Tyler O'Neal, Staff Editor INDUSTRY

WVU researchers find first hints of low-frequency gravitational wave background

In data gathered and analyzed over 13 years, the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) Physics Frontiers Center (PFC) has found an intriguing low-frequency signal that may be attributable to gravitational waves.

NANOGrav researchers - including a number from West Virginia University's (WVU's) Department of Physics and Astronomy and the Center for Gravitational Waves and Cosmology - measure the times of arrival of radio pulses from exotic stars called pulsars with large radio telescopes, including the Green Bank Telescope (GBT) in Pocahontas County, West Virginia. Pulsars are small, dense stars that rapidly rotate, emitting beamed radio waves, much like a lighthouse. The results from this most recent dataset show perturbations in the arrival times from these pulsars that may indicate the effects of gravitational waves, as reported recently in The Astrophysical Journal Letters. The most likely source of these gravitational waves is the combined signal from all the supermassive black hole pairs at the cores of merged, distant galaxies.

NANOGrav has been able to rule out some effects other than gravitational waves, such as interference from the matter in our own solar system or certain errors in the data collection. These newest findings set up direct detection of gravitational waves as the possible next major step for NANOGrav and other members of the International Pulsar Timing Array (IPTA), a collaboration of researchers using the world's largest radio telescopes.

Dustin MadisonDustin Madison, a postdoctoral researcher at WVU, comments "We can't yet say with confidence that what we're seeing is gravitational waves, but if it is, the "signal" makes a lot of sense given what we think we know about supermassive black holes. This was always how this was going to play out...enticing hints of a signal before we would be able to definitively claim a detection. We're on the right track to make that definitive assessment in just a couple of years." Looking to the future, he thinks researchers will then be able to characterize the signal and learn more from it for years and years to come. {module INSIDE STORY} 

Gravitational waves are ripples in space-time caused by the movements of incredibly massive objects, such as black holes orbiting each other or neutron stars colliding. Astronomers cannot observe these waves with a telescope-like they do stars and galaxies. Instead, they measure the effects passing gravitational waves have, namely tiny changes to the precise position of objects - including the position of the Earth itself. Gravitational waves were first detected in 2015 by NSF's Laser Interferometer Gravitational-Wave Observatory (LIGO) by a team including other researchers at WVU. As light from distant objects, gravitational waves are a cosmic messenger signal - one that holds great potential for understanding "dark" objects, like black holes.

NANOGrav chose to study the signals from pulsars because they serve as detectable, dependable Galactic clocks. These small, dense stars spin rapidly, sending pulses of radio waves at precise intervals toward Earth. Pulsars are in fact commonly referred to as the universe's timekeepers, and this unique trait has made them useful for astronomical study.

But gravitational waves can interrupt this observed regularity, as the ripples cause space-time to undergo tiny amounts of stretching and shrinking. Those ripples result in extremely small deviations in the expected times for pulsar signals arriving on Earth. Such deviations indicate that 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 works to detect minute changes in the Earth's position due to gravitational waves stretching and shrinking space-time.

WVU Professor and NANOGrav member, Sarah Burke-Spolaor explains, "This signal is incredibly enticing. It could be that our orchestra is tuning up, hinting that we're about to hear the grand symphony of waves from supermassive black holes that we expect pervades the Universe," Burke-Spolaor reflects. She adds, "If this signal is indeed gravitational waves, future study will offer unique insights into how the biggest black holes and galaxies in our universe form and evolve." Sarah Burke-Spolaor{module INSIDE STORY}

"NANOGrav has been building to the first detection of low-frequency gravitational waves for over a decade and today's announcement shows that they are on track to achieving this goal," said Pedro Marronetti, NSF Program Director for gravitational physics. "The insights that we will gain on cosmology and galaxy formation are truly unparalleled."

NANOGrav is a collaboration of U.S. and Canadian astrophysicists and a National Science Foundation Physics Frontiers Center (PFC). Maura McLaughlin, WVU Professor and Co-Director of the NANOGrav PFC, added "We are so grateful for the support of the NANOGrav PFC, that's allowed us to dramatically increase both the number of pulsars being timed and the number of participants working on NANOGrav research over the past six years". WVU has played a significant role in the PFC; 12 of the 63 authors on this paper are WVU faculty, postdocs, and students. And low-frequency gravitational wave detection is one of the main aims of the Center for Gravitational Waves and Cosmology, formed in 2015 along with the award of the PFC. As, Duncan Lorimer, WVU Professor and Eberly College Associate Dean for Research, notes "The long-term institutional support provided by the College and University has played a critical role in NANOGrav's success since its inception in 2007".

