Download planetary nebulae

Intro to Stars and Galaxies!!!
In the night sky there are
thousands of stars
Where do stars come from?
• The raw material that makes up
stars comes from the interstellar
medium
• Interstellar space is composed of
a thin gas laced with microscopic
dust particles.
• A place where the gas and dust
clumps into clouds is called a
nebula.
The nebulae are
70% hydrogen
and 30% helium
by mass. The
amount of other
elements is less
than1%.
At the end of their life, giant stars die in
enormous explosions than send out
shockwaves into the interstellar clouds
A
shockwave
from an
exploding
star rips
through the
rarefied gas
and dust of
a nebula.
The
shockwaves
make the
clouds collapse.
What force
do you think
makes them
collapse?
GRAVITY!
Spiral galaxies like our own are filled with
interstellar dust and gas. The pink glow is
caused by hydrogen excited by the radiation
from young stars.
Colliding galaxies
also make
interstellar clouds
collapse and
detonate star
formation in their
arms
Such is the distance
between stars, that
although each galaxy
can contain hundreds
of billions of star, a
head on collision
between galaxies will
rarely result in a single
collision of stars!
So how do the
galaxies have an
effect on each
other?
GRAVITY!
The Eagle
Nebula: a
vast region
of star
formation.
So, how
big is it?
The white
circle shows
the relative
size of our
entire solar
system
The glow is
caused by
young stars
Scientists believe that the
pressure and
temperature in the centre
of the collapsing cloud
forms a protostar.
How do they know this?
Let’s look at the evidence
The Orion nebula is a vast cloud of gas and dust
1500 light years from Earth. This image was taken
through a small amateur telescope using a digital
camera.
The following images were taken with the
Hubble Space Telescope using filters that only
let through wavelengths given out by the
glowing atoms of particular elements.
Imaged in
light given
out by
excited
Hydrogen
atoms
Imaged in
light given
out by
excited
Oxygen
atoms
Imaged in
light given
out by
excited
Nitrogen
atoms
Click to
combine
images
Combined
Can you
see where
stars are
forming?
These globules of
dense nebula are
called proplyds.
Could they be hiding
protostars inside
them?
Hubble Space
Telescope can sense
a wavelength that is
given out by hot
things and can
penetrate the gas and
dust – Infrared
Infrared
This reveals
many more
stars and
hotspots
hidden
inside the
dust and
gas.
Are any of
them inside
proplyds?
Click to
combine
images
Click to
combine
images
H+O+N+IR
What does
each
proplyd
have at its
center?
H+O+N+IR
Each
proplyd has
a star or hot
protostar at
its centre.
From evidence like this, we know that forces build
inside the protostar until they are great enough to
fuse hydrogen atoms together into helium.
In this conversion a tiny amount of mass is
turned into a large amount of energy.
For a star of the Sun’s size, 5 million tonnes start
to be converted into energy every second. The
protostar detonates into a star.
Luckily the Sun has a mass of 2 billion billion
billion tonnes. So there is enough to last for a
very long time. The Sun has been shining for
about 5 billion years and in all that time it has
only lost 1% of its mass.
Understanding how stars evolve
requires both observation and ideas
from physics.
• Our Sun serves as the primary evidence
that stars are not permanent.
– Nuclear Fuel in the Sun cannot last
forever.
– Our Sun is similar to the stars we see in
the night sky.
The new star erodes
the surrounding
proplyd with its
radiation. Eventually
the area clears,
revealing the star and
a surrounding disk
that can form a
planetary system.
Inside, a
structure forms
and the star
settles down to
fuse its
hydrogen.
The force
of gravity
crushing
the star is
balanced
by the
outward
force
created by
fusion in its
core.
The force of
gravity
crushing the
star is
balanced by
the outward
force of the
radiant
pressure
created by
fusion in its
core.
