Simulating Galaxies

Physicists Just Created the Most Detailed Simulation of the Universe in History

The centers of massive galaxy clusters are super hot (red), while bright structures show diffuse gas from the intergalactic medium shock heating at the boundary between cosmic voids and filaments. 

The centers of massive galaxy clusters are super hot (red), while bright structures show diffuse gas from the intergalactic medium shock heating at the boundary between cosmic voids and filaments.
(Image: © TNG Collaboration)

The formation of galaxies is a complex dance between matter and energy, occurring on a stage of cosmic proportions and spanning billions of years. How the diversity of structured and dynamic galaxies we observe today arose from the fiery chaos of the Big Bang remains one of the most difficult unsolved puzzles of cosmology.

In search of answers, an international team of scientists has created the most detailed large-scale model of the universe to date, a simulation they call TNG50. Their virtual universe, some 230 million light-years wide, contains tens of thousands of evolving galaxies with levels of detail previously seen only in single-galaxy models. The simulation tracked more than 20 billion particles representing dark matter, gases, stars and supermassive black holes, over a 13.8-billion-year period.

The unprecedented resolution and scale allowed the researchers to gather key insights into our own universe’s past, revealing how various oddly shaped galaxies morphed themselves into being and how stellar explosions and black holes triggered this galactic evolution. Their results are published in two articles to be featured in the December 2019 issue of the journal Monthly Notices of the Royal Astronomical Society

TNG50 is the latest simulation created by the IllustrisTNG Project, which aims to build a complete picture of how our universe evolved since the Big Bang by producing a large-scale universe without sacrificing the fine details of individual galaxies.

“These simulations are huge datasets where we can learn a ton by dissecting and understanding the formation and evolution of galaxies within them,” said Paul Torrey, associate professor of physics at the University of Florida and co-author of the study. “What’s fundamentally new about TNG50, is that you’re getting to a sufficiently high mass and spatial resolution within the galaxies that give you a clear picture of what the internal structure of the systems looks like as they form and evolve.”

The model’s attention to detail comes at some cost. The simulation required 16,000 processor cores of the Hazel Hen supercomputer in Stuttgart, Germany, running continuously for more than a year. The same calculation would take a single processor system 15,000 years to compute. Despite being one of the most computationally heavy astrophysical simulations in history, the researchers believe their investment has paid off.

“Numerical experiments of this kind are particularly successful when you get out more than you put in,” Dylan Nelson, a postdoctoral fellow at the Max Planck Institute for Astrophysics in Munich, Germany, and co-author of the study, said in a statement. “In our simulation, we see phenomena that had not been programmed explicitly into the simulation code. These phenomena emerge in a natural fashion, from the complex interplay of the basic physical ingredients of our model universe.”

The violent simulated birth of a galaxy cluster where dark matter structures (in white) merge together while supermassive blackholes and supernovae expel cosmic gas away (gas motion is shown in red).

The violent simulated birth of a galaxy cluster where dark matter structures (in white) merge together while supermassive blackholes and supernovae expel cosmic gas away (gas motion is shown in red). (Image credit: TNG Collaboration)

That emergent phenomenon might be essential to understanding why our universe appears as it is today 13.8 billion years after the Big Bang. TNG50 allowed researchers to see firsthand how galaxies may have emerged from the turbulent clouds of gas present shortly after the universe was born. They discovered that the disk-shaped galaxies common to our cosmic neighborhood naturally emerged within their simulation and produced internal structures, including spiral arms, bulges and bars extending from their central supermassive black holes. When they compared their computer-generated universe to real-life observations, they found their population of galaxies were qualitatively consistent with reality

As their galaxies continued to flatten into well-ordered rotating disks, another phenomenon began to emerge. Supernova explosions and supermassive black holes at the heart of each galaxy created high-speed outflows of gas. These outflows morphed into fountains of gas rising thousands of light-years above a galaxy. The tug of gravity eventually brought much of this gas back unto the galaxy’s disk, redistributing it to its outer edge and creating a feedback loop of gas outflow and inflow. Apart from recycling the ingredients for forming new stars, the outflows were also shown to change their galaxy’s structure. The recycled gases accelerated the transformation of galaxies into thin rotating disks.

Despite these initial findings, the team is far from finished dissecting their model. They also plan to release all of the simulation’s data publicly for astronomers across the world to study their virtual cosmos.

