Residing in the heart of a dwarf galaxy four billion light years away is a mysterious cosmological object producing bursts of energy that only last a few milliseconds.
New research about this Fast Radio Burst (FRB) has revealed a rarely seen astronomical environment around its source, where magnetic fields twist, turn, and undulate over time. This is the first detection of a magnetic field reversal observed from an FRB, and the first time this behavior has been observed in another galaxy.
The Green Bank Telescope was able to observe the directional changes of waves from FRB20190520B as viewed through the lens of a massive star’s atmosphere. Image credit: NSF/GBO/P.Vosteen.
Astronomers have long searched for the mysterious origin of FRBs. Discovered in 2007 by a team of scientists at West Virginia University, these mysterious transient radio pulses are considered puzzles of the universe because the cause and origin of FRBs are still unknown.
An international team, led by a graduate research assistant at West Virginia University, Reshma Anna-Thomas, found the first evidence of magnetic field reversal in any FRB during the campaign. This discovery also strengthens the idea that at least a fraction of FRBs originate in a binary system, which is a system of two stars that orbit each other.
Shares Anna-Thomas, “We hoped to discover a high value of rotation measure, indicating an extreme magnetized plasma environment but surprisingly, we also found that it is highly variable and that the integrated magnetic field flips direction.”
Anna-Thomas and team used the National Science Foundation’s Green Bank Telescope (GBT) to observe FRB 20190520B for seventeen months—which is very brief, on astronomical time scales. The peculiar characteristics of the FRB inspired a deeper dive into the data, such as the high local dispersion measure, which is a sign of a dense local environment, and a persistent radio source co-located with the FRB. Data from Australia’s Parkes Telescope, also known as Murriyang, helped to complete this picture and strengthen their conclusion.
Magnetic fields with such extreme turbulence and reversals have not been observed before in the cosmos, although there is a pulsar in our galaxy that comes close. That pulsar is in a binary system with a highly massive star. The researchers interpret their FRB’s observed magnetic properties as likely arising from the turbulent corona of a massive star, which provides a stunning lens through which we view the FRB binary. Explains Sarah Burke Spolaor, a professor and astronomer at WVU, “The furiously undulating and streaming plasma wind from the massive star’s atmosphere provides an ever-changing magnetic field along our line of sight to the FRB source. Polarization happens when light waves fluctuate in a specific orientation, and magnetic fields can realign that orientation. This is how we were able to observe the light’s changing orientations.”
Adds Ryan Lynch, a GBO scientist who supported this research, “The high sensitivity of GBT, its capabilities for observing high frequencies, and to record full polarization data, were crucial for the study. It’s one of the best telescopes available for studying FRBs.”
The Green Bank Observatory and the National Radio Astronomy Observatory are major facilities of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.
West Virginia University’s Center for Gravitational Waves and Cosmology (GWAC) addresses cutting-edge astrophysics problems that can be solved most effectively through interdisciplinary collaboration across physics, astronomy, mathematics, computer science and engineering. The Center explores the origins of the universe and the fundamental processes involved in galaxy formation, stellar evolution, and star formation. Through the agency of a collaborative network of experts, our mission focuses on research, education and outreach.
Reshma Anna-Thomas and Sarah Burke Spolaor acknowledge support for their research from NSF grant AAG-1714897.
