The elliptical galaxy NGC 1270 is located about 240 million light-years away. But it is not alone. It is part of the Perseus Cluster (Abell 426), the brightest X-ray object in the sky and one of the most massive objects in the universe.
NGC 1270 stars in a new image from the Gemini North telescope. However, the image does not show the dark matter that has a tight grip on the galaxy and the other galaxies in the Perseus Cluster.
Ancient astronomers would be amazed at what we have learned about the universe. Even 20th century astronomers like Edwin Hubble would be amazed at the power of our modern telescopes and what they have shown us. Back then, distant galaxies appeared blurry and were called nebulae. Even the nature of Andromeda, our nearest galactic neighbor, was uncertain. In 1920, Hubble and others debated whether Andromeda and other objects they saw were small objects in the outer regions of the Milky Way, nebulae, or other galaxies.
The German philosopher and enlightenment philosopher Immanuel Kant coined the term “island universes” to describe all these fuzzy objects and indicate their true nature. The idea of other galaxies beyond our own goes back a long way, but there was no way to test it. Then, in 1924, Edwin Hubble ended the debate. He was able to show that individual stars in some of these so-called “nebulae” were actually located far outside the Milky Way.
The discovery was crucial and we now know that the universe is populated by hundreds of billions or even trillions of other galaxies like our own Milky Way.
Today, astronomers use powerful telescopes to study other galaxies in detail. They've even used the James Webb Space Telescope to look back in time to the earliest galaxies in the universe. Anyone can quickly examine hundreds of amazing images of other galaxies of all kinds.
Huge objects like the Perseus Cluster alert us to the existence of something even more mysterious and difficult to understand than the nature of galaxies. Something connects these individual galaxies into a cohesive group, and we call it dark matter.
There are a growing number of scientific voices suggesting that we should stop calling it dark matter and instead use the more accurate term invisible matter. But whatever we call it, dark matter makes up most of the matter in the universe, dwarfing the “normal” matter that interacts with light and makes up stars, planets, and us.
As cosmology has advanced, scientists have mapped the large-scale structure of the universe. These maps show how galaxies and their groups are organized along filaments of dark matter that serve as frameworks. The Perseus Cluster is associated with the Perseus-Pegasus filament, a long, thin galaxy structure that stretches over a billion light-years.
A computer model of the large-scale structure of the universe using the Illustris simulator. This image shows the dark matter and gas involved in the formation of galaxies and galaxy clusters, as well as the filaments that connect them. Photo credit: Illustris TNG
If there were no dark matter, scientists believe the universe would be far more homogeneous. The galaxies would be more evenly distributed in space. But that's not what we see, and NGC 1270 and the rest of the Perseus Cluster show it clearly.
Currently, scientific theory suggests that a web of invisible dark matter pulls galaxies together. They are located where the massive tendrils of dark matter intersect. That's where his attraction is strongest.
In short: without dark matter, the Perseus Cluster and NGC 1270 would not be where they are and would not be grouped together. The star cluster and all other groups, star clusters and superclusters are firmly in the grip of dark matter.
American astronomer Vera Rubin played a large role in our modern understanding of dark matter. She observed that stars and gas at the outer edge of a galaxy were moving much faster than the galaxy's visible mass predicted. Newtonian physics suggests that they should move slower. Rubin and her colleagues assumed that there must be a large amount of invisible matter beyond the visible edges of galaxies. Eventually she found that there must be six times more dark matter than visible matter in galaxies.
Rubin faced many obstacles before her results were accepted. As a woman, she was not part of the male-dominated world of astronomy in the 1970s. Early in her career she was denied access to some facilities, which slowed her progress. Now she is receiving full recognition and is being mentioned alongside Hubble and other influential figures in astronomy. One of the most powerful and unique observatories of all time is named after her.
Regardless of what we call it and who discovered it, our universe is dominated by something we don't fully understand.
It is remarkable that scientists can map invisible matter by inference alone, without knowing what it is. The most widely accepted understanding of dark matter is found in the Lambda-CDM (Lambda Cold Dark Matter) model of cosmology, also called the Standard Model of Big Bang cosmology. It successfully recreates many of the things we observe in the universe, including the formation of galaxies, the expansion of the universe, and of course the large-scale structure of the universe.
But even Lambda-CDM can't tell us what dark matter is. Most people think it is some kind of particle, but if it is, it is extremely elusive.
However, that doesn't stop us from seeing its effect when we observe objects like NGC 1270 and the Perseus Cluster.
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