The Cosmic Zoo–our Universe–is the bizarre domain of diverse, strange beasts, many of which are unlike anything that we are familiar with on our own little planet lost in Space. Oddities of many sorts collect in darkly mysterious and remote regions of our Universe–and some of these weird occurrences are violent in nature, such as the crashing collisions of fiery stars that blast into each other, and the cataclysmic explosive deaths of massive stars that blow themselves into oblivion when they go supernova. In July 2013, astronomers reported that they had detected a strange population of brief radio bursts coming from far beyond our Milky Way Galaxy–the first short radio bursts that have been spotted emanating from other galaxies. The sources of these mysterious bursts are unknown, but cataclysmic occurrences such as stellar collisions and supernovae blasts, are thought to be the most likely triggers.
“This is one of the most important radio discoveries in the last couple of decades,” Dr. Scott Ransom commented in the July 4, 2013 Nature News. Dr. Ransom, an astronomer at the U.S. National Radio Astronomy Observatory (NRAO) in Charlottesville, Virginia, was not part of the study.
A radio burst is a brief surge of light that emanates from a point in the sky, composed of longer electromagnetic wavelengths in the radio portion of the light spectrum. A single radio burst was spotted in 2007, but astronomers were not certain if it came from within our Milky Way or from somewhere far beyond our Galaxy.
The objects that we are familiar with–our own planet, our Moon, the Sun, the Solar System, and the visible, luminous objects that dwell in the Universe such as stars, as well as the galaxies that they ignite with their silvery fires–compose the portions of the Cosmic Zoo that we have long been aware of, and that we are now beginning to explore.
But the Cosmic Zoo is also the domicile of many strange beasts, belonging to bizarre species that have never been observed before, and whose identity is yet to be determined and defined. Most of our Universe is mysterious–inscrutable, perhaps. But, being a curious species, we seem to have the need to explore that which is unknown in our Cosmos.
Radio Bursts From Long Ago And Far Away
The new radio bursts–four in total–come traveling to us from billions of light-years away, indicating that they do indeed originate from unknown and mysterious sources beyond our own Galaxy. The discovery of this quartet of weird bursts was reported in the July 5, 2013 issue of Science by an international team of astronomers that used the Parkes Observatory in Australia. The article is titled A Population of Fast Radio Bursts at Cosmological Distances.
“Short radio bursts are really tricky to identify. Our team had to search 11 months of data covering a large sky area,” explained Dr. Sarah Burke Spolaor in a July 8, 2013 NASA Jet Propulsion Laboratory (JPL) Press Release. Dr. Spolaor, who is of the JPL located in Pasadena, California, developed the software that was used by the team. The software was designed to search for single pulses in the radio data, and then to determine which of them were genuine signals rather than local interference. Local interference, for example, can come from spark plugs, aircraft, and cell phones. Obviously, this amounts to a huge, and very difficult, computational task.
Even though radio signals, that vary over days to months, have been detected traveling to Earth from remote galaxies for decades, such brief bursts from beyond our Milky Way have never before been definitively spotted, according to Dr. Dan Thornton, a study co-author. Dr. Thornton is an astronomer at the University of Manchester in the UK and Australia’s Commonwealth Scientific and Industrial Research Organization. He and his team set out to search for extragalactic radio bursts, following the event that was observed back in 2007, that indicated one such signal had possibly been found. Using archived data from the 64-meter Parkes ‘scope–the same instrument that had detected the first candidate burst six years earlier–Dr, Thornton and his team discovered the bursts that seemed to be traveling to us from beyond our Milky Way.
“The radio bursts last for just a few milliseconds and the farthest one that we detected was 11 billion light-years away,” Dr. Thornton explained in the July 8, 2013 JPL Press Release.
As radio waves make their long journey through ionized material in Space, they meet up with a vast sea of electrons that slows down the lower-frequency components of the signals–but leaves the higher-frequency components almost entirely alone. This causes a narrow radio signal–that is traveling a very long distance–to spread out or disperse. The quartet of radio signals spotted by Dr. Thornton and his colleagues are so widely spread out that the distribution of electrons in our Galaxy can account for only a mere 3-6% of their dispersion. This suggests very strongly that all four of the radio bursts originate from beyond the Milky Way. The signals also come from different regions of the sky.
Our sky is literally full of innumerable bursts and flares of varying descriptions and origins. Gamma-rays, for example, are believed to be triggered by the death throes of giant, massive stars when they collapse into stellar mass black holes. Gamma-rays are routinely observed by a network of ‘scopes both Earth-bound and Space-borne–including NASA’s Fermi and Swift. When one of this vast network of ‘scopes spots a burst, it can signal to the others so that they rapidly spin to the site for coordinated observations.
The newly discovered quartet of radio bursts are most likely of a different origin than gamma-ray bursts, even though both types of bursts consist of light waves churned out by violent and cataclysmic events occurring at vast distances. The brightness and brevity of the quartet of radio bursts hint that they were emitted by some kind of relatively small, but highly energetic body, such as a magnetar. A magnetar is a neutron star that sports an extremely strong magnetic field. The radio bursts “are signalling the existence of a cataclysmic event involving large amounts of mass and or energy,” Dr. Thornton said in the July 4, 2013 Nature News. However, their source remains cloaked in mystery because astronomers were not able to precisely locate where the extremely brief signals were coming from.
The quartet of bursts are similar to the pulses observed emanating from pulsars, neutron stars whose rapid rotations regularly sweep–like lighthouse beacons– through the blackness of Space. Because of their weak emission, most of the known pulsars dwell within our Galaxy or in one of its nearby satellite dwarf galaxies, the Large and Small Magellanic Clouds. However, the newly spotted quartet of bursts are different because they originate from greater distances, far beyond the Milky Way. The sources of the radio bursts are undoubtedly exotic by our familiar standards–strange beasts, indeed, inhabiting our weird Cosmic Zoo! The range of suspects include emissions from evaporating black holes, sources that involve supernovae blasts, and magnetars. The bursts could also originate in the hearts of galaxies where compact stars dance around—before they hurl themselves into the hungry mouths of supermassive black holes that weigh millions to billions of times more than our Sun.
But these mysterious bursts could also represent an entirely new and previously unknown species of exotic beast.
Models of the electron content of intergalactic Space indicate that the quartet of remote bursts traveled between 5.5 billion and 10 billion light-years of Space to reach our planet–much further away than our Galaxy. But their origin remains cloaked in bewitching mystery because the astronomers could not pinpoint where these very brief signals came from.
If astronomers can ultimately pinpoint the distances, they can use the dispersion of the radio signals to measure the number of electrons in intergalactic Space. The quantity of electrons is representative of the quantity of baryons–protons and neutrons which compose the nuclei of atoms–that swim around in the Space between galaxies.
This number is of great interest because it could help solve a longstanding Cosmic mystery about why the abundance of protons and neutrons within galaxies is much less than the total number that observations of the ancient Universe indicate should be swimming around today. This newly discovered species of bursts could ultimately locate the missing baryons of the Cosmic Zoo.
