Week 1 - Lesson 1.2 Star Formation Flashcards
On a dark night you can practically watch stars being born. The fuzzy area in the sword in the constellation Orion is
the ________. A close up shows the nebula with around 3,000 stars. New stars are being born there.
.Orion nebula
This have a life cycle, just like people. These are born, grow, change over time, and eventually grow old and die.
Most ____ change in size, color, and class at least once in their lifetime. What astronomers know about the life
cycles of _____ comes from data gathered from visual, radio, and X-ray telescopes
.star
—- are born in a cloud of gas and dust called a nebula (Figure 1.4). Our Sun and solar system formed out of a
nebula.
.stars
The _____of Creation (Figure 1.5) are within the Eagle Nebula. The _____ are thought to be a large region where
stars are forming. The dark areas may be stars that are about to begin.
.pillars
For a _____ to form, gravity pulls gas and dust into the center of the nebula. As the material becomes denser, the
pressure and the temperature increase. When the temperature of the center becomes hot enough, nuclear fusion begins. The ball of gas has become a _____
Our Sun was probably born in a nebula, like Orion in the top image.
.star
These form in a nebula.
.stars
This is a cloud of dust and gas.
.nebula
This can be spotted with the naked eye or simple telescopes
.nebulae
In the very beginning, both space and time were created in _______ . It happened 13.7 billion years ago.
Afterwards, the universe was a very hot, expanding soup of fundamental particles. The universe expanded rapidly
during inflation and expands at a more or less constant rate now. As it grows, it cools.
.big bang
When the universe was 3 minutes old, it had cooled enough for these protons and neutrons to combine
into nuclei. This is known as the time of _______. Hydrogen, helium, lithium, and beryllium were produced.
.nucleosynthesis
At this time the universe had cooled sufficiently for atoms to exist. Echoes from these first atoms can still be seen in
the ________. But this process only created the lightest four elements. How did the other
88 natural elements come about? To understand this, we need to understand fusion
.cosmic microwave background
All protons have positive charge and therefore repel one other. How then, can they be packed tightly into a nucleus?
What holds them there?
The answer is another force, the strong force. When protons collide with enough energy,
their electric repulsion can be overwhelmed by this new force and they will be bound together.
Three important fusion processes are:
.the proton-proton chain which details how helium is made in our sun, the
CNO cycle which explains how hydrogen is fused in hotter stars, and the triple alpha process which accounts for
the helium fusing that occurs in mature stars. Sketches of these three processes are shown below. In each case, the
sketch is incomplete. These reactions occur in chains with more than one possible path. Only the most probable
paths are shown below.
Another important concept is the behavior of an ____. When a ___ is compressed, its temperature increases.
When a ___ expands, its temperature drops. This is why a bike pump warms up when in use. It is also why air
rushing out of a balloon feels cool. Now back to our story
.ideal gas
The atoms left over by the big bang were gravitationally attracted to one another and condensed into huge clouds.
The gravitational pressure on the centers of these clouds heated them to temperatures of millions of degrees.
This led to
.fusion of hydrogen into helium. Stars were born. As the fuel in their cores is used up, the cores shrink
and warm. This causes hydrogen fusing to occur in the outer parts of the star, its shell. This new source of energy
causes the star to expand and cool, turning it into a red giant
Once all the hydrogen in the core has been used up, helium is fused into carbon, nitrogen and oxygen. This causes the core to expand and cool once again. The shell, which is still fusing hydrogen, also cools. When all the helium has been used, the core contracts and warms. This heats up the shell which now starts fusing helium. The star enters a
.second red giant phase.
At this point, low-mass stars (below 8 solar masses) eject their outer layers and evolve into
.white dwarfs
If the star has a mass of more than _____ solar masses (called a _____) its gravity is strong enough to fuse neon
after it has finished fusing carbon. This forms more oxygen and magnesium. Afterwards, oxygen will be fused into
sulfur, silicon, phosphorus, and magnesium. Then silicon will be fused to new elements as heavy as iron. Each
stage burns more quickly, at a higher temperature, and at a greater density. As each new stage begins, the earlier
stages continue their reactions in onion-like shells about the core. The star heats up and expands as each new phase
begins. It constantly loses mass to its stellar wind.
.8,Supergiant
Some of the reactions which lead to the creation of these new elements also produce ____. These ____ are
captured by some of the new atoms to form different isotopes. This process cannot create a nucleus with more than 26 protons (iron) because at that point the energy it takes to overcome the electric repulsion is greater than the energy
released by the strong force. Creating elements heavier than iron requires energy, it doesn’t release energy
.neutron
The heaviest elements are created in ______,
.supernovae
The supernova just described is termed a ______because it contains the emission lines of metals.
Type II Supernova
The first four elements were present after _______.
.big bang
On a dark night you can practically watch _____ being born. The fuzzy area in the sword in the constellation Orion is
the Orion nebula. A close up shows the nebula with around 3,000 stars. New _____ are being born there.
Stars
In the very beginning, both space and time were created in Big bang . It happened 13.7 billion years ago.
Afterwards, the universe was a very hot, expanding soup of fundamental particles. The universe expanded rapidly
during ______ and expands at a more or less constant rate now. As it grows, it cools.
Inflation
