Fast radio burst
Fast radio bursts (FRBs) are brief, intense pulses of radio waves originating from distant galaxies. First detected in the early 2000s, FRBs differ from pulsars in that they do not have a consistent repeating pattern. The first recognized FRB, known as the Lorimer burst, was identified in 2007, originating from billions of light-years away and implying an extraordinarily powerful source. While FRBs have been confirmed to exist, their exact causes remain a mystery, leading to numerous theories, including the possibility that they are linked to neutron stars.
Research has revealed that the rarity of FRBs complicates efforts to understand them. Only a handful of bursts were observed in the first decade after their discovery, with FRB 121102 being the only one confirmed to repeat. Advances in technology, particularly with the Canadian Hydrogen Intensity Mapping Experiment (CHIME), have since increased the number of detected FRBs and provided insights into their properties. Scientists believe that studying these bursts could enhance our understanding of the composition of the universe and the nature of the interstellar medium. Despite progress, as of 2024, the fundamental nature and sources of FRBs remain one of astronomy's enduring enigmas.
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Fast radio burst
Fast radio bursts (FRBs) are very brief, very strong radio wave pulses found in outer space. They are similar to pulsars but do not repeat regularly as pulsars do. Scientists are unsure what causes them, and dozens of theories have been developed to explain them. Fast radio bursts were first detected by humans in the early days of the twenty-first century, but they were not identified until 2007. It took ten more years before scientists were able to locate the source of one fast radio burst in a distant galaxy.
Background
Scientists have studied pulsars since they were first discovered in 1967. Pulsars are the remains of stars as much as eight times the size of the sun. Sometimes when these stars die in a supernova blast, they leave behind a core that becomes compressed by its own gravity and forms a neutron star. These neutron stars spin rapidly and let off intermittent pulses of radiation that resemble the spinning beam of a lighthouse.
On August 24, 2001, the Parkes radio telescope in New South Wales, Australia, recorded some images of what were initially thought to be pulsars. However, when researchers reviewed the footage years later in 2007, they found a burst that only occurred once. This burst did not exhibit the regular repeating pattern associated with pulsars. The phenomenon was named the Lorimer burst, after Duncan Lorimer, the West Virginia University astrophysicist who codiscovered it.
This burst was just five milliseconds long but seemed to come from billions of light-years away, based on the ways the waves dispersed. As Lorimer and his associates studied the burst, they realized that if it came from as far away as they believed, its source would have to have been five hundred million times more powerful than Earth's sun. However, researchers were initially unable to detect any similar bursts and began to think it might be an anomaly, or that it might have been a misinterpretation of some common source. Similar bursts had been seen that were later determined to have been caused by weather, instrument malfunctions, or other Earth-bound causes.
In 2010, another researcher, Sarah Burke Spolaor, a doctorate student at Swinburne University of Technology in Australia, was reviewing the same images from the Parkes telescope. She found images that were similar to the Lorimer burst but could be attributed to sources other than a distant galaxy. These images would later be found to have been caused by people opening a microwave door while it was still running.
This caused many to doubt that Lorimer's discovery was from a far-off source. Lorimer and others found four other potential bursts, but because they were found by the same team working on the same telescope, many researchers were still reluctant to consider them as a unique discovery. In 2014, however, a team at the Max Planck Institute for Radio Astronomy in Germany observed additional bursts while doing research in Puerto Rico at the Arecibo Observatory. Another team working in West Virginia discovered another burst in 2015, erasing doubt that fast radio bursts were a unique occurrence.
Overview
Although scientists have accepted the existence of fast radio bursts, they have been unable to reach agreement on what they are or how they are made. As many as thirty theories exist to explain how they happen and what causes them. One theory is that they are actually released by neutron star, just like pulsars, but existing telescopes are not sensitive enough to detect some of the flashes. However, even scientists who agree that neutron stars could be the source differ in how far away they think these stars are from Earth.
Part of the difficulty in discerning the source is the rarity of fast radio bursts. In the decade after the phenomenon was first identified, less than thirty-five FRBs were discovered, and only one ever repeated to provide scientists with additional data to pinpoint its location. That repeating FRB, designated 121102 for the date on which it was first noted, was spotted nine times over the course of six months when researchers studied it in 2016. This study was done with a highly sensitive radio telescope known as the Karl Jansky Very Large Array, or VLA. Through research with the VLA and several other large, highly technical devices, scientists were able to determine that FRB 121102 is located in a small, hard to detect dwarf star galaxy in the Auriga constellation, which is three billion light-years away from Earth.
Researchers investigating FRB 121102 theorized that its source was a neutron star, possibly a form of neutron star known as a magnetar. The research team released its findings in early January 2017. Although this work helped to identify the source of this specific fast radio burst, researchers were cautious about assuming other FRBs come from similar sources. FRB 121102 was different from other bursts in the way it repeated, so it was considered possibly closer to a pulsar than to other FRBs. It is also possible that it is another type of space object entirely.
The number of recognized FRBs gradually increased as technology and detection methods improved, including the use of artificial intelligence to identify further bursts from FRB 121102. One notable project was the Canadian Hydrogen Intensity Mapping Experiment (CHIME) radio telescope, which debuted in late 2017 and detected its first burst the next year. The telescope extended the range of frequencies at which bursts were detected. CHIME also led to the discovery of the second known repeating FRB, which was announced by scientists in early 2019. CHIME had detected 536 FRBs by 2021.
As scientists learn more about FRBs and their sources of origin, it is anticipated they can be used to help determine information about the space between Earth and the burst. Once bursts are better understood, they can be used to determine what space is made of. For instance, the way the radio waves of a burst are dispersed will help scientists figure out how much of the universe is made of neutrons, electrons, and protons. FRBs will also help to determine what is inside the vast clouds of gas and other substances that are in space and how these clouds affect the space bodies around them. By 2024, the source of FRBs had not yet been discovered and remained one of the most important mysteries in astronomy.
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