Tyler O'Neal, Staff Editor APPLICATIONS

Our closest neighbor, the Andromeda galaxy, has a fascinating history that can be uncovered through galactic archaeology

Researchers from the University of Hertfordshire in the UK have uncovered fascinating information about the Andromeda galaxy, which is our closest neighbor in the universe. After analyzing the elemental abundances in Andromeda, they concluded that the galaxy's formation was more intense and powerful than that of our own Milky Way. The research conducted by Professor Kobayashi throws new light on the impact and nature of the merging of two gas-rich galaxies, which most likely triggered a significant amount of star formation in Andromeda between 2 and 4.5 billion years ago.

A team of international astrophysicists, led by Professor Chiaki Kobayashi, has used state-of-the-art supercomputer modeling to study the history of the galaxy through galactic archaeology. This approach involves examining the chemical composition of stars and the development of their host galaxy to reconstruct its past. The study focuses on the elemental abundances in Andromeda, particularly the presence of both planetary nebulae and red-giant branch stars.

The analysis reveals that Andromeda's formation was more dramatic and forceful than that of our own Milky Way. After an intense initial burst of star formation that created the galaxy, a secondary layer of stars was produced between 2 billion and 4.5 billion years ago, most likely caused by what scientists call a "wet merger" - a merging of two gas-rich galaxies that instigates a large amount of star formation.

Scientists have long believed that Andromeda experienced a merger of two galaxies, based on the position and motion of individual stars in the galaxy. Professor Kobayashi's research sheds new light on the nature and impact of such a merger using the chemical composition of stars. It explains how stars and elements were formed throughout the history of Andromeda.

Professor Kobayashi, who is an astrophysics professor at the University of Hertfordshire’s Centre for Astrophysics Research, has explained that by analyzing the chemical abundance of different ages of stars in Andromeda, we can better understand the origins and history of this galaxy. According to her, Andromeda is a spiral disc galaxy similar in many ways to our own Milky Way. However, her new research confirms that Andromeda's history is significantly more intense and dramatic, with bursts of activity forming stars in abundance and two distinct eras of star formation.

Professor Kobayashi’s theoretical model predicts that there are two distinct chemical compositions of stars in the two-disc components of Andromeda. One composition has ten times more oxygen than iron, while the other has a similar amount of oxygen and iron. This modeling has been confirmed by the spectroscopic observations of planetary nebulae and also by those of red-giant stars with the James Webb Space Telescope (JWST).

The new study is an extension of Professor Kobayashi’s ongoing, ground-breaking research into the origin of elements in the Universe. According to her, oxygen is one of the alpha elements produced by massive stars along with neon, magnesium, silicon, sulfur, argon, and calcium. While oxygen and argon have been measured with planetary nebulae, JWST is required to measure other elements, including iron, as Andromeda is so far away. She believes that in the coming years, JWST and ground-based large telescopes will keep looking at Andromeda, which will give further weight to the new findings.

The latest research shows that number of days considered 'hail-prone' have decreased over much of the country, but increased over the southwest and southeast where there are large population centres. Photo: Getty images/Andrew Merry
The latest research shows that number of days considered 'hail-prone' have decreased over much of the country, but increased over the southwest and southeast where there are large population centres. Photo: Getty images/Andrew Merry

Probability of hail occurring in Australia has significantly altered in the past 40 years

Tyler O'Neal, Staff Editor APPLICATIONS

The UNSW Sydney and the Bureau of Meteorology have discovered that the number of days considered ‘hail-prone’ has decreased across much of Australia but has increased by up to approximately 40 percent in some heavily populated areas. The atmospheric conditions required for a hailstorm to form include instability, enough moisture, and wind shear. These findings are important for agricultural, insurance, and city planning sectors to build resilience against future hail events and to protect densely populated areas from damage.

