Unit 16D: Understanding the fundamental concepts outlined in astrophysics and
cosmology.
Section 1: Planetfacts 2020)
The Lifecycle of stars
Formation of stars
Molecular clouds are stars that are made within
different concentrations of interstellar gas and dust.
The cold temperatures of the molecular clouds allow
the gases to become molecular, here atoms bind
together. interstellar gas clouds, have molecules like
carbon monoxide and hydrogen which are the most
common within the clouds. extreme temperatures cause the gas to clump to high densities. Stars
begin to form when densities reach a certain point A star begins to form when it gathers so much
mass which causes it to collapse under the force of its own gravity, the cloud core is denser than the
outer cloud therefore they collapse first followed by the outer. When the cores collapse, they
fragment, into clump, forming protostars.
Protostars Earthsky 2019
they form stars, but the core is not hot enough, so for
fusion to take place. Their formation can be encouraged
by disturbances in gas clouds that compress the gas
surrounding nearby stars. When the cloud flops it spins
and protostars are formed, the cloud then flattens and
there is a prostellar disk spinning around the protostars,
the disks slow the rotation of the protostars, the rotation
of the protostars, generates a strong magnetic field which
also generates an outer flow of particles into space,
protostellar wind. Dust environs the protostars, blocking the light they emit so they become hard to
see in the visible spectrum. However, the protostars send out high speed streams of gas into space,
which the wind clears away the extra gas from the protostars allowing it to come into view. A
protostar becomes a main sequence star when its core temperature exceeds 10 million K, the
temperature needed for hydrogen fusion to operate.
The main sequence
Stars fuse hydrogen atoms forming helium atoms in their cores, in
nuclear fusion, during this they release a large amount of energy. In this
process a star is said to be in its main sequence phase of its life. Within a
star, the core accounts for a minor amount of its radius, In this region all
of the energy of the star is released. The energy released in the core
must travel through a radiative zone, where photons of energy are
absorbed and re-emitted, this energy is carried through a convective
zone where columns of hot plasma carry gas to the surface of the sun
where it is then released. A star gradually uses up the supply of hydrogen
in its core, this ensures the leftover helium to build up. The temperature
inside the star continuously increases because the star radiates away
Art station 2019
, energy but the main phase sequence lasts a long time, until all the energy has run out. This has the
ability to last around another 7.5 billion years before it runs out of fuel, causing it to die.
Red giant
A red giant is much larger than a main sequence star, as stars
convert hydrogen to helium the process which produces light, as
time passes the heavier helium sinks to the core of the star, the
hydrogen then becomes depleted, so it no longer generates enough
energy to support outer layers. The star begins to collapse therefore
the pressure and temperature rise eventually reaching levels that
are suitable enough to support the helium to fuse into carbon. A red
giant is produced because the star needs to radiate the heat energy
by the process of helium burning. The star may then compress as
the star will run out of its fuel, hydrogen, that is produced by a
nuclear reaction. Carbon is formed, in the red giant, as a result of the compression caused previously
which causes the star to heat up. The temperature of the star will continuously increase and fuse out
of the core of the star; this will then create a ring of energy and will cause friction against the outer
part of the star, significantly increasing the size of the star, transforming it into a red giant.
White dwarf
White dwarfs are formed when a star has lost all of its nuclear fuel.
Towards the end before this stage occurs, this type of star gets rid
of its outer material and which consequently creates a planetary
nebula. After this process, only the hot core of the star remains. The
core then transforms into a burning white dwarf, that may have a
temperature of over 1000 K, after this, the white dwarf, cools down
for a period of a billion years.
Supernovas
Supernovas can occur when a white dwarf, that consists of
carbon and oxygen, will still matter from a neighbouring star,
the white dwarf will eventually have so much matter that will
as a result, cause the star to explode and cause a supernova.
A second type of supernova can occur: this happens at the
end of a star’s lifecycle. At this point a star is running out of its
nuclear fuel, and some of its mass flows into the star’s core.
As more and more mass accumulates, the core becomes
heavy of mass and cannot withstand its own gravitational
force and this causes the core to collapse. This then results in the giant explosion of a supernova.
Death of stars:
Neutron stars
Neuron stars are those that have powerful magnetic fields; they can produce powerful beams
around its magnetic poles. On earth, it is observed as pulses of radiation that occurs whenever the
magnetic pole sweeps past the line of sight. These columns of radiation are known as pulsars, the
