Fluctuating magnetic fields hint at a solution to baffling fast radio bursts from space

Fast radio bursts—intense flashes of radio energy from outer space lasting fractions of a millisecond—have astronomers baffled since it was first spotted in 2007. A single burst of energy in its short life can emit as much energy as the sun emits in a few days.

The vast majority of short-lived pulsations originate outside our Milky Way galaxy. We don’t know what produces most of them, or how.

in New research published in Scienceswe noted repeatedly A quick blast of radio For more than a year, signs have discovered that it is surrounded by a strong but highly variable magnetic field.

Our results indicate that the source of this cosmic explosion may be a binary system consisting of a neutron star spinning through winds of dense, magnetized plasma produced by a massive companion star or even a black hole.

A fast radio blast that never stops repeating

The recurring eruption known as FRB 20190520B was Discovered in 2022 By astronomers at the Five Hundred Meter Aperture Spherical Radio Telescope (FAST) in China. Repetition Fast radio blasts Rare, but FRB 20190520B is the rarest of all: it’s the only one that never rests, producing radio bursts a few times an hour, sometimes in several Radio frequencies.

After finding this intriguing object for the first time, astronomers scrambled to follow up the initial observation using other radio wavelengths.

Further investigation showed that FRB 20190520B resides in an extremely dense environment in a dwarf galaxy 3.9 billion light-years away. There is also material surrounding the FRB source that produces strong, continuous radio emissions.

This has led to suggestions that the source of the explosion is a young neutron star in a complex environment.

strong magnetic fields

What else can we learn about these intergalactic fireworks and their environment? We made observations of FRB 20190520B using CSIRO’s Parkes Radio Telescope, Moriang, in New South Wales and the Green Bank Telescope in the United States.

To our surprise, FRB 20190520B was shown to produce strong signals at relatively high radio frequencies. It turns out that these high-frequency signals are highly polarized – which means that Electromagnetic waves They “wave” more aggressively in one direction than in others.

We found that the direction of this polarization changes at different frequencies. Measuring how much it changes tells us the strength of the magnetic field the signal is traveling through.

As it turns out, this measure of polarization indicates that the environment around FRB 20190520B is highly magnetized. What’s more, the strength of the magnetic field appeared to vary over the 16 months that we observed the source—and even completely flipped direction twice.

This change in magnetic field direction around a fast radio burst had not been observed before.

Fill in the image

What does this tell us about FRB 20190520B? The most popular theories to explain recent observations of FRBs involve binary systems consisting of a neutron star and either another massive star or a black hole.

While we cannot rule out other hypotheses yet, our results favor the massive stars scenario.

Massive stars are known to have strong stellar winds with magnetic fields organized around them. If the source of the bursts were moving in and out of the region of the stellar wind as it traveled through its orbit, we would expect a reversal of the direction of the observed magnetic field.

The timescale of the magnetic field reversal, the measured change in apparent field strength, and the dense plasma surrounding the source of the eruption all correspond to this image.

What then?

Our observations may provide important evidence to support the hypothesis that fast radio frequency repeating sources have a massive companion capable of producing highly magnetized plasmas.

Most importantly, the binary hypothesis gives us a prediction for the future. If this is true, then changes in the polarization of radio signals from FRB 20190520B should go up and down over longer timescales.

So we’ll watch. Future observations with Murriyang and the Green Bank Telescope will reveal whether FRB 20190520B is really in binary system—or whether the universe will surprise us again.

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