“There’s a huge road ahead of us now that we have these simulations completed,” Torrey said. “A whole team of researchers are working to better understand the detailed properties of the galaxies that form and what emergent trends show up in that data.”

Originally published on Live Science.


On Sacred Story & Worldview

Sacred Story for Our Time

Is it possible that the human future depends upon a new sacred story—a story that gives us a reason to care? Could it be a story already embraced by a majority, although it has neither institutional support nor a place in the public conversation?
Cosmology Essay Cover Photo

Photo by Kohy.

“For people, generally, their story of the universe and the human role in the universe is their primary source of intelligibility and value,” Thomas Berry wrote in The Dream of the Earth. “The deepest crises experienced by any society are those moments of change when the story becomes inadequate for meeting the survival demands of a present situation.”

The challenge before us is to create a new civilization based on a cosmology—a story of the origin, nature, and purpose of creation that reflects the fullness of our current human knowledge.

We live at such a moment. Humanity’s current behavior threatens Earth’s capacity to support life and relegates more than a billion people to lives of destitution. This self-destructive behavior and our seeming inability to change have deep roots in the stories by which we understand the nature and meaning of our existence. The challenge before us is to create a new civilization based on a cosmology—a story of the origin, nature, and purpose of creation—that reflects the fullness of our current human knowledge; a story to guide us to mature relationships with one another and a living Earth.

Three Cosmologies

Three distinct cosmologies have each had their influence in shaping the Western worldview. Two are familiar. The third—and most relevant to the task at hand—has ancient roots, and may in one form or another be the most widely held. It has virtually no public presence.

MichelangeloThe cosmos is created and ruled by a Distant Patriarch. This is the cosmology most commonly associated with the institutions of Judaism, Christianity, and Islam. It views creation as the work of an all-knowing, all-powerful God. From his home in a separate, sacred dimension called Heaven, He observes and judges our obedience to His commandments handed down to us through sacred texts and interpreted by His anointed religious authorities.

This cosmology focuses attention on our individual relationship with a personal but distant God, as expressed in Michelangelo’s famous rendering of a God portrayed in the image of man. By implication, our human relationships with one another and with nature are secondary to this primary relationship. Although some adherents believe that we have an obligation to care for God’s creation in this life and to show compassion to our fellow human beings, in many interpretations of the Distant Patriarch story, life on Earth is but a way station on the path to paradise. Nature exists for our temporary human use and comfort. Those who demonstrate their closeness to God by their pious religious observance and special knowledge of His intention properly exercise authority over the rest of us.


Photo by QQ7.

The cosmos is a Grand Machine.
This is the cosmology commonly associated with science. It is the standard story of Newtonian physics, evolutionary biology, and the institutions of secular academia. In this cosmology only the material is real. The formation and function of the cosmos and the evolution of life are consequences of a combination of physical mechanism and random chance. Life is an accidental outcome of material complexity and has no larger meaning or purpose. Consciousness and free will are illusions.

By this reckoning, the cosmos is much like a mechanical clock-works gradually running down as its spring unwinds. Building on the mechanistic determinism of classical physics, classical biology holds that life evolves through a combination of chance genetic mutation and a competitive struggle by which the fitter survive and flourish as the weaker perish.

According to the Grand Machine cosmology, a brutal competition for survival, territory, and reproductive advantage is the basic law of nature, and these same instincts define our human nature. Indeed, as economists of a social Darwinist perspective assure us, our competitive instinct is the primary and essential driver of human prosperity and progress. The defining debate turns on the question of whether this instinct best serves society when free from government interference or when guided by public regulation and incentives.

3. Integral Spirit

Photo by zroakez.

The cosmos is a manifestation of Integral Spirit.
This cosmology has ancient roots and a significant modern following, but lacks institutional support and public visibility. By its reckoning, all of creation is the expression of an integral spiritual intelligence engaged in a sacred journey to discover and actualize its possibilities through an ongoing process of becoming. Our world and the material universe of our experience are more than God’s creation—they are God made flesh. God is in the world and the world is in God, yet they are not identical. Although the spirit is imminent, it is also transcendent, a concept religious scholars refer to as panentheism.

Brain scientists tell us the human brain evolved to reward cooperation, service, and compassion.

We come to know the nature, purpose, and intention of this divine force through both our inner experience and our observation of its physical manifestation. All beings, stars, planets, humans, animals, plants, rocks, and rivers are expressions of this divine force—each with its place and function in the journey of the whole.

