gravitational radiation
A systematic "wiggling" of the curvature of space sends out gravitational
waves of space curvature. Carry energy, angular momentum from a binary star system.
an expansion that transports energy from a binary star system
why do we observe 2 white dwarfs in orbit in some cases?
if neither is filling roche lobe and are simply orbiting, gravitational radiation will occur. Carries energy out, causes orbit to shrink and WDS to spiral together.
what happens with this drag?
Falls inward, speeds up,
Get more gravitational radiation, more inspiral
over billions of years, white dwarfs will spiral together
of the white dwarfs, which has the smaller roche lobe?
the white dwarf supported by quantum pressure with larger mass has the smaller radius, i.e. a smaller roche lobe
What happens to the Roche lobes as the
WDs spiral closer by gravitational
radiation?
They both get smaller
Which ?lls its Roche Lobe ?rst?
Must be the smaller mass
As small mass WD loses mass, its radius gets larger,
but its Roche Lobe gets smaller! Runaway mass transfer.
Small mass WD transfers essentially all its mass to larger mass WD
which white dwarf will fill its roche lobe first?
the smaller mass one with the larger radius. as it fills its roche lobe and transfers matter into the larger mass smaller radius it kills itself. star tries to get fatter, roche lobe gets smaller
what could occur when this happens?
you could end up with one large mass white dwarf
if this large mass hits the chandresekar limit, what could happen?
could get an explosion ----->supernova
Two possible ways that a binary system can lead to a type 1A supernova
1) The ?rst white dwarf to form, from the originally most massive star, grows to very near the Chandrasekhar mass, ignites carbon and explodes while the other star is still transferring mass. My preferred explanation, but not ?rmly proven.
2) Two white dw
why is the type 2 light curve different?
as type II stars are already very large, they dont have to expand/cool very much and have the original energy from the explosion which explains the plateau
when is the maximum light output seen?
2 weeks after explosion
type II supernovas in red giants
have head start, radius already about the size of Earth's orbit; light on plateau comes from heat of original explosion
ejected matter _______ as it expands
cools
what must happen in white dwarfs (1a) or bare cores (type 1b, 1c) in order for them to be sufficiently transparent to radiate?
must expand huge factor of greater than 1,000,000
what happens to heat in the explosion?
it is all dissipated in the explosion
by the time it is transparent enough to radiate, there is no heat from the original explosion left to radiate
what is needed for type 1 a, b, c supernovas to shine?
a secondary source
what elements do type 1a start off with?
carbon
oxygen
number of protons equal to number of neutrons
composition of iron
26 protons and 30 neutrons
what does this reveal?
iron is not instantaneously created in explosion, process must be slow
carbon and oxygen burns too fast for weak nuclear force to convert p to n
what happens in type 1b, 1c collapse?
similar process
Shock wave hits silicon layer with #p = #n, burns too quickly for weak nuclear force
to convert p to n.
how do type 1a and 1b, c make iron (or something similar to iron)?
type 1a makes iron from its fast explosion
type 1b, 1c send shock to hit layer of silicon and form the element closest to iron, nickel 56
how many protons and neutrons does nickel 56 contain?
28 protons and 28 neutrons
(same total amount as iron)
is nickel 56 unstable to radioactive decay??
yes
what causes the radioactive decay with associated with iron?
the slow moving force of converting protons into neutrons
composition of cobalt 56 and iron 56
cobalt: 27p, 29 n
iron: 26 p, 30 n
nickel decays into ____. how long does this take?
cobalt. this takes weeks
cobalt decays into _____. how long does this take?
iron. this takes months
why are type 1as brighter than type 1bs and 1cs?
they produce more nickel 56 in the initial explosion
The thermonuclear burning of C and O
in a white dwarf makes about 0.5 - 0.7
solar masses of nickel-56.
how much nickel 56 does a type 1b/c (those that blast the silicon layer) produce?
0.1 solar masses
how much nickel 56 does type II produce?
also about .1 solar masses
what is different about this?
the explosion energy radiated from the red giant envelope in the plateau
tends to be brighter. After the envelope has expanded and dissipated,
the remaining radioactive decay of Cobalt-56 is seen.
supernova 1987A
The first supernova observable by the naked eye in about 400 years. It is directly observable only
in the southern hemisphere.
� Large Magellanic Cloud - small irregular satellite galaxy about 170,000 light years from the
Milky Way, the site of the explos
rings around 1987 A
The rings around SN 1987A were created by the star before it exploded, perhaps when it consumed a companion star. implies that the supernova has expanded out, hitting the rings and makes shine. RINGS WERE SHED BEFORE EXPLOSION
most important thing about 1987 a
we detected neutrinos
core collapse event
most neutrinos passing through missed the earth
about 19 were detected in 10 second bursts
what did these neutrinos imply?
that a neutron star had formed, though this neutron star could not be found
possible explanations to why the neutron star could not be found
1987 A could be similar to CAS A and have formed a dim neutron star
OR
that neutron star formed, but some matter fell back in and crushed the neutron star to become a black hole
what enables neutron stars to withstand pressure from gravity?
