Y12 Stars and Planetary Systems Flashcards
Define a planetary system.
a set of objects that orbit around a star. They form around the same time stars are.
Where does a planet first form?
In the protoplanetary disk. This forms when a clump in the stellar nebula collapses causing a protostar to form with a disk. The disk continues to flatten, heat up, and spin rapidly forming it.
What “forms” in the disk?
Particles of dust clump together (accreted), which forms planetismals.
What happens to the planetismals?
The planetismals continue to accrete. When the planetismals get big enough, they attract each other through gravity. Sticking together. Process continues until planets form. Rocky first then gravity.
Where do rocky planets and gaseous planets form?
Rocky planets form inside the frost line whereas gaseous planets form outside the frost line.
What happens when the star becomes a main sequence star in the solar system?
The solar winds from the MS star stream out, pushing out any remaining dust out of the solar system. Preventing anymore planetismals to form.
Define a frost line.
A temperature line that separates the formation of rocky planets and gaseous planets.
Define accretion.
The accumulation of matter under the influence of gravity to form planets.
Describe the process of rocky planets forming.
- Planetismals form from the accretion of dust.
- Rocky and metallic planetismals form inside frost line.
- planetismals accrete and form rocky planets.
- Dense material formed at core, less dense material forms crust.
- H and He go beyond frost line.
- Atmospheres form around planet with enough gravity to hold onto them.
Describe the process of the outer gas planets’ formation.
- Planetismals form from accretion of dust.
- Rocky, metallic, and icy planetismals form outside frost line.
- Planetismals accrete, forming gaseous planets.
- H and He attach by gravity.
- Rocky material sunk to centre of planet, forming the core.
- Ice and gas (H+He) are held by gravity around the planet.
How did the asteroid belt form?
Jupiter’s gravity effected the orbits of some planetismals that were accreting during the time. As a result, they broke and formed asteroids. (Failed planets)
Asteroids have a highly irregular shape that weren’t big enough to be round.
How was our moon formed?
- A planetismal size of Mars struck Earth after the solar system formed.
- Large volume of heated material was ejected from object’s outer layers.
- Disk material formed, accreted and became the moon. (Explains why moon’s rock is similar to that on Earth.
Name 3 ways moons can be formed
- By collision
- From a circum-planetary disk.
- Captured asteroids or KBOs (orbit wrong way round)
Describe a Sun-sized star in its main sequence stage.
The longest and most stable part of the star’s life. Nuclear fusion occurs, H fused to He, which releases vast amounts of energy as heat and light.
What is a red giant?
After all the hydrogen is used up, a red giant forms. Helium now fused to Carbon and O in the hotter core. Core carries on contracting and heating up. Outer layers expand and cool. The star is red because it is cooler, but it has a high luminosity due to its size.
What happens at the core of the star?
In the hot and dense core, nuclear fusion occurs. Releasing vast amounts of light and heat.
What is the outer shell of a star?
Photosphere: it is made up of H and He hot gas. This shell helps move heat from the core to the surface of the star. Heat and light released into space.
What is hydrostatic equilibrium?
It is what keeps a star stable. The balance of gravity pulling a star’s atoms to the centre and outward pressure of heat and light radiating.
Describe giants and supergiants
Giants and Super-giants:
* When stars run out of H they become giants and supergiants.
* Core becomes hotter and denser - more than 1.4 Msun
What is a white dwarf star?
A small, very dense, hot star mostly made of carbon. It’s what remains after a red giant loses its outer layers.
What are red dwarf stars?
Red dwarves are the smallest kind of star on the main sequence and have the lowest temperature of the catefory.
Fuses H to He only
Brown dwarfs?
Brown dwarfes are considered failed stars that never acheived nuclear fusion in their core.
How are stars organised by their color and temperature?
They are organised through spectral classes. Organised by spectral type hottest to coolest: OBAFGKM. (Oh Boy An F Grade Kills Me)
Small, cool K and M class stars are the most common. Whereas large and very hot stars are rare.
