Galaxies
Articles in this section
How Big Is the Universe?
The observable universe is estimated at about 92 to 93 billion light-years across, but the whole universe is probably larger, and it is unknown whether it is finite or infinite.
What Is Dark Matter?
Dark matter is an invisible form of matter that interacts through gravity and makes up most of the matter in the universe. Its nature is still unknown despite nearly a century of study.
Galactic Crash Now a Coin Flip: Andromeda Collision Forecast Revised
For years the Milky Way was said to be heading for a head-on crash with Andromeda in a few billion years. A 2025 study using Hubble and Gaia data puts the odds closer to 50-50.
What Is the Milky Way? A Guide to Earth's Home Galaxy
The Milky Way is a barred spiral galaxy about 100,000 light-years across, with a supermassive black hole at its center and a star count that is still only roughly known.