Astrophysics Flashcards
What is 1 light year equal to in meters? (Astrophysics)
9.46 x 10^15
What is the gravitational field strength on the surface of Earth? (Astrophysics)
9.8Nkg-1
What is the gravitational field strength on the surface of Mars? (Astrophysics)
3.7Nkg-1
What is the gravitational field strength on the surface of the Moon? (Astrophysics)
1.6Nkg-1
What is the gravitational field strength on the surface of the Sun? (Astrophysics)
270Nkg-1
What is meant by gravitational field strength? (Astrophysics)
The gravitational force per unit mass
What is meant by Gravitational potential of a point in Space? (Astrophysics)
The work done in moving unit mass from infinity to that point.
What is the result of a conservative field? (Astrophysics)
The energy required to move mass is dependent on the path taken.
What is a gravitational potential ‘well’ (Astrophysics)
A way of conceptualising the gravitational potential field in a body such as a planet.
What happens as a gravitational potential well gets deeper? (Astrophysics)
More energy will be required by an object trying to escape it.
What provides a centripetal force on a satellite when held in orbit around the Earth? (Astrophysics)
Earth’s gravitational force
What is escape velocity? (Astrophysics)
The minimum velocity required by a mass, m, to just escape from a planet’s gravitational field and reach infinity with zero velocity and zero kinetic energy.
Deriving Escape Velocity (Astrophysics)
Ek + Ep = 0
1/2 mv^2 + (-GMm / r ) = 0
1/2 mv^2 = GMm / r
v^2 = 2GM / r
Vesc = (sqrt.) 2GM / r
What is the Equivalence Principle? (Astrophysics)
Gravity pulling in one direction is equivalent to acceleration in the other.
That is, there is no way to distinguish between the effects on an observer of a uniform gravitational field and of a constant acceleration.
How does time run when there is a stronger gravitational field? (Astrophysics)
Slower
- Moving clocks run slow, high clocks run fast *
Curvature of Spacetime (Astrophysics)
A massive object like a star warps time and space through its gravity.
The larger the mass, the more spacetime curvature takes place.
Explain the rubber sheet analogy in relation to Curvature of Spacetime (Astrophysics)
- Matter tells space how to curve
- Curved space tells matter how to move
-The heavier the object the deeper the resulting gravitational well.
What is Evidence for the warping of Spacetime? (Astrophysics)
Gravitational time dilation
Gravitational Lensing
What is Gravitational time dilation? (Astrophysics)
Where time passes more quickly because the force of gravity is weaker.
What is Gravitational lensing? (Astrophysics)
The bending of light from a distant light source due to the presence of a large mass.
What happens when Mercury orbits around the Sun? (Astrophysics)
Shifts slightly in its elliptical path every orbit.
Why is Mercury’s orbit altered when orbiting the Sun? (Astrophysics)
The disturbance of spacetime by the Sun’s mass.
What is a world line? (Astrophysics)
A curve in spacetime joining the positions of a particle throughout its existence.
:. Defines the position of an object in 3 dimensions (x, y and z) and 4th dimension of time (t).
What does the z-axis of a spacetime diagram represent? (Astrophysics)
Time
How is an object travelling at a constant speed represented on a spacetime diagram? (Astrophysics)
A straight horizontal line
How is an object which is accelerating represented on a spacetime diagram? (Astrophysics)
A curved line outwards.
How is an object which is not moving represented on a spacetime diagram? (Astrophysics)
A straight vertical line.
What is a black hole? (Astrophysics)
A region in space where the pull of gravity is so great that nothing, not even light, can escape its pull.
Is the escape velocity from close to a black hole greater or less than the speed of light? (Astrophysics)
Greater than.
Where may supermassive black holes be found according to evidence? (Astrophysics)
The centre of large galaxies.
Is light able to escape from the gravitational pull after a star has collapsed past the event horizon. (Astrophysics)
No
What is the singularity of a black hole? (Astrophysics)
The centre point of a black hole where gravity becomes infinite
What is the Schwarzschild radius? (Astrophysics)
The distance from the singularity to the event horizon.
What are ways that you can detect black holes? (Astrophysics)
- Emission of x-rays
- Gravitational lensing
- Binary x-ray systems
What determines what colour a star will appear as? (Astrophysics)
The surface temperature.
- Cooler the star, redder it will appear
- Hotter the star, more blue it will appear
What gives the total energy being emitted at all wavelengths by a black body? (Astrophysics)
The Stefan-Boltzmann Law.
What is a black body? (Astrophysics)
A body that absorbs all EM radiation incident on it and also emits all wavelengths of EM radiation.
What type of stars are the least massive? (Astrophysics)
Red dwarfs
What type of stars are the most massive? (Astrophysics)
Blue giants
What does the mass of a star determine (Astrophysics)
Its lifetime, and therefore its overall fate.
What is the luminosity of a star (Astrophysics)
A measure of how bright it actually is, not how bright it appears to us on earth.
What is the apparent brightness of a star? (Astrophysics)
A measure of how bright a stars appears on Earth.
Formation of Stars (Astrophysics)
CGNHM
- Huge clouds of gas and dust
- Gravity causes clouds to shrink
- Nuclear fusion occurs (hydrogen => helium by p-p chain)
- Hydrostatic Equilibrium - When gravitational force is balanced by thermal pressure outwards
- Main sequence.
Low Mass Stars (Astrophysics)
Cloud of gas and dust => Main sequence => Red giant => White dwarf
High Mass Stars (Astrophysics)
Cloud of gas and dust => Main sequence => Red supergiant => Supernova => Black hole (very high mass) OR Neutron star (high mass)
What is a Charge Coupled device? (CCD) (Astrophysics)
A chip found behind the lens in a digital camera that stores images.
It is used to detect astronomical objects.
What is an Inertial frame of reference? (Astrophysics)
A frame of reference in which an observer is not accelerating with respect to another.
That is, an observer will move at a constant speed with respect to another.
What is a Non-Inertial frame of reference? (Astrophysics)
A frame of reference in which an observer is accelerating with respect to another.
That is, an observer will not move at a constant speed with respect to another.
What does the bottom cone on a world line diagram represent (Astrophysics)
Observable past events
