ASTR 1120 ASTR 1120 General Astronomy: General Astronomy: Stars - - PowerPoint PPT Presentation

ASTR 1120 ASTR 1120 General Astronomy: General Astronomy: Stars & Galaxies Stars & Galaxies

• Homework

Homework #4 on MA due today, by 5pm #4 on MA due today, by 5pm

• Homework #5 on MA due Tue,

Homework #5 on MA due Tue, 10/20, by 5pm. 10/20, by 5pm.

• If your clicker grade on CU learn is

If your clicker grade on CU learn is “ “0 0” ” and and you have been in class, please you have been in class, please e-mail us your e-mail us your Clicker ID Clicker ID SECOND MIDTERM THURSDAY 10/15 SECOND MIDTERM THURSDAY 10/15

Comparing Three Types of Stellar Comparing Three Types of Stellar Explosions Explosions

• White

White Dwarf Nova Dwarf Nova

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

• White Dwarf Supernova

White Dwarf Supernova

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

• Massive Star Supernova

Massive Star Supernova

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

Where is fusion happening in a Where is fusion happening in a nova 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 Clicker Question

Where is fusion happening in a Where is fusion happening in a nova 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 Clicker Question

Where is fusion happening in a Where is fusion happening in a white white dwarf supernova 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 Clicker Question

Where is fusion happening in a Where is fusion happening in a white white dwarf supernova 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 Clicker Question

Where is fusion happening in a Where is fusion happening in a massive star supernova 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 Clicker Question

Where is fusion happening in a Where is fusion happening in a massive star supernova 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 Clicker Question

The Stellar Graveyard The Stellar Graveyard

What What’ ’s In The Stellar Graveyard? s In The Stellar Graveyard?

• Lower mass stars white dwarfs

– Gravity vs. electron degeneracy pressure

• High mass stars

High mass stars (M>8M

(M>8Msun

sun but M<30-40M

but M<30-40Msun

sun)

)

• neutron stars

neutron stars

– Gravity vs. neutron degeneracy pressure

• Even more massive stars black holes

– Gravity wins

Neutron Stars Neutron Stars

Neutron star over NYC

• Structure determined by

Structure determined by gravity vs. neutron gravity vs. neutron degeneracy pressure degeneracy pressure

• Radius ~ 10 km

Radius ~ 10 km

• Mass

Mass less than ~ 3 less than ~ 3 M MSun

Sun

• Made of degenerate

Made of degenerate neutrons neutrons

– – More massive = smaller !! More massive = smaller !!

• Crushing gravity at its

Crushing gravity at its surface, not a nice place surface, not a nice place to visit to visit

QUEENS QUEENS BROOKLYN BROOKLYN STATEN STATEN ISLAND ISLAND BRONX BRONX MAN MAN

Size of a neutron star

Mount Everest Neutron Star

Weight of a neutron star

Pinhead of

Observing the Observing the ‘ ‘First First’ ’ Pulsar: Pulsar: BIG discovery BIG discovery

• Jocelyn Bell

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

• Named it LGM-1 (Little

Named it LGM-1 (Little Green Man) Green Man) Just Just WHAT could cause WHAT could cause signal signal? ? 1.3 sec period 1.3 sec period

“ “Pulsar Pulsar” ” = rotating

= rotating neutron star neutron star

Fierce magnetic fields Fierce magnetic fields + sizzling electrons + sizzling electrons + fast rotation + fast rotation

• finest

finest “ “lighthouse lighthouse” ”

Thomas Gold 1968 Thomas Gold 1968

Pulsars and Neutron Stars Pulsars and Neutron Stars

Pulsars are lighthouses Pulsars are lighthouses in our Galaxy! in our Galaxy!

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

The Crab pulsar also The Crab pulsar also pulses in visual light pulses in visual light

Crab Crab Nebula Nebula SNR SNR

infrared infrared radio radio

• ptical
• ptical

x-ray x-ray

Pulsar Demo Pulsar Demo

Neutron Star in the Lab Neutron Star in the Lab + Sound of Pulsars + Sound of Pulsars

Synchrotron Radiation Synchrotron Radiation

• Fast electrons in

Fast electrons in strong magnetic strong magnetic fields fields

• spiraling

spiraling along along magnetic fields magnetic fields

• Different shape

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

Visible vs. X-ray emission Visible vs. X-ray emission

• Thermal light

Thermal light from from stars stars

• visible and IR

visible and IR

• Synchrotron light

Synchrotron light from from neutron neutron stars stars

• X-ray

X-ray and radio and radio

Visible light Visible light X-ray light X-ray light

What is a pulsar? 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 Reading Clicker Question Clicker Question

What is a pulsar? 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 Reading Clicker Question Clicker Question

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

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

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

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

Neutron Stars in Binary Systems Neutron Stars in Binary Systems

• Mass transfer builds

Mass transfer builds very hot very hot accretion disk accretion disk around neutron around neutron star: star:

• intense x-ray emission (

intense x-ray emission (continuosly continuosly) from disk ) from disk

• explosive

explosive helium burning helium burning (in bursts) (in bursts)

• n NS =
• n NS = X-ray

X-ray Burster Burster

• matter falling in can

matter falling in can “ “spin up spin up” ” the neutron star (or pulsar) the neutron star (or pulsar) If white dwarfs can do it, so can neutron stars! If white dwarfs can do it, so can neutron stars!