Download Lives of Stars - Madison County Schools

Lives of Stars
Notes
The Lives of Stars
• A star is not organic, therefore it IS
NOT alive.
• Astronomers typically talk about the life
cycle of a star as if it were actually a
living thing. A star forms, exists, then
ceases to exist - equate this to a
hurricane, which forms, wreaks havoc,
then dies.
The Lives of Stars
• All stars begin as a nebula. A nebula is
a large cloud of gas and dust. A nebula
spreads out over huge areas of space.
• Disturbances cause some of the lighter
gases (hydrogen and helium) to begin
collapsing under the force of gravity.
Each of these nebulae
could give birth to
dozens, hundreds, or
even thousands of new
stars.
Lives of Stars
• When the gases collapse together with enough
mass that a star might form, this is known as a
protostar.
• Eventually, the protostar will begin fusing
hydrogen gas into helium, producing nuclear
fusion. At this point, it is an actual star, it is said
that the star has been born.
• http://www.astro.ex.ac.uk/people/mbate/Cluster/
Animations/ClusterXT1810Z_H264B.mov
Lives of Stars
• Stars with less mass live longer than stars with
more mass. Stars with less mass than Sol can
live up to 200 billion years. They burn through
their energy very slowly, so they are also cooler.
• Stars with mass equal to Sol live for about 10
billion years.
• Stars with masses 15 times the mass of Sol may
only love about 10 million years. They burn
through their fuel very rapidly and are much
hotter.
Death
of
Stars
• Eventually, all stars run out of the fuel
needed to perform nuclear fusion. When
this occurs, the star begins to die.
•
•
Keep in mind that all stars are in a battle
within themselves. There is the outward
explosion force of nuclear fusion, and the
inward force of its own gravity. For the
main life of a star, these two forces are
balanced.
When a star runs out of fuel, the two
forces become unbalanced and the star
will begin to change size.
Death of Stars
•
•
For low-mass and medium-mass stars,
when hydrogen runs out, the outward force
of nuclear fusion will cause the star to
expand outward and cool. This next step
forms a RED GIANT (a cooler star about
250 times larger).
Eventually, the red giant will run out of fuel
as well and blow out its outer layers as a
planetary nebula, leaving behind its core, a
WHITE DWARF star.
•
•
•
•
•
Death of Stars
The white dwarf that results is usually about the size of
Earth.
But it still contains most of the original mass of the sun,
meaning that it is about one million times denser than the
original star.
One teaspoon of white dwarf material would weigh as
much as an 18-wheeler.
Even though a white dwarf has no fuel, it continues to
glow using leftover energy for billions of years. Eventually
this core stops glowing and the leftover is called a black
dwarf.
Our universe (at 13.75 billion years old) is still too young
Death of Stars
•
•
•
A star with a huge mass has a different life cycle.
When a supergiant runs out of fuel, it explodes.
The explosion of a supergiant star is called a
supernova.
A single supernova can be so bright that it can
outshine the entire galaxy (300,000,000,000
stars) it was in.
Supernovae can be seen from Earth. There are
historic records of some stars that were so bright
that they could be seen during the day for weeks
at a time.
http://chandra.harvard.edu/photo/2010/sn1979c/SN19
79C_anim_lg_web.mov
Death of Stars
•
•
•
Sometimes, the ejected material from a
supernova turns into a nebula that contains not
only hydrogen and helium, but also heavier
elements such as iron, calcium, carbon, gold,
silver, etc.
This nebula can begin to collapse and form new
stars and planets.
Our solar system formed from this type of
scenario. All of the material for everything in this
solar system came from a supernova that
exploded in this area of the Milky Way.
Death of Stars
• Some of the core of a star that has gone
supernova can stay behind and form a neutron
star.
• A neutron star can contain up to three times the
mass of our sun, but all packed into the space of
only 25 kilometers.
• This density is approximately equivalent to the
mass of the entire human population
compressed to the size of a sugar cube.
http://en.wikipedia.org/wiki/File:Neutron_Star_Manhatt
an.ogv
Death of Stars
http://en.wikipedia.org/wiki/File:Millisecond_pulsar_and
_accretion_disk_-_NASA_animation_(hi-res).ogv
Deaths of Stars
• The stars with the greatest mass
become black holes when they die. A
black hole is an object with very strong
gravity that does not give off any light. A
black hole has gravity so strong that
nothing escapes its pull - not even light.
http://webb.nmu.edu/Webb/ArchivedHTML/Seaborg/Gi
ant%20black%20holes/Galactic_BH_lg.mpg
Death of Stars
• NASA has recently concluded that at
the center of most elliptical galaxies
(like our own Milky Way) there exists a
supermassive black hole, and in some
cases, multiple black holes.
• These black holes can contain millions
to billions more mass than our own sun.