Week 1 - Lesson 1.2 Star Formation

Question 1

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.

Answer 1

.Orion nebula

Question 2

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

Answer 2

.star

Question 3

—- 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.

Answer 3

.stars

Question 4

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.

Answer 4

.pillars

Question 5

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.

Answer 5

.star

Question 6

These form in a nebula.

Answer 6

.stars

Question 7

This is a cloud of dust and gas.

Answer 7

.nebula

Question 8

This can be spotted with the naked eye or simple telescopes

Answer 8

.nebulae

Question 9

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.

Answer 9

.big bang

Question 10

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.

Answer 10

.nucleosynthesis

Question 11

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

Answer 11

.cosmic microwave background

Question 12

All protons have positive charge and therefore repel one other. How then, can they be packed tightly into a nucleus?
What holds them there?

Answer 12

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.

Question 13

Three important fusion processes are:

Answer 13

.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.

Question 14

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

Answer 14

.ideal gas

Question 15

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

Answer 15

.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

Question 16

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

Answer 16

.second red giant phase.

Question 17

At this point, low-mass stars (below 8 solar masses) eject their outer layers and evolve into

Answer 17

.white dwarfs

Question 18

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.

Answer 18

.8,Supergiant

Question 19

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

Answer 19

.neutron

Question 20

The heaviest elements are created in ______,

Answer 20

.supernovae

Question 21

The supernova just described is termed a ______because it contains the emission lines of metals.

Answer 21

Type II Supernova

Question 22

The first four elements were present after _______.

Answer 22

.big bang

Question 23

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.

Answer 23

Stars

Question 24

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.

Answer 24

Inflation

Question 25

At first, the universe was dominated by ______. Soon, quarks combined together to form baryons (protons and
neutrons)

Answer 25

Radiation

Question 26

Today, about 90% of the universe is still ____. Remember that only the nuclei of these atoms were created at
this time. The universe was still far too hot to allow these nuclei to attract electrons and form atoms. That didn’t
happen for another 300,000 years, at the time of recombination.

Answer 26

Hydrogen

Question 27

Similar processes take place between neutrons and protons and between small nuclei. This building up of heavier nuclei is called

Answer 27

Nuclear fusion

Question 28

.the proton-proton chain which details how ____ is made in our sun

Answer 28

Helium

Question 29

This explains how hydrogen is fused in hotter stars,

Answer 29

CNO cycle

Question 30

This accounts for
the helium fusing that occurs in mature stars.

Answer 30

Triple alpha process

Question 31

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

Answer 31

Red giant

Question 32

During these cycles, convection within the star increases. After hydrogen fusing is stopped, the first dredge-up
carries oxygen, nitrogen, and carbon from the CNO process to the surface of the star. After helium fusing stops, a
second dredge-up carries more of these elements from the triple alpha reactions to the surface.

Answer 32

second red giant phase.

Question 33

If the star has a mass greater than 2 solar masses, a third dredge-up can occur. This time mostly carbon and carbon molecules are brought to the surface. These stars are called ______ stars. They have very active solar winds and are typically surrounded by a sooty planetary nebula.

Answer 33

AGB or carbon stars

Question 34

are carbon-oxygen-rich and made of super-dense matter. Most of their hydrogen and helium are lost to the
stellar wind. These stars are so dense that they form a new type of “degenerate” or nuclear matter.

Answer 34

White warfs

Question 35

_____ stars do not evolve into white-dwarves. The gravitational pressure on these stars does not allow their
cores to expand and cool. Their gravity is so great that not even the degenerate electron pressure in the core can cool it. After helium fusing ends in these stars, carbon fusing begins creating oxygen, neon, sodium, and magnesium

Answer 35

High-mass

Question 36

the fantastic death of ____ stars. As the core of the _______
becomes saturated with iron, its pressure and temperature increase. Eventually, the blackbody radiation from the
core produces gamma rayspowerful enough to break apart the iron atoms in the core. This further increases the
pressure to a point where electrons and protons are fused into neutrons. This releases lots of energy in the form of
neutrinos. The core cools and contracts; the inner shells rush to fill the void. As the core reaches nuclear density it
become rigid and even bounces back a little. When the onrushing material feels this bounce, it creates a wave. As
the wave spreads to outer, less-dense regions, it speeds up. Soon it is a shock wave and combines with the wave of
neutrinos. The star is doomed. This process blows the star apart releasing 1046 joules of energy. This shock wave is
the only place hot and dense enough to fuse elements heavier than iron, elements up to and including uranium

Answer 36

Supergiant

Question 37

________ have no such lines. They are caused by a binary star system with a red giant and a white dwarf
(remember that 70% of stars are binary). Matter that flows off the red giant collects on the white dwarf and increases
the pressure on its core. Eventually carbon fusing begins in the white dwarf, but this time the star is made of
“degenerate” matter and cannot expand to cool off. The result is a runaway reaction which ends in a supernova

Answer 37

Type I Supernovae

Question 38

Elements up through magnesium were created in

Answer 38

Red giants

Question 39

Elements up through iron were created in

Answer 39

Supergiants

Question 40

the elements from iron to uranium were created in

Answer 40

Supernovae

Question 41

These atoms can meet one another in nebulae, on dust particles, and even in planets. When they do, chemical
reactions take place. These reactions eventually led to

Answer 41

life and then . . . us.