Spiral, elliptical, and others Why are the shapes of galaxies different?

The common denominator among all galaxies is that they are complex systems bound together by gravity, made of gases, stellar dust, and millions of stars with their planets and asteroid belts.

Astronomers estimate that there are about 200 billion galaxies in our observable universe, and each galaxy has a different shape that depends on the nature of the galaxy and the date of its formation. Despite this difference, the common denominator among all galaxies is that they are complex systems bound together by gravity, and are made up of gases, stellar dust, and millions - and sometimes billions - of stars with their planets and asteroid belts.

The shapes of the three galaxies

In 1926, the astronomer Edwin Hubble, whose name was given to the famous Hubble Space Telescope, developed a classification of the shapes of galaxies, and he was the first to think about this after finding the existence of many other galaxies. Universe.

According to the Harvard Astrophysics Center website , Hubble classified galaxies into 3 forms:

Spiral galaxies, like our Milky Way, have a disc-shaped and spiral arms around their centre.

Elliptical galaxies are a single distinct elliptical cloud with irregular rotation.

"Irregular" galaxies are galaxies with no definite shape or structure with no discernible nucleus or spin pattern, and are essentially chaotic points of stars.

Astronomical statistics indicate that about 78% of the galaxies are spiral, 18% of them are elliptical, and only 4% are irregular galaxies.

Spiral galaxies

A spiral galaxy, also called a spiral galaxy, is shaped like a fried egg , Cameron Hummels, a theoretical astrophysicist at Caltech, told Live Science . It has a spherical center like an egg yolk surrounded by a disk of gas and stars similar to an egg white. Most spiral galaxies contain a supermassive black hole in the center of the central bulge.

Edwin Hubble called the disk galaxies "late-type galaxies", because he suspected that their shape meant that they formed later in the history of the universe. Spiral galaxies are filled with blue stars. This supports her younger age.

Blue stars are generally large stars that burn faster and hotter, and their blue light has a higher frequency, and therefore is more energetic than red light.

The Milky Way and Andromeda, our closest galaxy about 2.5 million light-years away, fall into this category.

Elliptical galaxies

Hubble called elliptical galaxies early-type galaxies, the oldest galaxies in the universe. Due to the lack of gas and dust in this type of galaxies, the rates of star birth are very low. Elliptical galaxies are filled with old stars called red dwarfs, which do not burn at the same speed or heat.

Stars in elliptical galaxies have more random motion than stars in spiral galaxies. It is believed that elliptical galaxies are the product of galaxies merging with each other.

When two galaxies of equal mass merge, their stars begin to gravitate toward each other, disrupting the rotation of stars and creating new, more random orbits, Robert Bassett, an astrophysicist who studies the evolution of galaxies at Swinburne University, Australia, tells Live Science.

lenticular galaxies

According to the " labroots " website, lenticular galaxies are located between the spiral and elliptical galaxies, and are distinguished from others by their lens-like appearance with a protrusion in the middle and the presence of a halo surrounding them, and they lack spiral arms. This type of galaxy is the least common in the universe.

Theorists speculate that they form when spiral galaxies use up all their gas and can't form any new stars, and the galaxy's stars start interacting and gravitating toward each other to create a lens-like shape.

These galaxies are still under study, as many scientists are currently conducting specialized studies and research on the origins of these lenticular galaxies.

Irregular galaxies

These galaxies lack distinctive shapes, and astronomers refer to them as strange or irregular galaxies because of their shapes, and their irregular appearance is believed to be caused by distortions caused by a nearby or passing large galaxy. These galaxies also contain little dust.

How do galaxies form?

The physics of how galaxies form is not known or fully established , Raja Guhathakurta , an astrophysicist at the University of California, Santa Cruz, tells HowStuffWorks. However, it is widely believed that most spiral galaxies begin their lives as rotating clouds of gas and dust.

Gravity is trying to pull those rotating amorphous bodies, and over time the pull is forced to contract due to gravity and energy loss due to friction. Because of the "conservation of angular momentum" principle, when a rotating object contracts, it rotates at a faster speed.

Ultimately, spiral galaxies form when shapeless clouds of gas and dust flatten at high speed. The same physical forces affect the appearance of the pointed "arms" that can be seen around the edges of these galaxies as well.

On the other hand, elliptical galaxies form when two spiral galaxies of similar mass merge together. Although that merger may not be the only process by which elliptical galaxies form.

Also, mergers in elliptical galaxies do not happen quickly, usually taking hundreds of millions or billions of years. And not all intergalactic mergers result in elliptical galaxies. The Milky Way, for example, has merged with many dwarf galaxies, which are among the smallest types of galaxies in the universe, yet still maintain the shape of their disk.

However, the spiral galaxies Andromeda and the Milky Way are moving straight towards each other at 120 kilometers per second, and after about 4 billion years the two galaxies will meet, eventually creating a more random elliptical galaxy.

Astrophysicists believe that the Sun will rush to the edges of a new, futuristic elliptical galaxy, which scientists have already dubbed "Milkomeda".

Despite what scientists know so far, the formation and evolution of the galaxy is one of the biggest open questions in the field of astronomy and astrophysics, in addition to the fact that the galaxies that we can see with current technology are only a small part of all galaxies in the universe, because most galaxies in the universe are dark and distant Too much to see with current telescopes.

What scientists have discovered so far about galaxies and their three-dimensional shapes, Bassett says, is inferred by using thousands of two-dimensional images and relying on other properties such as the galaxy's color and motion to fill in the blanks.