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B.C. astronomers make stellar find in hunt for Fast Radio Bursts

February 10, 2020

B.C.’s CHIME radio telescope array, superimposed against an image from the 8 m Gemini North telescope showing SDSS J015800.28+654253.0 , the host galaxy of FRB 180916 (indicated by the green circle).—Gemini Observatory / NSF’s National Optical-Infrared Astronomy Research Laboratory / AURA / CHIME

Radio astronomers at the CHIME array in British Columbia have discovered the first Fast Radio Burst (FRB) that repeats on a reliable schedule. This should allow researchers to study this mysterious interstellar phenomenon in a way that has not previously been possible.

FRBs are unimaginably powerful radio pulses of millisecond duration that are caused billions of light-years away by some unknown high-energy process. While FRBs are detected on Earth as faint whispers (sometimes compared to a cell phone call from the Moon), at their source they can represent as much energy expended in milliseconds as our sun gives off in 80 years.

Astrophysicists do not understand the high-energy process behind FRBs but they would certainly like to.

Unfortunately, previously discovered FRBs—back to the first one, identified 13 years ago—have either been single flashes of radio energy, or repetitive in an unfathomably random way—all of which makes them very hard to study.

Radio signal from a long time ago, in a galaxy far, far away

Another image of the CHIME radio telescope’s four 100-metre long, half cylinders, located in B.C.’s Okanagan.—CHIME

Enter the Fast Radio Burst (FRB), named “180916.J0158+65″—one of eight new repeating FRBs discovered by a team of radio astronomers at British Columbia’s Canadian Hydrogen Intensity Mapping Experiment (CHIME).

CHIME is an interferometric radio telescope array located at Okanagan Falls, about 10 km from Penticton, B.C.

FRB 180916.J0158+65 is a unique discovery, in that it repeats at predictable intervals, according to a paper published online February 3, 2020, by the CHIME/FRB Collaboration of 72 scientists.

Between September 2018 and October 2019 the CHIME team found that FRB 180916.J0158+65 switched its energy bursts on for four days then switched them off for the next 12 days, for a total cycle of 16.35 days.

And though some cycles did not produce visible bursts, all of the visible bursts that were produced synced up exactly to the 16.35 day cadence.

The CHIME team says that it was joined in detecting FRB 180916.J0158+65 by the European Very-long-baseline-interferometry Network (EVN).

Periodicity offers possible clues to process

“The discovery of a 16.35-day periodicity in a repeating FRB source is an important
clue to the nature of this object”, explains the CHIME paper. It could, for example, be an indication of “orbital motion, with either a stellar or compact-object companion”.

“Stellar” equals a proper star, while “compact object” refers to a collapsed stellar remnant, such as a white dwarf, neutron star, or black hole.

The CHIME paper explains that while a lower-mass black hole is a viable option, the involvement of a supermassive black hole companion (like the one thought to lurk at the centre of our Milky Way galaxy) is unlikely, given the source’s location in the outskirts of a massive spiral galaxy (SDSS J015800.28+654253.0).

Other scientific websites indicate that the location of FRB 180916.J0158+65 was pin-pointed, with the help of the EVN, to a star-forming region of its host galaxy, roughly half-a-billion light years away from us. This makes it by far the nearest FRB yet identified.

Are some FRBs just unidentified pulsars?

The first-known FRB—the Lorimer Burst—was discovered by the astrophysicist and West Virginia University professor Duncan Lorimer and/or one of his undergraduate students, David Narkevic, in 2007, while they were looking through pulsar survey data.

Like FRBs, pulsars are also energy-emitting stellar objects. But pulsars are understood to be neutron stars that emit highly regular pulses of electromagnetic energy as they rotate (the conventional comparison is to lighthouses).

The amount, duration and periodicity of energy emitted varies by pulsar but each pulsar is apparently predictably clock-like in its individual, repetitive operation.

At first glance, FRBs appear to be considered a completely separate phenomenon all their own. But when an FRB exhibits the attribute of regular periodicity, the possibility has to be entertained that it may just be a pulsar we haven’t gotten to know yet.

Before the CHIME paper gets too deep into the mathematics, it devotes a solid page to suggesting how FRB 180916.J0158+65 may be explained by various scenarios involving pulsars, including “black widow” binary systems, consisting of a low-mass star and a powerful millisecond pulsar, massive O/B stars with highly eccentric companion pulsars, and X-ray pulsars that function as magnetars—neutron stars with especially powerful magnetic fields.

This is all very interesting in a remote and “ivory tower” sort of way but it’s unconnected to everyday life, you may be thinking.

However, the many mysteries posed by FRBs appear to involve, as-yet unknown aspects of fundamental physics. This means that even tiny steps towards piecing together this far-off interstellar puzzle could lead to disproportionately big advances in practical fields, such as energy, computing and transportation.

For example, the discovery of the quantum mechanical magnetoresistance effect, known as giant magnetoresistance (GMR) in 1988 underlies all magnetic hard drive technology today. And a thorough understanding of quantum tunnelling (essential for nuclear fusion in stars) gave us the solid state memory technology that makes both flash drives and mobile computing possible. Click the image to enlarge it.

From → British Columbia

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