Life and Death of a Star
Colour
Pressure
white
electron
cold
dwarfs
nebula
100
blue
carbon
protostar
fusion
shorter
helium
gravity
Hydrogen
Sequence
Life of a Star
In our galaxy alone, there are 400 billion stars. The pillars of creation are clouds of dust and gas and new stars are in the
process of being born in the central regions. __________________, the lightest element on the periodic table is the key
component of stars. Within a nebula, clumps of this gas and dust slowly coalesce into smaller clouds over millions of
years, pulled together by the force of ________________.
Each cloud can produce from a few dozen to thousands of stars. To form a star the size of our sun, it takes a clump of
gas and dust _______ times the size of our solar system. These clouds start off their lives bitterly _____________, at
temperatures hundreds of degrees below 00F. But as gravity fragments and compresses them, the heat begins to soar.
Within a few hundred thousand years, the cloud spins into a flattened disc. Gravity coalesces the center of the disc into
a sphere where the heat rises to 2 million degrees! This glowing system is now known as a ___________________.
10 million years later, the core gets so hot that it can sustain thermonuclear __________________. The hydrogen atoms
are moving fast enough that they will fuse and form a _______________ atom. This nuclear reaction produces the
energy to power the star throughout its life, giving it a constant source of light and heat.
Gravity is always a force on the star. It creates it and then tries to crush it. Stars are always working against
gravitational collapse. The heat from nuclear fusion gets all the particles moving about in the star and they bang
outwards and that produces a ____________________ that can hold the star up against gravity. Most of the stars life
will be in this state of equilibrium. It’s a phase scientists called the main __________________.
How hot a star is, is related to the _______________ of light that it emits. Small, cool red stars are known as red
____________. They can be as little as 1/10th the mass of the sun. They are the most common in the universe. On the
opposite end of the spectrum are the large, ______________ main sequence stars. They can be 20 times the mass of
the star and 10,000 times more luminous.
The more massive stars live much ______________ lives than the less massive stars. It seems like it shouldn’t be this
way because they have much more fuel to burn. However, this happens because it burns much more quickly.
Death of a Star
For all stars, life can't go on forever. It can only last as long as it has fuel to burn. If it runs out of fuel, fusion stops and
gravity wins. The death of different sizes of stars is also different. Massive stars explode in violent fury while smaller
ones are doomed to slowly fade away.
Smaller stars like our sun will slowly burn away its supply of hydrogen, nuclear fusion will cease and gravity will begin to
crush the star. In order to survive, the star will need a new source of fuel. It has helium on hand but in order to burn it,
the core needs to be 10 times hotter than it was to burn hydrogen. As it continues to contract inward, the core
becomes superheated by the gravitational pressure trying to crush it. Eventually it can fuse helium into _____________.
The star will quickly burn through its helium and the searing heat of burning helium will cause the star to swell. At that
point, the outer atmosphere will be held by gravity so weakly that it will start evaporating away. Through a series of
cosmic bursts, it will eject the outer envelope of gases outward. That will cause a planetary _________________
phenomenon. Beautiful shells of glowing gas will surround the core of the dying sun. However, the electrons in the star
don’t like being compressed and the pressure of them holds the star up against gravity. When the core of the star is
crushed to about the size of the earth, this ________________ degeneracy pressure takes over and gravity can collapse
the star no further. It’s left to slowly cool into a stellar remnant known as a _______________ dwarf.
supernova
Binary
Globular
Stragglers
neutron
pulsar
brown
black hole
planets
iron
More than half of all stars travel through life with at least one companion. Close _________________ stars can have
different fates than single stars. If a white dwarf is gravitationally bound to another star as part of a binary system, it
can essentially steal the life blood from its companion. It exerts such a strong gravitational pull that it will start siphoning
off a stream of hydrogen gas. Then it can grow in mass and eventually the mass of the white dwarf can reach an
unstable limit. At that point, it undergoes at catastrophic explosion where the whole thing goes off in a blinding
flash….what’s called a thermal nuclear runaway of the entire star. This is known as a Type 1A ____________________.
Although Type 1A come from exploding white dwarfs, Type 2A supernovas signal the dramatic deaths of much more
massive stars. When massive stars exhaust their hydrogen fuel, they have the raw power to start fusing other elements.
The ashes of one reaction become the fuel for the next reaction. This creates a layered star of heavier elements.
Eventually, as fusion continues, the massive star builds up a core of ____________. This becomes unstable and
eventually collapses. The collapse is violent and for a moment the core rebounds and kicks off one of the most massive
explosions since the big bang. Scientists believe these explosions are the source of the heavy elements that make up
everything around us. As material from these explosions spread out, it became the material of planets, moons, stars
and even the material in your body.
While the explosion of a Type 2 supernova showers the universe with heavy elements, the core is left intact. It is
gravity’s job to destroy this core but to do that, it has to overcome the electron degeneracy pressure. Gravity combines
the protons and electrons and turns them into neutrons. This allows the system to collapse further except neutrons
don’t like each other either and you end up with something more dense called a _______________ star. These can be a
small as 10 miles across. These are extremely dense: one teaspoon of this would weigh a billion tons. They also spin at
an incredibly high rate and have a high magnetic field. This forces a bunch of charged particles to go along the axis of
the field and they give off a focused beam of light. This star with a shining beam of light is called a ________________.
Some stars are so massive that not even a neutron star can hold up under the weight of their collapse and gravity will
crush them even further into an object of infinite density: a ___________________________. This is gravity’s victory
over mass. This collapse creates a region of space where matter is compressed into such a high density that its
gravitational field is inescapable. Not even light can escape it. A common misperception is that they suck up everything
in the universe. This is not true. Only objects that are close to it get sucked in.
Scientists have long suspected that there is another class of supernovas involving even bigger stars and even more
powerful explosions. The collapse so catastrophically that they leave no remnants, not even a black hole. In the fall of
2006, astronomers observed the largest explosion ever witnessed by man. Scientists are still studying the aftermath of
the explosion. They believe that these explosions are the seeds of the next generations of stars that then increase the
likelihood that the next generation will have _________________ that have the ingredients for life itself.
Using computer models, astrophysicists can see what happens when stars collide. The odds of two stars colliding in our
galaxy are quite low. But within a ________________ cluster, stars are packed a million times more densely than
elsewhere in the Milky Way. In these crowded collisions, stars collide on average once every 10,000 years. Large blue
stars known as blue _____________________ are younger than stars should be in this cluster. It is believed they are the
result of collisions of two main sequence stars. In the end, rather than a catastrophe, they form one more massive star.
There are other strange celestial objects that never got a chance to shine. Not quite planets and not quite stars, these
are the ________________ dwarfs. It is basically a failed star. They are very low temperature and emit very low light. It
doesn’t have enough mass to sustain nuclear fusion. Without fusion, they start to act like planets.