ASTR 1120 General Astronomy: Comparing Three Types of ...B.A white dwarf emitting pulses of hydrogen...
Transcript of ASTR 1120 General Astronomy: Comparing Three Types of ...B.A white dwarf emitting pulses of hydrogen...
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!