Fast Radio Burst Sheds Light On Missing Matter

Fast radio bursts are high energy astrophysical phenomena that reveal themselves as transient radio pulses that last for only a few milliseconds. The origin of these strange and mysterious bursts is unknown, although they are commonly thought to be extragalactic because of the anomalously high amount of pulse dispersion observed. However, it has alternatively been suggested that fast radio bursts may be born from nearby stars–or that they may even be tattle-tale signs of extraterrestrial intelligence. In February 2016, an international team of astronomers announced that by using a combination of radio and optical telescopes to determine the precise location of a Fast Radio Burst (FRB) in a galaxy far, far away, they had successfully conducted a unique census of the Universe’s matter content. Their result, published in the February 24, 2016 issue of the journal Nature, confirms current cosmological models of the distribution of matter in the Universe.

This study is important because, after decades of hunting, the astronomers succeeded in tracking an FRB to its galaxy of origin for the first time. The story of this discovery began on April 18, 2015, when the FRB was spotted by the 64-m Parkes radio telescope of the Commonwealth Scientific and Industrial Research Organisation (CSIRO) in Australia within the framework of the SUrvey for Pulsars and Extragalactic Radio Bursts (SUPERB) project. This triggered an international alert that told astronomers to follow it up with other telescopes. Within only a few hours, a number of telescopes all around the world were searching for the intriguing, mysterious signal, including CSIRO’s Australia Telescope Compact Array (ATCA) and the Effelsberg Radio Telescope in Germany.

Although FRB’s are mysterious, brilliant radio flashes of unknown origin, there is a long list of potential phenomena associated with them. FRBs are extremely hard to detect, and prior to this discovery only 16 of these weird radio flashes had been spotted.

“In the past FRBs have been found by sifting though data months of even years later. By that time it is too late to do follow-up observations,” explained Dr. Evan Keane in a February 24, 2016 Max Planck Institute for Radio Astronomy (MPifr) Press Release. Dr. Keane is Project Scientist at the Square Kilometre Array Organization and lead scientist of the study. The MPifr is in Bonn, Germany.

In order to overcome the difficulty of obtaining follow-up observations of FRBs, the astronomers developed their own observing system–SUPERB–to spot FRBs within mere seconds, and to immediately alert other telescopes around the world, when there was still enough time to hunt for more clues in the aftermath of the initial brilliant flash.

Because of the ATCA’s six 22-m dishes and their combined resolution, the scientists were able to precisely determine the exact location of the FRB signal with greater accuracy than had been possible in the past. The team was able to pinpoint a radio afterglow that lasted for about 6 days before finally fading away. This tattle-tale afterglow allowed the team to determine the precise location of the FRB about 1000 times more accurately than had been possible with earlier observations.

The mystery still demanded that yet another question be answered. The scientists used the National Astronomical Observatory of Japan (NAOJ)’s 8.2-m Subaru Optical Telescope in Hawaii to search for where the signal originated, and they identified an elliptical galaxy about 6 billion light-years away. “It’s the first time we’ve been able to identify the host galaxy of an FRB,” Dr. Keane continued to comment in the MPifr Press Release.

The optical observations also provided the astronomers with the redshift measurement for this distant object. The redshift refers to the speed at which the galaxy is traveling away from Earth as a result of the accelerated expansion of the Universe. This represents the first time that a distance has been successfully calculated for an FRB.

FRBs are classified according to the date that the bright radio burst was recorded, as YYMMDD–for example, the one recorded on 26 June 2011, would be designated as FRB 110626. The most ancient FRB discovered to date is FRB 010621.

Primordial Matters

According to the inflationary Big Bang theory, our Cosmos was born almost 14 billion years ago from an unimaginably tiny Patch, smaller than a proton, that–in the tiniest fraction of a second–expanded exponentially to achieve macroscopic size. This extremely tiny Patch, that experienced this faster-than-the-speed-of-light, runaway inflation, was much too small for a human being to see. In fact, it was so extremely small that it was almost, but not exactly, nothing. However, that little Patch was so dense, and so extraordinarily searing-hot, that all that we know emerged from it. The newborn Universe was filled with high energy particles that jitter-bugged around together in a magnificent, frenetic dance, in the primordial, wildly expanding fireball of the Big Bang. The beautiful baby Universe brimmed with a turbulent, swirling, whirling sea of sparkling, dazzling particles of light, called photons. The entire baby Cosmos was filled with the brilliance of a luminous, glaring fog of wonderful light, that resembled the surface of our Sun today–but was much brighter. What we can now observe almost 14 billion years after our Universe’s mysterious birth, is the greatly expanded, and still expanding, aftermath of our newborn Universe’s first cry of screaming brilliance. And now we stare up at the sky in wonder, helplessly observing from our tiny, obscure, rocky, blue Earth, how the fires of our Universe’s birth cool–and slowly burn out. Our Cosmos now expands darkly into the ashes of Eternity, fading like a strange ghost into a merciless, unknowing night of forevermore. Like the eerie smile of the Cheshire Cat, it is all fading away, in our Universal nightmare of a Wonderland.

