The Life Cycle of a Star
and the development of Black Holes
Charles Sturt University
For most part of human history, it has been
believed that the earth was the centre of the
‘Celestial Sphere’, with the stars stuck to the
inside of the sphere.
On right (Fig 1): A ‘Celestial Sphere’
model. Retrieved 2nd June 2014,
from; Spaceanswers, (n.d.).
• It is now known that the brightness of a star will
depend on a number of factors. These include; the size
and brightness of the star and also the distance away
the sun is from the viewing point (Earth). When stars
are farther away from Earth then they will appear dull.
However if a star is closer to earth it will appear
brighter (IPAC, n.d.).
• Stars also appear to ‘twinkle’ in the night sky. This is
result of the turbulence within our atmosphere. As the
atmosphere moves, the light travelling from the star
will refract in all different directions, giving the illusion
of a twinkling star (University, C. 2002, November 6).
• This however is not the case for planets which
can be observed from Earth. Planets do not
twinkle like stars . Stars are so far away that all
we can observe is a point of light in the sky.
Hence light will refract once exposed to our
atmosphere. Planets are closer and are actually a
quantitative size (which is very small), inturn
giving a more stable image because it is not
affected by the Earths atmosphere (University, C.
2002, November 6).
What is a Star?
• Stars are essentially giant balls of exploding gas,
which mainly consists of hydrogen and helium. The
nearest star to Earth, the Sun, is constantly exploding
in a nuclear reaction with the element hydrogen,
which makes the explosion similar to a hydrogen
bomb. These nuclear reactions are constantly
releasing energy into the universe, along with solar
winds and solar flares (QRG, n.d.). The only
protection the earth has from the solar winds and
flares is the magnetic field surrounding the Earth
(Association, N. E. (n.d.).
What is a Star? Continued…
Scientists believe that the core of the sun
consists of a 15 million degree Celsius plasma. This
plasma contains electrons and protons which have
been stripped from hydrogen atoms. These
protons are constantly colliding with other protons
which produces a helium nuclei in a nuclear fusion
Reaction, that releases energy into the universe.
The plasma makes up 90 per cent of a Star (QRG,
Life cycle of a Star
• -Red Giant
• -Red Dwarf
• -White Dwarf
• -Neutron Star
• -Black Hole
Above (Fig. 2): Diagram of the Life cycle of a Star.
Retrieved 25th May 2014, from; NASA, forwarded
by; Observatory, N. S. (n.d.).
• A Nebula is a cloud of gas (hydrogen) and dust
in space. A Star will form from the Nebula, as
it is the birthplace of a Star (Telescope, n.d.).
Above (Fig. 3): The Helix Nebula, Retrieved 1st June, 2014, from; NASA, 2012.
• A Star is a luminous globe of gas that produces its own
heat and light by nuclear reactions (fusion). A Star
consists of hydrogen and helium which creates a
surface temperature ranging between 2000°C to above
30,000�°C. The different range of temperature will
create different corresponding colours from red to
blue-white (Telescope, n.d.). A cooler temperature star
will radiate most of it’s energy in the form of infrared
radiation. Infrared radiation lands on the red region of
the electromagnetic spectrum and thus a cooler
temperature Star will appear red in colour. However, a
hot star will emit mostly ultra-violet wavelengths,
making them appear blue or white (Mutlaq, J. n.d.).
• This is a large bright star with a cool surface
temperature. It is formed during the later stages
of the evolution of a star. At this stage of its
evolution it will run out of ‘fuel’, which is in the
form of hydrogen. This is situated in the star’s
centre. Red Giants are very bright because they
are so large, however their surface temperature
is lower than that of our Sun, about 2000-
3000°�C (Telescope, n.d.).
Very large stars (Red Giants) are often called
• A Red Dwarf star is approximately one tenth
the mass and diameter of our Sun. A Red
Dwarf is a smaller and cooler temperature star
which is not as bright as other stars. Red
Dwarf Stars have an estimated lifespan of 100
billion years. This is because a Red Dwarf will
burn its fuel much slower as it is much smaller
and cooler than other Stars (Telescope, n.d.).
