Transcript Birth and Life of a Star

Birth and Life of a Star
What is a star? A star is a really hot ball of gas, with hydrogen fusing into helium at its core. Stars spend the majority of their lives fusing hydrogen, and when the
hydrogen fuel is gone, stars fuse helium into carbon. The more massive stars can fuse carbon into even heavier elements, which is where most of the heavy
elements in the universe are made. Throughout this whole process is that battle between gravity and gas pressure, known as equilibrium.
Nebula
Birth- the birth of a star begins in the
Stellar Nursery (nebula) where gas and
dust begin to combine to form the star.
A nebula is a cloud of dust and gas,
composed primarily of hydrogen (97%)
and helium (3%). Within a nebula, there
are varying regions when gravity causes
this dust and gas gather more atoms
(mass), their gravitational attraction to
other atoms increases, pulling more
atoms into the “clump” (star).
A star spends a brief childhood
as a protostar, a star powered
purely by its own gravitational
contraction. Energy is
generated within a protostar
and so it has some luminosity.
Main sequence star
A nebula is usually
made up of
hydrogen gas. It is
the first stage of a
star's cycle
Protostar
Main Sequence Phase starts when nuclear fusion
starts.
Nuclear Fusion is the joining of the nuclei of 4
Hydrogen atoms into a Helium atom. A small
amount of mass (0.7%) is lost at this point and this
mass is converted into energy; light and heat.
(Grade A)
Nebula
A Protostar is the beginning
stages of star formation when
gravity pulls in the gas and dust
from the star nursery. When the
gas and dust are combined, the
protostar reaches a temperature
of 1,800,000 degrees F!
The radiant forces generated by nuclear
fusion and the forces of gravity from its
mass are equal during the main sequence
phase. This phase can last billions of
years, brighter starts use Hydrogen more
quickly and so die younger. (Grade B)
Death of a Medium/Small star
At the onset of nuclear fusion the star is born and begins the process of
fusing Hydrogen into Helium and then Helium into Lithium . Our sun has
insufficient mass to fuse heavier elements than Carbon. Heavier
elements like gold, lead and iron are created in much larger stars.
The Expansion Phase: The Hydrogen in the core of the star has all been
used and the star starts to ‘burn’ Helium this has greater radiant forces
and so the outer layers expand to form a red giant.
One and a half billion years later, the surface of the star is 3.3 times the
size it is now, and its temperature about 4300 degrees.
Red Giant
White dwarf
As seen from earth, our Sun will look like a big orange disk. The problem
however is that the temperature on earth has increased by about 100
degrees because of this. So all the seas will have evaporated by that
time.
Many white dwarfs are about the same size as the Earth, and about 100 times
smaller than the Sun. They may weigh the same as the sun, which would make
them very dense. The heavier the white dwarf is, then the smaller its size will be.
A star like our Sun will become a white dwarf when it has run out of fuel. Near
the end of its life, it will go through a red giant stage, and then lose most of its
gas, until what is left settles down and becomes a young white dwarf.
White dwarf stars are extremely hot; so they emit bright white light. This heat is
what is left of the heat made when the star collapsed. Because white dwarfs are
extremely small, it takes them a long time to cool down. Eventually, all white
dwarfs will cool down into what is called a black dwarf. These are what is left of
the star after all of its heat and light has gone away.
Black dwarf
A white dwarf is what stars like the Sun become after they have exhausted their nuclear fuel. Near the end of its nuclear burning stage, this type of star
expels most of its outer material. Only the hot core of the star remains. This core becomes a very hot white dwarf, with a temperature exceeding 100,000
Kelvin, the white dwarf cools down over the next billion years or so.
Death of a Large Star
Red supergiants (RSGs) They are the largest stars in the universe in terms of
volume, although they are not the most massive. after burning their
hydrogen large stars become red supergiants during their helium-burning
phase.
Super Red
Giant
A supernova is when a very big star explodes. This happens when a
star totally runs out of energy to make heat and light. They are
very big and because of gravity they press on their centers very
hard and use up their energy very quickly, so they usually only live
for a few million years. Then they become a black hole or a
neutron star. Small stars do not explode. They cool and shrink
down into a white dwarf star.
Supernova
Supernovas and life
Without supernovas there would be no life on Earth. This is
because many of the chemical elements were made in supernova
explosions. These are called "heavy elements". Heavy elements are
needed to make living things. The supernova is the only way heavy
elements can be made. Other elements were made by fusion in
stars. Heavy elements need very high temperature and pressure to
form. In a supernova explosion the temperature and pressure are
so high that heavy elements can be made.
A neutron star is a very small and dense star made almost
completely of neutrons. They are what is left from the core of a
massive star after it has exploded as a supernova,
Neutron stars have a radius of about 10 kilometres (6.2 mi) and
a mass from about 1.4 to 5 times the mass of our Sun.
A black hole is a region of space from which nothing,
including light, can escape. It is has such an enormous mass
that its own gravity has caused it to collapse in on itself.
Around a black hole there is an undetectable surface which
marks the point of no return, called an event horizon. It is
called "black" because it absorbs all the light that hits it
Black hole
Supernovas are very big explosions. Some of the dust and gas from
the supernova can become a new nebula (Solar nursery).
Neuton Star
New nebula