L 2 Stars and Planetary Systems Flashcards
Describe a Sun-sized star in its main sequence stage.
The longest 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.
Structure of a star
A star has two main sections:
- A very hot and dense core where nuclear fusion occurs. Core continues contracting for most of the star’s life, temperature and density continue to increase.
- An outer gaseous shell made of H and He gas. Outer shell helps move heat from core to surface of star, heat and light released into space.
How does a main sequence star remain stable?
It remains stable because of the balance of gravity pulling a stars atoms to the centre and the pressure of heat and light radiating out (outward pressure).
Describe main sequence stars.
Main Sequence:
- Nuclear fusion converts H to He which releases vast amounts of energy
- This is a stable part of a star’s life cylce. When H runs out the become a giant/supergiant.
Describe giants and supergiants
Giants and Super-giants:
- When stars run out of H they become giants and supergiants.
- The core of star contracts and heats up, outer layers expand forming red giants/supergiants.
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 black dwarves?
Black dwarves are white dwarf stars that have lost their heat.
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.
Brown dwarves?
Brown dwarves 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.
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. 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.
