Fast radio burst source linked to ‘extreme’ environment
Astrophysicists have just discovered a major new clue about the environment that is home to a series of mysterious cosmic radio signals.
A new study shows that the only known repeating fast radio burst (FRB) source is in an ‘extreme’ environment which is among the most highly magnetized regions of space ever observed. Such an environment has only been seen around massive black holes, but could also plausibly be caused by a combination of other extreme astrophysical circumstances. The new measurements could offer a major clue to the FRB’s cause.
The findings were presented at the American Astronomical Society‘s winter meeting in Washington, D.C today and published in Nature. The research was conducted by a scientific collaboration that includes CIFAR R. Howard Webster Foundation Fellow Victoria Kaspi (McGill University) and Associate Fellow Scott Ransom (National Radio Astronomy Observatory).
“I had to read my email a few times to really digest it. I kept thinking, ‘No way, that can’t be right,’” said Kaspi, who is Director of CIFAR’s Gravity & the Extreme Universe program.
“We found something that is clearly in an extreme place and the extreme location may create a phenomenon that is one of the biggest astrophysical mysteries of recent times.”
Kaspi said this is a huge advance in understanding fast radio bursts. FRBs last only a few thousandths of a second but are far brighter and more powerful than any known short radio flashes, such as pulses from radio pulsars, a form of neutron star. FRB 121102 is especially unusual because it is the only known repeating burster and the first FRB to be pinpointed in the sky.
Though FRB 121102 is located three billion light years away, researchers were able to get a ‘glimpse’ inside its environment by examining the polarization of its radio emission in detail. The phenomenon of Faraday rotation describes the way polarized light behaves as it travels through substances in a magnetic field. By measuring Faraday rotation using data from the Arecibo Observatory (Puerto Rico) and the Green Bank Telescope (West Virginia), the scientists showed that the polarization of the radio light from this FRB must have travelled through an ultra-highly magnetic area of space dense with plasma.
One of FRB 121102’s radio bursts, as detected with the Arecibo telescope, and then converted to sound so one can hear the drift in the emission frequency with time. (Credit: Andrew Seymour (NAIC, Arecibo))
A leading hypothesis to explain the observations is that the environment contains a black hole 10 to 100 million times the size of the sun. The burst could come from a neutron star near a supermassive black hole that produces huge magnetic fields, or even shoots out hot, ionizing gas. Other possible models include an ultra-highly magnetized wind nebula, created by winds from a pulsar. The researchers have also proposed an environment with an ultra-highly magnetized supernova remnant powered by a young neutron star.
These new findings raise the question of whether FRBs could be a product of their environment.
“If you have an extreme object in an extreme environment, is that just a coincidence? FRBs have these huge explosions in radio waves and we don’t know why that occurs. Maybe this is a clue to the mechanism that produces these explosions,” Kaspi said. She is particularly interested in speaking with members of the Gravity & the Extreme Universe program who study compact objects like supermassive black holes, including the one in Earth’s galaxy.
The Canadian Hydrogen Intensity Mapping Experiment, better known as the CHIME telescope, offers another way to study FRBs. The Canadian-led initiative involves a number of CIFAR researchers and is based in Penticton, B.C. Originally designed for cosmological work, CHIME’s capabilities have been extended to enable it to be a world-leading FRB detector. The CHIME FRB team hopes to put a larger focus on collecting information to measure Faraday rotation now that it has proven to be critical to understanding FRBs.
“An extreme magneto-ionic environment associated with fast radio burst source FRB 121102” was published in Nature on Jan. 11.
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