An international team of astronomers has used mysterious fast radio bursts to solve a decades-old mystery of “missing matter,” material long predicted to exist in the universe but never detected — until now.

With this method, the researchers have now found all of the missing “normal” matter in the vast space between stars and galaxies. The team, which includes scientists based in Australia, the United States and Chile, announced its findings in a published May 27 in the journal Nature.

The missing matter that the scientists detected is not dark matter, which remains elusive and accounts for about 85% of the total matter in the universe. Instead, what the team detected is so-called “normal” or baryonic matter — like the protons and neutrons that make up stars, planets and people. But this missing baryonic matter was not in a location that astronomers can easily study.

“More than 90% of the atoms in the universe are not in galaxies, but in a very dilute phase between galaxies,” said co-author , an assistant professor of astronomy at the 91̽��. “The density of this dilute phase is on average about one electron per cubic meter, compared to the air we breathe, which is more like 10 to the 28th power — a 1 followed by 28 zeros — electrons per cubic meter.”

Due to this low density, astronomers had tried and failed for almost 30 years to detect this matter, according to lead author . But they knew it was out there.

“We know from measurements of the Big Bang how much matter there was in the beginning of the universe,” said Macquart, who is an associate professor at Curtin University in Perth, Western Australia, and scientist with the International Centre for Radio Astronomy Research, also in Australia. “But when we looked out into the present universe, we couldn’t find half of what should be there. It was a bit of an embarrassment.”

The researchers were able to directly detect the missing matter using fast radio bursts. These are brief flashes of energy that appear to come from random directions in the sky and last for just milliseconds. Scientists don’t yet know what causes them but it must involve incredible energy, equivalent to the amount released by the sun in 80 years. They have been difficult to detect as astronomers don’t know when and where to look for them.

In order to detect the missing baryonic matter, the researchers had to collect precise data on fast radio bursts. The team used the Australian Square Kilometre Array Pathfinder, a radio telescope in Western Australia, to detect fast radio bursts and pinpoint their origins within distant galaxies. This is the only telescope currently operating that both detects a fast radio burst and determines its galaxy of origin, according to McQuinn.

“When the burst arrives at the telescope, it records a live action replay within a fraction of a second,” said co-author Keith Bannister from the Commonwealth Scientific and Industrial Research Organisation, who designed the pulse capture system used in this research. “This enables the precision to determine the location of the fast radio burst to the width of a human hair held 200 meters away.”

When they found a galaxy that had belched out a burst, the researchers used data from optical telescopes to measure how far away the galaxy is from Earth. By knowing the fast radio burst’s origin and distance, the team could then use data on how the burst traveled through the vast, low-density space between galaxies to detect the missing baryonic matter.

“The radiation from fast radio bursts gets spread out by the missing matter in the same way that you see the colors of sunlight being separated in a prism,” said Macquart.

The team needed only six fast radio bursts to detect the missing baryonic matter, according to Macquart. In addition, the team pinned down the relationship between how far away a fast radio burst is and how the burst spreads out as it travels through the universe.

With this new technique to detect the previously missing baryonic matter, scientists now want to understand how it is distributed throughout the universe. Observing additional bursts will help them better understand the distribution of matter within these intergalactic regions, providing new information about the invisible structure of the universe, according to McQuinn.

“Understanding the locations of this missing matter — such as whether it is around galaxies or far from them — is likely key to understanding how galaxies form and take the shape they have today,” said McQuinn.

Additional co-authors are from the University of California, Santa Cruz; Shivani Bhandari and of the Commonwealth Scientific and Industrial Research Organisation in Australia; , , and of the Swinburne University of Technology in Melbourne; , and D.R. Scott with the International Centre for Radio Astronomy Research; Lachland Marnoch and Stuart Ryder of Macquarie University in Sydney; and at the Pontificia Universidad Católica de Valparaíso in Chile. The research was funded by the Australian Research Council and the Australian government.

For more information, contact McQuinn at mcquinn@uw.edu.

Adapted from a by Kirsten Gottschalk at the International Centre for Radio Astronomy Research.

Using one cosmic mystery to probe another, an international team of astronomers has analyzed the signal from a fast radio burst — an enigmatic blast of cosmic radio waves lasting less than a millisecond — to characterize the diffuse gas in the halo of a massive galaxy. , published online  Sept. 26 in Science, reveal that the massive galaxy sports an unexpectedly quiescent halo, with a very low density and weak magnetic field.

