Our home galaxy, the Milky Way, is known for its famous, bright spiral.
But we’re not the only ones with a shiny arm. Known as spiral galaxies, this class of galaxies represents about 60% of all galaxies in the universe. Found in low-density regions of the universe, spiral galaxies are not common in all corners of the universe. In fact, they are rare among galaxy clusters.
And it turns out that there is a part of the universe called the Supergalactic Plane, which is a huge flat structure stretching almost a billion light-years across, filled with bright elliptical galaxies and glowing disks – but, interestingly, no spiral galaxies. An international team of researchers wanted to know: Why are spiral galaxies like our Milky Way missing from the Supergalactic Plane? And what can this tell us about the evolution of our galaxy?
They may have found an answer. New research published in the journal Nature Astronomy reports that spiral galaxies are scarce in the Supergalactic Plane because in this region galaxies are often merging with other galaxies.
Think of it like a very populated city or a very busy highway. Through these mergers, spiral galaxies transform into elliptical galaxies, egg-shaped galaxies without spiral arms, which leads to the growth of supermassive black holes. (These black holes live up to their name, sometimes billions of times more massive than our Sun.) In contrast, spiral galaxies that don’t populate the Supergalactic Plane evolve in isolation, allowing them to maintain their perfect spiral.
“Our simulation reveals the intimate details of galaxy formation, such as the transformation of spirals into ellipticals through galaxy mergers.”
The team of researchers reached their conclusion using the SIBELIUS (Simulations Beyond the Local Universe) supercomputer simulation. Through this simulation, they followed the evolution of the universe over 13.8 billion years, from the beginning of the universe to today. The researchers said the final simulation was consistent with observations of our universe through telescopes.
“It’s rare, but not a complete anomaly: our simulation reveals the intimate details of galaxy formation, such as the transformation of spirals into ellipticals through galaxy mergers,” said co-author Professor Carlos Frenk in a press release. “Furthermore, the simulation shows that our standard model of the Universe, based on the idea that most of its mass is cold dark matter, can reproduce the most remarkable structures in the Universe, including the spectacular structure of which the Via Dairy is part of it. ”
Distribution of the brightest galaxies in the Local Universe, observed in the 2MASS survey (left panel) and reproduced in the SIBELIUS simulation (right panel). (Dr Till Sawala)Astronomers believe the Milky Way is about 13.51 billion years old. However, what happened during each phase of its evolution and how long these phases took to reach its current form today remains unclear. One leading theory is that the Milky Way’s collision with a dwarf galaxy nearly 10 billion years ago was a turning point, triggering the changes that gave rise to our modern galaxy. Others believe that our galaxy may have matured earlier than previously thought. Anyway, just like humans, galaxies go through different stages of maturation.
A separate study published in The Astrophysical Journal Letters highlights unexpected observations in “teenage galaxies,” that is, galaxies that formed two to three billion years after the Big Bang.
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In the study, a group of scientists from Northwestern University analyzed results from the CECILIA (Chemical Evolution Constrained using Ionized Lines in Interstellar Aurorae) survey, which used NASA’s James Webb Space Telescope (JWST) to study the chemistry of distant galaxies. The results showed that these so-called teenage galaxies go through an uncomfortable growth spurt during adolescence, similar to that of humans.
“Using JWST, our program targets adolescent galaxies when they were going through a complicated period of growth spurts and changes,” Northwestern’s Allison Strom, who led the study, said in a press release. “Adolescents often have experiences that determine their trajectories into adulthood. For galaxies, it’s the same thing.”
To make these discoveries, Strom and his collaborators used JWST to observe 33 distant teenage galaxies for 30 hours straight. They then combined spectra from 23 of these galaxies. Strom emphasized that the biggest surprises were the nickel observations and the discovery that teenage galaxies were extremely hot.
“This is just additional evidence of how different galaxies probably were when they were younger,” Strom said. “Never in my wildest dreams did I imagine we would see nickel.”
Light from 23 distant galaxies, identified with red rectangles in the Hubble Space Telescope image at the top, has been combined to capture incredibly faint emissions from eight different elements, which are labeled in the JWST spectrum at the bottom. (Aaron M. Geller, Northwest, CIERA + IT-RCDS)
Gwen Rudie, a staff astronomer at Carnegie Observatories, clarified to Salon in an email that the elements in these galaxies are not a surprise, but the ability to measure their light is “unprecedented” and underscores the power of JWST.
“The pattern we see in the light from these different elements (how brightly the signatures of each element shine) is very different from what we see in local galaxies – and in our own galaxy,” said Rudie. “So explaining why the pattern in their spectra is different and what that means for these early galaxies is the next big puzzle.”
Rudie added that astronomers have a good idea of how galaxies like the Milky Way formed, but are “missing very important clues.” The most important thing, she said, is the chemical composition of the galaxy.
Strom further elaborated that the greatest growth of a galaxy occurs during this period, explaining why it is an important time period to study. It may also hold clues as to why the Milky Way has its spiral arm.
“By studying this, we can begin to explore the physics that made the Milky Way look like the Milky Way,” she said. “And why it might look different from neighboring galaxies.”