ASTR 1120General 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 intoheavier elements.

B. On the surface, hydrogen is being fusedinto helium.

C. No fusion occurs in a nova, the lightcomes from the collapse (and bounce)of the star.

Clicker Question

Where is fusion happening in a nova?

A. In the core, carbon is being fused intoheavier elements.

B. On the surface, hydrogen is being fusedinto helium.

C. No fusion occurs in a nova, the lightcomes 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 intoheavier elements.

B. On the surface, hydrogen is being fusedinto helium.

C. No fusion occurs in a white dwarfsupernova, the light comes from thecollapse (and bounce) of the star.

Clicker Question

Where is fusion happening in a white

dwarf supernova?

A. In the core, carbon is being fused intoheavier elements.

B. On the surface, hydrogen is being fusedinto helium.

C. No fusion occurs in a white dwarfsupernova, the light comes from thecollapse (and bounce) of the star.

Clicker Question

Where is fusion happening in a

massive star supernova?

A. In the core, carbon is being fused intoheavier elements.

B. On the surface, hydrogen is being fusedinto helium.

C. No fusion occurs in a massive starsupernova, the light comes from thecollapse (and bounce) of the star.

Clicker Question

Where is fusion happening in a

massive star supernova?

A. In the core, carbon is being fused intoheavier elements.

B. On the surface, hydrogen is being fusedinto helium.

C. No fusion occurs in a massive starsupernova, the light comes from thecollapse (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 bygravity vs. neutrondegeneracy pressure

• Radius ~ 10 km

• Mass less than ~ 3 MSun

• Made of degenerateneutrons– More massive = smaller !!

• Crushing gravity at itssurface, not a nice placeto 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 in1967 (+AnthonyHewish) discoveredpulsars by accident!

• Named it LGM-1 (LittleGreen Man) JustWHAT could causesignal?

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

optical

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 ofhydrogen gas.

C. A red giant expanding and contractingin 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 ofhydrogen gas.

C. A red giant expanding and contractingin 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 neutronstar:

! 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!