Expansion and Hubble's Constant

Question 1

Cepheid Variables

Answer 1

Cepheid variables are pulsating stars with a known period-luminosity relationship. Comparing the absolute and apparent magnitudes allows them to determine the distance to the galaxy

Question 2

Type Ia Supernovae

Answer 2

Type Ia supernovae are incredibly bright stellar explosions that occur in binary star systems. By measuring the apparent brightness of a Type Ia supernova in a distant galaxy and comparing it to the known intrinsic brightness, astronomers can calculate the distance.

Question 3

Tully-Fisher Relation

Answer 3

By measuring the rotational velocity of a spiral galaxy, typically using the Doppler shift of its spectral lines, and estimating its intrinsic brightness, astronomers can determine the distance to the galaxy.

Question 4

Surface Brightness Fluctuations:

Answer 4

The fluctuations are related to the distance to the galaxy, with more distant galaxies exhibiting larger fluctuations

Question 5

Redshift and Hubble’s Law:

Answer 5

the redshift of light from galaxies is caused by the expansion of the universe. By measuring the redshift of a galaxy’s spectral lines, astronomers can determine its recessional velocity.

Question 6

Velocities of galaxies (from redshifts)

Answer 6

Redshift is a phenomenon where the light emitted by an object, such as a galaxy, appears to shift towards longer wavelengths (redder) due to the expansion of the universe v = H0 * d,

Question 7

Hubble’s Law

Answer 7

recessional velocity of a galaxy is proportional to its distance from us. v = H0 * d,

Question 8

Hubble’s constant,

Answer 8

denoted by H0, represents the rate of the universe’s expansion.

Question 9

The large scale structure of the universe

Answer 9

It encompasses the patterns and arrangements of galaxies, galaxy clusters, superclusters, cosmic voids, and the overall filamentary structure that connects them.

Observations have revealed that the universe is not uniformly distributed but exhibits a hierarchical structure. At the largest scales, galaxies tend to form clusters, and clusters themselves are grouped into superclusters, which are the largest known structures in the universe. These superclusters are interconnected by vast cosmic filaments, forming a “cosmic web” or “foam-like” structure.

The overall structure of the universe is shaped by the gravitational interactions between matter and dark matter, which is an unseen form of matter that outweighs ordinary matter by a significant margin