence of

a high mass star. Low mass stars end in white dwarfs with

planetary nebulae around them. The weight watcher rule: big things go early,

smaller things live longer.

Good Job. Folks !!!!!!

Large mass stars and the main Large mass stars and the main sequencesequence

What do they do on the main sequence? CNO cycle: Carbon, nitrogen, oxygen cycle1. High temperatures needed for this cycle to

take place (~ 15 million 0K).2. H is used along with C as a catalyst to

produce He atoms.

Large mass stars on the main Large mass stars on the main sequence continued…sequence continued…

3. Stay stable; hydrostatic equilibrium

Main Sequence turn-off Almost the Same as with low mass star:

1. Depletion of H in core2. He core contracts

3. Temperatures rise igniting H layer4. Increased pressure drives envelope of star outward

creating a super giant or giant.5. This cycle repeats many times depending on mass.

6. When it does, at each new stage heavier elements are created.

Fusion of heavy elements.Fusion of heavy elements. As temperature increases with depth, the ash of each burning stage becomes the fuel for the next stage.

So as each element is burned to completion at the center, the core contracts again, heats again, and so on…

Once inner core turns to Iron, fires cease in the core, internal outward pressure dwindles and hydrostatic equilibrium is destroyed. Gravity takes over and……..

BanG !!!!!BanG !!!!!

The star implodes! (falls in on itself!) Core temperature rises again, all heavy elements in

core undergo Photodisintegration, undoing the fusion process of the previous 10 million years. End up with electrons, protons, neutrons, and photons in core.

Core compresses, stops and rebounds with a vengeance!

During this rebound, a shock wave sweeps through the star blasting all the overlying layers, including the heavy elements just formed outside the iron core into space: a Type 2 Supernova has occurred.

The brightness of a supernova may rival the brightness of the entire galaxy in which it resides. This period is short ~ few days, maybe a month.

Big and little bangsBig and little bangs Novae and supernovae are two different

types of beasts. A nova is an increase in the brightness of an

accreting white dwarf star that is undergoing a surface explosion.

The temporary and rapid change in luminosity can occur over a period of a few days.

On the average, 2 or 3 novae are observed every year.

As to type 1 supernovae, a star has to have a buddy for this to occur.

Type 1 supernovae and white dwarfsType 1 supernovae and white dwarfs When an accreting white dwarf exceeds a maximum value of 1.4

solar masses (Chandresekhar mass), electrons inside cannot provide the pressure needed to support the star.

Star begins to collapse, temperature rises to the point where carbon fusion takes place.

Fusion taking place everywhere throughout the star causes it to explode – Type 1 supernova (carbon-detonation supernova).

Star is believed to be blasted to bits

Type 2 supernova remnantType 2 supernova remnant

Crab nebula A supernova

remnant. 1st seen in 1054

A.D. 1800 pc from

Earth. About 2 pc wide Has a neutron

star, pulsar..Speaking of which

=>

Large mass star endings Large mass star endings (chapter 22)(chapter 22)

What remains after a supernova (type 2) explosion?

More than what you get from a type 1 explosion, that’s for sure!

1. Neutron stars

2. Black holes

Creatures of the deepCreatures of the deep

Neutron stars A ball (size: that of a large city

~ 20 km) of neutrons left after a supernova explosion.

Density: 1017 – 1018 kg/m3 , weight: thimbleful of neutron star material would weigh 100 million tons.

Gravity extremely powerful; you’d weigh a lot more on this star!

Carry strong magnetic fields.

Spin very fast! (a consequence of the conservation of angular momentum)

Black Holes Chandrasekhar limit for a

neutron star: 3 solar masses. Above this limit the star cannot support itself against its own gravity – collapse.

General Relativity says that this collapse punches a hole in space-time called a singularity.

This singularity is surrounded by a an event horizon, which defines the absolute edge outside of which a photon of light can escape.

Lets look at neutron stars first;Lets look at neutron stars first; If you’re a

neutron star you can decide to announce your presence by becoming a Pulsar

Crab pulsar: Hubble telescope

Pulsar emissionPulsar emission

Extremely rapid rotation and combination of a strong magnetic field dictates signal properties seen by us.

We see the pulses when they sweep across the Earth

Discovered by Jocelyn Bell, a grad. Student at Cambridge University,In 1967.Her thesis advisor won the Nobel Prize forit in 1974.

Black holes and the speed of lightBlack holes and the speed of light Special relativity says that the limiting speed in

the universe is the speed of light.

Black holes and curved space-timeBlack holes and curved space-time

General relativity says that any mass creates a dent or depression in space-time.

The bigger the mass, the greater the depression

Page 584 figure 22.15

Proof

proofproof

Deflection of starlight measured in 1919, confirmed the general theory.

Planetary orbits deviate from Kepler’s ellipses, they actually precess

So.. What happens around a Black So.. What happens around a Black Hole?Hole?

Gravitational red shift.

Light energy is drained near the event horizon.

No escape of light/radiation upon entering event horizon.

Getting close to event horizon, causes spagetification, when you’re stretched out long ways.