A galaxy is a gravitationally bound system of stars, stellar remnants, interstellar gas, dust, and dark matter.Galaxies range in size from dwarfs with just a few billion stars to giants with one hundred trillion stars, each orbiting its galaxy’s center of mass. Galaxies are categorized according to their visual morphology as elliptical, spiral and irregular. Many galaxies are thought to have black holes at their active centers. Approximately 170 billion to 200 billion galaxies exist in the observable universe. Most of the galaxies are 1,000 to 100,000 parsecs in diameter and usually separated by distances on the order of millions of parsecs (or megaparsecs). The space between galaxies is filled with a tenuous gas having an average density of less than one atom per cubic meter. The majority of galaxies are gravitationally organized into associations known as galaxy groups, clusters, and superclusters. At the largest scale, these associations are generally arranged into sheets and filaments surrounded by immense voids.
These are 5 amazing galaxies:
1. Sombrero Galaxy The Sombrero Galaxy is an unbarred spiral galaxy in the constellation Virgo located 28 million light-years from Earth. The galaxy has a diameter of approximately 50,000 light-years, 30% the size of the Milky Way.
2. Messier 83 is a barred spiral galaxy approximately 15 million light-years away in the constellation Hydra. It is one of the closest and brightest barred spiral galaxies in the sky, making it visible with binoculars.
3. Antennae Galaxies, also known as NGC 4038/NGC 4039, are a pair of interacting galaxies in the constelattion Corvus. They are currently going through a starbust phase, in which the collision of clouds of gas and dust, with entangled magnetic fields, causes rapid star formation.
4. Whirlpool Galaxy, also known as Messier 51a, M51a, or NGC 5194, is an interacting grand-design spiral galaxy with a Seyfert 2 active galactic nucleus in the constellation Canes Venatici.
5. The Porpoise Galaxyalso known as Arp 142 looks like a dolphin. the eye of the dolphin being the core of a large spiral galaxy that is being distorted by the tidal influence of an even larger galaxy below it. The area to the left of the “eye” that looks like the nose of the dolphin, is in fact a huge star forming region, in which young, hot new stars illuminate the surrounding gas and dust clouds. It is expected that in about a billion or so years, the dolphin shape will have transformed itself into a regular galaxy as the merger runs itscourse.