Our understanding of the universe has seen an unparalleled upturn in the last century. In the 1920s, the nature of a special type of cosmic object, referred to at the time as spiral nebulae, was still a cause for widespread debate in the astronomical community.
A number of astronomers insisted that these spiral nebulae were all located within our own galaxy, the Milky Way. Others argued that they had to be separate galaxies, located at significantly larger distances outside our galaxy. Due to the work of Edwin Hubble and several other astronomers, we now know that the latter theory was indeed correct – there are billions, possibly trillions, of galaxies in the known universe.
Observing galaxies and their constituents using just the visible part of the electromagnetic spectrum can only shed light on a small section of the fabric of the cosmic tapestry. Observations in ultraviolet, infrared, microwave and radio wave frequency ranges have all given us a different glimpse on some targets and even opened up a plethora of previously unobserved objects.
One such phenomenon, only recently observed, are fast radio bursts. As the name implies, these observed signals are fast – occurring on the scale of milliseconds – and are of a radio wave frequency. Therefore, radio telescopes such as the Green Bank Telescope and the Australian Square Kilometre Array Pathfinder (ASKAP) have been used to observe these strange phenomena.
The occurrences have been confirmed to originate outside the Milky Way, coming therefore from distant galaxies. One thing was immediately certain to astronomers; to be observable from millions or billions of light years away, such signals would need to be originating from unimaginably energetic events.
Somewhat unsurprisingly, leading hypotheses for their origin are therefore some of the more exotic events occurring in the universe, pertaining to some of the most exotic cosmic bodies known. These include extremely rapidly rotating pairs of black holes or neutron stars – with the latter commonly referred to individually as pulsars, or in extreme cases, magnetars. Magnetar hyper flares have in fact been suggested as possible progenitors for such observations.
One distinctive feature of some fast radio bursts, or FRBs, is their seemingly erratic repetitive nature. Although most FRBs are single events, with no repeated bursts measured from the same source, others have been observed more than once, seemingly originating from the same galaxy, though these occurrences have been sporadically recorded.
A particular FRB has recently stirred interest due to periodic repetitions recorded with a cycle of around 16 days, with four days of clustered activity followed by 12 days of dormancy.
FRB180916.J0158.65 is the closest recorded FRB to date, measured at a distance of 500 million light years from Earth, and is the first FRB to show this regular periodicity. The phenomenon is, to date, still unexplained, although further measurements with radio telescope arrays will help shed further light on their possible origin.
Josef Borg is currently a PhD student within the Institute of Space Sciences and Astronomy, University of Malta, and also the president of the Astronomical Society of Malta.
Did you know?
• A gamma-ray burst may have resulted in mass extinction events in the Ordovician-Silurian period. Gamma-ray bursts occur from some of the most energetic events in the cosmos, such as supernova or hypernova explosions. It has been suggested that such a hypernova within 6,000 light years of Earth could have rapidly stripped the Earth’s atmosphere of half of its ozone, immediately subjecting the planet’s surface to extremely high levels of ultraviolet radiation. This would have exposed several surface-dwelling organisms to such radiation, and could have kick-started an extinction event around 450 million years ago. This remains only a hypothesis, however, as no evidence for the occurrence of such a gamma-ray burst has been found to date.
• Magnetars are extremely rapidly rotating neutron stars with some of the strongest magnetic fields known. Neutron stars are known to rotate rapidly, a remnant from their formation process at the end of the life of a giant star. While typical neutron stars rotate once on their own axis in a few seconds, magnetars are neutron stars rotating once in under a second. They have some of the strongest known magnetic fields, with a 10-100 billion tesla field, compared to Earth’s 30-60 microtesla field, such that they would render the chemistry of life impossible from a distance of 1,000km!
• A strong gamma-ray burst originating in the Large Magellanic Cloud was recorded in 1979. On March 5, 1979, two Soviet spacecraft, Venera 11 and Venera 12, were hit with a blast of gamma radiation. This contact raised the radiation readings on both the probes from a normal 100 counts per second to over 200,000 counts a second, in just a fraction of a millisecond. The gamma ray blast continued spreading. Eleven seconds later, the Nasa probe Helios 2, in orbit around the sun, was also inundated with radiation. Soon after, Venus was hit and the Pioneer Venus Orbiter was also saturated with the wave of radiation. Earth received the wave of radiation a few seconds later, saturating the sensors of three US defence Vela satellites, the Soviet Prognoz 7 satellite and the Einstein Observatory.
For more trivia, see: www.um.edu.mt/think
Sound bites
• New solar orbiter mission launches successfully: A United Launch Alliance Atlas V rocket lit up the skies over Cape Canaveral Sunday night at 11.03pm. EST (4.03 UT on February 10) with the first space science mission of 2020: the joint ESA/Nasa Solar Orbiter. Mission controllers from the European Space Operations Centre report that the spacecraft is healthy and has already signalled home while deploying its solar panels. It’s now en route to an orbit around the sun.
https://www.skyandtelescope.com/astronomy-news/new-solar-orbiter-mission-launches-successfully/
• First light from the world’s largest solar telescope: The Daniel K. Inouye Telescope, being built on Haleakalā in Hawaii, has seen the first light. The telescope has imaged convection cells, also termed granules, each roughly the size of Texas. The motions within each cell are akin to those in a pot of boiling water, with plasma welling up in the centre of each cell, cooling near the surface, then sinking down the sides. In the process, each granule transports heat (and magnetic fields) from the sun’s interior into the outer atmosphere or corona.
https://www.skyandtelescope.com/astronomy-news/first-light-worlds-largest-solar-telescope/
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