The galaxies they are huge groups of stars that interact gravitationally, and always revolve around a common center. There are hundreds of billions of galaxies in the universe, each containing more than a trillion stars at a time, varying in size, shape and brightness. For example: Andromeda, NGC 6822, Centaurus A.
The planet Earth, like the entire Solar System, belongs to one of all those galaxies called Milky Way (translatable as ‘milk path’), which bears that name because seen from Earth, the galaxy appears in the sky as a milk stain.
The galaxies they are made up of stars, gas clouds, planets, cosmic dust, dark matter, and energy are the elements that necessarily appear in a galaxy. At the same time, some substructures such as nebulae, star clusters, and multiple star systems make up galaxies.
Classification of galaxies
The different forms of the galaxies give rise to a morphological classification, from which each group in turn has some characteristics.
- Spiral galaxies. They get their name from the shape of their disks in which stars, gas, and dust are concentrated in spiral arms, extending outward from the central nuclei of galaxies. They have spiral arms looped more or less tightly around a central core, and they are rich in gas and dust with a high rate of star formation.
- Elliptical galaxies. Rather, they contain old stars, and therefore have no gas or dust.
- Irregular galaxies. They do not have a particular shape and are among them the smallest galaxies.
History of galaxies
The Persian astronomer is usually pointed out al-Sufi as the first to intuit the existence of galaxies, and then to the French Charles Messier as the first compiler, at the end of the century XVIII, of non-stellar objects that included about thirty galaxies.
All galaxies have a source and one evolution, the first being formed about 1000 million years after the big-bang. The formation took place from the atoms of hydrogen and helium: with the fluctuations of density it is that the largest structures began to appear, which later gave rise to the galaxies as they are known today.
Future of galaxies
In the future, it is to be expected that new generations of stars They occur as long as spiral galaxies have molecular clouds of hydrogen in their arms.
This hydrogen is not unlimited but has a finite supply, so once the formation of new stars is depleted it will come to an end: in galaxies like the Milky Way, the current era of star formation is expected to continue for the next few years. one hundred billion years, to decline when the smallest stars begin to fade.
Examples of galaxies near Earth
A large number of galaxies will be listed below, starting with those closest to Earth along with their distance from our planet:
| Magellanic Clouds (200,000 light years distant) | Leo (700,000 light years away) |
| The dragon (300,000 light years away) | NGC 6822 (1,700,000 light years away) |
| Ursa Minor (300,000 light years away) | NGC 221 (MR2) (2,100,000 light years away) |
| The sculptor (300,000 light years away) | Andromeda (M31) (2,200,000 light years away) |
| The hearth (400,000 light years away) | The triangle (M33) (2,700,000 light years away) |
Examples of more distant galaxies
- z8_GND_5296
- Wolf-Lundmark-Melotte
- NGC 3226
- NGC 3184
- Galaxy 0402 + 379
- I Zwicky 18
- HVC 127-41-330
- Comet Galaxy
- Huchra lens
- Pinwheel Galaxy
- M74
- VIRGOHI21
- Black Eye Galaxy
- Sombrero Galaxy
- NGC 55
- Abell 1835 IR
- NGC 1042
- Dwingeloo 1
- Phoenix dwarf
- NGC 45
- NGC 1
- Circinus Galaxy
- Southern Pinwheel Galaxy
- NGC 3227
- Canis Major Dwarf
- Pegasus dwarf
- Sextans A
- NGC 217
- Pegasus Spheroidal Dwarf
- Maffei II
- Fornax Dwarf
- NGC 1087
- Galaxy Baby Boom
- Virgo stellar stream
- Aquarius Dwarf
- Dwingeloo 2
- Centaurus A
- Andromeda II