The True Origins of Gold in Our Universe May Have Just Changed, Again


When humanity finally detected the collision between two neutron stars in 2017, we confirmed a long-held theory – in the energetic fires 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 – including gold – propagated throughout the Universe.

But a new analysis has revealed a problem. According to new galactic chemical evolution models, neutron star collisions don’t even come close to producing the abundances of heavy elements found in the Milky Way galaxy today.

“Neutron star mergers did not produce enough heavy elements in the early life of the Universe, and they still don’t now, 14 billion years later,” said astrophysicist Amanda Karakas of Monash University and the ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D) in Australia.

“The Universe didn’t make them fast enough to account for their presence in very ancient stars, and, overall, there are simply not enough collisions going on to account for the abundance of these elements around today.”

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

The first stars formed as gravity pulled together clumps of these materials. In the nuclear fusion furnaces of their cores, these stars forged hydrogen into helium; then helium into carbon; and so on, fusing heavier and heavier elements as they run out of lighter ones until iron is produced.

Iron itself can fuse, but it consumes huge amounts of energy – more than such fusion produces – so an iron core is the end point.

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

To create elements heavier than iron – such as gold, silver, thorium and uranium – the rapid neutron-capture process, or r-process, is required. This can take place in really energetic explosions, which generate a series of nuclear reactions in which atomic nuclei collide with neutrons to synthesise elements heavier than iron.

But it needs to happen really quickly, so that radioactive decay doesn’t have time to occur before more neutrons are added to the nucleus.

We know now that the kilonova explosion generated by a neutron star collision is an energetic-enough environment for the r-process to take place. That’s not under dispute. But, in order to produce the quantities of these heavier elements we observe, we’d need a minimum frequency of neutron star collisions.

To figure out 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 astrophysical observations and chemical abundances in the Milky Way available. They included theoretical nucleosynthesis yields and event rates.

They laid out their work in a periodic table that shows the origins of the elements they modelled. And, among their findings, they found the neutron star collision frequency lacking, from the early Universe to now. Instead, they believe that a type of supernova could be responsible.

These are called magnetorotational supernovae, and they occur when the core of a massive, fast-spinning star with a strong magnetic field collapses. These are also thought to be energetic enough for the r-process to take place. If a small percentage of supernovae of stars between 25 and 50 solar masses are magnetorotational, that could make up the difference.

“Even the most optimistic estimates of neutron star collision frequency simply can’t account for the sheer abundance of these elements in the Universe,” said Karakas. “This was a surprise. It looks like spinning supernovae with strong magnetic fields are the real source of most of these elements.”

Previous research has found a type of supernova called a collapsar supernova can also produce heavy elements. This is when a rapidly rotating star over 30 solar masses goes supernova before collapsing down into a black hole. These are thought to be much rarer than neutron star collisions, but they could be a contributor – it matches neatly with the team’s other findings.

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

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

“Half of carbon is produced from dying low-mass stars, but the other half comes from supernovae. And half the iron comes from normal supernovae of massive stars, but the other half needs another form, known as Type Ia supernovae. These are produced in binary systems of low mass stars.”

This doesn’t necessarily mean that the estimated 0.3 percent of Earth’s gold and platinum traced back to a neutron star collision 4.6 billion years ago has a different origin story. It’s just not necessarily the whole story.

But we’ve only been detecting gravitational waves for five years. It could be, as our equipment and techniques improve, that we find neutron star collisions are much more frequent than we think they are at this current time.

Curiously, the researchers’ models also turned out more silver than observed, and less gold. That suggests something needs to be tweaked. Perhaps it’s the calculations. Or perhaps there are some aspects of stellar nucleosynthesis that we are yet to understand.

The research has been published in The Astrophysical Journal.

A Strange Form of Life Could Flourish Deep Inside of Stars, Physicists Say

by Michelle Starr

When searching for signs of life in the Universe, we tend to look for very specific things, based on what we know: a planet like Earth, in orbit around a star, and at a distance that allows liquid surface water. But there could, conceivably, be other forms of life out there that look like nothing that we have ever imagined before.

Just as we have extremophiles here on Earth – organisms that live in the most extreme and seemingly inhospitable environments the planet has to offer – so too could there be extremophiles out there in the wider Universe.

For instance, species that can form, evolve, and thrive in the interiors of stars. According to new research by physicists Luis Anchordoqui and Eugene Chudnovsky of The City University of New York, such a thing is indeed – hypothetically, at least – possible.

It all depends on how you define life. If the key criteria are the ability to encode information, and the ability for those information carriers to self-replicate faster than they disintegrate, then hypothetical monopole particles threaded on cosmic strings – cosmic necklaces – could form the basis of life inside stars, much like DNA and RNA form the basis of life on Earth.

“Information stored in the RNA (or DNA) encodes the mechanism of self-replication,” Chudnovsky told ScienceAlert.

“Its emergence must have been preceded by the massive formation of random RNA sequences until a sequence was formed capable of self-replication. We believe that a similar process would occur with necklaces in a star, leading to a stationary process of self-replication.”

Strings and monopoles are thought to have emerged in the early Universe, as it cooled down from the Big Bang, and the particle soup of quark-gluon plasma that filled it underwent a symmetry-breaking phase transition and condensed into matter – like vapour condensing into liquid.

Although we have yet to detect cosmic strings (one-dimensional linear objects) or monopoles (elementary particles with only one magnetic pole), a lot of thought has gone into how they might behave.

In 1988, Chudnovsky and his colleague, theoretical physicist Alexander Vilenkin of Tufts University, predicted that cosmic strings could be captured by stars. There, the turbulence would stretch the string until it formed a network of strings.