Contrary to prevailing theories of social Darwinism, the Integral Spirit cosmology recognizes that life is a fundamentally cooperative enterprise.

Indigenous wisdom keepers speak of the creator’s original instructions to humans to get along with one another and nature. Brain scientists tell us the human brain evolved to reward cooperation, service, and compassion—suggesting that the creative processes of evolution have programmed these original instructions into our brains and DNA.

Extreme individualism, greed, and violence are pathological and signs of physical, developmental, cultural, and/or institutional system failure. Caring relationships are the foundation of healthy families and communities. The Golden Rule common to all major faiths is a better guide to appropriate moral behavior than mechanistic rules are.

The Integral Spirit cosmology postulates that we humans participate in and contribute to the divine journey. We can apply our distinctive capacities for reflective consciousness and choice either to advance creation’s evolutionary thrust toward ever more creative possibility, or to disrupt it. Together, our individual choices determine our collective fate and shape the course of the journey far beyond our time.

We find threads of this story in the traditional wisdom teachings of indigenous peoples and the mystical traditions of all faiths, including the Abrahamic faiths. In his expression of his Jewish faith, Jesus taught, “The Kingdom is within.” Muhammad taught, “Wherever you turn, there is the Face of Allah.”

The Integral Spirit cosmology is consistent with the findings of quantum physics, which reveals that the apparent solidity of matter is an illusion and at the deepest level of understanding only relationships are real. I find that Integral Spirit is the underlying cosmology of a reassuring number of religious leaders and devout members of many faiths, including a great many Catholic nuns, as well as most people who define themselves as spiritual, but not necessarily religious.

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Black Holes Before the Big Bang? New Theory

“Some Primordial Black Holes Have Existed Before the Big Bang” — A Radical Theory Proposed



In recent years, cosmologists have begun to think seriously about processes that occurred before the Big Bang. Alan Coley from Canada’s Dalhousie University and Bernard Carr from Queen Mary University in London, published a paper in 2011, where they theorized that some so-called primordial black holes might have been created in the Big Crunch that came before the Big Bang, which supports the theory that the Big Bang was not a single event, but one that occurs over and over again as the Universe crunches down to a single point, then blows up again.

In some circumstances, they say, black holes of a certain mass could avoid this fate and survive the crunch as separate entities. The masses for which this is possible range from a few hundred million kilograms to about the mass of our Sun.

The theory is based on the fact that the Earth, and the rest of the known Universe is occasionally bombarded with unexplained bursts of gamma rays — something that could, according to Coley and Carr, be the result of primordial black holes running out of energy and disintegrating. These small black holes ought to evaporate away in relatively short period of time, finally disappearing in a violent explosion of gamma rays. Some cosmologists say this thinking might explain the gamma ray bursts that we already see from time to time.

Primordial black holes are thought to be of a different type than the regular kind that are formed when a supernova occurs but rather formed in the first “moments” after the Big Bang. Primordial black holes would be smaller and created by the energy of the Big Bang itself and would then have been widely dispersed as the Universe expanded.

In their theory, however, Coley and Carr suggest that some of these black holes, if they actually exist, might have been created by the collapsing Universe as part of the Big Crunch, and then somehow escaped being pulled into the pinpoint singularity comprised of everything else. And then, after the Big Bang, they simply assimilated with the newly formed Universe.

A key problem they agree on is that it would likely be impossible to tell the difference between pre- and post Big Bang primordial black holes.

The theory raises major questions for cosmologists: if the Universe contracts, then blows up, over and over, has this gone on forever? Or is it possible that our view of the Universe is so limited that we’re only seeing one tiny fraction of it, and thus, any theories or explanations we offer, are little more than guesses.

Image at the top of page shows co-orbiting supermassive black holes powering the giant radio source 3C 75. Surrounded by multimillion degree x-ray emitting gas, and blasting out jets of relativistic particles the supermassive black holes are separated by 25,000 light-years. At the cores of two merging galaxies in the Abell 400 galaxy cluster they are some 300 million light-years away.
Such spectacular cosmic mergers are thought to be common in crowded galaxy cluster environments in the distant Universe. In their final stages the mergers are expected to be intense sources of gravitational waves.

More information: Persistence of black holes through a cosmological bounce, B. J. Carr, A.A. Coley, arXiv:1104.3796v1 [astro-ph.CO]

The Daily Galaxy via MIT Technology Review

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