New observations show that magnetic fields in galaxies are 14 billion times stronger than assumed. Ingenious calculations explain why it is so powerful.
Magnetic fields are not unique to Earth. They're everywhere. Also in galaxies. Galaxies are huge clusters of stars. There are more than 200 billion galaxies in the universe. Each consists of a few million to several trillion stars.
It turns out that magnetic fields in galaxies are surprisingly strong, and must have been strong when the galaxies were young.
How magnetic fields arise and evolve has a lot to say about what the universe looks like today.
Knowledge of magnetic fields is important for understanding black holes, cosmic radiation, and how stars form and collapse, says Robert Wessing, a postdoctoral fellow in cosmology in the Department of Theoretical Astrophysics at the University of Oslo (UiO).
In his doctoral thesis, he developed completely new methods for studying magnetic fields in galaxies. His calculations show how magnetic fields in galaxies are strengthened, and why magnetic fields are stretched, twisted, and bent.
It's not easy to search
Unfortunately, searching for galaxies is not easy. If Vissing could have experimented with galaxies in a real laboratory and observed what happens over time, he would have gotten the most accurate answers. But this is unfortunately not realistic. Galaxies occupy a huge amount of space. The Milky Way Galaxy alone is more than 100,000 light-years across. Such large laboratories do not exist.
It's no easy feat that Vissing wants to study how magnetic fields in galaxies have evolved from the time they were created and three billion years in the future. No researcher has that much time, not even one as young as Wessing, who still has forty years left in his career.
Extensive simulations
Therefore he had to use a completely different scientific method. He used simulation. Simulation allows you to experience reality on a computer.
-You simulated how magnetic fields in galaxies evolve over time.
There are many different simulation models. Wessing created a digital model. This model uses numerical analysis to find approximate solutions to a set of mathematical equations that cannot be solved exactly.
– We discovered that magnetic fields develop very quickly in galaxies. Here we are talking about a hundred million years. That's very fast in galactic time. Magnetic fields are 14 billion times stronger than astrophysicists previously thought.
Successful theory
His question is how could that happen.
There was no shortage of theories.
One of them is the dynamo theory.
Dynamo theory is about the conversion from kinetic energy to magnetic energy. And for those who have suppressed your physics knowledge from school: kinetic energy is the energy an object has due to its speed. Magnetic energy is the energy contained in a magnetic field.
There are different types of dynamo theory.
Some people assume that turbulence can be very effective in converting kinetic energy into magnetic energy.
When Wessing incorporated the dynamo's own mathematics into his models, he obtained simulations that matched current observations.
He also looked at the different stages in the evolution of magnetic fields.
First, magnetic fields must be formed. There are many theories about this. The formation occurred right after the Big Bang or when the first stars formed.
At a later stage, Wessing was able to prove that the magnetic fields were well organized. All spiral arms in galaxies move in the same direction.
– With the help of the rotation of galaxies, magnetic fields can be arranged in this way.
Heavy duty calculator
Simulation is not trivial. Wessing simulated how the magnetic field in 40 galaxies changed over three billion years. These galaxies are of the same type as the Milky Way – our galaxy.
The simulations were performed on a National Sigma2 heavy computing machine. Although Wessing performed the calculations on a thousand parallel processors, it took a full month to run the program. Without a heavy calculator, the simulation would have taken 83 years.
In the next run, Wessing will simulate many different types of galaxies in the sling. Then it needs access to 10,000 parallel processors. If he did not improve the program further, new simulations would take years of the calculator's heavy computing power. So Wessing is exploring how to perform simulations using faster numerical methods.
This fall, Wessing received the Yara Birkeland Award for her work. The award committee described his research as “an important contribution to theoretical astrophysics” and “a valuable contribution to understanding the dynamics around the galactic magnetic field and black holes.” This is the first time that the Yara Birkeland Prize has been awarded to a research fellow at the Institute of Astrophysics at UiO.
This article was first published in Forskningsmagasinet Apollon. is reading The original is here.
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