NANOGrav created their pulsar timing array by studying 47 of the most stably rotating "millisecond pulsars" with both the GBT and the Arecibo Observatory in Puerto Rico as reported in the January 2021 Astrophysical Journal Supplements. Not all pulsars can be used to detect the signals that NANOGrav seeks - only the most stably rotating and longest-studied pulsars will do. These pulsars spin hundreds of times a second, with incredible stability, which is necessary to obtain the precision required to detect and study gravitational waves.

Of the 47 pulsars studied, 45 had sufficiently long datasets of at least three years to use for the analysis. Researchers studying the data uncovered a spectral signature, a low-frequency noise feature, that is the same across multiple pulsars. The timing changes NANOGrav studies are so small that the evidence is not apparent when studying any individual pulsar, but in aggregate, they add up to a significant signature.

Potential Next Steps

To confirm direct detection of a signature from gravitational waves, NANOGrav's researchers will have to find a distinctive pattern in the signals between individual pulsars. At this point, the sensitivity of the experiment is not currently good enough for such a pattern to be distinguishable. 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, by pooling NANOGrav's data together with those from other pulsar timing array experiments, a joint effort by the IPTA may reveal such a pattern. Students and faculty at WVU are important contributors to this effort, and in fact, 24 WVU students have traveled to IPTA partner countries to undertake research abroad as part of NSF-funded programs led by WVU.

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.

While the next several years hold a great deal of scientific promise, they are not without challenges. With the recent collapse of the Arecibo Observatory's 305-meter telescope, NANOGrav will be seeking alternate sources of data and working even more closely with their international colleagues. Although significant delays in detection are not expected, due to years of very sensitive Arecibo data already contributing to their datasets, the loss of Arecibo is a terrible blow to science in general. For NANOGrav, it may impact the ability to characterize the background and detect other types of gravitational-wave sources in the future in the absence of another instrument. The loss of the telescope also directly impacts the graduate studies of several WVU Ph.D. students. NANOGrav members are deeply saddened by the collapse and its impact on the staff and the island of Puerto Rico.

Publications referenced in this article

Gravitational Wave Search:
https://iopscience.iop.org/article/10.3847/2041-8213/abd401

Narrowband Dataset:
https://iopscience.iop.org/article/10.3847/1538-4365/abc6a0

Wideband Dataset:
https://iopscience.iop.org/article/10.3847/1538-4365/abc6a1

For more information about NANOGrav, please visit the website at http://nanograv.org.

At cosmic noon, puffy galaxies make stars for longer

Tyler O'Neal, Staff Editor INDUSTRY

Galaxies with extended disks maintain productivity, research reveals

Massive galaxies with extra-large extended "puffy" disks produced stars for longer than their more compact cousins, new modelling reveals.

In a paper published in the Astrophysical Journal, researchers led by Dr Anshu Gupta and Associate Professor Kim-Vy Tran from Australia's ARC Centre of Excellence in All Sky Astrophysics in 3 Dimensions (ASTRO 3D), show that the sheer size of a galaxy influences when it stops making new stars. An ensemble of twenty-five disk galaxies. The view on the left shows light emitted in the H-alpha line from interstellar gas as a result of ongoing star-formation, while the panels on the right shows the optical light emitted by a mix of young (bluer) and old (redder) stars. Each galaxy can be seen rotated edge-on below its face-on view. CREDIT TNG Collaboration

{module INSIDE STORY} "There's a period in the life of the Universe known as the 'cosmic noon', which occurred about 10 billion years ago," said Dr Gupta.

"That was when star formation in massive galaxies was at its peak. After that, gas in most of these galaxies grew hot - in part because of the black holes in the middle of them - and they stopped forming stars.

"In galaxies that are really, really stretched out, however, we found that things didn't heat up as much and the black holes didn't exert such a great influence, so stars kept getting made over a longer period."

Dr Gupta and Dr Tran, both of whom are based at the University of NSW, Sydney, found that they could predict the end of star formation based on the size of a galaxy's disk - the flat, circular region surrounding its centre, comprising stars, hydrogen gas and dust.

"Where the stars in the disk are widely distributed - you could call it 'puffy' - the gas stays cooler, so continues to coalesce under gravity and form new stars," said Dr Gupta.

"In galaxies with more compact disks, the gas heats up quite quickly and is soon too energetic to mash together, so the formation of stars finishes by just after cosmic noon. Puffy disks keep going much longer, say as far as cosmic afternoon tea."

To make their findings, the researchers, with colleagues from Melbourne, Germany, Mexico and the United States, used cosmological galaxy formation simulations from an international collaboration known as the IllustrisTNG project.

This was integrated with deep observations from an Australian-led project known as the Multi-Object Spectroscopic Emission Line (MOSEL) Survey.