Draw a copy
of this
diagram and
label the
forces
Gravity
Draw a copy
of this
diagram and
label the
forces
Pressure
of fusion
Pressure
of fusion
Pressure
of fusion
Pressure
of fusion
Gravity
Gravity
Gravity
How long do stars live for?
Bigger stars have more fuel, so they live
longer?
What do you think?
Discuss this and take a vote
What is the pattern between mass and lifetime?
What explanation can you find for this in the table?
Solar Masses
Surface Temp
(0C)
25
15
3
1.5
1
0.75
0.5
35000
30000
11000
7000
6000
5000
4000
Lifetime
(million yrs)
3
15
500
3000
10000
15000
200000
The bigger the star, the shorter its lifetime.
Reason - big stars are hotter, so burn their fuel
quicker. More mass, means more gravity,
needing more radiant energy to balance the star..
Solar Masses
Surface Temp
(0C)
25
15
3
1.5
1
0.75
0.5
35000
30000
11000
7000
6000
5000
4000
Lifetime
(million yrs)
3
15
500
3000
10000
15000
200000
For Stars up to 1.5 times the size of our
Sun:
When the hydrogen is used up, the star’s
core shrinks and starts to fuse helium.
The intense radiation released puffs up
the outer layers, which cool and glow red.
The star is now a Red Giant
The Sun is half way through its
hydrogen burning life. How long until
it runs out of hydrogen?
1 solar mass stars burn hydrogen for
10,000,000,000 years
So the Sun has 5,000,000,000 years
of hydrogen burning left
Orbits of
Mars Earth
The Sun as a Red
Giant in 5,000,000,000
years time
Red giant
stars in
Auriga
300 million km
Dormant
hydrogen
fusing
shell
Carbonoxygen
core
Heliumfusing
shell
The core of the red giant now fuses helium into
bigger atoms but it eventually completely runs
out of fuel to fuse
With no fusion energy to keep
the core inflated, it collapses
for one last time. The carbon
is crushed into a diamond the
size of the Earth.
The outer layers of the Red
Giant are shed into space as
giant gas and dust shells.
They are illuminated by the
remaining tiny White Dwarf
star.
Astronomers thought these dim clouds
looked a bit like planets so they called
them planetary nebulae.
With modern telescopes like the
Hubble Space Telescope,
astronomers have shown planetary
nebulae to be some of the most
beautiful objects in the Universe.
What do you thinks these planetary
nebulae are called?
Astronomers
call this the
Eskimo
Nebula
Astronomers
call this the
Glowing Eye
Nebula
Astronomers
call this the
Hourglass
Nebula
Astronomers
call this the
Cat’s Eye
Nebula
Astronomers
call this the
Ring Nebula
Astronomers
call this the
Spirograph
Nebula
Astronomers
call this the
Eight Burst
Nebula
Astronomers call
this the Ant
Nebula
Astronomers
call this the
Red Spider
Nebula
Astronomers
call this the
Eye Nebula
Astronomers
have not given
this nebula a
name yet
The life of a star up to
1.5 solar masses Hydrogen runs out and
click to start
the core shrinks and
starts Helium burning.
The star swells into a Red Giant.
The star burns
Hydrogen.
Fuel runs out and
core shrinks
into a White dwarf
The Protostar forms in a collapsing
layers form a
proplyd of a nebula
planetary nebula
An ancient cluster
of over a million
stars reveals
some remaining
red giants and
many white
dwarfs
Stars of more than 1.5 Solar
masses have a very different fate
They burn fiercely as Blue Giant stars
and use their fuel up quickly
Betelgeuse
Bellatrix
Alnilam
Mintaka
Alnitak
Orion Nebula
Rigel
Saiph
The blue giant star Bellatrix, in the constellation
Orion, is coming to the end of its hydrogen fuel
When the star runs out of
hydrogen and starts to burn
Helium, it swells into an
enormous red star –
a Red Super Giant
Betelgeuse in the constellation is a red super
giant, here imaged by HST
Betelgeuse dwarfs all other stars
What sort of star do you think
Sirius B is?