Combination of quantum pressure from neutrons and repulsion of
neutrons at very close distances by strong nuclear force
maximum mass of neutron star
analog to the chandresekar mass (2 solar masses). quantum pressure of neutrons plays a role but since nuclear forces are squeezing/pushing back neutrons, we dont know the true mass. A neutron star can't have too much matter
the vast majority of neutron stars are
alone in space (about 2000)
how many neutron stars have binary companions, ordinary stars, white dwarfs, other neutron stars, and black holes in orbit with them?
20-30
what do radio pulsars need in order to radiate?
they must be rotating and magnetic
a wiggling magnetic field will
wiggle the electric field. they will feed on eachother creating electromagnetic radiation
simplest configuration of this
North and South Poles (dipole) with lines of forces connecting poles
can ionized plasma move across lines of force? why or why not?
no...only along them. this is because lines of force drag plasma around like bead on a wire (plasma locked onto lines of force)
what happens If the plasma blobs are aligned with the rotation axis?
the system is too symmetric to "wiggle.
If blobs of plasma are off-center from the rotation axis, they are
whipped around by the rotating magnetic ?eld and generate
radiation
radio pulsars
rotating, magnetic neutron stars with
magnetic axis tilted with respect to spin axis.
Most radio pulsars rotate about
once per second
younger pulsars rotate
faster
crab pulsars rotate about
30 times per second, would destroy anything in its path
ingredients in making radiation from a neutron star
rotation
magnetic field
tilted magnetic field
radio emission from "thunder storms," and blobs of plasma come from
tilted poles or the speed of light cylinder
speed of light cylinder
distance from the neutron star's rotation axis at which plasma whipped around by "stiff" magnetic field would be moving at speed of light. when everything is locked in the rotation we can assume that the matter towards the outside is moving faster as it h
what do the tilted poles cause?
they whip the magnetic field around, then huge electric fields create huge currents (thunderstorms) that create radio static
AKA THEY CAUSE RADIO WAVES OMGZ
where is most power found?
high energy gamma rays that occur in the regions beyond the neutron star near the speed of light circle
where are radio pulsars found?
alone in space
or in a nontransferring binary system
the vast majority of radio and gamma rays are found
alone in space
how many have binary companions?
2 dozen
how do binaries measure mass?
keplers law
neutron stars in binary systems
companion star fills roche lobe, matter falls into acretion disk, dumps onto neutron star. matter from acretion disk is very hot, so hot that when it hits neutron star it will create x-ray radiation on that spots
when the star is magnetic and rotating you will see
the the lighthouse effect with x-ray radiation
neutron stars in binary systems with mass transfer
Mass transfer ?oods the magnetic ?eld/poles with gas/plasma, short
circuits, kills the radio (and gamma-ray) mechanism.
tying the magnetic field, magnetic poles, and neutron star x ray radiation together
in strong magnetic fields, matter connects to and flows ALONG magnetic lines of force. This channels matter to magnetic poles. This matter slams into neutron stars at the poles, gets hot and emits x-rays. This kills gamma and radio waves
will you get x-ray radiation magnetic poles are aligned (not tilted)?
yes. you just won't get lighthouse pulsars
standing shock wave
when a star first blows up it is dense, opaque. light can't leak out. outer matter must expand and cool to 100x the size of earth's orbit
super luminous supernovae
new class of supernovae, 10 to 100 times bigger than normal SN. discovered by texas supernovae search. long time ti rise to maximum light suggests need of large mass about 100 times the mass of the sun
extremely bright
why are they so bright?
shell shock model
pair instability supernova
shell shock model
proposes that the progenitor star expelled a dense shell of material to a star 100x the radius of earth's orbit before explosion. material exploded in SN collides with the shell that radiates the heat if the collison very effectively
pair instability supernova
a very large star has to be hot for pressure to hold it up. An 100 solar mass star will get so hot that it will turn heat/photons into matter and antimatter (electrons and antielectrons). This loss of heat will cause star to lose pressure, and it will sta
soft-gamma ray repeaters
objects that emit intense bursts of low energy gamma rays and X-rays for a
few minutes every few years. Periodic "pulses" after the initial flash. rates at which the pulses slow down imply
they are magnetars. One soft gamma-ray repeater actually caused au
theory on soft gamma ray repeaters
they break outer layer of iron like crust of neutron star that is threaded by magnetic lines of force, convert magnetic energy into heat or completely rearrange magnetic field configuration (swapping of north and south poles)
magnetars
highly magnetic neutron stars (100 to 1000 times stronger than the crab nebula pulsar)
anomalous x-ray pulsar
requires large magnetic fields but have not been sent to burst
widely believed to be magnetars
formation might be related to superluminous supernovas
most relevant to a radio pulsar
a neutron star rotating with a tilted magnetic field
most relevant to an x-ray pulsar
a neutron star with a tilted magnetic field accretes matter from a binary companion (wont be pulsed unless tilted)
most relevant to a soft gamma ray repeater
a neutron star has a magnetic field 100x stronger than that of a crab nebula