"The IllustrisTNG simulations required millions of hours of supercomputer time," said Dr Tran.

"And the MOSEL survey needs both the WM Keck Observatory in Hawai'i and the Hubble Space Telescope.

"The results mean that for the first time we've been able to establish a relationship between disk size and star-making. So now astronomers will be able to look at any galaxy in the Universe and accurately predict when it will stop making stars - just after lunch, or later in the cosmic afternoon."

The Milky Way, incidentally, is a massive galaxy that is still making stars. That's because it was something of a cosmic late-starter. When cosmic noon arrived it was very small - containing only one-tenth of the star mass it hosts today - and did not attain 'massive' status until much, much later.

As a result, the gas and dust within it has not yet warmed up enough to quench the star-making process.

It is not, however, an extended puffy galaxy, so it will quench, relatively speaking, sooner rather than later.

"Cosmic noon was a long time ago," said Dr Gupta. "I'd say that by now the Universe has reached cosmic evening. It's not night-time yet, but things have definitely slowed down."

 

UTEP researchers make discoveries to better understand SARS-CoV-2 virus

Tyler O'Neal, Staff Editor INDUSTRY

An effort led by Lin Li, Ph.D., assistant professor of physics at The University of Texas at El Paso, in collaboration with students and faculty from Howard University, has identified key variants that help explain the differences between the viruses that cause COVID-19 and Severe Acute Respiratory Syndrome (SARS).

A team comprised of researchers from UTEP and the historically Black research university in Washington, D.C., discovered valuable data in comparing the fundamental mechanisms of Severe Acute Respiratory Syndrome Coronavirus (SARS-CoV) and SARS-CoV-2 -- also known as COVID-19 -- to better understand how these viruses attack the human body. Their findings are published in an article titled "Spike Proteins of SARS-CoV and SARS-CoV-2 Utilize Different Mechanisms to Bind with Human ACE2" that recently appeared in the scientific journal Frontiers in Molecular Biosciences.

"We are very excited and interested in the timely work that Dr. Li and his collaborators have reported," said Robert Kirken, Ph.D., dean of UTEP's College of Science. "As the SARS-COV2 continues to evolve through its passage by infected humans, the rapid identification and assessment of these mutants using the research and testing approaches they have established will be critically important for the development of new vaccines and therapeutics." Lin Li, Ph.D., assistant professor of physics at The University of Texas at El Paso, discovered valuable data in comparing the fundamental mechanisms of Severe Acute Respiratory Syndrome Coronavirus (SARS-CoV) and SARS-CoV-2 -- also known as COVID-19 -- to better understand how these viruses attack the human body. His research was published in the scientific journal Frontiers in Molecular Biosciences. CREDIT Courtesy: Lin Li, Ph.D{module INSIDE STORY}

In comparing the viruses, researchers found that both are very similar in sequence and almost identical in structure. Using supercomputational approaches, they were also able to identify mutations of SARS-CoV that make SARS-CoV-2 significantly more contagious and prone to cause serious infections.

"We found that because of mutations, the binding from SARS-CoV-2 to the human cell is much stronger compared with SARS-CoV," Li said. "This might be one of the reasons why SARS-CoV-2 is spreading much faster and is difficult to control. SARS-CoV-2 also uses a much smarter strategy to attack the human cell than SARS-CoV. For example, when SARS-CoV infects or binds to the human cell, it uses several key residues or amino acids to do so, while SARS-CoV-2 uses more residues, making it more robust and easier to completely hijack the human cell.

"We identified the most important residues for SARS-CoV-2 to bind to the human cell. This type of data is key for drug development to cure or treat infections caused by these types of viruses. These fundamental rules and features can also be used for future disease control when perhaps 10 years from now, there's a SARS-CoV-3 or 4."

Researchers from both universities focused on examining one of the virus' four main proteins, known as the spike protein, that initiates infection to the human body. They discovered that from SARS-CoV to SARS-CoV-2 there is an interesting change in mechanism of the binding domain of the spike protein.

"The binding domain needs to flip out so that it can bind to the human cell, but we found some strange mutations that happened. Like the hinge of a door, the binding domain may affect the flip mechanism of SARS-CoV-2. It may be more flexible, making it easier to bind to the human cell," Li said.

The team included an interdisciplinary mix of undergraduate and graduate students, postdoctoral researchers and faculty from both UTEP and Howard University. Yixin Xie, a UTEP graduate student and research assistant, served as the paper's first author, and led the calculation and analysis portions of the project while working closely with other UTEP and Howard University students remotely due to the pandemic.

In the future, the goal of the team is to expand their research to study the mechanisms of all four proteins to better understand the inner workings of these viruses even more to help combat COVID-19 and related viruses.