This document provides an overview of star formation, evolution, and death. It discusses how stars form from clouds of hydrogen and helium in nebulas. Once stars accumulate enough mass, nuclear fusion begins in their cores. The document outlines the life cycles of stars of different masses, from red giants to supernovae and the formation of neutron stars or black holes. Key stages in a massive star's death are described, such as the core collapse that causes type II supernovae and the ejection of heavier elements into space.
2. Star Basics
The universe is full of stars.
Somewhere between approximately 1022
and 1024 stars are currently believed to exist.
That’s more stars than grains of sand on the
Earth!
Stars are probably the most important
objects in the universe.
Every element larger than helium comes
from stars. We are technically stardust.
3. Star Formation
Clumps of mostly hydrogen form
large molecular clouds inside
nebulas.
As they accrete more matter, the
core becomes denser and
becomes a protostar.
Eventually, the mass reaches a
critical point at which the internal
temperature is hot enough to
ignite nuclear fusion.
The energy released from nuclear
fusion stabilizes the star against
it’s massive gravity.
4. Star Size
The sun and
planets.
The sun to VY
Canis Majoris
VY Canis
Majoris is the
largest known
star.
An estimated
9 billion suns
could fit inside
it!1
5. Star Death
Stars will last as long as they have fuel to
burn.
Most stars, like the Sun, are fueled from
the nuclear fusion of hydrogen into helium
in the star’s core.
This occurs at around 10-15 million K in the sun,
and around 100 million K on earth.3
When fusion stops, there is no longer
enough internal pressure to hold the star
up against it’s own gravity and the star
begins to collapse.
6. Star Death II
In about 5 billion years, the Sun will
enter a red giant phase, initiating the
end of it’s life cycle.
This occurs when all of the hydrogen
in the core is fused into helium.
The lack of pressure in the core
allows the star to compress, which
begins heating the star further.
This heat allows fusion in the outer
shell of the core to begin, and the star
swells tremendously.
At it’s maximum size, the Sun’s perimeter
will just engulf the Earth, disintegrating it.
7. Supernovae
Stars at least 8 times the mass of the Sun
undergo a more epic finale called a
supernova.
There are many types of supernovae, but
in any case they are the most energetic
explosions in the known universe.
During a supernova, a massive star can
eject more energy than the Sun will put out
in it’s entire lifetime.
This is an equivalent of 200 trillion trillion
100 megaton H-bombs going off in a
matter of seconds.4
8. Core Collapse Supernovae
Massive stars undergo core collapse,
resulting in a type-II supernova.
Process:
All of the stars hydrogen fuses into helium;
fusion ceases, diminishing internal pressure.
Gravity overpowers the internal pressure
and crushes the core, heating it up further.
Eventually, heat and pressure are strong
enough to fuse helium into carbon, and the
process repeats, fusing atoms into new
heavier elements.
This continues up to iron. The atomic
structure of iron causes it to absorb energy
during fusion.
Gravity overcomes the star, and a major
collapse occurs
9. Core Collapse Supernovae
II
The inner core collapses in ¼ of a sec from
the size of the Sun to the size of Manhattan.
The outer layers falling in nearly as fast,
collide with this new core and rebound with a
force comparable to nothing else in the
universe.
The speed and intensity of the ejected outer
layers can outshine the entire surrounding
galaxy for several weeks.
The blast is so powerful, it creates all of the
elements heavier than iron, spewing them
deep into space.
12. Neutron Stars
The remnant cores of these supernovae collapse
into neutron stars.
At this stage, the force of gravity is so strong, it
overcomes the repulsion of electrons.
In the core of the star, electrons are combined with
protons to make neutrons and expel neutrinos.
The star becomes stable from the internal pressure
of the neutron repulsion.
The result is the remnants of a star so dense, a
teaspoon of it would weight around 10 billion tons on
earth!
13. Other Types of Neutron
Stars
Pulsars-
Neutron stars spin so fast
(100’s of times a second) that
electrons caught in the
intense magnetic field heat
up and emit radiation out of
the poles.
All neutron stars do this, but
the radiation can only be
seen if the beam faces the
earth, making it appear to
pulsate.
14. Magnetars
The most magnetic objects in the
universe.
Magnetars are believed to form when
a neutron star is created with a very
fast spin.
The phenomenon known as dynamo
action causes an intense magnetic
field around the star from the
convection of ionized gas.
‘Starquakes’ in the crust of the star
disrupt this field and the star emits
massive amounts of magnetic energy.
If within a 1000 miles, a magnetar
would rip the iron from your blood!
15. Black Holes
The ultimate in star death.
Stars at least 20 times the mass of the
Sun end their lives as black holes.
Currently, physicists can only speculate
what happens at the center of black
holes.
16. Black Holes II
When the cores of the largest stars collapse, they
have such enormous gravity that the repulsion of
even neutrons can’t withstand it.
At this point, the force of gravity is so strong that not
even light can escape it.
Theoretically, with an infinite density, it can even
warp time itself.
There is much about black holes that can’t be
explained with our current understanding of physics.
The current laws of physics cannot explain what
happens at the center of black holes, though there
are many interesting theories.
17. Works Cited
1. Wittkowski, M.; Hauschildt; Arroyo-Torres, B.;
Marcaide, J.M. (5 April 2012). "Fundamental
properties and atmospheric structure of the
red supergiant VY CMa based on
VLTI/AMBER spectro-interferometry".
Astronomy & Astrophysics 540: L12.
2. Giacobbe, F. W. (2005). "How a Type II
Supernova Explodes". Electronic Journal of
Theoretical Physics 2 (6): 30–38
3. http://www.efda.org/fusion/how-fusion-works/
4. http://www.time.com/time/magazine/article/0,9
171,836188,00.html