Download Life of a star - bahringcarthnoians

By Andy Hu, Mitchell Dawes, Jeremy Zhang and Eamon
Roche
Our galaxy is filled with these irregular shaped clouds called
“nebulae” which form stars. There are nebulas with animal shaped
things like the horsehead nebula and the eagle nebula nebulas are
cold as -263 degrees Celsius, which scientists think is 10 degrees
from absolute zero! These nebulas are cold and thin but they have
the perfect ingredients for giving birth to a star. The death of a
light-weight star can form a nebula. The perfect example is the
Helix nebula , which now is being illuminated by the dying star
inside it.
Name of the
nebula
How far away
Diameter
Eagle nebula
7000 light-years 315 light-years
NGC 1999
1500 light-years 1 light-year
Horsehead
nebula
1300 light-years 4 light-years
Helix nebula
680 light-years
5 light-years
A star’s life begins when clumps of gas and dust come together from it’s own gravity.
Gravity pushes these clumps together to make more pressure. Small amounts of gas
and dust fizzle out. If the clump is big enough, the centre of the forming star boosts
over 10 million degrees Celsius. A nuclear reaction begins as hydrogen atoms fuse
together to make helium. The heat makes the star shine and that star’s life begins in
the vast universe.
Cycle of a Star
There are different types of stars like blue ones which don’t live long
and middle-aged stars like our Sun or big dying stars called supergiants.
While a star is burning, first, it burns the hydrogen for about 10 billion
years, then burns the helium and any other flamable things like dust.
A Star
The pressure at the centre of a star becomes so enormous in the red giant stage that silicon
and carbon fuse together to make iron. Once iron is formed, the star fails to give off energy
and catastrophically collapses into an explosion. An example of this is Eta Carinae. In 1841, Eta
Carinae suffered a violent outburst after suddenly collapsing , and blew 2 giant clouds of dust
that have been expanding since. The two clouds just became twice as bright as before and it
will explode as a supernova in the next few thousand years. After collapsing as a supergiant, it
will either become a neutron star (a star that is dying and is sending out intense radio signals),
a white dwarf or a black hole.
The death
Eta carinae
A supernova is an explosion that is more energetic than a nova. Supernovae are extremely
bright and cause a burst of radiation that often briefly outshines a galaxy, before fading from
view. During this short time a supernova can radiate as much energy as the Sun is expected to
emit over its entire life span.
The Big Bang produced hydrogen, helium, and traces of lithium, while all heavier elements are
made in stars and supernovae. Supernovae tend to enrich the surrounding space with
elements other than hydrogen and helium.
Each stellar generation has a slightly different composition, going from an almost pure mixture
of hydrogen and helium to a more metal-rich composition. The different abundances of
elements in the material that forms a star affect the star's life, and may affect the possibility of
having planets orbiting it.
Black holes are probably the most puzzling objects in astronomy. A black hole’s
gravity is so intense that it bends light! Black holes are infinitely small and have
infinite space. There are supermassive black holes which lies at the centre of
most galaxies and there are small ones which suck in nearby stars and just gets
sucked in by a supermassive one. Black holes have a ring of shredded up
nebulas and stars called accretion.
A red giant is a luminous giant star in a late phase of evolution, with between half and 10
times the mass of our sun. They have a large radius (up to hundreds of times larger than
our sun) and their surface temperature is 5,000° Kelvin and lower. They are yelloworange to red in colour.
Red giants have burnt up all the hydrogen fuel in their cores. When this happens,
nuclear reactions stop, the core begins to get smaller, and a shell outside the core heats
up and starts fusing hydrogen to helium. The higher temperatures make enough energy
to increase the star's brightness by a factor of 1,000–10,000. The outer layers then
expand, beginning the red giant phase.
The Sun is predicted to become a red giant. As its radius expands it will become large
enough to swallow the inner planets, up to Earth. But don’t panic, because this won’t
happen for about 4.5 billion years.
If a red giant has not enough mass to generate the core temperatures required to
fuse carbon, a mass of carbon and oxygen will build up at its center. After shedding
its outer layers to form a planetary nebula, it will leave behind its core, which forms
the white dwarf.
The visible radiation emitted by white dwarfs varies over a wide range, from an Otype to a M-type. White dwarf surface temperatures can be over 150,000 K to
under 4,000 K.
A white dwarf is very hot when it is formed but it has no source of energy so it will
gradually radiate away and cool down. Over a very long time, a white dwarf will
cool to temperatures at which it won’t be visible, and become a black dwarf. But
since no white dwarf can be older than the age of the Universe, no black dwarfs
exist yet.
Composition of a white
dwarf
A white dwarf is a small
star composed mostly of
electron-degenerate
matter.
If the collapsing core at the centre of a supernova contains between 1.4 and 3 solar
masses, the collapse continues until electrons and protons combine to form
neutrons, producing a neutron star. Because it contains so much mass packed into a
small volume, the gravity at the surface of a neutron star is very big. If a neutron star
forms in a multiple star system it can collect gas by stripping it off nearby
companions.
Neutron stars have powerful magnetic fields which accelerate particles around its
poles producing powerful beams of radiation. These beams sweep around as the
star rotates. If the beam is oriented so that it points toward the Earth, we observe it
as pulses of radiation that happen whenever the pole of the neutron star sweeps
past the line of sight. In this case, the neutron star is known as a pulsar.
Hertzprung-Russell diagrams plot each star
on a graph measuring the star's absolute
magnitude or brightness against its
temperature and colour.
Stars tend to fall only into certain regions on
the diagram.
The most predominant is the diagonal, going
from the upper-left (hot and bright) to the
lower-right (cooler and less bright), called
the main sequence.
White dwarfs are found in the lower-left, and
the subgiants, giants and supergiants are
above the main sequence.