From The ARC Centres of Excellence for All Sky Astrophysics in 3D (AU) via : “Too much heavy metal stops stars producing more”


From The ARC Centres of Excellence for All Sky Astrophysics in 3D (AU)


January 11, 2022

Many stars in the center of the Milky Way have high heavy metal content. Credit: Michael Franklin.

Stars are giant factories that produce most of the elements in the universe—including the elements in us, and in Earth’s metal deposits. But how do stars produce changes over time?

Two new papers published in MNRAS here and here shed light on how the youngest generation of stars will eventually stop contributing metals back to the universe.

The authors are all members of ASTRO 3D, the ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions. They are based at Monash University (AU), The Australian National University (AU), and The Space Telescope Science Institute (US).

“We know the first two elements of the periodic table—hydrogen and helium—were created in the Big Bang,” says Amanda Karakas, first author of a paper studying metal-rich stars.

“Over time, the stars that came after the Big Bang produce heavier elements.”

These “metal-rich” stars, like our sun, spew out their products into space, enriching the composition of the galaxy over time.

These objects affect us directly as around half of the carbon and all elements heavier than iron are synthesized by stars like our sun.

About 90 percent of all the lead on Earth, for example, was made in low-mass stars that also produce elements such as strontium and barium.

But this ability to produce more metals changes depending on the composition of a star at its birth. “Introducing just a tiny bit more metal into the stars’ gas has really large implications on their evolution,” says Giulia Cinquegrana. Her paper uses modeling from the earlier paper to study the chemical output of metal-rich stars.

“We discovered that at a certain threshold of initial metal content in the gas, stars will stop sending more metals into the universe over their lifetime,” Cinquegrana says.

The sun, born about 4.5 billion years ago, is a typical “middle-aged” star. It is “metal-rich” compared to the first stellar generations and has a heavy element content similar to many other stars in the center of the Milky Way.

“Our papers predict the evolution of younger stars (most-recent generations) which are up to seven times more metal-rich than the sun,” says Karakas.

“My simulations show that this really high level of chemical enrichment causes these stars to act quite weirdly, compared to what we believe is happening in the sun,” says Cinquegrana.

“Our models of super metal-rich stars show that they still expand to become red giants and go on to end their lives as white dwarfs, but by that time they are not expelling any heavy elements. The metals get locked up in the white dwarf remnant,” she says.

“But the process of stars constantly adding elements to the universe means that the make-up of the universe is always changing. In the far distant future, the distribution of elements will look very different to what we see now in our solar system,” says Karakas.

The papers are published in MNRAS, issue Jan 2022 and Feb 2022.

See the full article here .


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The ARC Centre of Excellence in All Sky Astrophysics in 3 Dimensions (AU)

Unifies over 200 world-leading astronomers to understand the evolution of the matter, light, and elements from the Big Bang to the present day.

We are combining Australian innovative 3D optical and radio technology with new theoretical supercomputer simulations on a massive scale, requiring new big data techniques.

Through our nationwide training and education programs, we are training young scientific leaders and inspiring high-school students into STEM sciences to prepare Australia for the next generation of telescopes: the Square Kilometre Array and the Extremely Large Optical telescopes.

The objectives for the ARC Centres of Excellence (AU) are to to:

Undertake highly innovative and potentially transformational research that aims to achieve international standing in the fields of research envisaged and leads to a significant advancement of capabilities and knowledge.

Link existing Australian research strengths and build critical mass with new capacity for interdisciplinary, collaborative approaches to address the most challenging and significant research problems.

Develop relationships and build new networks with major national and international centres and research programs to help strengthen research, achieve global competitiveness and gain recognition for Australian research

Build Australia’s human capacity in a range of research areas by attracting and retaining, from within Australia and abroad, researchers of high international standing as well as the most promising research students.

Provide high-quality postgraduate and postdoctoral training environments for the next generation of researchers.

Offer Australian researchers opportunities to work on large-scale problems over long periods of time.

Establish Centres that have an impact on the wider community through interaction with SKA Murchison Widefield Array (AU), Boolardy station in outback Western Australia, at the Murchison Radio-astronomy Observatory (MRO), on the traditional lands of the Wajarri peoples.

The Murchison Radio-astronomy Observatory,on the traditional lands of the Wajarri peoples, in outback Western Australia will house up to 130,000 antennas like these and the associated advanced technologies.

EDGES telescope in a radio quiet zone at the Murchison Radio-astronomy Observatory in Western Australia, on the traditional lands of the Wajarri peoples.

SKA ASKAP Pathfinder Radio Telescopehigher education institutes, governments, industry and the private and non-profit sector.