This discovery gave scientists a rare glimpse of galactic halos, which contain clues to how gas feeds onto and is expelled from galaxies. Astronomers think these galactic halos could be more massive than the galaxies themselves, and that studying them could reveal how galaxies form.

“The signal from this fast radio burst went just by the edge of a galaxy, giving us our first glimpse into the structure of the most diffuse halo gas that surrounds galaxies,” said co-author , an assistant professor of astronomy at the 91̽��. “This event demonstrates a technique that is going to transform our understanding of this diffuse gas.”

McQuinn proposed this technique in a 2014 published in the Astrophysical Journal Letters.

Vast halos of low-density gas extend far beyond the luminous parts of galaxies where the stars are concentrated. Although this hot, diffuse gas makes up more of a galaxy’s mass than stars, and may make up as much as half of the gas in the universe, it is nearly impossible to see. In November 2018, astronomers detected a fast radio burst that passed through the halo of a massive galaxy on its way toward Earth, allowing them to learn about the nature of the halo gas from this elusive radio signal.

Astronomers still don’t know what produces fast radio bursts, and only recently could trace some of these very short, very bright radio signals back to the galaxies in which they originated. The November 2018 burst, named FRB 181112, was detected and localized by the instrument that pioneered this technique, Australian Square Kilometre Array Pathfinder, a radio telescope in Western Australia operated by the Commonwealth Scientific and Industrial Research Organisation. Follow-up observations with European Southern Observatory’s Very Large Telescope in Chile identified not only its host galaxy but also a bright galaxy in front of it.

“When we overlaid the radio and optical images, we could see straight away that the fast radio burst pierced the halo of this coincident foreground galaxy and, for the first time, we had a direct way of investigating this otherwise invisible matter surrounding this galaxy,” said co-author at Swinburne University of Technology.

A galactic halo contains both dark matter and baryonic matter — or ordinary matter — which is expected to be mostly hot ionized gas. While the luminous part of a massive galaxy might be around 30,000 light-years across, its roughly spherical halo is ten times larger. Halo gas fuels star formation as it falls in toward the center of the galaxy, while other processes, such as supernova explosions, can eject material out of the star-forming regions and into the galactic halo. One reason astronomers want to study the halo gas is to better understand these ejection processes, which can shut down star formation.

“The halo gas is a fossil record of these ejection processes, so our observations can inform theories about how matter is ejected and how magnetic fields are threaded through galaxies,” said , a professor of astronomy and astrophysics at the University of California, Santa Cruz and lead author on the paper.

Contrary to expectations, the results of the new study indicate a very low density and a relatively feeble magnetic field in the halo of this intervening galaxy.

“The radio signal was largely unperturbed by the galaxy, which is in stark contrast to what previous models predict would have happened to the burst,” said Prochaska.

FRB 181112 consisted of several pulses, each lasting less than 40 microseconds — ten thousand times shorter than the blink of an eye. McQuinn helped lead the interpretation of this signal. The short duration of the pulses puts an upper limit on the density of the halo gas, because passage through a denser medium would lengthen the radio signals. The researchers calculated that the density of the halo gas must be less than a tenth of an atom per cubic centimeter, which is equivalent to several hundred atoms in a volume the size of a balloon.

“Like the shimmering air on a hot summer’s day, the tenuous atmosphere in this massive galaxy should warp the signal of the fast radio burst,” said co-author , an astronomer at the International Center for Radio Astronomy Research and associate professor at Curtin University. “Instead we received a pulse so pristine and sharp that there is no signature of this gas at all.”

The density constraints also limit the possibility of turbulence or clouds of relatively cool gas within the halo, which astronomers have theorized might be present in halos.

The FRB signal also yields information about the magnetic field in the halo, which affects the polarization of the radio waves. Analyzing the polarization as a function of frequency gives a “rotation measure” for the halo, which the researchers found to be about a billion times weaker than an ordinary refrigerator magnet, said Prochaska.

Since these results come from only one galactic halo, the team cannot say whether the low density and magnetic field strength are unusual or if previous studies of galactic halos have overestimated these properties. But radio telescopes can use fast radio bursts to study many more galactic halos and resolve their properties.

