Tyler O'Neal, Staff Editor CHEMISTRY

Arecibo observatory helps find possible 'first hints' of low-frequency gravitational waves

Data from Arecibo Observatory in Puerto Rico has been used to help detect the first possible hints of low-frequency disturbances in the curvature of space-time.

The results were presented yesterday at the 237th meeting of the American Astronomical Society, which was held virtually, and are published in The Astrophysical Journal Letters. Arecibo Observatory is managed by the University of Central Florida for the National Science Foundation under a cooperative agreement.

The disturbances are known as gravitational waves, which ripple through space as a result of the movement of incredibly massive objects, such as black holes orbiting one another or the collision of neutron stars.

It's important to understand these waves as they provide insight into the history of the cosmos and expand researchers' knowledge of gravity past current limits of understanding.

Although the gravitational waves are stretching and squeezing the fabric of space-time, they don't impact humans and any changes in the relative distances between objects would change the height of a person by less than one one-hundredth the width of a human hair, says Joseph Simon, a postdoctoral associate in the Center for Astrophysics and Space Astronomy at the University of Colorado Boulder. Representative illustration of the Earth embedded in space-time which is deformed by the background gravitational waves and its effects on radio signals coming from observed pulsars. (Credit: Tonia Klein / NANOGrav){module INSIDE STORY}

Simon presented the findings to the society today, is the lead researcher of the paper, and is a member of the North American Nanohertz Observatory for Gravitational Waves, or NANOGrav, the team that performed the research.

NANOGrav is a group of more than 100 astronomers from across the U.S. and Canada whose common goal is to study the universe using low-frequency gravitational waves.

In 2015, NSF's Laser Interferometer Gravitational-Wave Observatory (LIGO) made the first direct observation of high-frequency gravitational waves using interferometry, a measurement method that uses the interference of electromagnetic waves.

The new findings made by NANOGrav researchers are unique because the astronomers found possible hints of low-frequency gravitational waves by using radio telescopes since they cannot be detected by LIGO. Both frequencies are important for understanding the universe.

Key to the research were two NSF-funded instruments - Green Bank Telescope in West Virginia and Arecibo Observatory in Puerto Rico.

Arecibo Observatory, with its 1,000-foot diameter dish, provided very precise data, while the Green Bank Telescope, which has much larger sky coverage, sampled a wider range of information needed to discriminate gravitational wave perturbations from other effects, Simon says.

"We time roughly half the pulsars with each telescope," he says. "Each telescope provides about half of our total sensitivity in a complementary way."

Although the researchers used Arecibo data for the study, they are no longer able to make observations with it since the observatory collapsed in December following broken cables in August and November.

"It was a truly horrible day when the telescope collapsed," Simon says. "It feels like the loss of a good friend, and we are so saddened for our friends and colleagues in Puerto Rico. Going forward, we hope to increase the amount of time we use on the Green Bank Telescope to at least partially compensate for Arecibo's loss. Another large collecting area radio telescope must be built in the U.S. soon if we want this research area to flourish."

The researchers were able to detect possible hints of low-frequency gravitational waves by using the telescopes to study signals from pulsars, which are small, dense, rotating stars that send out pulses of radio waves at precise intervals toward Earth.

This regularity makes them useful in astronomical study, and they are often referred to as the universe's timekeepers.

Gravitational waves can interrupt their regularity, causing deviations in pulsar signals arriving on Earth, thus indicating the position of the Earth has shifted slightly.

By studying the timing of the regular signals from many pulsars scattered over the sky at the same time, known as a "pulsar timing array," NANOGrav was able to detect minute changes in the Earth's position possibly due to gravitational waves stretching and shrinking space-time.

NANOGrav was able to rule out some effects other than gravitational waves, such as interference from the matter in the solar system or certain errors in the data collection.

To confirm direct detection of a signature from low-frequency gravitational waves, NANOGrav researchers will have to find a distinctive pattern in the signals between individual pulsars. At this point, the signal is too weak for such a pattern to be distinguishable, according to the researchers.

Boosting the signal requires NANOGrav to expand its dataset to include more pulsars studied for even longer lengths of time, which will increase the array's sensitivity. In addition, pooling NANOGrav's data together with those from other pulsar timing array experiments, a joint effort by the International Pulsar Timing Array, may reveal such a pattern. The International Pulsar Timing Array is a collaboration of researchers using the world's largest radio telescopes.

At the same time, NANOGrav is developing techniques to ensure the detected signal could not be from another source. They are producing supercomputer simulations that help test whether the detected noise could be caused by effects other than gravitational waves, in order to avoid false detection.

"It is incredibly exciting to see such a strong signal emerge from the data," Simon says. "However, because the gravitational-wave signal we are searching for spans the entire duration of our observations, we need to carefully understand our noise. This leaves us in a very interesting place, where we can strongly rule out some known noise sources, but we cannot yet say whether the signal is indeed from gravitational waves. For that, we will need more data."

Benetge Perera, a scientist at Arecibo Observatory who is a specialist in using observations of pulsars for the detection of gravitational waves, says the research aims to open a new window in the spectrum of gravitational wave frequencies.

"A low-frequency gravitational wave detection would enhance our understanding of supermassive black hole binaries, galaxy evolution, and the universe," says Perera, who is also a member of NANOGrav.