Hailstorms occur when the atmosphere has all the necessary components for hail formation. Dr. Tim Raupach, a researcher in atmospheric science at the UNSW Climate Change Research Centre, explains that hailstorms are measured and modeled, which makes it difficult to understand how they have changed over time or how they are expected to change in the future. To gain a better understanding of the frequency of hail events, the researchers used historical estimates of atmospheric conditions as a "proxy" for hail occurrence over the past forty years to create a continental map of how hail hazard frequency has changed across Australia. The latest study is the first continental-scale analysis of hail hazard frequency trends for Australia. The team of researchers, which included scientists from the Bureau of Meteorology, hopes that this research will help improve our understanding of hail events, which is important for the insurance industry, as well as agricultural and city planning sectors.

Not all thunderstorms are capable of producing hail. Hailstorms require certain atmospheric conditions to develop. One of the essential factors is atmospheric instability, which means that there is a tendency for updrafts to form. Updrafts occur when there is warm air near the ground and cooler air higher up. When a little bit of warm air rises and gets into the cool air, it draws air up leading to updrafts formation, as explained by Dr Raupach.

Another crucial factor is the presence of sufficient moisture in the updraft to create supercooled liquid water and ice, which swirl around in the upper part of the storm. Additionally, hail must be large enough to survive melting as it falls to reach the ground as a block of ice, as explained by Dr Raupach.

Lastly, wind shear, the change in the wind's properties by height, enhances hail formation. Dr Raupach explains that wind shear is the wind changing direction or velocity as you go higher in the atmosphere. When there is a lot of wind shear, the storm tends to be more severe and prone to forming hail.

When all these factors are present, the atmospheric conditions become hail-prone.

Researchers have developed a method to estimate hail-prone days in Australia over the past four decades. They created a "hail proxy" by combining the necessary ingredients for hail formation and applied it to 40 years of reanalysis data. Reanalysis products combine observations with supercomputing weather modeling to estimate the past atmosphere's state. Using this method, the researchers were able to produce a map of how the number of hail-prone days per year has changed across the entire continent, with a resolution of about 30 kilometers per pixel.

The hail proxy enabled the researchers to estimate atmospheric conditions on a grid of points across the country, instead of relying on spotty surface records. The Bureau of Meteorology's long-term weather radar archive was used to compare radar observations with the reanalysis hail proxy. Radar observations were collected from 20 Bureau radar sites across the country, with each site having between 12 and 24 years of records. The radar results corroborated the pattern of results seen through the statistical analysis of historic estimates.

According to Dr. Raupach, there has been a decrease in the number of hail-prone days in most parts of Australia, except for the southeast and southwest regions where large population centers are located. The annual number of hail-prone days has increased by approximately 40% around Sydney and Perth, which is about a 10% increase per decade in the number of hailstorm-causing days. Although there are fewer hail-prone days, the chances of hail occurring are higher when there are more such days. These changes in the data are all relative. Even though not every hail-prone day results in hail, an increase in the number of hail-prone days increases the likelihood of hail.

Although the exact reasons behind the changes in hail patterns are still unknown, the research team has taken into account the possible influence of climate change. Dr Raupach explains that while it is not a climate attribution study, the team considered how hailstorms may behave in a warmer environment.

There is a general expectation that climate change may result in less frequent surface hail due to increased melting. The warmer atmosphere causes more hail to melt before it hits the ground. However, a warmer atmosphere would be more unstable, which means there may be larger hailstones. Large hailstones are more likely to survive increased melting, so hail that does occur could be larger, and therefore more severe.

The team discovered that the changes in hail-prone day patterns are primarily driven by changes in extreme atmospheric instability, which are very complex and regionally dependent. In regions with increased instability, there might be more generation of hail and larger hailstones, which may survive more melting. Conversely, in areas where instability decreases, there may be a dampening effect.

The links between climate change and hailstorms are multifaceted, and more work needs to be done to understand how these patterns will continue to change under warming conditions.

The findings of this study are crucial in our understanding of hail risks. According to Dr. Raupach, the agricultural and insurance industries, as well as city planning, can benefit from this information. Hailstorms can destroy crops and cause significant damage that leads to insured losses, making hail a primary concern for the insurance industry in Australia. The research underscores the importance of building resilient infrastructure that can withstand the potential increase in hail hazards in the future. Dr. Raupach aims to extend his research by using supercomputing and climate models to predict future trends in hailstorms and help plan for the impact of such changes on agriculture, insurance, and densely populated areas.

