What parameters does Hubble’s law relate to each other?
Cepheid star period and luminosity
galaxy classification and mass
galaxy mass and distance
galaxy rotation speed and luminosity
galaxy recession velocity and distance
The Correct Answer and Explanation is:
Correct Answer: galaxy recession velocity and distance
Explanation:
Hubble’s Law is a fundamental concept in cosmology that describes the relationship between a galaxy’s recession velocity (how fast it is moving away from us) and its distance from Earth. The law is mathematically expressed as:
$$
v = H_0 \times d
$$
Where:
- $v$ is the recession velocity of the galaxy (measured in kilometers per second, km/s)
- $d$ is the distance to the galaxy (usually in megaparsecs, Mpc)
- $H_0$ is the Hubble constant, which defines the rate of expansion of the universe
This relationship was first observed by Edwin Hubble in 1929 when he discovered that galaxies farther away from Earth are moving away faster than nearby galaxies. He observed this by analyzing the redshifts of galaxies—where light from galaxies is shifted toward the red end of the spectrum, indicating they are moving away.
The significance of Hubble’s Law is profound. It provides strong evidence for the expansion of the universe, which supports the Big Bang theory—the idea that the universe started from an extremely hot, dense state and has been expanding ever since. Before Hubble’s discovery, it was generally thought that the universe was static and unchanging.
Hubble’s Law is still used today to estimate the distances to faraway galaxies. Once the redshift (and therefore recession velocity) is known, the distance can be inferred using the Hubble constant. However, the exact value of $H_0$ is still under active research, with slight variations depending on the method used to calculate it.
None of the other choices (like Cepheid period-luminosity or galaxy mass-distance) describe the specific parameters related by Hubble’s Law, though some are used in related astronomical measurements.