Astronomers face a difficult problem with the Universe's giant galaxies. There are only a few things that can make a giant of the universe. Mergers must have been important.

The process of galaxy mergers is still shrouded in mystery. A new study that has been done for ten years shows observations and direct measurement of the merger process.

It seems logical that galaxies grow larger by merging with others. Where else can they get so much mass? Galaxies are the largest structures in the universe. The larger the group, the smaller the group is made of distinct, individual galaxies that are unrelated to each other. To grow so massive it had to acquire a lot of mass. Large-scale mass can only be found in other galaxies.

There is a lot of work being done in the area of galaxy formation. Observations and conclusions have not kept up with the times.

According to the hierarchical model of galaxy formation, small galactic building blocks formed first, only to coalesce into ever larger galaxies over the lifetime of the Universe. Image Credit: ESO/L. Calçada
According to the hierarchical model of galaxy formation, small galactic building blocks formed first, only to coalesce into ever more giant galaxies over the lifetime of the Universe. Image Credit: ESO/L. Calçada

Many images captured by the Hubble and other telescopes look like galaxies merging There was more than meets the eye when it came to the Hubble Space Telescope. The space telescope didn't have the technology to see the most distant and ancient stars.

This image is a collage of six galaxy mergers captured by the Hubble Space Telescope. Top Row Left to Right: NGC 3256, 1614, 4195 Bottom Row Left To Right: NGC 3690, 6052, 34 - Credit ESA/Hubble/NASA
This image is a collage of six galaxy mergers captured by the Hubble Space Telescope. Top Row Left to Right: NGC 3256, 1614, 4195 Bottom Row Left To Right: NGC 3690, 6052, 34 – Credit ESA/Hubble/NASA

The Hubble Space Telescope couldn't see red-shifted galaxies when it began. Astronomers couldn't say if what Hubble saw was real or if it was the result of Hubble's limitations.

The problem with post-merger galaxies is that they can have weird shapes. Post-merger morphologies can be created by star formation. Astronomers were not sure what they were seeing in the early 1990s. Were they only seeing the active regions of the galaxies, and not the rest of the stars? Was it possible that they were looking at the aftermath of the merger?

It was difficult for astronomer to make conclusions about the effects of galaxy mergers.

A new paper based on Hubble observations is reaching some new conclusions. A simulation-driven Deep Learning Approach for Separating Mergers and Star-forming Galaxies is the new paper. It has been published in a journal. The leader of the study was a professor at the University of Manchester.

IllustrisTNG 100 is one of three massive simulations in the Illustris TNG project. There are processes that drive galaxy formation. Some of the world's fastest supercomputers are included in the order in which they are listed. The previous simulation increased the resolution. The IllustrisTNG 100 was the right size and resolution for the study.

TNG 50, TNG 100, and TNG 300. Image: IllustrisTNG
TNG 50, TNG 100, and TNG 300. Image: IllustrisTNG

The group of researchers were trying to distinguish between the two phenomena. Large active star-formation regions look similar to post-merger galaxies. There are other things that can cause spikes in star formation. The researchers had to be certain that they were differentiating between post-merger and non-merger galaxies before they could make any conclusions.

This is a Hubble telescope image of NGC 2623, a late-stage merger between two spiral galaxies. Mergers compress the gas in both galaxies triggering a spike in active star formation. But some distant galaxies experience intense star formation not triggered by mergers, and it's difficult to differentiate between the two. Image Credit: By ESA/Hubble, CC BY 4.0, https://commons.wikimedia.org/w/index.php?curid=63401428
This is a Hubble telescope image of NGC 2623, a late-stage merger between two spiral galaxies. Mergers compress the gas in both galaxies triggering a spike in active star formation. But some distant galaxies experience intense star formation not triggered by mergers, and it’s difficult to differentiate between them. Image Credit: By ESA/Hubble, CC BY 4.0, https://commons.wikimedia.org/w/index.php?curid=63401428

There are other factors that make it hard to distinguish between active and inactive SFRs. When it comes to highly-dispersed, rotating galaxies, they are similar in many ways. Post-merger galaxies can be mimicked by SFRs. Astronomers have had to untangle post-merger galaxies from other SFRs for a long time.

The Hubble got an instrument in 1998. Astronomers were able to study high red shift galaxies. Astronomers hadn't seen just active star-forming regions when they looked at Hubble images. The authors wrote that this implied that the stellar mass was out of balance.

Astronomers concluded that distant galaxies are not normal. It wasn't clear why these high-redshift galaxies were so strange. Astronomers suspected that it was related to how they formed, but the details of how these distant galaxies grew to be so strange remained a mystery.

The team took 160,000 images from the TNG 100 and compared them to the Hubble images. They used machine learning to separate post-mergers from star-forming galaxies in 80% of the time. They trained their machine learning tool after building it. The 80% success rate was an improvement over previous efforts. The researchers wanted to overcome the challenge of distinguishing post-merger galaxies from star-forming ones. The paper's goal is to distinguish mergers from star-forming galaxies by using their structure.

We're accustomed to gorgeous Hubble images of galaxies, but that's not what makes up scientific data. This figure from the study shows some of the galaxy images in the data. On the left are some of the post-merger galaxies identified in the study, and on the right are star-forming galaxies. Each one is shown with its redshift and stellar mass. Image Credit: Conselice et al. 2022.
We’re accustomed to gorgeous Hubble images of galaxies, but that’s not what makes up scientific data. This figure from the study shows some of the galaxy images in the data. On the left are some of the post-merger galaxies identified in the study, and on the right are star-forming galaxies. Each one is shown with its redshift and stellar mass. Image Credit: Conselice et al. 2022.

The same problem has been worked on by other researchers. Many of these authors collaborated on earlier papers. This work is a continuation of the work that was done in the past to understand galaxy mergers.

The researchers wrote that their machine-learning-driven approach provides a new way to investigate the formation history of galaxies with models that are informed by simulations. They point out that there are still some limitations that need to be overcome. We are limited to high-mass major-merger cases due to the limitations of the simulations and observations. It is1-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-6556 is1-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-6556

The James Webb Space Telescope is poised to contribute. There will be a new window to incorporate the effect of minor mergers and lower-mass systems. This will be a major step towards discovering unresolved questions about the evolution of the universe.

One of the most dominant processes in the evolution of the galaxy is galaxy mergers. According to the study, the average massive galaxy has undergone three separate mergers over the last 10 billion years.

What significance does this have for our new civilization? It is our home and it is a giant universe. The study says a lot about our situation.

A merger is in the works. Our universe will collide with the other universe in a few billion years. The two halos could be interacting. The result will be a huge universe filled with a lot of stars.

The Milky Way has had mergers in the past.

It's possible that our own Milky Way galaxy has undergone at least one of these mergers, which changed its shape and formation history. Mergers could be the origin event for how stars including our own Sun formed, as well as feeding the matter that grows central black holes.

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