Transcript Death of massive stars

The Deaths of Massive Stars
The Deaths of Massive Stars
• Massive stars live spectacular lives and
destroy themselves in violent explosions.
• Because of their high mass, they can fuse
heavier elements since they can achieve
higher pressures
and temperatures
in their cores.
Nuclear Fusion in Massive Stars
• At higher temperatures than carbon fusion,
nuclei of oxygen, neon, and magnesium fuse to
make silicon and sulfur.
• At even higher temperatures, silicon can fuse to
make iron.
• Iron is the last
element to form
by fusion.
Nuclear Fusion in Massive Stars
The heavy elements are used up, and fusion goes very
quickly in massive stars.
Hydrogen fusion can last 7 million years in a 25-solar-mass
star.
The same star will fuse its oxygen in 6 months and its
silicon in just one day.
Supernova Explosions of Massive Stars
• Silicon fusion
produces iron—
the most tightly
bound of all
atomic nuclei.
Supernova Explosions of Massive Stars
• As a star develops an iron core, energy
production declines, and the core
contracts.
–Nuclear reactions involving iron begin.
–However, they remove energy from the
core—causing it to contract even
further.
–Once this process starts, the core of the
star collapses inward in less than a tenth
of a second.
Types of Supernovae
Type I supernovae are formed by the collapse and explosion of a
white dwarf star. Their light curves exhibit sharp maxima and then
die away gradually. They from from Population II stars in elliptical
galaxies.
Type II supernovae are produced by the collapse and explosion of
a massive star. They die away more sharply than the Type I (about
15 days), but then their magnitude
plateaus until about 100 days past
their explosion. They form from
Population I stars in spiral galaxies.
Observations of Supernovae
• In AD 1054, Chinese astronomers saw a
‘guest star’ appear in the constellation
known in the Western tradition as Taurus
the Bull.
– The star quickly became so bright that it was visible in the
daytime.
– After a month, it slowly faded, taking almost two years to
vanish from sight.
Observations of Supernovae
• When modern astronomers turned their
telescopes to the location of the guest star,
they found a
what is now
known as the
Crab Nebula.
Observations of Supernovae
The Recycling of Stardust
Neutron Stars
• A supernova will produce one of two
star remnants: A neutron star or a
black hole.
• A neutron star contains a little over
1 solar mass
compressed to a
radius of about
10 km.
Nuclear arithmatic
• A proton has a mass of 1 and a
charge of +1.
• An electron has a mass of 0 and a
charge of -1.
• A neutron has a mass of 1 and a
charge of 0.
1 proton+ 1 electron = 1 neutron +
lots of energy! (annihilation)
Formation of Neutron Stars
• The collapse would force protons to combine
with electrons and become neutrons.
Neutron Stars
• The matter is so dense
that a single teaspoon
would weigh ten billion
tons on Earth.
• Predictions show that the
stars have a 1km surface
crust that consists of iron
10,000 times more dense
and stiff than on Earth.
The Make-up of a
Neutron Star
Formation of Neutron Stars
• The rapidly - spinning star creates collimated
beams of radiation visible in X-ray and radio
wavelengths.
• If these beams sweep over Earth, we see
them as a series of regular pulses: a
pulsating star, or pulsar.
Click on image at
left to play an
animation.
Discovery of Pulsars
In November 1967, Jocelyn Bell found a new, regular
pattern in data from a radio telescope. Originally she
and her team suspected they had made the first
detection of alien life, and named it LGM 1. What they
really found was the first pulsar.
Magnetars
• A magnetar is a
neutron star with a
magnetic field so
strong that it slows
the star’s rotation and
causes quakes.
• These quakes cause
small bursts of
gamma radiation.
Quark Stars
• Quark Stars are
smaller and more
dense than neutron
stars. They can get as
small as 11 km across.
• The physics of a quark
star is unknown.
Gravity may not be
needed to hold it
together.
• The matter of a quark
star is strange- really
“strange”!
A Real Quarker!
• This is RX J1858-3754,
one of the first quark
stars studied by the
Chandra X-Ray
Observatory. It is in
the constellation of
Centaurus.
Hypernovae
• Hypernovae are much
more luminous and 100X
more powerful than
supernovae
• Source of gamma-ray
bursts
• Hypernovae can be
thought of as “failed
supernovae”, because
most of the star does not
explode off into space
Formation of Black Holes
• When the most massive stars collapse,
gravity wins.
• If the contracting core of a star becomes
small enough, the escape velocity in the
region around it is so large that no light
can escape. It is a black hole.
Black Holes
• A black hole is a region
of space that has so
much mass
concentrated in it that
there is no way for a
nearby object to escape
its gravitational pull.
• It can be identified by
either how much space
it takes up or by the
mass.
Black Holes
• It is a common misconception to think of
black holes as giant vacuum cleaners that
will suck up everything in the universe.
A black hole is just a dead star with a massive
gravitational field.
At a reasonably large distance, its gravity is no
greater than that of a normal object of similar mass.
If the Sun became a black hole, the planets’ orbits
would not change at all.
Black Holes
• The event
horizon is the
boundary
between the
isolated volume
of space-time
and the rest
of the universe.
The Search for Black Holes
• The areas around black holes (their accretion
disks) can be detected using X-ray and radio
telescopes.
• Black holes can also be detected if a star is seen
to orbiting a non-visible point.
What Happens After A Black Hole?
• One fanciful idea is that a
black hole is attached to
something called a white
hole that is in another
universe.
• It does the exact opposite
of a black hole, it spits
things out.
• But, a white hole has never
been discovered.