The real origin of gold in our universe has just changed, it can happen again

When humanity finally detected a collision between two neutron stars in 2017, we confirmed a long-held theory – in the energetic flames of these incredible explosions, elements heavier than iron are forged.

And so, we thought we had an answer to the question of how these elements are involved – including gold throughout the universe.

But a new analysis reveals a problem. According to the new galactic chemical evolution model, neutron star collisions do not come close to the abundant production of heavy elements found in the Milky Way galaxy today.

“Neutron Star Mergers Didn’t Produce Enough Heavy Elements in the Universe’s Early Life, and They Still Don’t, 14 Billion Years Later,” Amanda Karakas, Monash University’s Astronomer and ARC Center of Excellence for All Sky Astrophysics Having said. 3 Dimensions in Australia (ASTRO 3D).

“The universe did not make them fast enough for their presence in very ancient stars, and, overall, there is not enough collision going on around today to account for the abundance of these elements.”

Stars are the forges that produce most of the elements in the universe. In the early universe, after being cooled enough to turn primordial quark soup into matter, it formed hydrogen and helium – still the two most abundant elements in the universe.

The first strands, formed as gravity, drew clumps of these materials together. In the nuclear fusion furnaces of their cores, these stars form hydrogen into helium; Then helium in carbon; And likewise, using heavy and heavy elements, they are lightly flushed out until they produce iron.

Iron only can do Fuse, but it consumes an enormous amount of energy – such fusion produces more – hence an iron core is the end point.

“We can think of stars as giant pressure cookers where new elements are created,” Karkas said. “The reactions that make up these elements also provide energy that keeps the stars bright for billions of years. As the stars age, they produce heavier and heavier elements as they create heat inside them.”

To make heavier elements from iron – such as gold, silver, thorium, and uranium – a rapid neutron-capture process, or R-process, is required. This can actually occur in energetic explosions, which produce a series of nuclear reactions in which atomic nuclei collide with neutrons, elements heavier than iron.

But this needs to happen really quickly, so that there is no time for radioactive decay before more neutrons are added to the nucleus.

We now know that the Kilonova explosion resulting from the collision of a neutron star is an energetically sufficient atmosphere for the R-process. It is not under dispute. But, in order for us to produce quantities of these heavy elements, we would need a minimum frequency of neutron star collisions.

To locate the sources of these elements, the researchers constructed galactic chemical evolution models for all stable elements from carbon to uranium, using the most up-to-date astrological observations and chemical abundances available in the Milky Way. They included theoretical nucleosynthesis yields and incidence rates.

periodic table(Chikki Kobayashi et al. Sahm Kili)

He carried out his work in a periodic table showing the origin of the elements he modeled. And, among his findings, he found a lack of neutron star collision frequency from the early universe until now. Instead, they believe that a type of supernova may be responsible.

These are called magnetorotational supernovas, and they occur when the core of a massive, fast-spinning star with a strong magnetic field collapses. These are considered to be sufficiently energetic for the R-process. If a small percentage of stars with a mass of 25 to 50 solar masses are magnetorotational, it can make a difference.

“Even the most optimistic estimates of the frequency of neutron star collisions cannot account for the abundance of these elements in the Universe,” Karkas said. “It was a surprise. It looks like spinning supernova with strong magnetic fields, the real source of most of these elements.”

Previous research has found a type of supernova called colapsar supernova that can also produce heavier elements. This is when a star rotating over 30 solar masses goes supernova before falling down into a black hole. These are thought to be much rarer than neutron star collisions, but they can be a contributor – this neatly matches up with other findings from the team.

They found that massive stars less than about eight solar masses produce carbon, nitrogen, fluorine, and almost all elements are heavier than iron. Stars with more than eight solar masses produce most of the oxygen and calcium needed for life, along with the rest of the elements between carbon and iron.

“Apart from hydrogen, there is no single element that can be formed by only one type of star,” explained astrophysicist Chiaki Kobayashi of the University of Hertfordshire in Britain.

“Half of the carbon is produced from low-mass stars, but the other half comes from supernovas. And half of the iron comes from the usual supernovas of larger stars, but the other half needs another form, called a Type IA supernova. Is. These are produced. In binary systems of low-mass stars. ”

This does not necessarily mean that neutrons of an estimated 0.3 percent of Earth’s gold and platinum 4.6 billion years ago have a different origin story behind hitting the star. This is not necessarily the whole story.

But we have only been detecting gravitational waves for five years. It may be, as our equipment and technology improves, that we find that neutron star collisions are much more frequent than we think they are at this present time.

Curiously, the researchers’ models also yielded more gold than observed silver, and less gold. It suggests that some need to be tweaked. Perhaps it is a calculation. Or perhaps there are some aspects of stellar nucleosynthesis that we have not yet understood.

The research has been published in The Astrophysical Journal.


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