Download The Life Cycle of Stars

The Life Cycle of Stars
Star Beginnings
1. A star has its beginning deep inside a massive cloud of interstellar gases and dust called a nebula. A
nebula consists primarily of hydrogen and helium.
2. Parts of nebulas collapse in on themselves. When it reaches a certain density, gravitational forces begin to
pull the gas and dust particles close together. Over time, this gravity causes regions of greater density to
form within the nebula, forming a protostar.
Nuclear Fusion
In nuclear physics, nuclear fusion is a nuclear reaction in which two or more atomic nuclei collide at a very high
speed and join to form a new type of atomic nucleus. During this process, matter is not conserved because some
of the matter of the fusing nuclei is converted to photons (energy). If light nuclei are forced together, they will
fuse with a yield of energy because the mass of the combination will be less than the sum of the masses of the
individual nuclei. E=mc^2
The Hertzsprung-Russell Diagram
It originated in 1911 when the Danish astronomer, Ejnar Hertzsprung, plotted the absolute magnitude of stars
against their colour (hence effective temperature). Independently in 1913 the American astronomer Henry Norris
Russell used spectral class against absolute magnitude. Their resultant plots showed that the relationship between
temperature and luminosity of a star was not random but instead appeared to fall into distinct groups.
90% of stars (including the Sun) plotted on the H-R diagram fit into a diagonal band which they called the main
sequence.
The Death of a Star
After spending approximately 10 billion years as a main sequence star, a star’s available hydrogen will have been
converted to helium by nuclear fusion. -> helium-rich core->less hydrogen to burn->core begins to
contract->heats the core->fusion restart in the outer layer->outer layers of the star expand and then cool->become
a red giant.
In about 5 billion years, our Sun will become a red giant. Star with a mass that is 10 times larger than that of the
Sun becomes a red supergiant.
As core contracts further->pressure rise->helium-rich core begins to undergo fusion->produces heavier elements,
such as carbon->as it expands, it sends gas and dust into space and begins to lose mass->caused it to move off the
main sequence band.
When nuclear fusion stops->the star’s core begins to collapse due to its own gravity->the outer layers of the star
drift away->hot core is all that remains (white dwarf)->cools down, all that remains is dark, cold matter (black
dwarf)
For stars tens of times more massive than the sun, the outer layers of the star explode outwards (supernova: a
stellar explosion that occurs at the end of a massive star’s life)
After the explosion, the core left behind becomes a neutron star (the gravity of a neutron star is 300000times that
of Earth.
When a star with an initial mass larger than 30 solar masses dies, it leaves behind a core so massive that it
collapses under its own gravity into a black hole. (light cannot escape)
Other Components of the Universe
Star cluster: a group of stars held together by gravity, there are two types of star clusters:
-open star clusters are collections of six to thousands of usually young stars.(approximately 20000 are found
within the main disc of the Milky Way)
-globular clusters are ball-shaped collections of thousands to millions of very old stars.
Types of Galaxies
Elliptical galaxy: a large group of stars that together make an elliptical of oval shape. (account for more than half
of all the galaxies we can see.
Spiral galaxy: a large group of stars that together make a spiral shape, such as the Milky Way.
Lenticular galaxy: a large group of stars that together make a shape that has a central bulge but no spiral arms.
Irregular galaxy: a large group of stars that together make an irregular shape.
The Milky Way Galaxy
-More than 200 billion stars and is more than 100000ly across.
-Two spiral arms.
-a supermassive black hole exists at the centre of the Milky Way.
Quasar (quasi-stellar): a distant, young galaxy that emits large amounts of energy produced by a supermassive
black hole at its centre. Quasars emit 100 to 1000 times more energy than the entire Milk Way.
Galaxy Clusters
The Milky Way is part of a group of more than 35 galaxies called the Local Group.
The Origin and Evolution of the Universe
Red shift: the phenomenon of light from galaxies shifting toward the red end of the visible spectrum, indicating
that the galaxies are moving away from Earth.
Big Bang theory: the theory that the Universe began in an incredibly hot, dense expansion approximately 13.7
billion years ago.
Questions:
1. Which galaxy classification does not belong?
(a) irregular
(b) spiral
(c) regular
3. A possible order of events in the evolution of stars is:
(a) nebula, fusion, core collapse
(b) fusion, nebula, core collapse
(c) nebula, core collapse, fusion
6. When a very large star (~ 30X larger than our Sun)“dies” it becomes a:
(a) white dwarf
(b) neutron star
(c) black hole
8. A possible order of events in the formation of the solar system is:
(a) nebula, Sun, planets
(b) planets, nebula, Sun
(c) nebula, planets, Sun
10. The following ripples are observed for an object moving in water. In what direction is it travelling?
(a) up
(b) down
(c) neither up nor down
State 2 reasons why the task of looking for planets is a very difficult one.
-Small compared to star
-Reflect light rather than produce it
The Hardest Logic Puzzle Ever
Three gods A, B, and C are called, in no particular order, True, False, and Random. True always speaks truly,
False always speaks falsely, but whether Random speaks truly or falsely is a completely random matter. Your task
is to determine the identities of A, B, and C by asking three yes-no questions; each question must be put to exactly
one god. The gods understand English, but will answer all questions in their own language, in which the words for
yes and no are da and ja, in some order. You do not know which word means which.