According to the new study, cosmic necklaces could form in a sequence of symmetry-breaking phase transitions. In the first stage, monopoles emerge. In the second, strings.

This can produce a stable configuration of one monopole bead and two strings, which in turn could connect to form one-, two-, and even three-dimensional structures – much like atoms joined by chemical bonds, the researchers say.

A one-dimensional necklace would be unlikely to carry information. But more complex structures potentially could – and they could survive long enough to replicate, feeding off the fusion energy generated by the star.

“Compared to the lifetime of a star, its lifetime is an instantaneous spark of light in the dark. What is important is that such a spark manages to produce more sparks before it fades away, thus providing a long lifespan of the species,” the researchers write.

“The complexity evolving through mutations and natural selection increases with the number of generations passed. Consequently, if lifetimes of self-replicating nuclear species are as short as lifetimes of many unstable composite nuclear objects are, they can quickly evolve toward enormous complexity.”

Hypothetically speaking, it’s perhaps possible that such a life-form could develop intelligence, and maybe even serious smarts, Chudnovsky says.

What such a species would look like is a feast for the imagination. But we don’t have to know what they look like to search for signs of their presence. Because such organisms would use some of the energy of their host star to survive and propagate, stars that seem to cool faster than stellar models can account for could be hosts for what the researchers call “nuclear life”.

Several such stars have been observed, and their slightly accelerated cooling is still a mystery. Stars that dim erratically without explanation could be a good place to look, too – like EPIC 249706694. The researchers are careful to note that to link these stars to nuclear life would be an extremely long bow to draw. But there are interesting anomalies out there. And interesting possibilities too.

“Since they would be evolving very fast, they could find a way to explore the cosmos beyond their star, as we have done,” Chudnovsky told ScienceAlert. “They could establish communication and travel between stars. Maybe we should look for their presence in space.”

It’s all extremely theoretical, but wild ideas can be a good way to make new discoveries. The researchers plan to continue their line of inquiry by developing simulations of cosmic necklaces in stars. It may not lead us to glittering star aliens – but even if it doesn’t, it could give us a better understanding of cosmic strings and monopoles.

“It is a fascinating thought that the Universe may be packed with intelligent life that is so different from ours that we failed to recognise its existence,” Chudnovsky said.

The research has been published in Letters in High Energy Physics.

Unusual Skull Turns Out to Be Ultra-Rare Hybrid of a Narwhal And a Beluga Whale


A skull long suspected of belonging to a rare Arctic hybrid has now had its unusual biology confirmed via DNA analysis.

According to the results, this strange beast had a beluga whale for a dad and a narwhal for a mum, and would have forged its own path, distinct from the lifestyles of both parents.

The skull was collected in 1990 by a hunter who found three of the unusual animals swimming in the waters off the coast of West Greenland. The animals described by the hunter were like no cetacean ever before seen, so the single skull he preserved from the hunt was taken to the Natural History Museum of Denmark, where it’s been ever since.

In 1993, a paper concluded that, based on its physical characteristics, the specimen was the hybrid of a narwhal (Monodon monoceros) and a beluga whale (Delphinapterus leucas) – the only two species in the Monodontidae family.

The skull didn’t exhibit the narwhal’s characteristic horn; in fact, it was pretty different from both species.

“The anomalous whale’s skull is much larger than those of normal narwhals and belugas. In particular, the rostrum and mandibles are relatively long and massive,” the researchers wrote in that 1993 paper.

“The dentition is unlike that of any known cetacean, but some features of the teeth are considered analogous to those of both narwhals and belugas.”

In the image above, you can see skulls of a beluga whale (top), the anomalous hybrid (middle), and a narwhal (bottom).

But before now, it was also still possible that the skull could have belonged to an anomalous beluga, researchers thought. Now, 26 years later, genetic analysis has clinched it.

Using genetic material extracted from the skull’s teeth, scientists from the University of Copenhagen conducted a genome-wide DNA sequencing and mitochondrial DNA analysis of the specimen.

They then compared the results of these to the genomes of eight living beluga whales and eight living narwhals, all from around the region where the skull was found.

The genome confirmed it. The skull belonged to a ‘narluga’ that the researchers determined to be male – half narwal, half beluga, with narwhal DNA that can only come from the female germline – in other words, mum.

This was a surprise, since narwhals and belugas are thought to have diverged 5.5 million years ago, and the gene flow between them ceased at least 1.25 million years ago.

In addition, narwhal horns are thought to be a secondary sex characteristic, which could indicate male belugas would have difficulty securing a female narwhal mate. The discovery or the narluga’s parentage suggests that successful matings can occur, even when dad isn’t, ahem, horny.

But the skull had more secrets to reveal. By analysing isotopes of carbon and nitrogen in the bone collagen, the scientists were able to reconstruct the animal’s diet. This was compared to the isotopes of 18 beluga whale skulls and 18 narwhal skulls.

The narluga skull had a higher concentration of carbon isotopes than both of its parent species – indicating that its source of food was different. High carbon isotope concentrations generally indicate benthic prey, suggesting that the narwhal foraged deeper for food than either of his parents.

Although the hunter who discovered the skull reported seeing three narlugas in the wild – all uniformly dark grey, with flippers like a beluga and tails like a narwhal – the skull is the only known evidence we have of this interspecies breeding.

But interbreeding between other cetacean species isn’t all that uncommon, such as a dolphin-whale hybrid seen swimming off the coast of Hawaii last year. And at least 16 other similar cases of cetacean hybridisation have been described in scientific literature – so you can bet your blowhole there are probably many others that scientists haven’t spotted.

Some of them may even be hiding in museum collections like this one was, just waiting for someone to come along and sequence their DNA.

The research has been published in Scientific Reports.