19. Stars Flashcards
What is a star?
A star is a celestial object primarily composed of hydrogen and helium that emits light and heat through nuclear fusion in its core.
What is a Nebula?
Cloud of dust and ice due to gravitational clumping
How is a star formed?
- Nebula
- Gravitational attraction increases forming variations in density
- Regions get hotter and denser as more matter gets pulled in
- Eventually a protostar forms
What is the life cycle of a low mass star?
- Red giant - cools, outer layers drift out to space as a planetary nebula
- Leaves behind a white dwarf (hot dense core)
- White dwarf stops collapsing on itsef due to ‘Electron degeneracy pressure,
- EDP only prevents collapse of stars up to Chandrasekhar limit - 1.44 solar masses
What is the life cycle of a massive star
- Much hotter - shorter lifetime
- As core runs out, temperatures sufficient to fuse heavier elements
- Star will swell to a red supergiant
- Various range of temperatures and elements at different temperatures
- Makes the star unstable and implosion of layers leads to an explosion: a supernova
What is a neutron star
Extremely dense
If mass of core is greater than 1.44 solar masses but less than 3 solar masses, core will keep collapsing to form this neutron star
What is a black hole
- Occurs when mass is greater than 3 solar masses
- Collapse will continue until nothing can escape
- extremely dense
- escape velocity is greater than the speed of light so light cannot escape
What is the Chandrasekhar Limit
1.44 solar masses
what is 1 solar mass (mass of sun)
1.99 x 10^30 kg
what are the conditions to be a planet
- a body with a spherical shape due to its own gravity
- no nuclear fusion
- orbit cleared of its debris
what is important to remember about hertzsprung-russel diagrams
- temperature increases from right to left at a logarithmic rate
- Our Sun is about 6000K
what is a black body
an object that absorbs all EM radiation
what can we say about an object at any given temperature above absolute zero
it emits EM radiation of different wavelengths and intensities (black body radiation)
Describe and explain, in detail, the following stages after a low mass star has evolved into a red giant
- reduction in energy released by fusion
- gravitational force is greater than that from
radiation and gas pressure - core collapses
- fusion no longer takes place in the core
- fusion continues in the shell around the core
- outer layers of star expand and cool
- outer layers are released
- reference to planetary nebula
- reference to white dwarf (left as remnant hot
core)