According to the current model, the Universe is thought to be composed of 70% dark energy, 25% dark matter, and 5% so-called “ordinary” atomic matter. Despite the misnomer, “ordinary” atomic matter is really extraordinary stuff. Even though “ordinary” atomic matter is the runt of the Cosmic litter of three, it is the substance that composes our familiar world–the stuff of planets, moons, trees, and people. It is the material that brought our Universe to life. Dark matter, which is much more abundant that atomic matter, is thought to be composed of exotic, non-atomic particles that do not interact with light, or any other form of electromagnetic radiation–which makes it transparent and invisible. However, scientists are almost certain that it is really there because of its gravitational effects on objects that can be seen–such as stars and galaxies. Even though the dark energy is thought to account for most of the Universe, its true nature is not well understood. It is often thought to be a property of Space itself, and it is the substance that is causing our Universe to accelerate in its expansion.

Of the atomic elements, only hydrogen, helium, and trace quantities of lithium and beryllium, were born in the Big Bang. All of the heavier atomic elements, termed metals by astronomers, were cooked up in the searing-hot, fiery hearts of the Universe’s trillions and trillions of stars–or else in supernova explosions, which are triggered by the dramatic deaths of the more massive stars.

The nuclear-fusing furnaces of the stars created increasingly heavier and heavier atomic elements out of lighter ones. The oxygen that we breathe, the water that we drink, the iron in our blood, the calcium in our bones, and the carbon that is the basis for life on Earth, were all manufactured in the nuclear-fusing fires of the Universe’s vast multitude of stars (stellar nucleosynthesis). The stars then hurled their newly-forged heavy metals out into Space, after they had burned up their necessary supply of hydrogen fuel. Traveling around in the space between stars, these freshly formed heavy atomic elements were then incorporated into the fires of dazzling baby stars of later generations.

Perhaps the two most important questions that still remain to be answered by astrophysicists are: What is really out there in the vastness of the mysterious Cosmos? What is it composed of? Without an answer to these key questions it is impossible for scientists to come to any strong conclusions about how the Universe evolved through time.

Protons, neutrons, and electrons are particles that compose atoms. The protons and neutrons are stuck together into atomic nuclei, and the atoms themselves are nuclei encircled by a cloud of electrons. Hydrogen–the lightest and most abundant atomic element in the Universe–is composed of one proton and one electron. Helium–the second lightest–is composed of two protons, two neutrons, and two electrons. Carbon is composed of six protons, six neutrons, and six electrons. Heavier atomic elements, such as iron, lead and uranium, are made up of even larger numbers of protons, neutrons and electrons. Astronomers call all material composed of atoms baryonic matter.

Until a little over a generation ago, astronomers believed that the Universe was made up almost entirely of this familiar baryonic matter—“ordinary” atoms! However, over the past thirty years, or so, there has been more and more evidence accumulating that indicates there are components of the Universe that we cannot see–the dark matter and the dark energy.

The mass that astronomers can attribute to galaxies, including our own barred-spiral Milky Way, is approximately ten times greater than the mass that can be associated with stars, gas, and dust in a galaxy. This mass discrepancy has been confirmed by observations of gravitational lensing, which is a prediction of Albert Einstein’s General Theory of Relativity (1915), whereby his calculations revealed that the gravity of massive objects can warp and bend light.

Fast Radio Burst Sheds Light On Missing Matter

In order for astronomers to understand the physics behind such FRB events, they must know certain basic properties, such as the precise position of the source, its distance, and whether it will repeat itself. “Our analysis leads us to conclude that this new radio burst is not a repeater, but resulting from a cataclysmic event in that distant galaxy,” Dr. Michael Kramer explained in the February 24, 2016 MPifr Press Release. Dr. Kramer is of the MPifr, and he is responsible for analyzing the radio profile’s structure of the event. MPifr’s Effelsberg Radio Telescope was also used for radio follow-up observations after the alert had been triggered.

FRBs exhibit a delay in the radio signal resulting from the amount of material it has traveled through (frequency-dependent dispersion). “Until now, the dispersion measure is all we had. But also having a distance we can now measure how dense the material is between the point of origin and Earth, and compare that with the current model of the distribution of matter in the Universe,” Dr. Simon Johnston explained in the MPifr Press Release. Dr. Johnston, a co-author of the study, is from CSIRO’s Astronomy and Space Science Division. “Essentially this lets us weigh the Universe, or at least the normal matter it contains,” he added.

Through their observations of galaxies, stars and hydrogen, astronomers have only been able to account for about 50% of the normal, so-called “ordinary” matter. The rest of this mysteriously missing matter cannot be seen directly–which is why it is “missing.”

“The good news is our observations and the model match, we have found the missing matter. It’s the first time a fast radio burst has been used to conduct a cosmological measurement,” Dr. Keane commented in the same Press Release.

“This shows the potential for FRBs as new tools for cosmology. Just think what we can do when we have discovered hundreds of these,” Dr. Kramer added in the February 24, 2016 MPifr Press Release.

In the future, the Square Kilometer Array, with its great resolution, sensitivity and wide field of view is expected to be capable of detecting many more FRBs–and also pinpoint their host galaxies. A much larger sample will help astronomers to make precision measurements of cosmological parameters such as the distribution of matter in the Universe, and shed new light on the nature of the dark energy from which most of our Universe is made.

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