Download X-ray binaries

Neutron Stars
Supernova remnant G11.2-03
The massive-star supernova was
observed by Chinese astronomers in
A.D. 386.
X-ray image
White dot is X-rays from the neutron
star itself.
The different colors represent
different X-ray wavelengths.
The cloud of dust and gas racing
outward is impacting the interstellar
medium with very high energy.
23 light years
A neutron star has up to 3 times the mass of the Sun,
but is the size of a city (~10 km)
Gravity on the surface is
enormous:
Escape speed is about half the
speed of light
If you landed on the surface,
you’d be immediately squashed
into a microscopically thin layer
of subatomic particles
(Field trip?)
This is matter with all the empty space squeezed out of it
Neutron Stars – extremely dense!
>
A paperclip made out of neutron star material would weigh more than Mt. Everest!
Neutron star structure
Atomic nuclei and electrons
Neutrons only, squeezed into
one large nucleus
May be superfluid
May be superconducting
We can’t make this stuff in the
lab on Earth, so we only have
theoretical models.
Which statement is correct?
A) A white dwarf is about the size of the Moon;
A neutron star is about the size of a football field.
B) A white dwarf is about the size of the Earth;
A neutron star is about the size of a city.
C) A white dwarf is about the size of a city;
A neutron star is about the size of the Earth.
D) A white dwarf is about the size of the Earth;
A neutron star is about the size of a football field.
E) A white dwarf is about the size of the Moon;
A neutron star is about the size of a city.
Neutron Stars were first hypothesized in the late 1930’s. No observational evidence
existed until…
The first pulsar was
discovered by Jocelyn Bell
in 1967
Extremely regular radio pulses, initially dubbed
“LGM”
Her advisor, Anthony Hewish, got
the Nobel Prize for the discovery
The Crab nebula has a pulsar at its
center:
A rotating neutron star
Note the secondary pulse:
That’s the beam coming out the
opposite side
The rotating neutron star directs a
strong beam of radiation along its
magnetic poles.
If the magnetic axis is not aligned
with the rotation axis, the beam
sweeps around like a light house.
Every time the beam sweeps past
us, we see a pulse.
The extremely strong magnetic field is a result of the collapse of the iron core of
a massive star. That collapse also leads to rapid spinning.
Pulsars must be
neutron stars, because
anything smaller
would fly apart at the
rotation rates we’ve
seen in pulsars.
We’ve found pulsars
that rotate up to 625
times per second!
Pulsars are observed to slow down over time.
The beams radiate away energy that comes from rotational energy.
A neutron star …
A. contains most of the mass of the star from which it formed.
B. is about the size of a small town.
C. can sometimes be a pulsar.
D. is so dense that one teaspoonful would weigh more than Mt.
Everest.
E. all of the above
Just like with white dwarfs, neutron stars in close binary pairs can accumulate
material from a red giant partner.
However, so much
gravitational energy is
released that the inner part of
the accretion disk can glow
brightly in X-rays.
These are called
X-ray binaries.
The infalling material brings angular momentum with it, causing the neutron
star to rotate faster and faster.
The fastest are called
millisecond pulsars
As hydrogen accumulates in an
outer layer, pressure at the
bottom of the layer sustains
fusion at a continuous rate.
X-ray Bursts
The helium layer heats up, and
when it hits about 100,000,000 K
fusion begins.
In a few seconds, it radiates
100,000 times as much power as
the Sun, all in X-rays.
Neutron ball
It can do it again in a few hours
or days.
Hydrogen layer, fusing
at the bottom
Inert helium, getting
hotter as more is added
Light curve of an X-ray burst
One of the differences between a nova and an X-ray burst is…
A) A nova destroys the white dwarf, but an X-ray burst does not destroy
the neutron star
B) A nova happens when hydrogen fusion occurs, but an X-ray burst
happens when helium fusion occurs
C) A nova happens when helium fusion occurs, but an X-ray burst
happens when hydrogen fusion occurs
D) A nova does not destroy the white dwarf, but an X-ray burst destroys
the neutron star.
Astro-Cash Cab!
Availya
James
Alyse
Isaiah
1) What is the upper mass limit of a neutron star?
About 1.4 solar masses
About 2 solar masses
About 3 solar masses
About 8 solar masses
2) What is found at the center of the Crab Nebula?
3) What is a millisecond pulsar? What causes / creates it?
4) True / False
All pulsars are neutron stars.