Download Death of Stars - Astronomy @ Walton High School

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To associate the stages in the death of (i) solarmass and (ii) heavier stars with planetary
nebulae and supernovae.
To show an awareness of the main
components of the HR diagram and relate
these to stellar death.
To describe the end-products of stars: white
dwarfs (for solar-mass stars); neutron stars (for
heavier stars) and black holes (for even
heavier stars!).
To understand how astronomers provide
evidence for neutron stars (pulsars) and black
holes.
To show an awareness of the main components of the HR diagram and relate
these to stellar death
This is a hertzprung russel
diagram. A log scale of
the luminosity of the star
(or absolute magnitude)
is plotted against the
spectral class (or
decreasing temperature
– non linear scale)
There is a band down
the middle with 90%
of the stars – main
sequence. These
‘burn’ hydrogen
Stars at the end of their
life are on either side
Sketch a diagram of an HR diagram in
your books. Annotate it appropriately. Try
and do it from memory
 If you are struggling use the internet to
help
 If you complete this try and describe
what the diagram tells us about the birth
and death of a star?
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Eventually the star burns up the hydrogen in its core and burns
the hydrogen in its outer core or shell.
It becomes brighter and expands to a red giant. Helium is now
being burnt by the star.
At this point different scenarios present themselves depending
on the mass of the star.
If the star has a very small mass it shrinks to a red dwarf, burning
its hydrogen and helium.
If a star, such as our Sun, has under 4 solar masses it will grow to a
red giant and eventually puff away its outer layers before
shrinking to a white dwarf, of under 1.5 solar masses.
If the star has between 4 and 25 solar masses it will grow to a red
super giant and explode as a supernova, leaving a neutron star
the size of Earth.
If it has over 25 solar masses it will again explode as a supernova
but will produce a black hole.
Read and
make summary
notes. Highlight
important info
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A supernova is the brightest event in space. There are two
types of supernova:
1 Similar to a nova where a dwarf takes material from a
giant. This time the explosion destroys the dwarf. Typically
this takes place when the mass of the white dwarf is over
1.4 solar masses.
2 When a star has a mass greater than 8 solar masses. The
red giant swells so much it collapses in on itself. These are
dramatic events as once they explode the core forms a
neutron star or a black hole.
The light curve shows a drastic increase in brightness
before receding to a small luminance after a few months.
A planetary nebula is usually seen in the region of a
supernova for years, sometimes centuries afterwards.
Read and
make summary
notes. Highlight
important info
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A star between 4 and 25 solar masses will grow to a red super
giant and explode as a supernova, leaving a neutron star
smaller than the size of Earth.
These stars are compressed so much that they are composed
entirely of neutrons, parts of the atom without electrical
charge.
This is the equivalent of the size of the Sun in the same area as
a city or the human population on Earth fitting inside an area
the size of a sugar cube.
Neutron stars rotate rapidly after formation, typically spinning
between fractions of a second and half a minute. We can
detect this because they emit radio pulses, and the ones we
detect are known as pulsars. Radio astronomy has also
detected brightness and temperature from neutron stars, and
astronomers have used x-ray astronomy to detect them
when matter from companion stars falls onto neutron stars.
Read and
make summary
notes. Highlight
important info
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No astronomer has ever seen a black hole, largely because there is too
much material surrounding it and also because it is black as the name
suggests.
Most astronomers accept they exist but there is a lot about them that we
don't know.
When a very large star explodes, the mass condenses so much that is
collapses in on itself. The gravity is still present.
It appears to pull in any material in the vicinity. Once matter goes past the
boundary of a black hole (called the event horizon) it cannot escape back
out again; not even light can escape which travels at 300,000 kilometres a
second.
Evidence from black holes comes from binary stars that get their solar
material pulled into the hole. This often forms an accretion disc of matter
circling the area. It orbits so fast it is hot enough to give off x-rays which we
can measure.
The black hole forces such a gravitational force on these particles it can
push them light years away, perpendicular to the disc in the form of particle
jets travelling near to the speed of light.
It is thought that most galaxies have a super massive black hole in their
centre.
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Research about some of our ‘known’
black holes and neutron stars. Obtain
some images if possible and how we can
tell they are there