Representation of the organic molecules studied, surrounded by water molecules (image: Tárcius Nascimento Ramos)
Representation of the organic molecules studied, surrounded by water molecules (image: Tárcius Nascimento Ramos)

Alternative method reduces supercomputer simulation time for the absorption spectrum from days to hours

Tyler O'Neal, Staff Editor APPLICATIONS

The absorption of light by molecules has various applications in microscopy, medicine, and data storage. A Brazilian physicist has proposed an alternative method that reduces the time required for supercomputer simulation of the absorption spectrum from two days to a few hours. The most suitable method for predicting the one- and two-photon absorption spectra of large molecules in solution is the semi-empirical method INDO/S. This method enables the development of novel compounds with greater efficiency.

Absorption spectroscopy is an analytical chemistry tool that can determine the presence of a particular substance in a sample by measuring the intensity of the light absorbed as a function of wavelength. Measuring the absorbance of an atom or molecule can provide important information about electronic structure, quantum state, sample concentration, phase changes, or composition changes. It can also help determine the interaction of molecules with each other, and their potential technological applications.

Molecules that have a high probability of simultaneously absorbing two photons of low-energy light are highly useful in various fields. They can be used as molecular probes for high-resolution microscopy, as a substrate for data storage in dense three-dimensional structures, or as vectors in medicinal treatments.

Direct experimentation to study the phenomenon can be challenging, and computer simulation is often used alongside spectroscopic characterization. Simulations provide a microscopic view that is difficult to obtain in experiments. However, simulating relatively large molecules can take several days of processing by supercomputers or even months by conventional computers. To address this issue, physicist Tárcius Nascimento Ramos and his team have proposed an alternative calculation method in an article published in The Journal of Chemical Physics.

Ramos explains that they evaluated the performance of a semi-empirical method that was widely used in past decades but has been neglected in recent years because of its approximative nature. Using this method, they were able to reduce the calculation time to just four hours on a conventional computer. This low computing cost allowed them to consider a large statistical sample for simulations of molecules in solutions, which isn't feasible with the currently dominant method - density functional theory (DFT). DFT is a mathematical tool used in quantum mechanics to describe the electronic properties of complex systems without having to investigate the individual wave functions of each electron.

"The alternative method we used was INDO/S [intermediate neglect of differential overlap with spectroscopic parameterization]. It's based on the wave function of the molecular system but resolves approximately. Parts of the complex and computationally costly calculations are replaced by tabulated values obtained by adjusting experimental spectroscopic data. This makes the method highly efficient for theoretical studies of large molecular compounds," Ramos explained.

The practicality of the method used in this study is evident when considering the molecule being studied, which is derived from stilbene and contains over 200 carbon, oxygen, and hydrogen atoms. These large and flexible molecules pose a challenge as their electronic properties change when their shape changes, making conventional simulations time-consuming and expensive.

At the end of the study, the researchers characterized the one- and two-photon absorption spectra for this class of molecules, bridging the experimental gap. The most suitable method for predicting the absorption spectra of large molecules in solution was found to be the often neglected semi-empirical method. This discovery can pave the way for molecular engineers to develop novel compounds more efficiently for various applications.

It is worth noting the difference between one- and two-photon absorption. Molecules absorb photons only when they can assume excited states compatible with the energy of the photons. The selection rules for one-photon absorption differ from those for two-photon absorption, making the latter more suitable for refined uses due to its high spatial resolution of excitation resulting from its non-linear optical nature.

"Microscope imaging with two-photon absorption has far higher resolution and can be used to characterize deep tissue with less damage to the surrounding structures. In the case of data storage, the high resolution means 3D structures can be created with precision and plenty of detail, so that points inside materials can be encoded with high data density per volume," Ramos explained.

Computer modeling of two-photon absorption by organic molecules in solution was the subject of Ramos's Ph.D. research. The JCP article refers to another step forward in this investigation.