Elliptical Galaxy – Definition & Detailed Explanation – Astronomical Objects Glossary

What is an Elliptical Galaxy?

Elliptical galaxies are one of the three main types of galaxies in the universe, along with spiral and irregular galaxies. They are named for their elliptical shape, which is different from the spiral arms of spiral galaxies. Elliptical galaxies are composed mostly of older stars, gas, and dust, and are typically found in galaxy clusters. They are the most common type of galaxy in the universe, making up about 60% of all galaxies.

Characteristics of Elliptical Galaxies

Elliptical galaxies are characterized by their smooth and featureless appearance. They lack the spiral arms and disk structure seen in spiral galaxies. Instead, they have a more rounded or elongated shape, ranging from nearly spherical to highly elongated. Elliptical galaxies also tend to have a reddish color, indicating that they contain mostly older stars.

Elliptical galaxies are also known for their lack of ongoing star formation. Unlike spiral galaxies, which have active star-forming regions in their spiral arms, elliptical galaxies have very little gas and dust, which are the raw materials for star formation. This means that elliptical galaxies are populated mostly by older stars, with little to no new stars being formed.

Formation of Elliptical Galaxies

Elliptical galaxies are thought to form through a process called galaxy mergers. When two galaxies collide and merge together, the resulting galaxy can take on an elliptical shape. This process disrupts the spiral structure of the original galaxies and causes the stars to move in random orbits, resulting in the smooth appearance of elliptical galaxies.

Another possible way that elliptical galaxies form is through the collapse of massive gas clouds early in the universe’s history. These gas clouds collapse under their own gravity, forming dense regions of stars that eventually evolve into elliptical galaxies.

Classification of Elliptical Galaxies

Elliptical galaxies are classified based on their shape and size. The Hubble classification system categorizes elliptical galaxies on a scale from E0 to E7, with E0 being the most spherical and E7 being the most elongated. The classification is based on the ratio of the major axis to the minor axis of the galaxy.

Elliptical galaxies are also classified based on their luminosity, with giant elliptical galaxies being the most massive and brightest, while dwarf elliptical galaxies are smaller and less luminous. The luminosity of an elliptical galaxy is determined by the total amount of stars it contains.

Size and Shape of Elliptical Galaxies

Elliptical galaxies come in a wide range of sizes, from small dwarf galaxies with only a few billion stars to giant elliptical galaxies with trillions of stars. The size of an elliptical galaxy is determined by its mass and the number of stars it contains.

The shape of an elliptical galaxy can vary from nearly spherical to highly elongated. The shape is determined by the orbits of the stars within the galaxy, with more elongated galaxies having stars that move in more elongated orbits.

Notable Elliptical Galaxies

One of the most famous elliptical galaxies is M87, located in the Virgo cluster. M87 is a giant elliptical galaxy with a supermassive black hole at its center. The black hole in M87 is one of the largest known black holes, with a mass billions of times that of the sun.

Another notable elliptical galaxy is Centaurus A, which is located in the Centaurus constellation. Centaurus A is an elliptical galaxy with a prominent dust lane across its center, which is thought to be the result of a recent merger with a spiral galaxy.

In conclusion, elliptical galaxies are an important and common type of galaxy in the universe. They are characterized by their smooth and featureless appearance, lack of ongoing star formation, and older stellar populations. Elliptical galaxies form through galaxy mergers or the collapse of massive gas clouds, and come in a wide range of sizes and shapes. Notable elliptical galaxies include M87 and Centaurus A, which provide valuable insights into the formation and evolution of galaxies.