Astrophysics Part 2 – Flashcards
Unlock all answers in this set
Unlock answersquestion
Kepler's Third Law
answer
Square of the period of any planet is proportional to the cube of the semi major axis of its orbit
question
Stellar Parallax
answer
Created by orbital position. Max shift is when the earth is at opposite sides of the sun. Once angle found, distance is calculated via trigonometry.
question
Photosphere
answer
Coolest part of the sun. Visible surface that emits all visible light.
question
Low mass star
answer
< 8 solar masses
question
High mass star
answer
> 8 solar masses
question
Low Mass Main sequence
answer
Fusion of H begun, low mass spends 99% of lifetime here
question
Red giant
answer
Inert He core shrinks down and then the star puffs up.
question
Helium Flash
answer
He begins to fuse in red giant due to a temperature rise.
question
Asymptotic red giant
answer
Occurs after helium flash. Carbon core.
question
Planetary Nebula
answer
Material of star thrown off by winds, leaving a carbon core.
question
White dwarf
answer
Dense and degenerate. No more fusion.
question
1.4 Solar Masses
answer
White dwarf mass limit
question
Degeneracy pressure
answer
When protons, neutrons and electrons are packed in as tightly as possible, exerting a quantum force
question
Nebula
answer
Pre-star formation. Interstella medium collapses down.
question
High Mass main sequence
answer
Massive and blue
question
Post main sequence high mass star
answer
After H core of a high mass star exhausted, core shrinks and heats
question
Red supergiant
answer
Hydrogen shell burning causing high mass star to expand
question
Beginning of He fusion in high mass star
answer
T ~ 10^8K
question
Blue supergiant
answer
Core has expanded after He fusion begins, slowing the fusion rate in a high mass star
question
Second Red giant phase
answer
After He core exhausted, core shrinks are C fusion begins in core.
question
Iron core
answer
Point at which star is doomed. Reactions from here onwards are endothermic
question
Core collapse supernova
answer
Neutrons are packed so tight that they implode releasing heaps of energy.
question
Fusion of heavy elements
answer
Type 2 supernovae powers...
question
Type 2 supernova
answer
Core collapse supernova
question
Neutron core
answer
Left by type 2 supernova
question
Neutron star
answer
M < 3 Solar masses. Detected via pulse radiation or binary system.
question
Black hole
answer
M > 3 Solar Masses
question
Pulse radiation
answer
Use to detect neutron stars using their fast rotation due to conservation of angular momentum.
question
Pulsar
answer
Neutron star spinning and releasing radio beams at a constant period
question
Neutron star accretion disk.
answer
Sends of x-rays after getting hot due to friction of matter from a binary star being pulled into a neutron star.
question
Neutron degeneracy pressure limit
answer
3 solar masses
question
Singularity
answer
Single point of mass as neutron star collapses into a black hole
question
Schwarzchild Radius
answer
where escape velocity is speed of light
question
Bright x-rays
answer
What we look for when detecting black holes.
question
Detatched
answer
Binary not transferring mass
question
Semi-attached
answer
Binary with one roche lobe filled
question
Contact binary
answer
Both roche lobes filled
question
Cataclysmic variable
answer
White dwarf accreting off donor star via roche lobe overflow
question
Dwarf nova
answer
Sudden large increase in brightness, then returns white dwarf to original state.
question
Direct imaging
answer
Used in exceptional circumstances. Needs a large planet with wide separation from parent star.
question
Astrometry
answer
Only useful for nearby stars as position shifts are very small and accuracy is important. Measures position of star and looks for wobbles
question
Wobbles small
answer
Downside of astrometry
question
Radial velocity
answer
Most sensitive to high mass planets close to the star
question
Inclination needed
answer
Downside of radial velocity
question
Transit
answer
Sensitive to smaller mass planets close to star. Dimming of light tells us about the planet.
question
area of star blocked / area of star
answer
Fractional change in flux during transit given by:
question
Gravitational lensing
answer
Sensitive to all masses, only large distances. Rare events.
question
Hot jupiter
answer
Mostly H and He, close to parent star, larger, short orbital period and low density.
question
Rocky planets
answer
More numerous than gas giants.
question
Temperature of planet
answer
Flux at surface x cross-sectional area
question
Earth's biosignatures
answer
Methane, liquid water and ozone
question
Spectrum of planet's light
answer
Where to search for signs of life
question
Terrestrial
answer
Small planet, with low mass, rocky and close to star
question
Jovian
answer
Large, high mass, icy/gaseous and far out
question
Asteroids
answer
Rocky bodies found in asteroid belt
question
Comets
answer
Ice and rock, found in Kuiper belt
question
100,000 ly
answer
Length of galaxy
question
Galactic bulge
answer
Centre of the galaxy
question
Halo
answer
Large region of low density around galaxy
question
Disk
answer
Thin with spiral arms embedded within
question
Detection of atomic H
answer
Atoms have different spins. When they have slightly more energy, they drop an energy state and release a photon
question
Molecular hydrogen
answer
Doesn't have strong radiative transitions, hard to detect so we use other molecules to trace it.
question
H2 regions
answer
Produced by young stars, looks like red glow. Young stars produce UV light that excites atoms.
question
Interstellar dust
answer
Heated to high temperatures via starlight which is absorbed a reemitted in the IR
question
Blue light
answer
Dust scatters this more easily
question
Scatters are absorbs
answer
What does dust do to light?
question
Interstellar extinction
answer
Light gets reddened and dimmed as light passes through a cloud.
question
Reddening
answer
The difference in colour we observed to that expected for object, called colour excess
question
observed - intrinsic
answer
colour excess given by...
question
Synchrotron Radiation
answer
Non-thermal. High energy electrons are accelerated and spiral in magnetic fields causing this.
question
Jets from blackholes and supernova remnants
answer
Most common source of synchrotron radiation due to very strong magnetic fields
question
Thermal radia emission
answer
Also known as Free-free emission. From free electrons with free protons in a hot ionised gas, where the proton gets accelerated by electron and releases radiation.
question
Signals can't travel faster than the speed of light
answer
What tells us that the size of Sgr A can't be more than a light hour in size.
question
Keplerin rotation curve
answer
Mass concentrated in centre, with the rotation curve declining as distance increases
question
Observed rotation curve of the milky way
answer
Speed stays roughly flat as distance increases after a big jump from zero.
question
Dark matter
answer
Why the observed rotation curve for the solar system is mostly flat due to not uniform density.
question
Baryonic dark matter
answer
Massive compact halo objects are a type of dark matter. Dead stars and brown dwarfs which are hard to see.
question
Non-baryonic dark matter
answer
WIMPS - have mass and do not react in a way giving off radiation.
question
Star ags star cycle
answer
Recycles gas from old stars into new stars. Each generation has heavier elements that previous stars. ISM steadily enriched
question
Hot bubbles
answer
Ionsied gas. Caused by supernovae. Atomic hydrogen forms as gas cools and then molecular clouds.
question
star formation
answer
after the molecular cloud stage in the star-gas-star cycle
question
nuclear fusion/heavy element formation
answer
After star formation in star-gas-star cycle
question
Returning gas
answer
Supernova and stellar winds do this after the nuclear fusion stage of the star-gas-star cycle
question
spiral arms
answer
Where do new stars form in our galaxy?
