Last Updated On: December 29, 2020

What is the most common type of galaxy?

There are different types of galaxies in the universe, but the most common is the elliptical-type galaxy.

Characteristics of elliptical galaxies

Elliptical galaxies are the easiest to find; however, other collections of younger stars usually overshadow them because of their age and low light output.

One of the main characteristics of elliptical galaxies is that they lack swirling arms. Instead, their main shape is an ellipse, much like a stretched circle (oval). They can also be observed in a circular shape.

In the novel Contact, written by Carl Sagan in 1985, he mentions Cygnus A’s elliptical galaxy, which coincidentally is one of the most famous such galaxies.

It is located about 600 million light-years from Earth. Cygnus A is a much talked about galaxy among astronomers because it is a powerful source of radial energies.

Cygnus A Galaxy. Courtesy from Wikipedia.

Smaller elliptical galaxies have tens of millions of stars, while larger ones can have more than 1 trillion stars. Some such galaxies can be very faint because of their possible variation in star numbers, and others very bright.

These galaxies are ancient, and their stars were formed a long time ago. They are so old that they consumed all the gas and dust around them, running out of material to form new stars.

Another essential feature is that the absence of young stars makes these galaxies yellow and red.

The Andromeda Galaxy

Andromeda is an elliptical galaxy. Image courtesy from Wikipedia.

The Andromeda galaxy is an elliptical-type galaxy and is the closest neighbor we have in the Milky Way. It is located about 2.5 million light-years from Earth. This galaxy is the farthest object that can be observed with the naked eye, as long as it is from a location that has the characteristics of having a very dark and light night.

With indescribable beauty, Andromeda hides an open secret: it is on a collision course with our galaxy, although we will still be safe for some billion years.

The collision course between Andromeda and the Milky Way will forever change the shape and structure of both galaxies. Scientists estimate that this collision will take about 4 billion years. The speed at which the two galaxies are approaching is about 112 kilometers per second (about 70 miles per second).

By that time, our sun will have become a red giant star, and it will have consumed all the planets in the solar system in which we live.

Classification of elliptical galaxies

According to the Hubble Classification Scheme, elliptical galaxies are classified from number 0 to number 7. The number indicates how elliptical the galaxy is.

E0 Elliptical Galaxies

They are elliptical galaxies that have a circular shape, in which no stretching occurs.

Type E7 Elliptical Galaxies

They are those elliptical galaxies that are totally stretched, forming an oval.

Other types of galaxies

Spiral galaxies

Illustration of a spiral galaxy. Image courtesy from Pixabay.

Spiral-type galaxies are twisted collections of stars and gas, which usually look beautiful. They are mainly composed of young, very high-temperature stars. Most of the galaxies that have been discovered by scientists have been spiral-type galaxies.

A classic example of a spiral-type galaxy is the Milky Way, which includes Earth. Spiral galaxies are typical in the universe. A little more than 70% of all the scientific community’s galaxies fall into this group.

In the center, spiral galaxies have a bulge, and around it is a flat sequence of rotating stars. In the center of this type of galaxy, the lump is composed of evolved stars, with little light emission. It is estimated that a supermassive black hole is located in the center.

Another peculiar characteristic of spiral galaxies is that in the center, they have a bar structure that crosses them from end to end, passing through their center. This bar is also observable in the Milky Way.

About 50% of the galaxies we can observe are spirals. Because they have significant amounts of gas and dust, these galaxies are believed to be younger than elliptical galaxies.

These galaxies are usually found in the universe’s low-density regions, in places where there are not many galaxies around.

Galaxy UGC 2885

Galaxy UGC 2885. Image courtesy of Wikipedia.

NASA and ESA (European Space Agency) jointly used the Hubble Space Telescope to take a new picture of the spiral galaxy UGC 2885, which is located 232 million light-years from Earth.

UGC 2885 is more than 8 million light-years long (more than seven times the Milky Way size). Astronomers estimate that it contains ten times more stars than our galaxy.

Classification of Spiral Galaxies

S0 type galaxies

These galaxies show properties of both spiral and elliptical galaxies. They seem to be a bridge between both widespread galaxy types.

They are skinny and have a very bright core, surrounded by a smooth lump with no distinctive features and contained in a faint outer envelope.

Sa type galaxies

They are normal, narrow spirals with strongly intertwined arms. They are generally visible by the presence of interstellar dust and by very bright stars in many cases.

Sb-type galaxies

This intermediate type of spiral galaxy usually has an average size number. Their arms are farther apart than those of the Sa type and appear less smooth.

They contain stars, stardust, and interstellar gas and dust. Sb-type galaxies show significant scattering in the details of their appearance.

Sc-type Galaxies

These galaxies have a tiny nucleus and many open arms with large angles. Their arms are bulky because they contain large irregular amounts of star clouds, star clusters, and gas clouds.

SB-type galaxies

A barred spiral galaxy SB is a spiral galaxy with a central bar composed of stars. The luminosity, dimension, and distribution of these galaxies make them indistinguishable from normal spiral galaxies.

Irregular Galaxies

Image of an irregular galaxy. Image courtesy from Wikipedia

They are those galaxies that do not have a regular shape that distinguishes them, as is the case with spiral or elliptical type galaxies. Irregular galaxies do not belong to the Hubble sequence’s standard classification, so they have a chaotic appearance. They do not have any nuclear protrusions and do not have spiral arms.

About 25% of all galaxies are believed to be irregular. Besides, some of these galaxies were, in the beginning, elliptical or spiral type galaxies, which over time and due to gravitational encounters with other forces, suffered deformations that caused the loss of their regular shape.

With abundant dust and gas, irregular galaxies are generally small in size, with approximately 10% of the mass of the Milky Way. For this reason, they are very prone to physical effects such as colliding with large galaxies.

Also known as peculiar galaxies, the closest to the Milky Way is the Canis Major Dwart irregular galaxy. Being a small galaxy with only 1 billion stars, the scientific community thinks our own galaxy is absorbing it.

VIDEO: Types of galaxies

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