Stellar Graveyard Chapter 13

7/29/2019 Stellar Graveyard Chapter 13

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Star Forming Regions M42 – The Orion Nebula (Fig. 7.2)

M45 – The Pleiades (Fig. 13.14)

M80 – Globular Cluster (Fig. 13.15)

Chalkboard Diagram

Life Track Flow Chart - the lives of low, medium

and high mass stars

The Milky Way

Clicker Question

Pulsars are really…

A. White Dwarf

B. Red Giant

C. Black HoleD. Neutron Star

E. None of these

Clicker Question

Which of the following is not

one of the last possible stages of

a star’s life? A. White Dwarf

B. Red GiantC. Black Hole

D. Neutron Star

Which event marks the beginning of a supernova?

A. The sudden collapse of an iron core into a

compact ball of neutronsB. The onset of helium burning after a helium flash

C. The beginning of neon burning in an extremely

massive star

D. The sudden initiation of the CNO cycle

Clicker Question

Our Sun is considered to be a _________.

A. low-mass star B. intermediate-mass star

C. high-mass star

D. brown dwarf

Chapter 13

Stellar Graveyard

White Dwarfs...

...are stellar remnants for low-mass stars.

...are found in the centers of planetary nebula.

...have diameters about the same as the Earth’s.

...have masses less than the Chandrasekhar mass

(1.4 Solar Masses).

Sirius

Subrahmanyan Chandrasekhar

(1910-1995)

Novas and Supernovas

Nova - a stellar explosions

Supernova - a stellar explosion that marks

the end of a star’s evolution – White Dwarf Supernova - occur in binary

systems in which one is a white dwarf

– Massive Star Supernova - occur when amassive star’s iron core collapses

Supernova 1998S in

NGC 3877

Supernova 1987a

Supernovae History

The star releases more energy in a just a few minutesthan it did during its entire lifetime.

» Example: SN 1987A

On July 4, 1054 astronomers in China witnessed a

supernova within our own galaxy. After the explosion of a massive star, a huge glowing

cloud of stellar debris - a supernova remnant - steadily

expands.

» Example: Crab Nebula

After a supernova the exposed core is seen as a

neutron star - or if the star is more than 3 solar masses

the core becomes a black hole.

Anazasi Pictographs

The Crab Nebula

“Listen to the Pulsar”

Pulsars

The first pulsars observed was originallythought to be a signal from extraterrestrials.

This was later shown to be unlikely after

many other pulsars were found all over thesky.

Also, it was found that each pulse had a

total power output equal to that of all theresources of Earth.

Pulsars…..Discovered in 1960’s The pulsing star inside the Crab Nebula

was a pulsar. Pulsars are rotating, magnetized neutron

stars.

Light House Model – Beams of radiation emanate from the magnetic

poles.

– As the neutron star rotates, the beams sweeparound the sky.

– If the Earth happens to lie in the path of the

beams, we see a pulsar.

http://www.jb.man.ac.uk/~pulsar/Education/Sounds/sounds.html

Rotation Rates of Pulsars

The neutron stars that appear to us as pulsarsrotate about once every second….or less.

Before a star collapses to a neutron star it probably rotates about once every 25 days.

Why is there such a big difference in rotation

rates?

Answer: Conservation of Angular Momentum

Neutron Stars

...are stellar remnants for medium-mass stars.

...are found in the centers of some white dwarf

supernova remnants.

...have diameters of about 6 miles.

...have masses greater than the Chandrasekhar

Black Holes

...are stellar remnants for high-mass stars.

– i.e. those greater than 3 solar masses

…have a gravitational attraction that is so

strong that light cannot escape from it.

…are found in some binary star systems and

there may be super-massive black holes in the

centers of some galaxies.

Black Hole

Black Holes…

…are spherical objects not funnels. …do not suck everything in.

…have been observed indirectly in X-ray

binary systems.

End of Chapter

How To Study

Review Sheet

Online Quiz

Homework Read Chapters 16, 17, 20

Homework 5

7. A8. D

Homework 6

7. E8. D

Messier Catalogue

Charles Messier made the first catalog of non-stellar “fuzzy” objects during the 1770's.

He made a list of 109 such objects that he

did not want to mistake for comets. These objects turned out to be the following:

– galaxies

– star clusters

– nebulae

End of Section.

N l th i

Nucleosynthesis

Fused Products Time TemperatureH

4He 10

7yrs. 4 X 10

12C Few X 10

6yrs 1 X 10

Ne,24Mg,

1000 yrs. 6 X 108

20 Ne +

24Mg Few yrs. 1 X 10

32S One year 2 X 10

28Si +

56Fe Days 3 X 10

56Fe Neutrons < 1 second > 3 X 10

Evolutionary Time Scales for a 15 M Star

E e B d et

Energy Budget

Fusion Stages

H He C Fe

The Crab Nebula

Supernova Remnants

Tycho’s SNR - 1572

Core Remnant

Too massive for electron degeneracy to

halt collapse (> 1.4 M

– Electromagnetic force Neutron Degeneracy can halt collapse

– M < 3 M

– Strong nuclear force – Neutron Star

PSR 0628 28

PSR 0628-28

Several more found at widely different

places in the galaxy

Power of a power equals total power potential output of the Earth

No Doppler shifts

PULSARS

Light Time Argument

An object which varies its light can be no

larger than the distance light can travel inthe shortest period of variation.

To Darken the Sun

Time Delay = Radius/c

500,000 km/300,000 km/s = 1.67 sec

Only candidates: White Dwarfs, Neutron Stars

Pulse Mechanisms

Binary Stars - How quickly can two stars orbit? Two WD about 1m

Two NS about 1s.

Neutron Stars in orbit should emit gravity waves which should

be detectable.

Oscillations - Depends only on density

WD about ten seconds

NS about .001s Little variation permitted.

Rotation - Until the object begins to break up.

WD about 1s

NS about .001s with large variation.

The Crab Pulsar

Rotating Neutron Star

Animation

SS 433

Synchrotron Radiation

Magnetic lines of force

Electron

Radiation

Glitches

Relative sizes

Earth White Dwarf Neutron Star

Mass Limits

Low mass stars

– Less than 8 M

on Main Sequence

– Become White Dwarf (< 1.4 M)» Electron Degeneracy Pressure

High Mass Stars

– Less than 40 M on Main Sequence – Become Neutron Stars (3 M

< M <1.4 M

» Neutron Degeneracy Pressure

Supermassive Stars

If stellar core has more than three solar

masses after supernova, then no known

force can halt the collapse

Black Hole

Space-Time

Space Time

No mass

Distortion

caused bymass

Predictions of General Relativity

Advance of Mercury’s perihelion

Bending of starlight

Advance of Mercury’s Perihelion

Advance of Mercury s Perihelion

Bending of Starlight

Light from star bent by

the gravity of the Sun

Apparent position

of the star

Low Gravity

Very small

amount of

bending

Stronger Gravity

Light at an angle is

bent noticeably

Exit Cone and Photon

Sphere

Photon Sphere

Near a Black Hole

Schwarzschild Black Hole

Singularity +

Event Horizon

Rs = 3(Mass)

Mass Rs

3 M 9 km

What Can We Know?

– gravity

Charge – Electric Fields

Rotation Rate

– Co-rotation

How Can We Find Them?

Look for X-ray sources

– Must come from compact source

» White Dwarf

» Neutron Star

» Black

– Differentiate by Mass

» WD - < 1.4 M

» NS - between 1.4 and 3 M

» BH - > 3 M

Cygnus X-1

Cygnus X 1

Stellar Graveyard Chapter 13

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