Mysterious Fast Radio Bursts (FRBs)

How Fast Radio Bursts Work: Fast radio bursts are brief, energetic blips of radio waves that originate far across the universe. At least one repeats, which has added to the challenge of explaining what might be creating them. Past observations have been accounted for, and specific features that should be seen going forward are predicted by a new model.

The story: A fast radio burst (FRB) is a quick radio signal that happens because of powerful space processes we don’t fully get yet. Recent discoveries suggest that these bursts might come from at least two different space events.

Two types: A telescope in Canada found 535 fast radio bursts, increasing the total count of these short but powerful events by four times. The eagerly anticipated findings reveal that researchers can categorize these mysterious occurrences into two types. The majority of bursts happen only once, while a smaller number repeat at regular intervals and last, on average, at least ten times longer.

Canadian Hydrogen Intensity Mapping Experiment (CHIME): The Canadian Hydrogen Intensity Mapping Experiment (CHIME) gathered these events during its initial year of functioning, from 2018 to 2019. The team shared their findings in an online meeting of the American Astronomical Society on June 9 and uploaded four preliminary research papers to the online archive arXiv.

Repeaters and one-offs: CHIME, situated close to Penticton in British Columbia, is a unique telescope that operates without any moving components. It consists of four half-pipe antennas, each stretching 100 meters in length. It focuses on a single narrow section of the sky at a time. However, as the Earth rotates, the telescope effectively surveys the entire sky. Digital processing chips then gather the signals, piecing them together to create a comprehensive image.

1. CHIME’s Initial Purpose: – CHIME was initially designed to map the distribution of matter in the Universe.

2. Additional Functionality: – Extra electronics were added to CHIME’s design to enable the detection of fast radio bursts (FRBs).

3. Initial Skepticism: – Initially, many in the field were skeptical about CHIME’s capability to detect fast radio bursts.

4. Vindication through Results: – The latest announcement regarding CHIME’s detection of fast radio bursts has vindicated its potential.

5. Two Distinct Types of FRBs: – CHIME’s results indicate the existence of at least two distinct types of fast radio bursts.

6. Repeater and One-Off Events:

– Out of the 535 detected, 61 were identified as ‘repeaters,’ emanating from 18 sources that emitted bursts multiple times.

– The remaining bursts were one-off events.

7. Differences in Duration: – One-off events have a much shorter duration compared to repeaters.

8. Frequency Band Differences: – Repeaters emit on a much narrower band of radio frequencies compared to one-off bursts.

9. Confirmation of Distinct Types: – CHIME’s results confirm the existence of two distinct types of fast radio bursts, settling previous uncertainties.

10. Previous Lack of Strong Evidence:

– Prior to CHIME’s findings, the evidence for distinct types was not strong.

– Some astronomers argued that observers might not have observed repeaters long enough to witness repeated bursts in the case of non-repeating bursts.

Vast distances to travel: Fast radio bursts often appear to last for a second or more, but this duration is misleadingly long. As these signals traverse vast distances across space, they encounter intergalactic matter, causing radio waves to spread across the spectrum. This phenomenon, known as dispersion, means that lower-frequency waves may reach Earth several seconds later than higher-frequency ones. Researchers have determined that, at the source, the actual emission of a radio burst typically lasts only milliseconds. In that brief time, the burst’s origin can release an astonishing 500 million times more energy than the Sun does in a comparable period. The extent of this dispersion in wavelengths gives a rough indication of the distance these waves have traveled. So far, researchers have traced back all detected bursts to other galaxies, except for one event that occurred within our own Milky Way.

Origin theories: In the last few years, scientists have kept a close eye on parts of the sky where bursts have occurred before. In certain instances, they’ve observed these bursts happening again with a consistent pattern. For instance, the ‘repeater’ identified by Spitler and her team in 2016 follows cycles of activity lasting about a day, emitting multiple bursts per hour and repeating every 160 days. This predictable repetition provides valuable hints about the potential causes behind these bursts.

Repeater Explanation:

Repetitive bursts may occur when a highly magnetized neutron star orbits an ordinary star in an elongated orbit.
As the neutron star periodically approaches its companion, bursts could result from its magnetic field scattering the highly energetic stellar wind.

Non-Repeater Explanation:

Non-repeating bursts may be the outcome of cataclysmic events, such as neutron star collisions or magnetic storms in young neutron stars known as magnetars.
Researchers linked an event in the Milky Way to a known magnetar, but doubts arose with the discovery of a burst from a ‘globular cluster’ in the galaxy M81.

Globular Cluster Burst:

The finding of a burst from a ‘globular cluster’ in the galaxy M81 challenges the magnetar theory.
Globular clusters are dense collections of very old stars and are considered unlikely hosts for magnetars.

Magnetar Theory Doubts: The observed burst from a globular cluster caused doubts regarding the magnetar theory, as these clusters are not traditionally associated with magnetars.

Varied Origins: The differing origins proposed for repeaters and non-repeaters suggest a diverse set of mechanisms leading to fast radio bursts.

Observational Challenges:

The observation of a burst from M81’s globular cluster highlights the challenges in attributing fast radio bursts to specific astrophysical phenomena.
It underscores the need for continued research and exploration to unravel the full range of sources contributing to these enigmatic cosmic events.

Summary: The first discovery of a fast radio burst in 2007 came as a shock to researchers. Theorists came up with a plethora of possible explanations.