What is apparent magnitude?
How bright a star appears to us from Earth.
What is absoulute magnitude?
The actual brightness of a star according to luminosity. This is measured unusually eg +25 is very dim and -10 is very bright.
What is luminosity?
Luminosity, L, is the amount of electromagnetic energy a star radiates per second.
Luminosity is often measured compated to the Sun, Sun = 1L_sun
What is a neutron star?
- Neutron stars are the remnant of a supernova
- the core becomes a very small and super dense star.
- composed of tightly packed neutrons
- They generally spin very fast and are then called pulsars.
What is a supernova?
A supernova is a very short-lived exploding star.
What is a black hole?
Black holes are formed from the collapse of a supernova from a massive star, unimaginably dense, no light can escape.
What is an HR diagram?
Hertzsprung-Russel Diagram
It plots luminosity (y-axis) against temperature (x-axis). Temperature corresponds to color OBAFGKM.
Key features of an HR diagram.
- MS stars fall along a diagonal band, from blue supergiants (class O) to red dwarfs (class M).
- Giants and Supergiants are in the upper right of diagram. Higher L, temp, and surface area.
- White dwarfs are in the lower left. Remnants of stars.
What is a stellar nebula?
A vast cloud of interstellar gas, dust, H, He, and plasma swirl, the birthplace of stars.
What is an Oort cloud?
An oort cloud is a theorized to be a giant spherical vast cloud of icy planetismals and source comets surrounding the Sun/planets/KBOs at distances ranging from 2000 to 200,000AU.
How does a star form in a stellar nebula?
What is a Kuiper Belt and how did it form?
The Kuiper Belt is a dough-nut-shaped region beyond Neptune, filled with icy planetismals and dwarf planets like Pluto, and is believed to be a remnant of the solar system’s formation.
What new elements are fused in the red supergiant?
After H is used up, new elements now become fused until iron Fe is reached. These elements are: Carbon, Neon, Magnesium, Oxygen, then finally Silicon, then an Fe core is produced.
What happens when a supergiant core collapses?
Iron atoms don’t fuse to make heavier elements, so outer layers gravitationally collapse towards centre of star in 15s.
* Nuclei pushed close together, e- are pushed into nuclei so heavier elements form
* Core reaches 100 billion degrees.
* Electrical forces between nuclei repel each other which overwhelms gravitational forces, thus a supernova.
* Scatters heavy elements in the universe.
* Shock wave blows away star’s outer layers.
What happens after the supernova occurs?
This depends on star’s remaning mass.
* 10 times mass of Sun: collapse into small dense neutron star. (1.4 times the mass of the Sun, only 14km in diameter, strong mag-field and spin).
* >10 times the Sun, star contracts temendously and becomes a black hole.
What happens after a red giant?
- Outer layers of star continue to expand, forms a planetary nebula.
- Core contracts more, He atoms fuse into core and forms carbon –> releases energy.
- When He and C in the core become stable, core is no longer hot enough to compress carbon atoms.
What happens after a planetary nebula occurs.
- Core stops fusing He, only C remains which is incredibly hot.
- It becomes a white dwarf and very slowly radiates away heat over a mil years.
- Becomes a black dwarf - cold lump of carbon.
Summarise all 4 types of MS stars and their life cycle.
- Massive Star ~ 30Msun: supergiant –> supernova –> Black hole (1m lifespan)
- Huge star ~ 10Msun: supergiant –> supernova –> Neutron star/pulsar (few mil lifespan)
- Sun-sized star ~ 1-5Msun: Red giant –> planetary nebula –> White dwarf –> black dwarf (10b years)
- Red dwarf ~0.1Msun: Stays in MS but becomes white dwarf –> black dwarf (50b lifespan)
What and where are comets?
They are objects from the Oort cloud and Kuiper Belt.
* They are made of ice and rock, travelling around the sun.
* As comet nears the sun, solar radiation heats the nucleus and ice sublimes to a tail of gas/dust forms.
