Question

What are the known galaxies outside of our own? What does each look like? What types are there and how many exist? How far away can we see them?

Answer 1

There are billions of galaxies in the universe, and astronomers have cataloged and studied a significant number of them. Here are some of the well-known types of galaxies and a brief description of their appearances:

1. Spiral Galaxies: These galaxies have a distinct spiral structure with arms that wrap around a central bulge. The arms often contain young stars, gas, and dust. The Andromeda Galaxy (M31) and our own Milky Way Galaxy are examples of spiral galaxies.

2. Elliptical Galaxies: Elliptical galaxies have a more rounded or elliptical shape. They lack the prominent disk and spiral arms seen in spiral galaxies and are typically composed of older stars. These galaxies vary in size, from small dwarf ellipticals to giant ellipticals. M87 is a notable example of a giant elliptical galaxy.

3. Irregular Galaxies: Irregular galaxies have irregular shapes and lack the characteristic structures of spiral or elliptical galaxies. They can be small or large and may contain abundant gas and dust. The Large and Small Magellanic Clouds are examples of irregular galaxies.

4. Lenticular Galaxies: Lenticular galaxies, also known as S0 galaxies, have a disk-like structure similar to spiral galaxies but lack prominent spiral arms. They are often considered transitional forms between spiral and elliptical galaxies.

5. Dwarf Galaxies: Dwarf galaxies are generally smaller and less massive than the larger spiral and elliptical galaxies. They can be irregular or have a more defined shape, such as dwarf spheroidal or dwarf elliptical galaxies. Many dwarf galaxies are satellites of larger galaxies.

It is challenging to determine the exact number of galaxies in the universe, but estimates based on observations from the Hubble Space Telescope and other instruments suggest that there could be more than 100 billion galaxies.

Regarding the visibility of galaxies, the observable universe is limited by the distance that light has had time to travel since the Big Bang, which is approximately 13.8 billion years. The farthest objects we can see, known as the cosmic microwave background radiation, exist at a distance of about 46.5 billion light-years. However, it's important to note that the expansion of the universe means that some galaxies that were once observable may now be beyond our current visibility due to their increasing distance from us.