Week 8 Flashcards
Is the space between stars empty?
No it is just full of particles in lower density
interstellar medium
the matter and radiation that exists in the space between the star systems in a galaxy. made up of Hydrogen, Helium, ~2% “metals”
Nebula
a cloud of dust and gas in space
warm clouds
mostly atoms and ions
Cold clouds
atoms, molecules, dust,
“molecular clouds”
Can IR light shine through nebula?
yes it can shine through dust
How are stars formed?
- Interstellar gas cloud starts to contract (shrink) due to their own gravity
- Getting smaller, denser, and hotter
- Spins faster
- Densest parts of the cloud become opaque and trap heat
- H-fusion begins when core reaches ~5 million degrees
What determines whether the gas cloud will become a star?
Mass (related to gravity + pressure)
What starts the collapse of a gas cloud?
Supernova shockwave, Colliding clouds, Turbulence in galaxy, Spontaneous cooling
Why do stars heat up as they form?
Gravitational Energy -> Kinetic Energy
Kinetic Energy = Thermal Energy
Protostar
a contracting mass of gas which represents an early stage in the formation of a star, before nucleosynthesis has begun.
What determines how small a star can be?
Mass affects temperature, and temperature must be high enough for fusion to occur (Mass > 0.08 Msun required for fusion)
Brown dwarf
no fusion, but still heat from gravitational contraction.
All about the same radius (~0.1 Rsun), regardless of mass.
How big can stars get?
As protostars collapse, core is so hot radiation pressure
blows off their outer layers. Less mass, less pressure
needed to counteract gravity, lower temp. Largest stable(ish) mass is ~120-150 Msun?
Low mass star
< 2 times the Sun
High mass star
> 8 times the Sun
Main Sequence stage
- Where a star begins and is for 90% of its life
- Fusing is occuring
- Stellar thermostat keeps luminosity and temperature stable
Intermediate mass star
2-8 times the Sun
What initially happens when a star runs out of hydrogen
- No more fusion
- Temp not hot enough to fuse helium
- Core will collapse (gravity overcomes pressure)
- Increase in pressure = hotter in shell
- Now hot enough for hydrogen fusion in shell around core.
What answer most accurately describes the end life of a star 8-20 times more massive than our Sun?
Deep in the star’s core, elements fuse into ever heavier elements until no more energy is available to hold itself up against gravity; the star explodes as a Supernovae and the core is crushed into a Neutron Star.
The Sun is a low mass star, what is the most likely sequence of events in its future?
It will use up it’s fuel in another 5 billion years, expanding to become a Red Giant, eventually it’s core will be a White Dwarf.
What are the most common stars in the Universe?
Low mass stars (K, M types) are the most common.
What happens in the core of a star fusing helium into carbon after all the helium is used up in the reaction?
Energy generation through fusion stops because carbon fusion requires higher temperature. The core collapses and helium starts fusing in shell.
The core of a star 1.5 times more massive than our Sun is crushed into a dense object, which of the following most accurately describes this state?
The degeneracy pressure from electrons stops the core’s further collapse, leaving behind a White Dwarf.
