Mysterious Lithium-producing stars analysed on Nectar

Image showing many types of stars in the universe, including the faint orange stars which contain Lithium
The many types of stars the study looked at, from young stars to old red giant stars. The research team found Lithium in the fainter orange stars, the red giants. Credit: ESA & NASA; Acknowledgement: E. Olszewski (U. Arizona) HST.

Here on Earth, Lithium is used in electric cars, giant solar-storage batteries, medicine, mobile phone batteries and heat resistant glass, but little is known about how the element is created in the universe. And to delve into that mystery, we need to look at the stars.

“Almost every element in the universe is created by stars,” explains Dr Simon Campbell, an ARC Future Fellow at the Monash University School of Physics and Astronomy.

“Everything except Hydrogen and Helium (and a little bit of Lithium) came from stars. To understand the universe, you have to understand how stars work.”

“Stars are real alchemists - they take Hydrogen and Helium and turn them into all the other elements in the periodic table, including gold and silver.”

Understanding how stars create and destroy elements as they evolve helps us understand the origin of the material that makes up galaxies, planets such Earth, and even ourselves. Now back to Lithium.

“There’s a mysterious group of stars - about 1% of red giants contain huge amounts of Lithium, but we don't know where the Lithium comes from,” said Simon.

“I met an astronomer at a conference and heard about their observations of this unexplained Lithium production in stars and said, ‘I can make a model of this to try to explain what they're seeing in the telescope data.’”

To investigate this mysterious group of Lithium-producing stars, Simon teamed up with observers in China and India and the Australian stellar survey known as GALAH (Galactic Archaeology with the Hermes spectrograph), which uses the largest optical telescope in Australia, the Australian Astronomical Telescope, located at the Siding Springs Observatory near Coonabarabran, NSW.

Simon’s contribution to the research involved computing detailed models of red giant stars, which he analysed using the Australian Research Data Commons (ARDC) Nectar Research Cloud. His models show that our current theories about how stars evolve do not predict this huge Lithium production at all. In addition, on analysing the observational data more, they found that actually all the stars were producing Lithium, in varying amounts. Simon's models could not explain this either. It also meant that our own star - the Sun - would produce Lithium in the future.

The team published a paper in Nature Astronomy in July 2020 describing their observations and models, and called for theorists to step up to try and explain why theories had not predicted that Lithium could be produced through stellar evolution.

The theorists jumped at the challenge. Immediately after the paper was published, two papers were published from Japan and the US on the theory behind how stars could produce Lithium as they evolve through this phase.

“It’s a hot topic right now,” said Simon, “There’s a lot of work to be done on the theory side to explain it.”

“Since the newly created Lithium will end up being blown off the star in stellar winds, it will also help us understand how much these stars enrich our Galaxy with Lithium, and eventually planets like Earth.”

Understanding the origin of the elements, one ARDC Nectar processor at a time

3D hydrodynamics simulation of part of a star
Three-dimensional hydrodynamics simulation of a section of the inside of a star. The colour scale shows the magnitude of the velocity of the gas (stars are mainly made of hot gas). The bottom half is heated by nuclear fusion energy, causing it to become highly turbulent/convective. The top half is stable, although some gravity waves can be seen (purple layers), which are similar to water waves on the ocean. This simulation was run at Pawsey, on the Magnus supercomputer, and the image was produced using the Pawsey visualisation machine Topaz. Image supplied by Simon Campbell.

Simon began his work on investigating Lithium and stars in 2019, modelling a cluster of lithium-producing stars on Nectar to follow their nucleosynthesis - the creation of elements on the periodic table.

“My work is very computational,” said Simon, “A laptop computer can only do so much. I use the Pawsey Supercomputer Magnus at one end of the scale and my laptop at the other end of the scale. In between is where I need more than a laptop but less than Pawsey.”

That’s where the ARDC Nectar Research Cloud plays a key role in Simon’s research. Nectar is Australia’s national research cloud, providing Australia’s research community with on-demand computing infrastructure and software.

“With Nectar I can have a machine with 10, 20, 30 processors, which means I have the power of many laptops or PCs.”

“I research the evolution of stars, so I can run 20 or 30 star models all at once on Nectar. Parallel work makes a big difference in terms of efficiency, and it’s very user friendly. I can access it all from my laptop, anywhere.”

“I make huge 3D simulations of star evolution on a supercomputer, but then I can compress them into 1D and 2D and do further analysis on Nectar,” said Simon.

It's Australia’s interconnected national research infrastructure that makes Simon's research possible.

Simon conducts complex simulations on the Magnus supercomputer at the Pawsey Supercomputing Centre in Perth, transfers the gigantic data files via Australia’s high speed research internet AARNet to his research data lifecycle hub on the Monash University 'Vault' storage facility (supported by the Monash eResearch Centre), and then accesses his 100 terabytes of data via Nectar.

“The really powerful thing about Nectar is that I can mount the saved data from the supercomputer via my Vault storage and analyse it on my Nectar machines,” said Simon.

The Vault was designed to allow users to seamlessly and securely transfer data to and from the peak supercomputing facilities, and then mount their Vault storage to analyse that data on Nectar.

Another helpful aspect of using Nectar is the continuity, said Simon. He can work on his analysis at home or at the university seamlessly. Nectar also runs 24/7, so Simon can run star models overnight and they are ‘cooked’ the next morning, which makes his research very efficient.

“Nectar is a very important part of my workflow,” explained Simon.

“I’ve also found Nectar is very useful for students. I’ve put a few PhD students on Nectar.”

Learn more about how Australian researchers can use the ARDC Nectar Research Cloud.

The ARDC is funded through the National Collaborative Research Infrastructure Strategy (NCRIS) to support national digital research infrastructure for Australian researchers.

Simon Campbell’s work was supported by resources provided by the Pawsey Supercomputing Centre with funding from the Australian Government and the Government of Western Australia.

Simon Campbell received funding for this research from the Australian Research Council through Future Fellowship FT160100046 and Discovery Project DP190102431.

 

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