A Star's Journey - Video Editor: Emily Yan
A Star's Journey - Scriptwriters: Emily Yan, Yizhen Wu
A Star's Journey - Narrators and Researchers: Amy Li, Emily Yan, Yizhen Wu, Nancy Guo, Abigail Zhang
The Earth, a planet full of wonders, dreams, and life, yet
it is merely only a small planet in our solar system: an insignificant
miniscule fragment compared to the remarkably vast universe
But all of these miracles would not have been able to happen without one important element:
the sun.
Our sun was born around
4.6 billion years ago as a main sequence star, which are stars that fuse hydrogen in their cores
and have a stable balance of outward pressure from nuclear fusion in its core and
gravitational forces pulling inward. It was noted by astronomers such as
Charles Messier and William Herschel that all stars begin as a nebulae
-also known as an interstellar cloud-, a mass of hydrogen gas or solid that is scattered in the universe.
A disturbance caused by shockwaves of a nearby supernova or comet
then sends a force that enables
particles to collide and clump together.
Slowly, these clumps gather nearby debris and as the mass increases,
gravitational pull increases too, therefore
attracting more particles.
Over the course of millions of years, the concentration slowly increases in temperature, pressure, and density
until it finally stabilizes and fusion of
hydrogen to helium begin in its core.
The star gradually exhausts
its hydrogen and begins
expanding, forming a red giant star. The expansion and dimness is mainly caused by the change of chemicals
fused in the star. After hydrogen burns out, the star
switches its source of energy to carbon, the heaviest element a main sequence star can contain.
This process may only take a few million years depending on the size of the star.
Beyond this, the star begins to use energy
instead of creating it. When the last of its helium energy is used up, the star blasts
out its outer layer as a planetary nebula and leaves behind an extremely small, dense white dwarf.
Slowly, the white dwarf uses up its remaining energy and at last cools to a black dwarf.
Except these late stages are different for massive luminous star. After the run of hydrogen, they expand to become a red supergiant,
hundred of times larger than their original size.
They begin fusion of helium to carbon, then carbon to oxygen,
neon, silicon, and other heavier elements until it finally reaches iron.
The star is unable to fuse iron into denser elements due to the inability to fuse more energy than it releases.
Since the amount of fusion happening inside the star does not reach the necessary quantity to balance against the inward pull of gravity,
the star collapses in a supernova.
A supernova creates much of the heavy elements in the universe, and is so powerful that the light it produces could be as bright as an
entire galaxy!
Depending on the size of star, it either becomes a dense neutron star
or collapses to a black hole.
To record the life cycle of different types of stars,
Ejnar Hertzsprung and Henry Norris Russell charted down hundreds of stars in the early 1900s
onto what became the H-R diagram.
The diagram shows a pattern of main sequence stars from the top left to bottom right,
with red giants at the top
right and dwarfs at the bottom left. The diagram lead to many crucial
discoveries on the life cycle of stars in the future.
So, how do stars fuse hydrogen to helium?
First, two protons within the core collide against each other.
One of them turns into a neutron due to beta decay and releases an anti-electron
with a neutrino.
This makes a
deuterium nucleus, which is a stable isotope of hydrogen.
Then a
third proton is added to the deuterium to form the light
isotope of helium-3.
When two helium-3 nuclei
collide, they form a nucleus of
ordinary helium,
helium-4
(which include two protons and two neutrons),
and emits two protons. In each of these steps,
considerable energy is also released.
Fusion is the main source of energy that power stars.
According to Einstein's famous equation, E equals MC squared, a small amount of mass loss would result in large energy release,
because C is the speed of light, around 300 million meters per second.
When atoms collide and combine, they lose a small amount of mass.
It might not be much, but sun loses 4.3 million tons per second due to billions of these collisions,
so energy produced is very impressive.
In the 1930s, Hans Bethe, a German-born American theoretical
physicist, along with other scientists, tied their work together and discovered that fusion was possible and was the main source of energy
in stars.
Few years later, researchers began to look for ways to initiate and control fusion reactions to produce useful energy on Earth.
Physicists contained the hot plasma with magnetic fields,
because fusion reactions required temperatures hundreds of millions of degrees.
It was too hot to be contained by any solid chamber.
After the invention of the laser, other researchers sought to heat fuels with a laser so suddenly that the plasma would not have time to escape
before it was burned in the fusion reaction.
Ultimately in the 1980s, European countries constructed JET, the biggest magnetic confinement plasma physics
experiment at Oxford, UK, which eventually achieved first plasma. As we adventure to more advanced technology,
scientists made significant process in fusion, but still cannot create stable plasma.
They are presently working to stabilize plasma in order to achieve high efficiency to produce energy on Earth.
All of these discoveries help us understand how stars function, which adds to our knowledge of the universe.
Despite how luminous
our sun currently is, it will one day ignite and burn out,
unable to produce light and warmth for our solar system. And one day, all stars in the universe will die,
leaving us in the darkness...
