Dark matter is nonluminous and cannot be seen directly. Thought to make up 85% of matter in the universe, its nature is not well understood. Unlike normal matter, it does not absorb, reflect, or emit light, making it difficult to detect.

The prevailing dark matter theory, known as cold dark matter, or CDM, assumes dark matter particles are collisionless, aside from gravity. A newer second theory, called self-interacting dark matter, or SIDM, proposes dark matter particles self-interact through a new dark force. Both theories explain how the overall structure of the universe emerges, but they predict different dark matter distributions in the inner regions of a galaxy. SIDM suggests dark matter particles strongly collide with one another in a galaxy’s inner halo, close to its center.

Typically, a visible galaxy is hosted by an invisible dark matter halo — a concentrated clump of material, shaped like a ball, that surrounds the galaxy and is held together by gravitational forces. Recent observations of two ultra-diffuse galaxies, NGC 1052-DF2 and NGC 1052-DF4, show, however, that this pair of galaxies contains very little, if any, dark matter, challenging physicists’ understanding of galaxy formation. Astrophysical observations suggest NGC 1052-DF2 and NGC 1052-DF4 are likely satellite galaxies of NGC1052.

“It is commonly thought that dark matter dominates the overall mass in a galaxy,” said Hai-Bo Yu, an associate professor of physics and astronomy at UCR, who led the study. “Observations of NGC 1052-DF2 and -DF4 show, however, that the ratio of their dark matter to their stellar masses is about 1, which is 300 times lower than expected. To resolve the discrepancy, we considered that the DF2 and DF4 halos may be losing the majority of their mass through tidal interactions with the massive NGC 1052 galaxy.”

Using sophisticated simulations, the UCR-led team reproduced the properties of NGC 1052-DF2 and NGC 1052-DF4 through tidal stripping — the stripping away of material by galactic tidal forces — by NGC1052. Because the satellite galaxies cannot hold the stripped mass with their own gravitational forces, it effectively gets added to NGC 1052’s mass.

The researchers considered both CDM and SIDM scenarios. Their results, published in Physical Review Letters, indicate SIDM forms dark-matter-deficient galaxies like NGC 1052-DF2 and -DF4 far more favorably than CDM, as the tidal mass loss of the inner halo is more significant and the stellar distribution is more diffuse in SIDM.

The research paper has been selected as an “editors’ suggestion” by the journal, an honor that only a select few papers receive each week to promote reading across fields.

Yu explained tidal mass loss could occur in both CDM and SIDM halos. In CDM, the inner halo structure is “stiff” and resilient to tidal stripping, which makes it difficult for a typical CDM halo to lose sufficient inner mass in the tidal field to accommodate observations of NGC 1052-DF2 and -DF4. In contrast, in SIDM, dark matter self-interactions could push dark matter particles from the inner to the outer regions, making the inner halo “fluffier” and enhancing the tidal mass loss accordingly. Further, the stellar distribution becomes more diffuse.

“A typical CDM halo remains too massive in the inner regions even after tidal evolution,” Yu said.

Next, the team will perform a more comprehensive study of the NGC 1052 system and explore newly discovered galaxies with novel properties in an effort to better understand the nature of dark matter.

Yu was joined in the study by Daneng Yang and Haipeng An of Tsinghua University in Beijing, China. Yu was supported by grants from the U.S. Department of Energy and the U.S. National Science Foundation.

During the early phases of the COVID-19 pandemic, concerns were raised that the use of the painkiller ibuprofen may lead to a more severe course of coronavirus disease. As use of ibuprofen and other NSAIDs is widespread, data on their safety is urgently needed to guide clinicians and patients. In the new study, researchers obtained data on all 9,326 Danish residents who tested positive for the SARS-CoV-2 virus between February 27, 2020 and April 29, 2020. Data were available on NSAID use, 30-day mortality, hospitalization, ICU admission, mechanical ventilation, and acute renal replacement therapy. 248 people (2.7%) had filled a prescription for NSAIDs within 30 days of their positive virus test.

The researchers found no association between any of the outcomes and NSAID use. Among NSAID users in a matched cohort who tested positive for the coronavirus, 6.3% (95% Confidence Interval [CI] 3.1-9.4) died, 24.5% (95% CI 18.6-30.4) were hospitalized and 4.9% (95% CI 2.1-7.8) were admitted to ICU. Of those who tested positive for the coronavirus but were not treated with NSAIDs, 6.1% (95% CI 4.4-7.8) died, 21.2% (95% CI 18.1-24.3) were hospitalized, and 4.7% (95% CI 3.2-6.2) were admitted to ICU. None of these differences between groups were statistically significant (mortality Risk Ratio [RR] 1.02, 95%CI 0.57-1.82, p=0.95; hospitalization RR 1.16, 95%CI 0.87-1.53, p=0.31; ICU admission RR 1.04, 95%CI 0.54-2.02, p = 0.90).

