Question

Irregular and elliptical galaxies contain large amounts of _______ and gas that make it difficult to distinguish individual stars. One mathematical tool that's used to quantify the rate of universal expansion is _______. The Milky Way, the Andromeda Galaxy, and 52 smaller galaxies are part of a cluster called the _______. Respond to the following based on your reading. How can you infer the existence of dark matter in a massive galaxy or in a cluster? Briefly describe why different types of universes would produce different shifts in the light observed from distant galaxies

Answer 1

1. dust

2. Hubble's constant

3. Local Group

4. Dark matter is massive enough to produce a gravitational redshift and gravitational microlensing in light from nearby stars or galaxies. The mass of visible matter also can be compared to the total mass of a galaxy or cluster. This invisible portion of the total mass is called dark matter.

5. In an expanding universe, objects are moving away from Earth, so the light they emit would have a redshift as observed from Earth. In a decelerating universe, light would have no redshift. Light would have a blueshift in a collapsing universe because all objects in that type universe would be moving toward each other.