Astronomers peer into the lair of a mysterious cosmic radio burster

(ASIAA Science Highlight, January 11, 2018)

An international team of astronomers has used two of the world's largest radio telescopes to show that a mysterious source of radio bursts is in an astonishingly extreme and unusual environment. This discovery suggests that the strange source is in the close vicinity of a massive black hole, or within a nebula of unprecedented power. The team presented their findings at the American Astronomical Society's winter meeting (#AAS231) in Washington, DC. The results appear on the cover of the January 11th edition of Nature.

Fast Radio Bursts (FRBs) are a recently discovered type of astrophysical signal coming from deep in extragalactic space. Their physical origin remains a mystery. Using data from the Arecibo Observatory, Puerto Rico, and the Green Bank Telescope, West Virginia, astronomers have now shown that the radio bursts from the source FRB 121102 have a property known as polarization. The behavior of this polarized light allows them to probe the source’s environment in a new way and to `peer into the lair’ of the mysterious burster.

Polarized light is likely familiar to anyone who has used polarized sunglasses to cut down on the glare of sunlight reflected off water. If polarized radio waves travel through a region with a magnetic field, the polarization gets ”twisted” by an effect known as Faraday rotation: the stronger the magnetic field, the greater the twisting. The amount of twisting observed in FRB 121102’s radio bursts is among the largest ever measured in a radio source, and the researchers conclude that the bursts are passing through an exceptionally strong magnetic field in a dense plasma (a hot, ionized gas).

“The extreme twisting seen towards this burst are only seen in galactic centers with massive black holes,” says Geoffrey Bower, ASIAA adjunct faculty and Chief Scientist for Hawaii Operations. “This discovery connects the new phenomenon of fast radio bursts to cosmic sources that we have pioneered the study of using ASIAA facilities, including the Submillimeter Array and the Atacama Large Millimeter Array.”

“The environments of massive black holes have the strong magnetic fields and high particle densities that are required to produce the twists seen in the burster,’’ Bower added. “These extreme properties drive accretion onto the black holes, which we are studying through high resolution imaging. The burster may give a new way to understand these unusual environments.”

Key to the discovery was detecting the bursts at higher radio frequency than ever before. “We developed a new observing setup at the Arecibo Observatory to do this, and our colleagues from the Breakthrough Listen project at the Green Bank Telescope confirmed the results with observations at even higher radio frequencies,” says Andrew Seymour, Staff Astronomer at Arecibo. “What’s more, the polarization properties and shapes of these bursts are similar to radio emission from young, energetic neutron stars in our galaxy. This provides support to the models that the radio bursts are produced by a neutron star,” he adds.

A year ago, the research team pinpointed the location of FRB 121102 and reported that it lies in a star-forming region of a dwarf galaxy at a distance of over 3 billion light years from Earth. At this great distance, an enormous amount of energy is needed to power each burst: roughly as much energy in a single millisecond as the Sun releases in an entire day. FRB 121102 is the only known repeating FRB, and this has also raised the question of whether it has a different origin compared to apparently non-repeating FRBs. “FRB 121102 was already unique because it repeats; now the huge Faraday rotation we have observed singles it out yet again. We’re curious as to whether these two unique aspects are linked”, says Daniele Michilli, PhD candidate at the University of Amsterdam and ASTRON, the Netherlands Institute for Radio Astronomy, and lead author of the paper.

“We are continuing to monitor how the properties of the bursts change with time”, says Jason Hessels, Associate Professor at the University of Amsterdam & ASTRON. “With these observations we hope to distinguish between the two competing hypotheses of a neutron star either near a black hole or embedded in a powerful nebula.”

With a number of wide-field radio telescopes now coming online, more such sources are expected to be discovered in the coming year, and astronomers are poised to answer more fundamental questions about FRBs.

Contact Geoffrey Bower:

645 N. A'ohoku Pl,

Hilo, HI 96720

+1 (808) 961-2945 (office)

+1 (510) 847-1722 (cell)

Original Paper: An extreme magneto-ionic environment associated with fast radio burst source FRB121102, D. Michilli et al., Nature, 11 January 2018.

The 305-metre Arecibo telescope, in Puerto Rico, and its suspended supportplatform of radio receivers is shown amid a starry night. A flash from the Fast Radio Burst source FRB 121102 is seen: originating beyond the Milky Way, from deep in extragalactic space. This radio burst is highly polarized, and the polarized signal gets twisted as a function of radio frequency because there is an extreme region of magnetized plasma between us and the source of the bursts.

Image credits: Image design: Danielle Futselaar - Photo usage: Brian P. Irwin / Dennis van de Water /

The 100-metre Green Bank telescope, in West Virginia, is shown amid a starry night. A flash from the Fast Radio Burst source FRB 121102 is seen traveling toward the telescope. The burst shows a complicated structure, with multiple bright peaks; these may be created by the burst emission process itself or imparted by the intervening plasma near the source.

Image credits: Image design: Danielle Futselaar - Photo usage:

One of FRB 121102’s radio bursts, as detected with the Arecibo telescope. The colour panel shows the brightness of the burst as a function of radio frequency and time, whereas the curve above shows the brightness of the burst summed across all observed radio frequencies. This movie illustrates how detecting the bursts at the highest possible time resolution has been critical in resolving their complex structures.

Movie credits: Andrew Seymour (NAIC, Arecibo)

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.

Movie credits: Andrew Seymour (NAIC, Arecibo)