Galaxies are massive collections of stars, dust, and gas that are held together by gravity. They come in a variety of shapes and sizes, ranging from small, irregularly-shaped dwarf galaxies to massive, spiral-shaped galaxies like our own Milky Way.
The universe contains billions of galaxies, each of which can contain anywhere from thousands to trillions of stars. Galaxies are not evenly distributed throughout the universe, but rather are found in clusters and superclusters, with vast regions of empty space between them.
Galaxies are thought to have formed from the gravitational collapse of primordial gas clouds, and their evolution is shaped by complex interactions between their stars, gas, and dark matter. Astronomers study galaxies using a variety of techniques, including observing them with telescopes across the electromagnetic spectrum, measuring their spectra to determine their composition, and studying their motion to determine their mass distribution.
How many galaxies are in the Universe?
The exact number of galaxies in the universe is still unknown, but astronomers estimate that there are likely billions of galaxies in the observable universe alone. The observable universe is the portion of the universe that we can currently see and study, which is limited by the distance that light has had time to travel since the Big Bang.
In 2016, a team of astronomers from the University of Nottingham used data from the Hubble Space Telescope and other observatories to estimate that there are at least 2 trillion galaxies in the observable universe. However, this number is only an estimate and may change as new observations and data become available.
It's also worth noting that the universe may be much larger than the observable universe, and there may be many more galaxies beyond our current ability to detect. So the total number of galaxies in the entire universe may be even larger than the estimated number in the observable universe.
Milky Way
The Milky Way is a barred spiral galaxy that is home to our solar system and billions of other stars. It is estimated to be around 13.6 billion years old and has a diameter of about 100,000 light-years.
The Milky Way is named after the band of light that is visible in the night sky, which is caused by the combined light of stars in the galactic disk. This band of light is actually the edge-on view of the galaxy's disk from our vantage point on Earth.
The Milky Way is part of a group of galaxies called the Local Group, which also includes the Andromeda Galaxy and dozens of smaller galaxies. The Milky Way's exact position in the Local Group is somewhat uncertain, but it is thought to be one of the larger galaxies in the group.
Our understanding of the Milky Way has been greatly advanced by recent astronomical observations, including those made by the European Space Agency's Gaia mission, which is creating a detailed 3D map of the galaxy's stars and structure.