The universe’s ‘missing matter’ problem has finally been solved

When Jean-Pierre Macquart came home from work one night in 2019, he was full of excitement. He had just helped, with the help of a team of international astronomers, solve a decades-old cosmic puzzle. He couldn’t wait to tell his wife.

Macquart had successfully weighed the universe for the first time and finally figured out where half of the normal matter was hiding. But when he stepped through the door and was ready to explain his monumental find, the ethereal secrets of the cosmos He had found that he was quickly replaced by the practical aspects of existence.

In a matter of minutes, he fought two children aged two and four, went to the kitchen, and helped his wife cook. When he thinks about the evening, he says that he probably helped with the food, but it wasn’t that memorable. His head was “still up in the sky”. The discovery he made earlier in the day, which he says has “put the mystery of the missing matter problem of the universe to bed” still played in his head.

In a new study published in the journal Nature Macquart and a team of international astronomers will report on their discovery for the first time on Wednesday. You reveal like a stream of bizarre signals sent from space helped solve an ongoing puzzle about normal matter in the universe – and how its technology opened up a whole new perspective on the cosmos.

The problem of the lack of matter

Macquart, astronomer at the International Center for Radio Astronomy Research in Australia, and his team searched the cosmos for fast radio bursts (FRBs) using a giant telescope array in the Australian outback called the Australian Square Kilometer Array Pathfinder. The extremely energetic eruptions travel through the vast emptiness of space and are captured by the 36 antennas from ASKAP, which are stationed in the radio-silent desert of Western Australia.

Macquart and a large number of institutions from around the world, who are part of the Commensal Real-Time ASKAP Fast Transients Survey team, recognized that the bursts can also be used to identify the “missing matter” of the universe.

The universe consists of “ordinary matter”, dark matter and dark energy. The latter components make up about 95% of the known universe and are incredibly mysterious. We know they exist, but we could never recognize them.

On the other hand, you have ordinary matter. Macquart explains that ordinary matter or baryonic matter is all the “stuff” that you and I are made of, and what makes up the planets, stars, and galaxies. “It’s everything you can imagine in the periodic table,” he says. Early calculations in the 1990s showed that this type of matter made up the other measly 5% of all matter in the universe, and scientists searched for it.

“When you watched … a few decades ago, you could only make up about half of it,” says Macquart. The scientists enumerated all the matter they could see – the galaxies, stars, planets, gases – and miserably missed their 5% target. The matter was missing in their measurements.

But astronomers had a clue where to find it. Over the years a number of different methods were used to try to identify the missing matter, but the researchers were unable to adequately identify it all the normal matter in the entire universe, mainly because it focused on certain regions of space. Macquart compares this to trying to say how big a dog is “just by looking at the size of its tail”.

With the new technique developed by the team – with FRBs – you can look at the whole dog.

“What FRBs do is go a long way [of space] Where [other] Techniques just fall over, “he says.

Explosion from the past

Fast radio waves are mysterious and fascinating cosmic phenomena. They were first identified in 2007, but their origins continue to elude scientists. They are still pretty rare, but we are getting better at finding them. New telescopes and radio fields such as ASKAP enable astronomers to locate the source of these radio wave bursts from space.

ASKAP is a key part of the new study because it basically always observes a large part of the sky, like a cosmic big brother. 10 trillion measurements are taken every second, and then an average of 1 billion measurements per second are taken to look for signs of FRBs.

To ping an ASKAP antenna on Earth, the radio waves travel from distant galaxies and go on a long journey that takes them through the vast nothing of space between galaxies. While we traditionally consider this region of space to be empty, it is actually full of particles like electrons that can hit the wave when it flies through the universe from up to 3 billion light years away.

“As the radio waves move through the cosmos, they interact with the free electrons and smear the radio signal,” said Geraint Lewis, an astrophysicist at the University of Sydney who was not involved in the study. It was this smearing of the radio signal that was the key to finding the missing matter.

According to Lewis, astronomers counted “the number of electrons that lie along our line of sight” back to the FRB sources, thus providing a measure of the hidden matter in the cosmos. After examining five different FRBs in five different locations, the team found that their measurements almost perfectly matched predictions about how much normal matter should exist in the universe.

The riddle was finally solved and cosmologists could breathe a little easier – their models for understanding the universe were not wrong.

“It calms what a real cosmic embarrassment could have been,” said Xavier Prochaska, astronomer at the University of California at Santa Cruz and co-author of the new paper, during a media briefing. “We all expected to discover it at some point, but it was an embarrassment until we did.”

Illustration of the cosmic network

After the missing matter puzzle is solved, the teams believe that they can use FRBs as a new tool to study the cosmos.

The FRB detection method is very sensitive compared to previous methods and enables researchers to recognize ordinary matter trapped in the huge gas-filled space between galaxies. This means that astronomers may be able to image the so-called cosmic network, the filaments that connect the universe to one another.

“The technology … will be a technology that we can use to find out where the gas is,” says Prochaska.

“As of today, we can mainly show you this picture from a computer simulation of the cosmic network, but give us five years and at least 100 more of these FRBs and we should be able to show you a high fidelity map of the real universe . “

The team will continue to search for FRBs with ASKAP, and Macquart notes that they are building a “giant machine” that will be able to find more bursts, increasing the detection rate 20-fold. Such a jump could allow the team to pick up 100 of the signals within a year and help change our view of the universe until the earliest days.

“Perhaps we can even say something about the era of reionization when the universe changed from neutral to ionized,” he says.

Of course, the missing matter makes up only a very small percentage of the total matter in the universe, and there are big cosmological questions that still need to be answered.

“Although we know where all of the normal material is distributed throughout the universe, we still have less than 5% of the cosmos bound,” says Lewis. “Dark matter and dark energy remain the next nut to crack.”

On the other hand, Macquart has another pressing riddle to turn his attention to after his discovery has been released to the world. Unlike the missing matter problem, it is one that many of us on Earth can easily understand. One that speaks a little more about the practical aspects of existence.

What on earth should I cook for dinner?