ASTR 1120 Review Comparing Three Types of Stellar General - - PowerPoint PPT Presentation

ASTR 1120 General Astronomy: Stars & Galaxies

• Homework #4 on MA due today, by 5pm
• Homework #5 on MA due Tue, 10/20, by 5pm.
• If your clicker grade on CU learn is “0” and

you have been in class, please e-mail us your Clicker ID SECOND MIDTERM THURSDAY 10/15

Comparing Three Types of Stellar Explosions

• White Dwarf Nova

– Binary systems only – Occurs in older star populations – White dwarf still survives

• White Dwarf Supernova

– Binary systems only – Occurs in older star populations – Nothing left inside

• Massive Star Supernova

– Found in young star formation regions – Make neutron stars or black holes Review

Where is fusion happening in a nova?

• A. In the core, carbon is being fused into

heavier elements.

• B. On the surface, hydrogen is being fused

into helium.

• C. No fusion occurs in a nova, the light

comes from the collapse (and bounce)

• f the star.

Clicker Question

Where is fusion happening in a nova?

• A. In the core, carbon is being fused into

heavier elements.

• B. On the surface, hydrogen is being fused

into helium.

• C. No fusion occurs in a nova, the light

comes from the collapse (and bounce)

• f the star.

Clicker Question

Where is fusion happening in a white dwarf supernova?

• A. In the core, carbon is being fused into

heavier elements.

• B. On the surface, hydrogen is being fused

into helium.

• C. No fusion occurs in a white dwarf

supernova, the light comes from the collapse (and bounce) of the star. Clicker Question

Where is fusion happening in a white dwarf supernova?

• A. In the core, carbon is being fused into

heavier elements.

• B. On the surface, hydrogen is being fused

into helium.

• C. No fusion occurs in a white dwarf

supernova, the light comes from the collapse (and bounce) of the star. Clicker Question

Where is fusion happening in a massive star supernova?

• A. In the core, carbon is being fused into

heavier elements.

• B. On the surface, hydrogen is being fused

into helium.

• C. No fusion occurs in a massive star

supernova, the light comes from the collapse (and bounce) of the star. Clicker Question

Where is fusion happening in a massive star supernova?

• A. In the core, carbon is being fused into

heavier elements.

• B. On the surface, hydrogen is being fused

into helium.

• C. No fusion occurs in a massive star

supernova, the light comes from the collapse (and bounce) of the star. Clicker Question

The Stellar Graveyard

What’s In The Stellar Graveyard?

• Lower mass stars white dwarfs

– Gravity vs. electron degeneracy pressure

• High mass stars (M>8Msun but M<30-40Msun)

neutron stars

– Gravity vs. neutron degeneracy pressure

• Even more massive stars black holes

– Gravity wins

Neutron Stars

Neutron star over NYC

• Structure determined by

gravity vs. neutron degeneracy pressure

• Radius ~ 10 km
• Mass less than ~ 3 MSun
• Made of degenerate

neutrons

– More massive = smaller !!

• Crushing gravity at its

surface, not a nice place to visit

QUEENS BROOKLYN STATEN ISLAND BRONX MAN

Size of a neutron star

Mount Everest Neutron Star

Weight of a neutron star

Pinhead of

Observing the ‘First’ Pulsar: BIG discovery

• Jocelyn Bell:

Cambridge (UK) graduate student in 1967 (+Anthony Hewish) discovered pulsars by accident!

• Named it LGM-1 (Little

Green Man) Just WHAT could cause signal? 1.3 sec period

“Pulsar” = rotating

neutron star

Fierce magnetic fields + sizzling electrons + fast rotation finest “lighthouse”

Thomas Gold 1968

Pulsars and Neutron Stars

Pulsars are lighthouses in our Galaxy!

Pulsars often discovered in supernova remnants. The Crab Nebula (known to be supernova remnant) Is a well known example.

The Crab pulsar also pulses in visual light

Crab Nebula SNR

infrared radio

• ptical

x-ray

Pulsar Demo

Neutron Star in the Lab + Sound of Pulsars

Synchrotron Radiation

• Fast electrons in

strong magnetic fields spiraling along magnetic fields

• Different shape

(powerlaw) from thermal radiation: emits at all wavelengths, strongest in radio

Visible vs. X-ray emission

• Thermal light

from stars visible and IR

• Synchrotron light

from neutron stars X-ray and radio

Visible light X-ray light

What is a pulsar?

• A. A neutron star emitting pulses of light.
• B. A white dwarf emitting pulses of

hydrogen gas.

• C. A red giant expanding and contracting

in very short (millisecond) pulses.

• D. A powerful gamma ray burst.
• E. Your heart during final exams.

Reading Clicker Question

What is a pulsar?

• A. A neutron star emitting pulses of light.
• B. A white dwarf emitting pulses of

hydrogen gas.

• C. A red giant expanding and contracting

in very short (millisecond) pulses.

• D. A powerful gamma ray burst.
• E. Your heart during final exams.

Reading Clicker Question

When a neutron star is formed, will we always see a pulsar?

• A. Yes, because due to conservation of angular

momentum the neutron star will always be spinning.

• B. Yes, neutron stars always give off pulses of

light which we can detect with sensitive enough telescopes.

• C. No, some neutron stars don’t spin.
• D. No, it depends on the orientation of the

neutron star’s magnetic field.

Clicker Question

When a neutron star is formed, will we always see a pulsar?

• A. Yes, because due to conservation of angular

momentum the neutron star will always be spinning.

• B. Yes, neutron stars always give off pulses of

light which we can detect with sensitive enough telescopes.

• C. No, some neutron stars don’t spin.
• D. No, it depends on the orientation of the

neutron star’s magnetic field.

Clicker Question Since white dwarfs in evolving binary systems come “alive” – what about neutron stars?

Binary WD: Hot accretion disks, novae, supernovae Neutron star: Radiation with more vigor, no SN MASS TRANSFER

Neutron Stars in Binary Systems

• Mass transfer builds very hot accretion disk around neutron

star: intense x-ray emission (continuosly) from disk explosive helium burning (in bursts) on NS = X-ray Burster matter falling in can “spin up” the neutron star (or pulsar) If white dwarfs can do it, so can neutron stars!