He says that despite the collapse of Arecibo Observatory, there are still many archived data to pore through to continue to learn about gravitational waves.

"Arecibo was very important as its timing data provided about 50 percent of NANOGrav's sensitivity to gravitational waves," he says. "I want to ensure that the sensitive data we collected before Arecibo's collapse has the highest possible scientific impact."

Bruce Lee's simulations highlight potential value of developing ways to reduce how long someone is contagious

Tyler O'Neal, Staff Editor CHEMISTRY

A new computational analysis suggests that a vaccine or medication that could shorten the infectious period of COVID-19 may potentially prevent millions of cases and save billions of dollars. The study was led by Bruce Lee along with colleagues in the Public Health Informatics, Computational, and Operations Research (PHICOR) team headquartered at the CUNY Graduate School of Public Health and Health Policy and the Lundquist Research Institute at Harbor-UCLA Medical Center, and publishes in the open-access journal PLOS Computational Biology.

While much of the public conversation surrounding COVID-19 vaccines and medications have focused on preventing or curing the infection, the vaccines and medications that may emerge could have subtler effects. Those that can't necessarily prevent or cure may still reduce how long someone is contagious. Results from PHICOR's computational simulation model show reductions in the contagious period of COVID-19 could avert thousands of hospitalizations and millions of cases and save billions of dollars. CREDIT Sarah Rebbert/PHICOR, 2020 (CC-BY){module INSIDE STORY}

To clarify the potential value of shortening the infectious period, Lee and colleagues created a computational model that simulates the spread of SARS-CoV-2, the virus that causes COVID-19. They used the model to explore how a vaccine or medication that can reduce the contagious period might alleviate the clinical and economic impact of the disease.

The simulations suggest that reducing the contagious period by half a day could avert up to 1.4 million cases and over 99,000 hospitalizations, saving $209.5 billion in direct medical and indirect costs--even if only a quarter of people with symptoms were treated--and incorporating conservative estimates of how contagious the virus may be. Under the same circumstances, cutting the contagious period by 3.5 days could avert up to 7.4 million cases. Expanding such treatment to 75 percent of everyone infected could avert 29.7 million cases and save $856 billion.

These findings could help guide research and investments into the development of vaccines or medications that reduce the infectious period of SARS-CoV-2. They could also help government agencies plan the rollout of such products and provide cost insights to guide reimbursement policies for third-party payers.

"There may be a tendency to overlook vaccines and other treatments that don't prevent a COVID-19 infection or cure disease," says Lee. "But this study showed that even relatively small changes in how long people are contagious can significantly affect the transmission and spread of the virus and thus save billions of dollars and avert millions of new cases."

"This study shows that vaccine and medication development efforts for COVID-19 should focus on the impact to actually help curb the spread of the COVID-19 pandemic, not just benefits of a single patient," says James McKinnell, a co-author of the study. "Widespread treatment, in combination with other prevention efforts, could prove to be the tipping point."

Japanese scientists make Ising models easier to implement physically for solving combinatorial optimization problems

Tyler O'Neal, Staff Editor CHEMISTRY

Given a list of cities and the distances between each pair of cities, how do you determine the shortest route that visits each city exactly once and returns to the starting location? This famous problem is called the "traveling salesman problem" and is an example of a combinatorial optimization problem. Solving these problems using conventional supercomputers can be very time-consuming, and special devices called "quantum annealers" have been created for this purpose.

Quantum annealers are designed to find the lowest energy state (or "ground state") of what's known as an "Ising model." Such models are abstract representations of a quantum mechanical system involving interacting spins that are also influenced by external magnetic fields. In the late 90s, scientists found that combinatorial optimization problems could be formulated as Ising models, which in turn could be physically implemented in quantum annealers. To obtain the solution to a combinatorial optimization problem, one simply has to observe the ground state reached in its associated quantum annealer after a short time. A method that can reduce the bit width of a quantum system called the "Ising model" to solve combinatorial optimization problems.{module INSIDE STORY}

One of the biggest challenges in this process is the transformation of the "logical" Ising model into a physically implementable Ising model suitable for quantum annealing. Sometimes, the numerical values of the spin interactions or the external magnetic fields require many bits to represent them (bit width) too large for a physical system. This severely limits the versatility and applicability of quantum annealers to real-world problems. Fortunately, in a recent study published in IEEE Transactions on Computers, scientists from Japan have tackled this issue. Based purely on mathematical theory, they developed a method by which a given logical Ising model can be transformed into an equivalent model with the desired bit width to make it "fit" a desired physical implementation.

Their approach consists of adding auxiliary spins to the Ising model for problematic interactions or magnetic fields in such a way that the ground state (solution) of the transformed model is the same as that of the original model while also requiring a lower bit width. The technique is relatively simple and completely guaranteed to produce an equivalent Ising model with the same solution as the original. "Our strategy is the world's first to efficiently and theoretically address the bit-width reduction problem in the spin interactions and magnetic field coefficients in Ising models," remarks Professor Nozomu Togawa from Waseda University, Japan, who led the study.

The scientists also put their method to the test in several experiments, which further confirmed its validity. Prof. Togawa has high hopes, and he concludes by saying, "The approach developed in this study will widen the applicability of quantum annealers and make them much more attractive for people dealing with not only physical Ising models but all kinds of combinatorial optimization problems. Such problems are common in cryptography, logistics, and artificial intelligence, among many other fields."