Home Science Outer Space According to simulations, the Milky Way is one in a million

According to simulations, the Milky Way is one in a million

0
1
According to simulations, the Milky Way is one in a million

Humanity is in a mutual relationship with nature. At first we thought we were at the center of everything, with the sun and the entire cosmos revolving around our little planet. We eventually realized that wasn’t true. Over the centuries, we’ve found that while Earth and life may be rare, our sun is pretty normal, our solar system is relatively unremarkable, and even our galaxy is one of billions of spiral galaxies, a type that makes up 60% of the galaxies in the world. universe.

But the Illustris TNG simulation shows that the Milky Way is special.

Illustris TNG is an ongoing series of large-scale simulations. The goal is to understand the mechanisms behind the formation and evolution of galaxies. The effort is a “series of large, cosmological magnetohydrodynamic simulations,” according to the Illustris TNG website. So far, the project has delivered three primary runs, each with a larger and higher resolution than the last: TNG 50, TNG 100 and TNG 300. Each run also focuses on different aspects of galaxy formation. TNG 300 is the largest, simulating an area of ​​nearly 300 million megaparsecs, over a billion light-years across, and containing millions of galaxies.

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

New research based on Illustris TNG shows that the Milky Way is special. But it is not special because of its intrinsic qualities. It is special in relation to its surroundings.

The findings are in a new paper based on Illustris TNG 300, published in the Monthly Notices of the Royal Astronomical Society. The title is “The unusual Milky Way local leaf system: implications for spin force and alignment.” The principal investigator is Miguel Aragón, a computational cosmologist and assistant professor at the National Astronomical Observatory, Universidad Nacional Autonoma de Mexico.

Must Read
Climate tipping points can fuel unstoppable changes on the planet. How close are they?

Illustris TNG simulates the large-scale structure of the universe. It shows how galaxies are arranged on filaments of dark matter that weave their way through vast cosmic voids. Some of the features it shows are cosmological walls, also known as galaxy walls. They’re massive features, and one of them — a wall called the Hercules-Corona Borealis Great Wall — is the largest known structure in the Universe, stretching 10 billion light-years across.

This image of TNG 50 shows the large-scale structure of cosmic gas in the early Universe at redshift three.  It shows a region of space 15 megaparsec across, where the cosmic web of gas filaments converge to drive galactic formation and growth.  Image credit: Illustris TNG 50.
This image of TNG 50 shows the large-scale structure of cosmic gas in the early Universe at redshift three. It shows a region of space 15 megaparsec across, where the cosmic web of gas filaments converge to drive galactic formation and growth. Image credit: Illustris TNG 50.

Cosmological walls are made up of galaxies. It is a subtype of filaments, but they are flattened and have cavities on both sides. The voids seem to squeeze the walls into their flattened shape. The cosmological wall closest to the Milky Way is called the Local Wall or Local Leaf.

The Local Sheet affects how the Milky Way and other nearby galaxies rotate on their axis. The Milky Way takes about 250,000,000 years to rotate, and the study shows that the rotation is more organized than if the galaxy were away from the Local Sheet.

The research also shows that the Milky Way is special. While typical galaxies are often much smaller relative to walls, the Milky Way is surprisingly massive relative to the Local Wall. According to the research, this is a rare cosmic event.

This video is from Illustris TNG 50 showing the formation of an elliptical galaxy. Credit: Illustris TNG

A feature that cosmologists study is speed spread. It describes how much spread there is in the speed of a group of astronomical objects. The speeds are spread around an average speed. The speed of objects near the Milky Way/Local Wall has a low spread, meaning they are not far from the average.

Must Read
Can weightlessness harm the drugs astronauts take in space?

This is unusual for a high-mass galaxy like the Milky Way in an environment like this close to the Local Wall. To better understand this, the researchers searched for Milky Way Analog (MWA) galaxies in Illustris TNG 300.

They found that MWAs in Local-Sheet analogs are rare. There was only one per 160–200?Mpc3 volume in the simulation. With their research they showed that the cold environment around the Local Leaf is responsible for this. “We find that a plate-like cold environment preserves, amplifies or simplifies environmental effects on the angular momentum of galaxies,” they write in their paper.

The Local Sheet in particular influences the rotation of the Milky Way. “…there are particularly strong alignments between the leaf spins and the galaxies,” they explain, adding that in the simulation, the galaxies near walls have low spin parameters.

This all affects how galaxies grow and merge over time, they think. It leads to less massive galaxies in these kinds of cosmic neighborhoods. That is why the Milky Way, with its high mass, is so unusual and why the simulation found only one in a space of up to 200 cubic megaparsecs.