A white dwarf
When a Red Super Giant runs
out of Helium fuel it has enough
heat and pressure in its core to
fuse Oxygen and Carbon to
make even bigger atoms
Eventually the star creates a core of iron
700 million km
Iron core
Silicon
Neon
Oxygen
Carbon
Helium
Hydrogen
The core of the red giant becomes an onion-like structure
with an iron core.
As the fuel runs out, the core
shrinks and gets hot enough to
fuse iron.
You don’t want to be in that part
of the Universe when a Red
Super Giant starts to fuse iron!
As the star fused hydrogen, helium,
carbon and oxygen it creates enough
energy to keep itself supported against
the crushing force of gravity.
Unlike the fusion of smaller atoms,
when iron fuses it sucks in energy.
The giant star is millions of years old
but it now collapses in seconds.
Billions of tons of star material hurtle
into the core and then bounce back out
in the biggest explosion in the
Universe.
The energy released outshines the
entire galaxy the star is in – up to
300,000,000,000 stars!
Here, one star in a
galaxy of billions fades
after it explodes as a
supernova.
At the time of the
explosion it would have
been brighter than the
entire galaxy.
The Tycho supernova
occurred in 1572 but
is still a rapidly
expanding, seething
explosion wiping out a
sizeable part of its
local universe. The
blue shell is the
distance travelled by
intense x rays at the
speed of light, heating
interstellar material to
20 million degrees
Celsius. The
explosion is at least
800 light years across.
You would only know
it was coming when it
hit you.
What remains from the explosion
depends on the size of the
original star
• 1.5 – 3 solar masses form one giant, 12 mile
diameter atomic nucleus composed only of
neutrons (all of the protons and electrons
have been squeezed together to form
neutrons).
• This is a neutron star. The force of its
tremendous gravity is balanced by the
repulsion of the neutrons.
What remains from the explosion
depends on the size of the
original star
• 3+ solar masses and there is no force
greater than the star’s gravity.
• The star collapse never stops, it disappears
leaving only it’s mass to create a gravity field.
• Nothing goes fast enough to escape, not
even light. This is a black hole.
A rotating neutron star (pulsar) is at the heart of the
crab nebula supernova corpse
The gravity near to a black hole is so strong that
even light does not go fast enough to get away
Black holes are made up of
two features
A singularity – all their mass is squeezed into a
point
An event horizon – the outer edge where the
force of gravity is great enough to stop light
escaping. The event horizon of the smallest
black holes created by supernovae should be
about 12km across.
But black holes will eat anything,
gas, dust, stars, even the centre
of galaxies.
As material spirals into a black
hole, it heats up and blasts
radiation out into space before it
disappears for ever.
A simulated picture of a black hole with a disk of matter spiralling inwards
What would happen if you fell
into a black hole?
The differences in gravity between your feet and your head would stretch you
out like spaghetti
Do you have a complete diagram
showing the life cycles of stars?
• It should show what stars form from
• What triggers star formation
• The different fates of different mass
stars
• How some star material is recycled
This is what your diagram should
look like
Credits
Written by Michael Cripps, Neatherd High School Norfolk UK
Website by Michael Cripps and Graham Colman of Taverham High School,
Norfolk UK
Images by Michael Cripps, Neatherd High School Students, ESA and NASA
Project sponsored by the UK Particle Physics and Astronomy Research Council,
the European Space Agency and Norfolk Education Business Exchange
Technical assistance by the scientists, engineers and educationalists of the
European Space Agency and NASA at the Space Telescope Science
Institute, Goddard Space Flight Centre and other institutions in the UK.
Special thanks to Helen Mason at Cambridge University and Dennis Christopher
at NASA, GSFC.
This resource and its content may be used freely for non commercial educational
purposes.