“Considering the available evidence, there is no reason to withdraw well-indicated use of NSAIDs during the SARS-CoV-2 pandemic,” the authors say. “However, the well-established adverse effects of NSAIDs, particularly their renal, gastrointestinal, and cardiovascular effects, should always be considered, and NSAIDs should be used in the lowest possible dose for the shortest possible duration for all patients.”

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The clinical manifestations of COVID-19 vary widely across different patient populations, despite the virus’s limited genetic diversity. To better understand the mechanisms that drive the diverse responses of infected individuals (hosts) among different patient demographics, researchers extracted and sequenced viral RNA from swabs collected from 430 COVID-19 positive cases and 54 negative controls. The scientists then analyzed the hosts’ antiviral and immune responses across infection status, viral load, age and sex.

Researchers found that immune cell responses were not activated until after three days following the onset of infection, and that immune cell composition and function fluctuated with viral loads, in a way that suggested a dysfunctional antiviral response in males and the elderly. While these findings have important implications for development of immunomodulatory treatments for SARS-CoV-2, additional studies are needed as swabs were taken from the nasopharynx, which is not a sensitive anatomic location for accurately examining markers of systemic inflammation.

Elderly individuals as well as men have suffered higher mortality rates since the onset of the SARS-CoV-2 pandemic and may indicate weaker immune responses underlying poor clinical outcomes. According to the authors, “Collectively, our data demonstrate that host responses to SARS-CoV-2 are dependent on viral load and infection time with observed differences due to age and sex that may contribute to disease severity.”

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The frog, Megaelosia bocainensis, was among seven total species — including four other declining species, and two that had disappeared locally for many years — that were detected. The findings appeared in a paper, “Lost and Found: Frogs in a Biodiversity Hotspot Rediscovered with Environmental DNA,” published in August in Molecular Ecology.

Megaelosia bocainensis. A disappeared species from Parque Nacional da Serra da Bocaina, Brazil, known only from this museum specimen collected in 1968, and detected by eDNA surveys. In the study, the researchers collected and screened environmental DNA (eDNA) in the biodiverse Atlantic Coastal Forest and Cerrado grasslands of Brazil.

The eDNA technique offers a way to survey that can confirm the presence of species undetected by traditional methods, providing a tool for conservation scientists to evaluate the presence of threatened species, especially those with low population densities and those not seen in years.

After careful research to identify species at various levels of threat in these regions of Brazil, the researchers used the eDNA method to search for 30 target amphibian species in six localities where the frogs were known to previously live.

“Little bits of DNA in the environment don’t tell us about how many individuals there are or whether those individuals are healthy, but it does tell us that the species is still present,” said senior author Kelly Zamudio, the Goldwin Smith Professor of Ecology and Evolutionary Biology in the College of Arts and Sciences.

“This is one more kind of survey data, and for species that are declining or locally disappeared, it not only means they are there, but there’s now the potential to study them in more detail,” she said, noting that for many species, very little is known.

Around the world, conservationists have been challenged to keep pace with declining and disappearing amphibians. At the same time, living organisms leave DNA traces in the soil, water and air. Now, scientists are increasingly using highly sensitive sampling techniques to detect eDNA for conservation purposes.

In the study, the researchers targeted 13 frog species that have totally disappeared and are presumed extinct; 12 frogs that have disappeared locally but are still found in other parts of their range; and five species that were once very abundant and are still there but hard to find.

The researchers hiked into the sampling sites carrying battery packs, a shoebox-sized peristaltic pump and backpacks of sterile tubing. They used the pump and tubing to draw up to 60 liters of stream or pond water through a capsule fitted with a filter for capturing DNA. A buffer was then applied to stabilize and preserve the DNA on the filter.

Back in the lab, the researchers extracted the DNA, genetically sequenced it, weeded out genetic material from humans, pigs, chickens and other organisms until they could isolate all the frog DNA.

“Now you’ve got a subset of genetic sequences that we know only belong to frogs, and then it’s step by step, going finer and finer, until you get to the genus and species you are looking for,” Zamudio said.

Identifying M. bocainensis required clever detective work: The species disappeared long ago, and there were no tissues from which to extract DNA for comparison with the eDNA. But the researchers did have the sequences for all the sister species in the genus Megaelosia and they knew the ranges of the sister species and M. bocainensis.

“We know there’s a Megaelosia there,” Zamudio said, “we just don’t know which one it is, but the only one that has ever been reported there historically is the one that went missing. Do we believe it? That’s how far the analysis can take us.”

Zamudio added that samples from nearby areas may be worth collecting for more signs of M. bocainensis.

Carla Martins Lopes, a researcher at São Paulo State University in Brazil, is the paper’s first author.

The Brazilian National Council for Scientific and Technological Development and the São Paulo Research Foundation funded the study.