According to foreign media reports, looking at the night sky, you can see stars from countless other galaxies. Some galaxies, like our Milky Way, are rotating blue disk galaxies; others are red globular galaxies or galaxies that are deformed, clustered, or somewhere in between. Why is it so different? It turns out that the shape of a galaxy can tell us the story of the galaxy’s long life .
Artistic rendering of Wolf’s astrolabe, which is a huge disk-shaped galaxy in the early universe.
Basically, the shape of galaxies can be divided into two categories: disk and ellipse. Cameron Hemmers, a theoretical astrophysicist at the California Institute of Technology, said that disk galaxies, also called spiral galaxies, are shaped like fried eggs. The centers of these galaxies are closer to the sphere, like an egg yolk surrounded by gas and stars (egg white). Both the Milky Way and the Andromeda Galaxy, which is the closest to us, belong to disk galaxies.
Theoretically, disk galaxies start from hydrogen clouds. Gravity attracts these gas particles together. As the hydrogen atoms get closer and closer, the clouds begin to spin and their total mass begins to increase. Of course, their gravitational force also increases. Ultimately, gravity collapses the gas into a rotating disk. Most of the gas is located on the edge of the disk, which is also where stars form. According to NASA, Edwin Hubble, who just proved the existence of extrasolar galaxies more than a century ago, referred to disk galaxies as late-type galaxies because he guessed that the shape of disk galaxies meant they were formed in the history of the universe Late.
Another elliptical galaxy, called an early-type galaxy by Hubble, was formed earlier as the name suggests. Robert Bassett, an observing astrophysicist who studies the evolution of galaxies at Swinburne University in Melbourne, Australia, said that the stars in elliptical galaxies do not rotate like in disk galaxies, but move more randomly. Elliptical galaxies are also considered to be the product of galaxy mergers. Bassett said that when two galaxies of equal mass merge, their respective stars begin to pull each other under the action of gravity, disrupting the rotation of the stars and forming more random orbits.
Of course, not every merging result is an elliptical galaxy. The Milky Way is actually very old and huge, but it still maintains the shape of a disk. The Milky Way increases its own weight by absorbing much smaller dwarf galaxies and collecting free gas from the universe. Bassett said, however, the Andromeda galaxy, which is the same disk galaxy as the Milky Way, is coming straight to our Milky Way. So, maybe billions of years later, these two spiral galaxies may merge, and then the stellar disks of each galaxy will offset each other’s rotation, creating a more random elliptical galaxy.
These mergers will not be completed in an instant. The merger of the two galaxies may take hundreds of millions or even billions of years. In fact, some of the ongoing galaxy mergers are so slow that they seem to be stationary from our perspective. Bassett said: “They are basically in exactly the same state, with respect to the entire human civilization, almost unchanged.” Hubble classifies these galaxies into another category-irregular galaxies. Observe these irregular galaxies, “you will find that they are generally in a state of chaos, composed of multiple parts,” Bassett said. “Irregular galaxies look like the remains of a large train.”
This galaxy is called Mrk 820 and is a lenticular galaxy. There are many other types of galaxies around Mrk 820, from elliptical galaxies to spiral galaxies and so on.
Finally, there is a less common shape: a lenticular galaxy. A lenticular galaxy is like a hybrid between an elliptical galaxy and a spiral galaxy. Bassett said that it is possible that when the disk galaxy runs out of all its gas and can no longer form any new stars, the existing stars begin to interact. The gravitational pull between them forms a shape that looks like a lentil—something like an ellipse, but still a rotating disk galaxy.
Bassett said that so far, the information that scientists know about galaxies and their 3D shapes has been inferred using thousands of 2D images and relying on other attributes, such as galaxy color and motion.
For example, the blue disk galaxy is younger. Blue stars are generally larger, burning faster and hotter (blue light has a higher frequency and is therefore more vibrant than red light). At the same time, there are a large number of ancient stars (also called red dwarfs) in elliptical galaxies, and these ancient stars burn not so fast or so hot.
Hemmers said that although we already know a lot about the huge celestial structures that surround us, there are still many places we don’t know, waiting for us to explore. “The formation and evolution of galaxies is one of the biggest open issues in astronomy and astrophysics,” he said.
For more such interesting article like this, app/softwares, games, Gadget Reviews, comparisons, troubleshooting guides, listicles, and tips & tricks related to Windows, Android, iOS, and macOS, follow us on Google News, Facebook, Instagram, Twitter, YouTube, and Pinterest.