Astronomy & Astrophysics 101: Galaxy

Galaxy NGC4826

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This Hubble Space Telescope picture options NGC4826 — a spiral galaxy situated 17 million light-years away within the constellation of Coma Berenices (Berenice’s Hair). This galaxy is sometimes called the “Black Eye,” or “Evil Eye,” galaxy due to the darkish band of mud that sweeps throughout one aspect of its shiny nucleus. Credit: ESA/Hubble & NASA, J. Lee and the PHANGS-HST Team, Acknowledgment: Judy Schmidt

A galaxy is a set of stars, mud, gasoline, and darkish matter held collectively by gravity. Galaxies comprise wherever from a number of hundred million to 100 trillion stars.

Galaxies are collections of stars, mud, gasoline, and darkish matter, that are sure collectively by the gravitational attraction that outcomes from their very own mass. A small dwarf galaxy incorporates a number of million stars, while the biggest identified galaxies can comprise as much as 100 trillion stars.

There are many various galaxy morphologies, together with elliptical galaxies and spiral galaxies. Many galaxies, together with the Milky Way, have supermassive black holes at their centers. If the black hole is active, then the galaxy’s active core is classified as an active galactic nucleus (AGN). Galaxies are highly dynamic, evolving considerably throughout their lifetimes and interacting with one another.

As they are so large and bright, it is possible to study galaxies that are extremely far away — galaxies more than 13 billion light-years distant from Earth have been observed. The speed of light is finite, meaning that, for example, if a galaxy 13 billion light-years away is observed, it is seen how it was 13 billion years ago. This makes the study of galaxies a fascinating opportunity to study ‘fossils’ from the history of the Universe, thus providing clues to how the Universe has evolved over time.

A galaxy is an ensemble of stars, mud, gasoline, and darkish matter which might be sure collectively by gravity. Galaxies comprise wherever between a number of hundred million to 100 trillion stars. Credit: ESA/Hubble, ESA, NASA & L. Calçada

One of the main scientific justifications for building Hubble was to measure the size and age of the Universe and test theories about its origin. Using Hubble, astronomers were able to study young galaxies in the early Universe and the most distant primeval galaxies.

Hubble has imaged and studied galaxies of all kinds, including elliptical, spiral, and irregular galaxies, and of various different sizes, including dwarf galaxies. In this image of Messier 60 and NGC 4647, Hubble has imaged both an elliptical and a spiral galaxy, allowing for a clear comparison of the two galaxy types. Elliptical galaxies, the yellow fuzzy objects seen in the image, are most often found close to the centers of galaxy clusters, while spirals, the bluish patches, are usually found further out and more isolated.

Word Bank Galaxy

Galaxy. Credit: ESA/Hubble & NASA, J. Lee and the PHANGS-HST Team

Hubble has also observed beautiful, rare galaxy merging events, during which galaxies undergo dramatic changes in their appearance and in their stellar content. These systems are excellent laboratories in which to trace the formation of star clusters under extreme physical conditions.

Some of Hubble’s most popular images have been of galaxies. You can explore the vast ESA/Hubble archive of more than 1500 galaxy images here.