Last Unit Flashcards
All the other stuff
What nuclear reactions happen to a star while it is on the main sequence?
Hydrogen fusion to helium
What triggers a star to leave the main sequence?
No more hydrogen in the core
What happens to the internal events of a star when it leaves the main sequence?
The core collapses, increasing it’s temperature.
The envelope swells, decreasing it’s temperature.
A shell is created where hydrogen is fused.
What happens during the helium flash?
The core is now hot enough to fuse helium.
The core becomes larger, shortening the envelope.
In a star like our sun what happens when it runs out of helium?
There is not enough mass to fuse carbon, so it will explode into a planetary nebula, ejecting a fraction of the envelope. A white dwarf will remain.
What are the properties of a white dwarf?
Very small, very hot star where no more nuclear reactions occur. Little luminosity.
What fate awaits stars with less than 5 solar masses?
A white dwarf
If a white dwarf gains enough mass and exceeds the Chandrasekhar limit (1.4 solar masses), what will happen to the star?
It will collapse into a neutron star giving rise to a supernova of type Ia.
What is the fate of a star with a mass greater than 5 but less than 15 solar masses?
It will become a neutron star.
What are the characteristics of a neutron star?
It is very small (~10km) but has a mass between 1.4 and 3 solar masses so it is very dense. It rotates really fast because of the conservation of angular momentum during it’s collapse. It also has a huge magnetic field.
How can a neutron star be observed?
As the companion of a star
As a pulsar (similar to a lighthouse)
What fate awaits a star should it have a mass greater than 15 times that of our sun?
Collapse into a black hole
If the mass of a star is less than 0.08 solar masses, what happens?
Nuclear reactions never start and is therefore called a brown dwarf.
What are the building blocks of the universe and how are they organized?
Galaxies, organized in Groups, Clusters and Superclusters.
What are the three main types of galaxies?
Spiral galaxies (~60%) Elliptical galaxies (~35%) Irregular galaxies (~5%)
How do we know we aren’t in the center of the galaxy?
The galactic halo is not centered around the Sun
The disk or the halo of a galaxy mostly consists of pop II stars
Halo
How many major arms does our galaxy have?
2
What is the rotation curve of a galaxy?
He rotation differential (not as a rigid body) the variation of vrot with distance.
On what order of years does it take the sun to revolve once around the galaxy?
200 million years
What is 90% of the mass of our galaxy?
Dark matter
What are some possible candidates for dark matter?
MACHOS (faint stars, failed stars, planets, etc.)
WIMPS (neutrinos? exotic particles?)
What is the cosmological principle?
The idea that we are not a special case in the universe.
What supports the cosmological principle?
- The homogeneity of matter distribution (same density everywhere)
- The isotropy of the Hubble flow (same in every direction)
- The isotropy of the cosmic microwave background
