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Galaxy Simulations Are at Last Matching Reality

by Alice Turner 4 years ago in space
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Producing Surprising Insights Into Cosmic Evolution

Since the earliest days of computers, scientists have looked into their potential for simulating the cosmic processes that led to the creation of the near limitless amounts of galaxies in the observable universe. The shortcomings of previous computer technology limited their practical applications in this regard. However, thanks to the levels of processing power offered by modern computer hardware, along with refinement in algorithm scripting, simulations are reaching a point where they can begin to accurately replicate the mathematical values involved with the development of an individual galaxy. What’s more is that computer technology is advancing exponentially, meaning that progress is accelerating at a truly impressive rate.

Run the Numbers

As these galactic simulations improve, they’re developing a new role in cosmic research. Whereas before information would flow in one direction from astronomers’ studies of real galaxies to the programmers trying to model them, these simulations can now provide astronomers with fresh insights into the development of real cosmic bodies, allowing predictions to make up for the shortcomings of the observation process. Such developments offered by the latest modeling have shown that the earliest galaxies took on a peculiar pickle-like shape; that thin spiral-shaped galaxies show surprising resilience in the face of collisions; and that galaxies form stars at a much slower rate than scientists researching the universe’s evolution previously suspected.

Mapping the Stars

The simulations also provide cosmologists with the pause for thought. Many in the community hope that the processes fuelling galaxy formation will be relatively straightforward, governed by a few core principles of astrophysics. However, simulations suggest that a galaxy’s development is a much more complicated business than previously suggested and that understanding the factors behind accounts for the formation of an individual galaxy’s structure will be a lot more arduous than previously thought.

The Modeler’s Guide to the Galaxy

According to current scientific thought, the universe is comprised out of three basic parts: 5 percent physical matter of the kind that comprises planets and stars; 26 percent dark matter that appears to be governed solely by gravity and made from a particle that it hasn’t yet been possible to detect; the remaining 69 percent is thought to be some form of energy that stretches space and governs the expansion and contraction of the universe, and there is speculation that this dark energy may be a function of the vacuum of space itself. At the moment of the big bang, the universe expanded outwards in ripples of roiling subatomic particle activity, followed by the gradual coalescence of regions of dark matter moving under their own gravity. This in turn attracted gas that formed into clumps, known as haloes, which eventually condensed into hydrogen stars. Roughly 500 million years after the big bang, the first galaxies had formed. The following 13 billion years would see them drift along tides of cosmic gravity and slowly merge amongst themselves.

Dark Matters

That we know all this is partly through the aid of computer simulations. In the 1980s, they aided with the development of dark matter theory, which developed in parallel with advances in modeling. Drawbacks began to make themselves apparent, however. Milestone simulations like Millennium helped map the effect of dark matter on haloes, but failed to calculate the way haloes could impact the behaviour of dark matter. The simulations of today are starting to take these concerns into account, and attempt to simulate the forces of heat, light, and radiation that normal matter generates under pressure, in addition to the gravitic influence it shares with its dark counterpart. These physics have to be modeled using equations of hydrodynamics, which are incredibly difficult to calculate, even with the assistance of the most powerful supercomputers.

Trial and Error

Modelers tend to approach these problems by breaking the problem down to the smallest possible parts and then run interactions of the separate elements with each other through incredibly high volumes of permutations to simulate the impact of these effects over millions of years. Unfortunately, the process strains the computing abilities of even the most powerful supercomputers, but today, the latest models have come closer than ever to producing accurate models of cosmic development. Hydrodynamic simulations have begun generating the correct amount of galaxies, themselves of the right size and shape: spiral disks, spherical dwarfs, and squat ellipticals, amongst others.

The Life of a Galaxy

The simulations show that galaxies tend to go through certain distinct phases in their development. Young galaxies thunder with activity as the clash and merge with each other, causing frantic bursts of star formation, and it’s this period that is particularly fiendish for modelers to attempt to map. After a few billion years, activity subsides and galaxies tend to stabilise, and much later they start entering a phase of old age where the number of gas drops and stars stop being born.

Missing Galaxies

Currently, simulations are a long way from being able to accurately replicate phenomenally complex models like individual star development, but they are instructive in calculating the impact of feedback effects like black holes and have already overturned many prior assumptions about the behaviour of galaxies: astrophysicists had previously assumed that gas enters an expanding galaxy equally from all directions, but simulations show that gas actually flows into a galaxy along waves of dark matter running through the halo. Simulations have been especially useful in filling in the gaps about our understanding of the many enigmas of the behaviour of dark matter. The “missing satellites” problem was one such conundrum: some of the earliest simulations suggested that smaller dark matter haloes spawn in the wake of larger ones, meaning that our galaxy should be in proximity to a high number of orbiting dwarf galaxies, but only a handful was ever detected. Later, more sophisticated simulations took into account the influences of ordinary matter, with its significant gravitational effect, on the scenario, showing how it could compromise a halo’s integrity and cause gas to evacuate, gutting a young galaxy and leading to its structural collapse. Lo and behold, the missing satellites problem is a problem no more.

Predicting a Universe

Perhaps the most significant lesson scientists can take away from the findings of simulations is not that their broader understanding of cosmology needs to be revised from the ground up, but rather that the biggest roadblocks to understanding lie in their grasp of astrophysics at smaller scales, especially with regards to star formation. The end goal for many modelers is to reduce their reliance on the trial-and-error tuning of the parameters of their modeling and work with astrophysicists to ground their models more concretely in the laws of physics. To do this, simulations must be scaled down significantly. Some researchers believe this will eventually lead to the discovery of a unified law of galactic physics based solely on mass and radius, while others feel that accurate modeling will always be a hotchpotch of subjectively understood variables with a heavy dose of doubt, much like the modern process of attempting to generate an accurate weather forecast. Whatever the case, mutual cooperation between modelers, researchers like Elon Musk with his SpaceX and Max Polyakov with newly relaunched Firefly Aerospace, or astrophysicists like Stephen Hawking and Carl Sagan is likely to be the fastest path to humanity acquiring a greater understanding of the stars.


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Alice Turner

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