Fast radio bursts (FRBs) are a mystery in themselves. Find out how they enabled scientists to determine the mass of conventional matter in the Universe.
We’ve discussed dark matter many times in these pages. That’s the bizarre, invisible matter that scientists can’t account for when they study how gravity affects the structure and motion of distant spiral galaxies.
Cosmologists sometimes call dark matter “missing matter,” but in this story, we’re looking at missing matter of the conventional kind. Scientists at the International Centre for Radio Astronomy Research (ICRAR) have solved a puzzle that has baffled astronomers for decades.
Cosmologists can calculate how much matter there was in the Universe at the start of the Big Bang. However, when they calculate the amount of matter observable in our present-day Universe, about half of it goes unaccounted for.
75% of Conventional Matter is Between Galaxies
That’s because about 75% of the conventional matter in the Universe is thinly distributed in between the galaxies. Scientists have tried to measure it using spectrograms, but the results have been spotty.
However, the journal Nature just published a paper by a research team led by Associate Professor Jean-Pierre Macquart of Australia’s Curtin University. Professor Macquart and his team have used a new technique to solve the conventional missing matter mystery.
Back in 2007, Professor Duncan Lorimer at the Parkes Observatory in Australia was reviewing old records on pulsars with his student David Narkevic. They noticed a pulse of radio energy close to a nearby dwarf galaxy called the Small Magellanic Cloud.
Flash of Radio Energy Lasted Less Than 5 Microseconds
The flash of radio energy lasted less than 5 milliseconds. It caught their interest because they could tell that it had come from deep space rather than either the Milky Way or the Small Magellanic Cloud.
This was the first discovery of what we now call fast radio bursts. Radio astronomers call this first instance of these bursts of radio waves the Lorimer Burst in Professor Lorimer’s honour.
Most fast radio bursts originate outside of our galaxy in what scientists called the intergalactic medium. Astronomers haven’t been able to pin down their cause or origin.
AStronomers Haven’t Pinned Down cause or origin
Some of the hypotheses about where fast radio bursts come from include collisions between neutron stars or black holes. Others involve unusually energetic supernovas or even extraterrestrial intelligence.
Whatever the source, it must have enormous power. Generating one fast radio burst releases as much energy in a nanosecond as our sun does in 80 years.
Bizarre, as fast radio bursts are, Professor Macquart and his team realized that they could use them to detect missing matter in-between galaxies. Fast radio bursts spread out into spectra when they pass through particles of matter, something like how sunlight spreads into a rainbow because of water droplets in the atmosphere.
Fast Radio Bursts Spread Out Into Spectra
Team member Professor J. Xavier Prochaska explained that “The discovery of fast radio bursts and their localization to distant galaxies were the key breakthroughs needed to solve this mystery,” he said.
To calculate the dispersion measure of these fast radio bursts, the researchers used the Australian Square Kilometre Array Pathfinder (ASKAP) radio telescope. It’s a forerunner to the planned Square Kilometre Array (SKA), which sites in Australia and South Africa will host.
Study co-author Associate Professor Ryan Shannon said, “ASKAP both has a wide field of view, about 60 times the size of the full Moon, and can image in high resolution. This means that we can catch the bursts with relative ease and then pinpoint locations to their host galaxies with incredible precision.”
“Able to Determine the Density of the Universe”
Professor Marquart described the stunning results. “We’ve now been able to measure the distances to enough fast radio bursts to determine the density of the Universe,” he said. “We only needed six to find this missing matter.”
From these six samples, the team could estimate the density of matter in the space through which the fast radio bursts had travelled. They measured how the presence of photons and neutrons in space had diffused the radio signals.
From there, they could calculate the matter density throughout the Universe. This reconciled the team’s findings with the mass at the time of the big bang.
REconciled Findings with the Mass at the Big Bang
Their results support what the matter density of the Universe should be based on the Cosmic Microwave Background (the trace energy from the Big Bang explosion). They also coincide with the number of atoms that the Big Bang generated (Big Bang Nucleosynthesis).
The study findings also tell us why the missing matter was so hard to spot. “Intergalactic space is very sparse,” Professor Marquart said. “The missing matter was equivalent to only one or two atoms in a room the size of an average office.”
Genius has been described as seeing what everyone has seen and thinking what no one else has thought. The team from ICRAR has given us a stunning example of that.
Solved one of the Deepest Mysteries in Cosmology
They took a look at an unexplained phenomenon and asked themselves how they could put it to use. Rather than puzzling over why fast radio bursts were there, they put them to work and, in the process, solved one of the deepest mysteries in cosmology.
Determining the energy density of the entire Universe based on six fast radio bursts, each of which is over in a flash, is quite an achievement. A lot of astronomical discoveries are like that.
The media focus on the flashy adventures of space exploration. Even so, the vast majority of astronomy comes from more straightforward innovations on the ground.
Vast Majority of Astronomy is Innovations on the Ground
Humanity’s ingenuity, gleaning every speck of information out of what’s visible from our vantage point, astounds me. Over the last century or so, we’ve learned far more about the nature of the Universe than we did in the previous ten millennia.
Of course, the more profound mystery is dark matter. At least in the case of ordinary missing matter, scientists knew what to look for.
They realized that ordinary matter consists of baryons—particles like protons and neutrons. All that we know about dark matter is that it seems to cause gravity.
All WE Know About Dark Matter is that It Causes Gravity
Nobody has ever spotted the particles of which physicists think dark consists. These Weakly Interacting Massive Particles (WIMPs) are still nothing more than speculation.
Of course, that applied to the Higgs Boson as well until CERN discovered it It wouldn’t surprise me in the slightest if some similarly ingenious technique finds the elusive dark matter and its particles.
As long as our curiosity continues to drive us to learn the whole story of our place in the Universe, we’re sure to solve the dark matter mystery too, in time. No doubt that knowledge will lead us to even more profound questions.
We always have more to learn if we dare to know.
Cosmic Bursts Unveil Universe’s Missing Matter
A census of baryons in the Universe from localized fast radio bursts
The 5 Big Questions We Need Cosmology to Answer
Missing Matter Missing in 19 Dwarf Galaxies
Dark Matter: Is That What’s at the Centre of the Milky Way