Researchers have developed conditions like those inside gigantic galaxy clusters in a lab and this is allowing scientists to answer many questions that haven’t been answered till date.
One of the most puzzling questions pertains to why the hydrogen gas in galaxy clusters is searingly hot—about 10 million degrees Kelvin, or roughly the same temperature as the center of the sun—which is so hot that hydrogen atoms cannot exist. Instead the gas is a plasma consisting of protons and electrons. Scientists say that there isn’t a straightforward explanation as according to normal physics the gas should have cooled within the age of the universe. But it hasn’t.
The challenge for anyone trying to solve this puzzle is that you can’t exactly create these kinds of powerfully hot and magnetic conditions in your backyard.
However, there is now one place on Earth where you can: the most energetic laser facility in the world. The National Ignition Facility at Lawrence Livermore National Laboratory is able to create such extreme conditions—though only for a tiny fraction of a second in a volume the size of a dime.
Scientists from UChicago, the University of Oxford, and the University of Rochester worked together to use the National Ignition Facility—located in Livermore, California—to create conditions similar to the hot gas in gigantic galaxy clusters.
“The experiments conducted at the NIF are literally out of this world,” said Jena Meinecke, who was the first author on the paper.
The scientists focused 196 lasers onto a single tiny target, creating a white-hot plasma with intense magnetic fields that exists for a few billionths of a second.
This was long enough for them to determine that instead of a uniform temperature, there were hot and cold spots in the plasma.
This dovetails with one of the theories that has been proposed for how heat is trapped inside galaxy clusters. Normally, heat would be easily distributed as electrons collide with each other. But the tangled magnetic fields inside the plasma can affect these electrons, causing them to spiral along the direction of magnetic fields—which can prevent them from evenly distributing and dispersing their energy.
In fact, in the experiment they saw that the conduction of energy was suppressed by more than a factor of 100.
The simulations were done with a computer code called the FLASH codes, which was developed at the University of Chicago and is now hosted at the University of Rochester’s Flash Center for Computational Science, which is led by Tzeferacos. The code allows scientists to simulate their laser experiments in exquisite detail before they do them, so that they can achieve the results they seek.
This is critical because the scientists only get a precious few shots at the facility—if something goes wrong, there’s no redo. And because the experiment conditions only last nanoseconds, the scientists have to make sure they make the measurements they need at exactly the right time. This means everything has to be precisely plotted out far ahead of time.