Week 9 Flashcards
What stars produce black holes?
The death of very massive stars (>20 Msun)
What causes black holes?
when gravity is stronger than any pressure
Space time continuum is torn!
(singularity is created)
Why are black holes black?
Because gravity is so strong even light cannot escape!
Escape velocity
The velocity needed to escape the gravity of the orbitee entirely
v(escape) =squareroot(2GM/r)
Escape velocity and black holes
Decrease radius at constant central mass increases escape velocity, decrease it enough and the escape velocity becomes greater than the speed of light and not even light can escape the hole
event horizon
edge of black hole
can our sun become a black hole?
No, Only much more massive stars
have enough gravity to collapse to BH after core fusion
ends.
BH gravity field
If a star (or any object) became a black hole, its
gravity would be different only near the event horizon
Supermassive black holes event horizon
gentler near the event horizon because Schwarschild radius is much bigger
Black hole tidal force
Tidal force near event horizon for a stellar Black Hole is very strong, will shred/stretch stars due to more gravity being felt on 1 side of the object then the other
small vs large black whole tidal force effect
- Small black holes shred their food
- Large black holes swallow whole
Time dilation near event horizon
Time passes more slowly because of strong gravitational field
How do you observe black holes if you can’t see them?
- watch things move near them (dynamical mass)
- watch matter fall into them (and emit light)
- Look for remaining star orbiting something invisible
Gravitational lensing by Black Holes
BHs distort space-time
strongly near event horizon:
Extreme light bending!
gravitational waves
- ‘Ripples’ in the fabric of space-time caused by violent and energetic processes (e.g. black hole collisions)
- Travel at the speed of light, carrying energy and angular momentum
What do gravitational waves do?
Gravity wave stretch/compress space as they
travel through it
easons we have to infer that a supermassive blackhole lurks in the centre of our galaxy?
Tight orbit of stars around an invisible companion & giant bubbles filled with gamma rays expelled from the galactic centre.
Description of the milky way
A disk 100,000 lightyears across filled with gas and stars, with a bulge of older stars in the galaxy centre.
Spiral galaxy
disk shaped, often have spiral arms
Elliptical galaxy
balls (sometimes flattened) of mostly old stars
Irregular galaxy
weird clumpy galaxies with no obvious symmetry, often small
An important part of the lifecycle of galaxies like the MW is the self-regulation of formation of future generations of stars. Which statement best describes this process?
Massive stars explode as Supernovae, heating nearby gas which then can’t form stars, and even forcing the gas out of the galaxy in a superbubble.
Sort based on mass contribution the following three components of the Milky Way, by most significant to least significant.
Dark Matter > Stars > Planets
When we observe the most distant galaxies what are we looking at?
because of the finite speed of light, we are observing how galaxies looked like in the past
