Canberra: A strange census has been conducted regularly by the astrophysicists for over the past 20 years. What they count is the whole ‘matter’ in the universe. Astronomers do this census by examining how bright flashes of radio waves from other galaxies, called Fast Radio Bursts (FRB), are distorted by particles on their way to Earth. Nature reports: The result of the experiment says that almost half of the Universe’s matter is missing for decades; may be lurking somewhere in the intergalactic space.
When commenting about this missing matter, one should not think about the dark matter that constitutes the major portion of the matter in the universe; but this missing one includes ordinary matter, called Baryons made of protons and neutrons. Observations of light emitted when the universe was young indicate that baryons should make up roughly 5 percent of all the mass and energy in the cosmos. But in the modern universe, all the matter that astronomers can easily see, like the stars and gas in galaxies, adds up to only about half of the expected amount of matter.
Scientists anticipate that the missing matter hides between galaxies, along the filaments of cosmic gas stretched between galaxy clusters. “But we haven’t been able to detect it very well, because it’s really, really diffused, and it’s not shining brightly”, says Jason Hessels, an astrophysicist at the University of Amsterdam. Scientists detect the Baryons using Fast Radio Bursts, which occur by energetic activity around neutron stars or black holes. A burst’s high-frequency, high-energy radio waves zip through intergalactic matter faster than its low-frequency waves. The more intergalactic matter that a radio burst’s waves pass through, the farther its lower-frequency waves fall behind — creating a detectable smear in the radio signal by the time it reaches Earth.
Now about groundwork, Xavier Prochaska, Astrophysicist of the University of California reports that they have examined five fast radio bursts from five galaxies, all detected by the Australian Square Kilometre Array Pathfinder (ASKAP), located at Murchison Radio-Astronomy Observatory (MRO) in the Australian Mid-West. For each FRB, the researchers compared the arrival times of radio waves of different frequencies to tally up the number of baryons that the burst encountered on its journey through intergalactic space. Then, using the distance between the FRB’s host galaxy and the Milky Way, Prochaska’s team could calculate the baryon density along that path. They could calculate the average density of matter as 1 Baryon per cubic meter.
But Michael Shull, Astrophysicist of the University of Colorado Boulder is of the opinion that taking five FRB is a very small number which comes to be too less to draw a conclusion about the matter density. “Once they get their error bars beaten down with many, many more bursts, I think that will really be the nail in the coffin on this baryon problem,” he says. To this time, all the researchers can say about the lost-and-found matter is that it is between galaxies. But with thousands of FRB observations, astronomers could start teasing out the slight variations in baryon density along the sight lines between the Milky Way and other galaxies to map out the cosmic web.