“Neutron stars are the collapsed cores of stars and densest stable material objects in the universe, much denser and colder than conditions that particle colliders can even create,” said Yunes, who also is the founding director of the Illinois Center for Advanced Studies of the Universe. “The mere existence of neutron stars tells us that there are unseen properties related to astrophysics, gravitational physics and nuclear physics that play a critical role in the inner workings of our universe.”

However, many of these previously unseen properties became observable with the discovery of gravitational waves.

“The properties of neutron stars imprint onto the gravitational waves they emit. These waves then travel millions of light-years through space to detectors on Earth, like the advanced European Laser Interferometer Gravitational-Wave Observatory and the Virgo Collaboration,” Yunes said. “By detecting and analyzing the waves, we can infer the properties of neutron stars and learn about their internal composition and the physics at play in their extreme environments.”

As a gravitational physicist, Yunes was interested in determining how gravitational waves encode information about the tidal forces that distort the shape of neutron stars and affect their orbital motion. This information also could tell physicists more about the dynamic material properties of the stars, such as internal friction or viscosity, “which might give us insight into out-of-equilibrium physical processes that result in the net transfer of energy into or out of a system,” Yunes said.

Using data from the gravitational wave event identified as GW170817, Yunes, along with Illinois researchers Justin Ripley, Abhishek Hegade and Rohit Chandramouli, used computer simulations, analytical models and sophisticated data analysis algorithms to verify that out-of-equilibrium tidal forces within binary neutron star systems are detectable via gravitational waves. The GW170817 event was not loud enough to yield a direct measurement of viscosity, but Yunes’ team was able to place the first observational constraints on how large viscosity can be inside neutron stars.

The study findings are published in the journal Nature Astronomy.

“This is an important advance, particularly for ICASU and the U. of I.,” Yunes said. “In the ’70s, ’80s and ’90s, Illinois pioneered many of the leading theories behind nuclear physics, particularly those connected to neutron stars. This legacy can continue with access to data from the advanced LIGO and Virgo detectors, the collaborations made possible through ICASU and the decades of nuclear physics expertise already in place here.”

The University of Illinois Graduate College Dissertation Completion Fellowship and the National Science Foundation supported this study.

For the first time, an interdisciplinary study has applied the theory of entropy to tourism, finding that travel could have positive health benefits, including slowing down the signs of ageing.

Entropy is classified as the general trend of the universe towards death and disorder. The entropy perspective suggests that tourism could trigger entropy changes, where positive experiences might mitigate entropy increase and enhance health, while negative experiences may contribute to entropy increase and compromise health.

“Ageing, as a process, is irreversible. While it can’t be stopped, it can be slowed down,” ECU PhD candidate Ms Fangli Hu said.

Ms Hu noted that positive travel experiences could enhance individuals’ physical and mental wellness through exposure to novel environments, engagement in physical activities and social interaction, and the fostering of positive emotions. These potential benefits have been acknowledged through practices such as wellness tourism, health tourism, and yoga tourism.

“Tourism isn’t just about leisure and recreation. It could also contribute to people’s physical and mental health,” Ms Hu added.

Travel therapy: Slowing down the clock

Travel therapy could serve as a groundbreaking health intervention when viewed through an entropy lens, she added. As an important aspect of the environment, positive travel experiences may help the body sustain a low-entropy state by modulating its four major systems.

Tourism typically exposes people to new surroundings and relaxing activities, and novel settings can stimulate stress responses and elevate metabolic rates, positively influencing metabolic activities and the body’s self-organising capabilities. These contexts may also trigger an adaptive immune system response.

Ms Hu said that this reaction improves the body’s ability to perceive and defend itself against external threats.

“Put simply, the self-defence system becomes more resilient. Hormones conducive to tissue repair and regeneration may be released and promote the self-healing system’s functioning.”

Leisurely travel activities might help alleviate chronic stress, dampen overactivation of the immune system, and encourage normal functioning of the self-defence system. Engaging in recreation potentially releases tension and fatigue in the muscles and joints. This relief helps maintain the body’s metabolic balance and increases the anti-wear-and-tear system’s effectiveness. Organs and tissues can then remain in a low-entropy state,” Ms Hu explained.

Travel encompasses physical activities such as hiking, climbing, walking, and cycling. Physical exertion can boost metabolism, energy expenditure, and material transformation, all of which help coordinate self-organising systems.

“Participating in these activities could enhance the body’s immune function and self-defence capabilities, bolstering its hardiness to external risks. Physical exercise may also improve blood circulation, expedite nutrient transport, and aid waste elimination to collectively maintain an active self-healing system. Moderate exercise is beneficial to the bones, muscles, and joints in addition to supporting the body’s anti-wear-and-tear system,” Ms Hu said.

On the flip side, the research has pointed out that tourists could face challenges such as infectious diseases, accidents, injuries, violence, water and food safety issues, and concerns related to inappropriate tourism engagement.

“Conversely, tourism can involve negative experiences that potentially lead to health problems, paralleling the process of promoting entropy increase. A prominent example is the public health crisis of COVID-19.”

The newly discovered planet TOI-1408c has a mass equivalent to eight Earths and circles very close to a larger planet, the hot gas giant TOI-1408b. After starting to study both planets and their star, TOI-1408, in detail, the researchers felt puzzled. The small planet has a very peculiar orbital motion. The interactions between the two planets and their star can be likened to a rhythmic dance.

“The small planet exhibits very unusual orbital behaviour and shows considerable variations regarding the time when it passes in front of its star, which is something that we don’t see as a rule. The small planet’s existence challenges existing theories on the formation and stability of planetary systems,” says Judith Korth, astrophysicist at Lund University and leader of the study.

The new study, published in The Astrophysical Journal Letters, shows that planetary systems can be considerably more complex than researchers have previously thought. The discovery of a small planet between a star and a gas giant is rare and offers a unique case study for the development of planetary systems. This could help the researchers to understand more about how planets are formed in other solar systems.

“Our results will help researchers to learn more about how planets are formed and how they behave when they are very close to each other, particularly in systems with giant planets,” says Judith Korth.

Exoplanets are planets located in a solar system other than our own. The first confirmed discovery was made in 1995. Since then, over 5,700 exoplanets have been discovered. The researchers’ discovery of the space oddity TOI-1408c was made possible by using NASA’s Transiting Exoplanet Survey Satellite (TESS). Since TESS was launched in 2018, it has observed over 7,000 potential exoplanets.

“I hope that our results can be used in future studies to discover even more planets in other systems, but also to better understand the large range of planetary systems that exist in our galaxy,” concludes Judith Korth.