• This is very small star which is extremely hot.
Hence the White Dwarf will appear white in
colour. This is the last stage in the life cycle of
a star (Telescope, n.d.).
• A Supernova is the explosive death of a star, that often results in the star obtaining
the brightness of 100 million suns for a short time. There are two main types of
Supernova which will occur:-
• Type I - The fist type of Supernova will occur in binary star systems. As a result the
gas from one star will fall on to a white dwarf, inturn causing it to explode
• Type II The second type will occur in stars which are ten times larger than our own
star. These are known as Super-Giant Stars. When the Stars nuclear fuel is
exhausted the iron core will collapse and then rebound, creating a massive
explosion (Mattson, D. B. 2011, January). (Fig. 4)
On right (Fig. 4): Supernova; Image captured by
infrared and X-ray imaging. Retrieved 1st June,
2014, from; NASA, December, 2008
The Neutron Star is produced when a Supernova explodes.
The explosion will force the protons and electrons to combine
and create a Neutron Star. Hence these Stars are composed
mainly of neutrons (Telescope, n.d.).
On left (Fig. 5): Neutron Star, the dense
collapsed core of a massive star. Retrieved 1st
June, 2014, from; NASA, August, 2008.
• Black Holes are formed from the remnants of a larger star that dies in a
supernova explosion (NASA, 2014, May 15).
• A black hole is an object so dense that nothing in the universe can escape
from it’s gravitational pull, not even light (NASA, 2014, May 15).
• Black Holes are among the most violent and energetic objects in the
universe - active galactic nuclei and quasars, which shoot off jets even as
they suck in surrounding gas. However, this does not apply for all Black
Holes. Often older ones like the black hole at the centre of the Milky Way,
are considerably more quiet (University, C. 2011, December 15).
On left (Fig. 6): Artist’s concept illustration of a
Feeding Black Hole. Retrieved 1st July, 2014, from;
NASA, August, 2012.
Theory of Black Holes
• The concept of the black hole was first proposed
in 1783. However it was Albert Einstein's theory
of general relativity, 1915, which was first able to
theoretically prove they could exist. Einstein was
able to demonstrate that gravity can bend the
path of light, just as it is able to bend the path of
other moving objects that have a mass. By
demonstrating his theory he was able to confirm
the notion that Black Holes exist (University, C.
2011, December 15).
• It is not possible to observe Black Holes directly, however we can observe
the effect it has on surrounding materials. The materials we can observe
include: gas and dust. The Black hole will either suck the material in or
will eject it away in the form of a ‘jet’. The material will eventually fall into
the Black Holes abyss, however not straight away. The material will move
around the black hole in an orbit, forming what is known as an Accretion
Disk (University, C. 2011, December 15).
• Material orbiting in the Accretion Disk will slowly lose potential energy
due to friction. The majority of this friction is due to a huge gravitational
pull near the Black Hole. This gravitational pull rips apart the material
whilst at the same time heating it to extreme temperatures (reaching
thousands of degrees in temperature). Smaller Black Holes will heat their
disks to millions of degrees. These extreme temperatures emit
wavelengths equivalent to the x-ray part of the spectrum. This makes
Black Holes some of the brightest objects in the Universe (University, C.
2011, December 15).
• The material which is not sucked into the Black Hole is ejected by
jets that move away from the accretion disk. These jets are moving
close to the speed of light. These jets have been observed in the
form of: quick; enormously energetic spurts.
• The reasoning for these jets are still not well known, however it is
believed that magnetic fields are required to produce these jets
(University, C. 2011, December 15).
On left (Fig. 7): Black Holes generate colossal jets
that blast out twin streams of heated matter.
Retrieved 1st June, 2014, from; NASA, May, 2012.
• Advancing technology is increasing our
understanding and discovery of the Universe,
in particular the formation of Stars and their
life cycles. A Star will transform and develop
itself over time from a: Nebula; Star; Red
Giant; Red Dwarf; White Dwarf; Supernova;
Neutron Star; and possibly a Black Hole.
These Black Holes are so dense that not even
light can escape it’s unrelenting fury.
Thank you for taking the
time to watch my