Spiral galaxy M 51 with magnetic field data. Credit: MPIfR Bonn
The origin of magnetic fields in our universe is a mystery. But magnetic fields are a key part of the interstellar medium and scientists are finding they may play a major role in galactic formation, such as helping to form the spiral arms of galaxies. Until recently, however scientists believed the strength of galactic magnetic fields increased over time as galaxies matured, and in the early universe, these magnetic fields were initially very weak. But, recently a team of scientists looking back to probe the ancient universe as it existed 8 to 9 billion years ago has found that the magnetic fields of ancient galaxies were just as strong as they are today, prompting a rethinking of how our galaxy and others may have formed.
Using the European Southern Observatory’s 8-meter telescope located in Chile, a team of scientists from the Los Alamos National Laboratory and the Swiss Federal Institute of Technology studied 70 galaxies similar to the Milky Way at optical wavelengths. They combined their data with 25 years of radio wave observations of magnetic fields that measured how far the radio waves were pulled toward the red end of the spectrum, known as “redshift” using Faraday rotation measures.
Serving as a looking glass into the past, the powerful telescope at the European Southern Observatory, adding to the radio rotation measures, allowed the scientists to observe surprisingly high magnetic fields between 8 billion and 9 billion years ago in the 70 galaxies studied. That means that several billion years before the existence of our own sun, and within only a few billion years of the Big Bang, ancient galaxies were exerting the tug of these strong magnetic fields.
“It was thought that, looking back in the past, earlier galaxies would not have generated much magnetic field,” said Philipp Kronberg of LANL. “The results of this study show that the magnetic fields within Milky Way-like galaxies have been every bit as strong over the last two-thirds of the Universe’s age as they are now-and possibly even stronger then.”
Astronomers had thought a mechanism called a dynamo, which transfers mechanical energy into magnetic energy was responsible for galactic magnetic fields. In that case, with the right configuration gas flow could generate a higher magnetic field from a weaker seed field. (Again, we have yet to understand how galactic magnetic fields originally form.) But this new research suggests that the magnetic fields in galaxies did not arise due to a slow, large-scale dynamo effect, which would have taken 5 billion to 10 billion years to reach their current measured levels.
“There must be some other explanation for a much quicker and earlier amplification of galactic magnetic fields,” Kronberg said. “From the time when the first stars and galaxies formed, their magnetic fields have probably have been amplified by very fast dynamos. One good possibility is that it happened in the explosive outflows that were driven by supernovae, and possibly even black holes in the very earliest generations of galaxies.”
This realization brings a new focus on the broader question of how galaxies form. Instead of the commonly held view that magnetic fields have little relevance to the genesis of new galaxies, it now appears that they are indeed important players. If so, strong magnetic fields a long time ago are one of the essential ingredients that explain the very existence of our galaxy and others like it.
Original News Source: Los Alamos National Lab