This figure from the study shows how velocity dispersal relates to mass, with mass shown on the x-axis. The legend in the upper right shows how each line in the graph represents a different velocity dispersal (sigma v.) The blue solid line is the mass function in cold (<25, high velocity dispersal) regions, and the black solid line is the mass function in warm (<40, low velocity dispersal) regions. The dotted lines are the same, but for regions near Cosmic Walls. It shows how lower velocity dispersal produces less massive galaxies near walls. There are also two shaded grey areas: light and dark grey. The light area represents the masses of Milky Way Analogues in the simulation, and the dark grey shows where the Milky Way actually is. Image Credit: Aragon et al. 2023.
This figure from the study shows how velocity dispersion relates to mass, with mass shown on the x axis. The top right legend shows how each line in the graph represents a different velocity dispersion (sigma v.) The blue solid line is the mass function in cold (<25, high-velocity dispersal) regions, and the black solid line is the mass function in warm (<40, low-velocity dispersion) regions. The dotted lines are the same, but for regions near Cosmic Walls. It shows how lower-speed dispersion produces less massive galaxies near walls. There are also two shaded gray areas: light gray and dark gray. The light area represents the masses of Milky Way analogues in the simulation, and the dark gray indicates where the Milky Way actually is. Image credit: Aragon et al. 2023.

The study reminds us of something crucial: context matters. If we look at the Milky Way as a separate object and compare it with other similar separate objects, it does not seem to be exceptional. But in relation to its environment it is. Our results emphasize the importance of carefully characterizing the environment around our galaxy. “The effect of Local Sheet environment geometry and cold on angular momentum processes may help us better understand current problems in galaxy formation…”

In a press release presenting the study, the authors refer to the Copernican bias. “This bias, which describes the successive removal of our special status in the nearly 500 years since Copernicus relegated the Earth from the center of the cosmos, would arise from the assumption that we reside in a completely average place in the universe,” said the press. release says. It shows the risk inherent in ignoring the environment of an object under study.

This work also shows a potential flaw in how scientists use simulations such as Illustris TNG. It is misleading to think that every point in the simulation is the same as every other point. Galaxies close to a cosmic wall can evolve very differently than at other points.

“So the Milky Way is special in a way,” says study leader Miguel Aragón. “Earth is obviously special, the only home of life we ​​know. But it is not the center of the universe or even the solar system. And the sun is just an ordinary star among billions in the Milky Way. Even our galaxy seemed to be just another spiral galaxy among billions of others in the observable universe.”

“The Milky Way has no particularly special mass or type. There are many spiral galaxies that look something like this,” said Joe Silk, another researcher. “But it is rare if you take the environment into account. If you could easily see the nearest dozen large galaxies in the sky, you would see that almost all of them lie on a ring embedded in the Local Sheet. That in itself is a bit special. What we recently discovered is that other galaxy walls in the Universe, such as the Local Sheet, very rarely seem to contain a galaxy as massive as the Milky Way.”

Spiral galaxies are common.  This image shows six spectacular spiral galaxies in images taken with ESO's Very Large Telescope (VLT) at Paranal Observatory in Chile.  Credit: ESO
Spiral galaxies are common. This image shows six spectacular spiral galaxies in images taken with ESO’s Very Large Telescope (VLT) at Paranal Observatory in Chile. Credit: ESO

“You may have to travel half a billion light-years from the Milky Way, past many, many galaxies, to find another cosmological wall with a galaxy like ours,” Aragón said. He adds: “That’s a few hundred times further away than the nearest major galaxy to us, Andromeda.”

So is it okay if we feel special again? We’re obviously special because we’re alive, and most of the matter we can see isn’t. But that doesn’t necessarily tell us how much other matter is still alive and whether we’re special. From a vantage point elsewhere in the universe, there could be a lot more living matter. Before the advent of modern astronomy, we had no idea if there was life elsewhere or how special Earth might be. We are wise to be careful with the word specialsaid one of the authors.

“However, you have to be careful about choosing properties that qualify as ‘special,’said Dr. Mark Neyrinck, another member of the team. “If we added a ridiculously restrictive condition to a galaxy, like that it must contain the paper we wrote about it, we would certainly be the only galaxy in the observable universe to do so. But we think this is ‘too big for his wall’ property is physically meaningful and perceptibly relevant enough to call it truly special.’

More:

NO COMMENTS

LEAVE A REPLY

Please enter your comment!
Please enter your name here