The Life-Cycle of a Star

Question 1

Stars Life-cycle

Answer 1

Stars have a life cycle and they evolve over time.

Question 2

Mass and Stars

Answer 2

The mass of a Star controls its
1. evolution
2. lifespan
3. how it dies

Question 3

Pillars of Creation

Answer 3

A stellar nursery where Stars are born, this is located more than 7000 light years away.

Question 4

Birth of Stars

Answer 4

Stars begin as a nebula that starts to contract due to gravity

Question 5

Nebula

Answer 5

A cloud of gas and dust

Question 6

Protostar

Answer 6

A ball of gas and dust that is pulled in by gravity, and gradually the center gets hotter. A protostar can be detected through infrared telescopes.

Question 7

Main Sequence Star

Answer 7

Main Sequence is the longest stage in the life. Nuclear fusion occurs in the core of the star, where hydrogen fuses into helium which gives star energy and releases light. The Sun is in the main sequence.

Question 8

HydroStatic Equilibrium

Answer 8

When the force due to pressure exactly balances the force due to gravity. There is outward thermal pressure from the interior because of nuclear fusion that equals the inwards gravitational force.

Question 9

Mass in Relation to Main Sequence

Answer 9

The smaller a star the longer the life. Stars that are more massive than our sun may remain in mains sequence for only 10 million years, while Stars less massive may remain for 100s of billions of years.

Question 10

When does a star begin to die?

Answer 10

A star begins to die when hydrogen runs low.

Question 11

Average Sized Dying Stars

Answer 11

When a star first dies a star’s center contracts and the outer layer expands and cools and starts to glow red and the star turns into a red giant, which can be more than 10x larger than the sun.

Question 12

Planetary Nebula

Answer 12

A red giant begins to shred its outer layers and begins to shrink.

Question 13

White Dwarf

Answer 13

The planetary Nebula has cast off its matter, and the star collapses into a dense hoot, and dim star that is smaller than the earth

Question 14

White Dwarfs More Info

Answer 14

Stars like the sun become a white dwarf after they have exhausted their nuclear fuel. All stars that are less massive than 8 times the mass of the sun (about 99% of all stars) will eventually become white dwarfs. SOME white dwarfs give off a last bang called a nova.

Question 15

Black Dwarf

Answer 15

The remnant white dwarf burns away all of its light and fizzles out turning into a Black Dwarf.

Question 16

Massive Dying Stars

Answer 16

Massive stars become larger than giants as they leave the main sequence (100 - 1000 times larger than the sun) and die explosively.

Question 17

Supernova

Answer 17

The explosion of a supergiant where the fusion of iron uses energy instead of releasing it. Gravity is greater than pressure

Question 18

Neutron Star

Answer 18

A result of a supernova. A small dense ball of neutrons that is extremely dense. 1 tsp = 100 million tons.

Question 19

Pulsar

Answer 19

A result of a supernova. A neutron star that is spinning and sending out beams of radiation that sweep through space.

Question 20

Black hole

Answer 20

A result of a supernova. The remnants of a supernova that are contracted even more than a neutron star, a black hole is so dense that light cannot escape.

Question 21

Importance of Black Holes

Answer 21

Every spiral galaxy (like our Milky Way) is thought to have a supermassive black hole at its center that acts like the Milky Way’s sun. The galaxy orbits the black holes like the planets in the solar system orbit their stars.

Question 22

Binary Star Systems

Answer 22

Binary stars are 2 stars orbiting a common center mass. The brighter star is the primary star, and the dimmer star is the secondary star. 88% of Stars are found in binary systems.

Question 23

The Importance of Massive Stars

Answer 23

During the fusion of hotter, massive stars, elements such as iron, oxygen, magnesium and silicon are created. These elements are released when the star goes supernova. These elements are necessary for life.

Question 24

Magnitude of Stars

Answer 24

Magnitude describes the brightness or luminosity of the star.

Question 25

Absolute Magnitude

Answer 25

Actual brightness the star gives off - the more negative the magnitude number, the brighter the star.

Question 26

Apparent Magnitude

Answer 26

The brightness we saw on earth, because closer stars appear brighter to us.

Question 27

Hertzsprung-Russel Diagram

Answer 27

Stars are ranked on the H-R Diagram based on their temperature and absolute magnitude. The color of a star is based on surface temperature, NOT mass. Most stars fall in the middle of the diagram (the main sequence) and very few are white dwarfs, giants/supergiants.

Question 28

Star Evolution

Answer 28

Stars are born, grow up, mature and die. A star’s mass determines what life path it will take. They are grouped based off

• Not Large Enough (< 0.008
  Ms - Mass of the Sun)
• Low Mass (0.008 - 2 Ms)
• Intermediate Mass (2 - 8
  Ms)
• High mass (>8Ms)

Question 29

Stellar Evolution

Answer 29

Out of 100 stars, 89 are low mass, 10 are Intermediate Mass and 1 is high mass.

Question 30

Missing the Main Sequence

Answer 30

If the mass of the protostar is under 0.008 then it does contain enough gravitational energy to reach a core temperature of 10^7 K. No Fusion occurs and the star is stillborn, which is called a Brown Dwarf.

Question 31

Brown Dwarf

Answer 31

A brown dwarf is very faint, emits infrared, and has a core made of hydrogen

Question 32

Jupiter is NOT a Brown Dwarf

Answer 32

Jupiter would need to weigh 13 times its mass to be a brown dwarf. Brown dwarfs can use deuterium ( a hydrogen isotope ) while Jupiter cannot.

Question 33

Fusion

Answer 33

Combining of lighter atomic nuclei into a heavier nucleus. Our sun does Fusion

Question 34

Fission

Answer 34

Splitting of larger, unstable nuclei into smaller more stable nuclei. Fission usually needs a free neutron to start this process.