Two new computer simulations are providing detailed insights about the cosmos, shedding light on dramatic star explosions and the Big Bang that created the universe nearly 14 billion years ago.
Scientists spoke about the independent models at a news conference last month at a meeting of the American Physical Society in Savannah, Georgia. One simulation models some of the most energetic explosions in the universe in three dimensions for the first time, revealing why some produce black holes and oddly shaped clouds of material. You can watch an animation on how supernovas mark black holes on Space.com.
"We believe this could cause some of the asymmetries astronomers see when they observe supernova remnants," Christian Ott of the California Institute of Technology said at the conference. Ott worked with a team of scientists led by Philipp Mösta, also of CalTech. [Supernova Photos: Great Images of Star Explosions]
The other simulation provides an amazing detailed map of the growth and development of the universe since it burst into existence with the Big Bang 13.8 billion years ago.
"At the end, we got a simulated universe, and it's something we can compare to observations," Rupert Croft of Carnegie Melon said. Croft was part of a team led by Nishikanta Khandai of the Brookhaven National Laboratory in New York.
Stars with masses ranging from 10 to 100 times more than the sun can end their lives in violent explosions known as supernovas. The expelled material creates beautiful objects known as supernova remnants (SNRs), combinations of stellar material and shock waves pushing outward through space. Most supernova remnants are fairly spherical, but some, such as SNR W49B, are oddly shaped.
Until now, models of these explosions have remained two-dimensional, producing results that can dramatically differ from observations. A new model that focuses on the interactions of the magnetic field with the supernova creates a less symmetrical result similar to several SNR that have been seen in the universe.
"We're trying to understand how some of the most energetic explosions in the universe work," Ott said. "For the first time, we're able to simulate it in three dimensions."
According to the new simulation, a rapidly spinning star with a collapsing strong magnetic field will find its field lines getting wound up around the spin axis. The wound-up field becomes unstable due to a process known as "kink instability," in which the magnetic forces within the plasma become uneven, with the forces on the interior growing larger than those on the exterior.
Initially, inward-pressing gas dominates the star, but over time the magnetic field grows stronger. Regions of high magnetic pressure begin to press outward, ultimately causing the star to explode.
In previous two-dimensional models, jets of streaming material drive the explosion, pushing outward symmetrically along the axes. But the more detailed 3D models show the magnetic fields disrupting and fizzling the jets, creating a wide, double-lobed flow.
Such explosions may be more likely to leave behind a black hole rather than the dense neutron star scientists suspect is created by most core-collapse supernovae. In these more common, less-extreme cases, the magnetic field plays a minimal role in the stellar explosion.
The process itself isn't unfamiliar, but the application to a supernova is.
"This is physics we're familiar with," Ott said. "It's just the first time we've seen it in a supernova because we've been able to simulate it in three dimensions."
The findings were published in the Astrophysical Journal Letters.
The complexity surrounding the evolution of the universe can make modeling the process a daunting task. But a new simulation resolves the growth of the universe down to the smallest galaxies, making it the most detailed of its kind.
The new model also supports the idea that the universe grew incredibly quickly shortly after its birth, expanding faster than the speed of light during a period of dramatic cosmic inflation.
"We'd like to simulate the whole universe, and we started with the Big Bang," Croft said. [The Big Bang to Now in 10 Easy Steps]
It took about 45 million core hours on a supercomputer for the simulation to map out the basic evolution of the universe. Scientists can compare the millions of galaxies produced in the simulation to those that exist in the known universe, finding a statistical measurement of those objects and others. They can also study the universe at various stages in its growth.
Scientists ran the first full simulation of the evolution of the universe in the late 1970s, with several following in the years since. Each model improved as knowledge about the universe grew — original models didn't include supermassive black holes or dark matter, for instance, because scientists didn't know of their existence.
Evolving technology allowed for greater detail to be examined in each subsequent study. The first paper could only create super-clusters of galaxies. The latest model shows just how far the process has come.
"We're actually able to resolve the tiniest galaxies that we can see," Croft said, referring to dwarf galaxies, which contain less than 1 percent as many stars as the Milky Way.
The simulations are available online, and more than 2,000 scientists have already put them to use, downloading them for a variety of research projects.
By comparing the results of the simulation with observational evidence, scientists can get an understanding of how well the theories that went into the simulation function when forming a universe.
Croft emphasized the model's role when it comes to understanding inflation. If inflation did not play a significant role in the evolution of the universe, the result should have been widely different from the universe observed today. Instead, the theoretical model matches up fairly well with reality.
"This shows us very directly that inflation seems to be correct," Croft said.
When paired with recent findings on primordial gravity waves, the case for inflation seems very strong.
"We don't have to investigate other ways of making our initial conditions," Croft said. "This simulation seems to fit the conditions fairly well."
The findings have been submitted for publication to the Monthly Notices of the Royal Astronomical Society and are available online as well.
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