Additional co-authors are Sunil Simha at UC Santa Cruz; Ryan Shannon, Adam Deller and Chris Flynn at the Swinburne University of Technology; Lachlan Marnoch and Stuart Ryder of Macquarie University; Keith Bannister, Shivani Bhandari, John Bunton, Elizabeth Mahony and Chris Phillips of the Commonwealth Science and Industrial Research Organisation; Rongmon Bordoloi of the North Carolina State University; Hyerin Cho of the Gwangju Institute of Science and Technology; Hao Qiu of the University of Sydney; and Nicolas Tejos of the Pontificia Universidad Católica de Valparaíso. The work was funded by the National Science Foundation, the Australian Research Council and the Pontificia Universidad Católica de Valparaíso.

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For more information, contact McQuinn at mcquinn@uw.edu.

Adapted from by the University of California, Santa Cruz.

The 126 were nominated by senior colleagues in their field, department or institution. Committees with the Sloan Foundation then examined each nominee’s research goals, publications and achievements and ultimately selected the winners. Each fellow will receive $55,000 to apply toward research endeavors. This year’s fellows come from 52 institutions across the United States and Canada, spanning fields from mathematics to biochemistry. The new Sloan Fellows at the 91̽��reflect this diversity, probing complex questions from neuroscience to quantum mechanics.

The wide view of history

Astronomer ‘s objective is to understand the influence of history on our present day, but not the Battle of Trafalgar or the Industrial Revolution. McQuinn is a theoretical astrophysicist who is trying to understand the drastic changes our universe underwent in its first billion years. In order to understand why the universe is structured as it is today, some 13 billion years after the Big Bang, McQuinn believes we must understand two significant transitions it went through when hot and dense material cooled and expanded rapidly. In the first event, when the universe was about 400,000 years old, the soup of electrons and protons produced in the Big Bang formed hydrogen atoms, liberating trapped light and making the universe transparent. Several hundred million years later, electrons from that same hydrogen became ionized by light from the first stars and galaxies as gravity began to shape the universe.

“We know very little about this period in history,” said McQuinn. “Yet it had a huge impact on where stars and galaxies are, what the material is between them and why the universe evolved into its present form.”

The quest for automation in software development

In the Department of Computer Science & Engineering, focuses on techniques for developing the software of tomorrow. Many of today’s technological marvels, from smartphones to space probes, rely on software that is developed manually by experts, at great cost. Torlak’s focus is on applying automated reasoning to key aspects of software development, making it easier and faster to produce software that will run reliably and efficiently.

To that end, she has developed Rosette, a programming language that makes automated reasoning available to a wide range of programmers. Rosette helps programmers automatically synthesize, verify and debug code.  It has been applied to synthesizing software that will power the next generation of ultra-low-power electronics and to verifying safety-critical software that drives state-of-the-art medical devices.

The next computer

Physicist is also focused on the future of computation, but on a decidedly smaller scale.  A theorist, he works on the promise of quantum computing and the challenges of designing and building a working quantum computer.

“Quantum computers would operate on the principles of quantum mechanics,” said Laumann. “Successfully designing one of these devices would represent a mastery of the laws of physics and potentially revolutionize the power of computation.”

We live in a universe structured on the principles of quantum mechanics, the infinitesimally small interactions that govern the size, behavior and properties of all known subatomic particles. But all of our current methods for computation — from calculations to information transmission — are based on the large-scale interactions among atoms and other particles. Exploiting the fundamental properties of quantum mechanics would unlock the potential for algorithms, calculations and computational power that are simply impossible today, but also requires mastering the physical interactions of individual particles on a large scale.

“But controlling these interactions on such a large scale gets exponentially difficult,” said Laumann. “We need theories to develop new hardware and processes to trap, manipulate and control these particles, which is one of the goals of my research.”

And the computer within

For biologist and data scientist , a member of the 91̽�� and data-science fellow with the 91̽��, computer-based methods could be the key to understanding how our brains process information, make decisions and execute tasks from walking to speaking.

“The cells in your brain literally talk to each other using electricity,” said Brunton. “The way you experience the world, produce sensations, reason and experience emotion are all built on a foundation of electrical processes going on within and between brain cells.”

Brunton’s research focuses on understanding how this electrical information is translated into computational processes. Scientists use electrodes to measure and record the electrical activity among groups of neurons and individual neurons in the brain. Brunton takes this information, recorded from human patients as well as research animals like mice and rats, and deciphers the computational processes that underlie this electrical activity.

“I want to understand what this very large collection of cells are saying and how they’re saying it,” said Brunton.

It’s a process that unfolded within her own brain when 91̽��professor Toby Bradshaw, the chair of the Department of Biology, informed Brunton that she had been named a Sloan Fellow for 2016.

“I didn’t believe it at first,” said Brunton. “I made him show me the email announcing it.”

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