5.5 Astrophysics and Cosmology Flashcards

Question

What is an absorption line spectrum?

Answer 1

Dark lines indicate frequencies that have been absorbed due to photons having energy exactly equal to the difference between energy levels in the atom

Answer 2

Opaque and non-reflective objects

Answer 3

Peak wavelength (maximum intensity) is inversely proportional to the absolute temperature of a black body

Answer 4

Total power radiated per unit surface area of a black body (luminosity) is directly proportional to the fourth power of the absolute temperature of the black body

Answer 5

The average distance from the Earth to the Sun

Answer 6

The distance travelled by light in a vacuum in one year

Answer 7

The distance at which a radius of one AU subtends an angle of one arcsecond

Answer 8

Technique used to find distances to stars close to Earth (<100 pc) Parallax - the apparent shift in the position of a star against the backdrop of distant stars as the Earth orbits the Sun Distance = 1 / parallax angle (arcseconds)

Answer 9

As the distance increases, the parallax angle decreases until it is too small to be measured accurately

Answer 10

The Universe is homogeneous - for a large enough volume, the density of the Universe is uniform, meaning that the same structures are seen everywhere The Universe is isotropic - looks the same in all directions (no centre or edge) The laws of physics are universal

Answer 11

When a wave source moves relative to an observer, the frequency and wavelength of the wave received changes

Answer 12

If a galaxy is moving towards Earth, the absorption lines move towards the blue end of the spectrum because the wavelengths appear shorter

Answer 13

If a galaxy is moving away from Earth, the absorption lines move towards the red end of the spectrum because the wavelengths appear longer

Answer 14

Compare the absorption spectrum of a specific element in a laboratory with the light from a distant galaxy Use the difference in observed wavelength and the Doppler equation to calculate the velocity of the galaxy

Answer 15

The recessional speed of a galaxy is directly proportional to its distance from Earth

Answer 16

Light from nearly all galaxies is red-shifted, showing that space is expanding in all directions

Answer 17

All matter was once contained in a single point (singularity) After a period of rapid expansion, the Universe became cooler and less dense, continuing to expand in all directions

Answer 18

A uniform microwave signal throughout the Universe When the Universe was young, the wavelength of high energy gamma photons became stretched out as space expanded and cooled Now, the temperature of the Universe is around 2.7K and the wavelengths of the photons lies in the microwave region of the spectrum

Answer 19

Assumes space has expanded uniformly over time If a galaxy is a distance d away and moving at a constant speed v then the time that has elapsed is equal to d/v which is equal to 1 / Hubble's constant The age of the Universe = 1 / Hubble's constant

Answer 20

Singularity - infinitely dense and hot Inflation - rapid, accelerating expansion Matter created in the first second of expansion as temperature decreases All forces are unified and then separate (gravity, strong, electromagnetic, weak) 3.8x10^5 years - atoms form, photons are free to travel, making microwave background radiation detectable

Answer 21

The theoretical energy driving the acceleration of the expansion of space as work has to be done in order to produce acceleration Makes up 68% of the Universe

Answer 22

There is not enough mass to keep solar systems in orbit in galaxies, suggesting that matter that is not visible to us must exist Makes up 27% of matter

5.5 Astrophysics and Cosmology Flashcards

(46 cards)