The Life-Cycle of a Star Flashcards
Stars Life-cycle
Stars have a life cycle and they evolve over time.
Mass and Stars
The mass of a Star controls its
1. evolution
2. lifespan
3. how it dies
Pillars of Creation
A stellar nursery where Stars are born, this is located more than 7000 light years away.
Birth of Stars
Stars begin as a nebula that starts to contract due to gravity
Nebula
A cloud of gas and dust
Protostar
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.
Main Sequence Star
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.
HydroStatic Equilibrium
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.
Mass in Relation to Main Sequence
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.
When does a star begin to die?
A star begins to die when hydrogen runs low.
Average Sized Dying Stars
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.
Planetary Nebula
A red giant begins to shred its outer layers and begins to shrink.
White Dwarf
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
White Dwarfs More Info
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.
Black Dwarf
The remnant white dwarf burns away all of its light and fizzles out turning into a Black Dwarf.
Massive Dying Stars
Massive stars become larger than giants as they leave the main sequence (100 - 1000 times larger than the sun) and die explosively.
Supernova
The explosion of a supergiant where the fusion of iron uses energy instead of releasing it. Gravity is greater than pressure
Neutron Star
A result of a supernova. A small dense ball of neutrons that is extremely dense. 1 tsp = 100 million tons.
Pulsar
A result of a supernova. A neutron star that is spinning and sending out beams of radiation that sweep through space.
Black hole
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.
Importance of Black Holes
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.
Binary Star Systems
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.
The Importance of Massive Stars
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.
Magnitude of Stars
Magnitude describes the brightness or luminosity of the star.
Absolute Magnitude
Actual brightness the star gives off - the more negative the magnitude number, the brighter the star.
Apparent Magnitude
The brightness we saw on earth, because closer stars appear brighter to us.
Hertzsprung-Russel Diagram
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.
Star Evolution
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)
Stellar Evolution
Out of 100 stars, 89 are low mass, 10 are Intermediate Mass and 1 is high mass.
Missing the Main Sequence
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.
Brown Dwarf
A brown dwarf is very faint, emits infrared, and has a core made of hydrogen
Jupiter is NOT a Brown Dwarf
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.
Fusion
Combining of lighter atomic nuclei into a heavier nucleus. Our sun does Fusion
Fission
Splitting of larger, unstable nuclei into smaller more stable nuclei. Fission usually needs a free neutron to start this process.
