It's been seen in the 1958 movie "The Vikings," the History Channel show "Vikings" and fantasy series such as "Game of Thrones." But did the Vikings actually do this?

To find out, we asked experts whether there is any archaeological or historical evidence to support the idea.

Archaeological evidence

Our sources noted that a burial like this would leave little archaeological evidence. Such "practices would leave little trace, and they are unverified by archaeological sources," Howard Williams, an archaeology professor at the University of Chester in the U.K., said in an email.

Erin McGuire, an anthropology professor at the University of Victoria in Canada, also noted this limitation. From "an archaeological standpoint, we have no evidence for this very common motif," McGuire told Live Science in an email, adding that it would be hard to differentiate a fire set by a fire arrow from a regular fire. Additionally, shipwrecks "with human remains are very, very rare globally," McGuire added. "It takes particular kinds of environmental conditions for them to be preserved and I know of none from the Viking Age."

However, the Vikings were master seafarers and frequently cremated their dead. And there is evidence that Vikings burned ships, McGuire noted. We "do have archaeological examples of ships and parts of ships that were burnt during funerary practices while still on land and were buried after being burned," McGuire said. These include the ninth-century Myklebust ship, a burnt Viking ship that was found in a burial mound in Norway and was built for a rich person, possibly a king.

Historical evidence and legends

Perhaps the closest historical evidence for the fire-arrow ritual comes from Ahmad ibn Fadlan, a 10th-century Arab traveler who went to the Volga River in what is now Russia and spent time with Viking groups there. In ibn Fadlan's written account, a Viking chieftain is placed on a boat, which is set ablaze.

However, there are some key differences between this account and the scene depicted in popular culture. First, there's no flaming arrow; rather, the boat was lit on fire by a person described as a chief mourner. Additionally, the boat and its dead chieftain were on land, not on the water.

Although not strictly historical, there are some legendary and mythical accounts of burials at sea that were possibly inspired by real events. "From medieval literature we have rare references to boats/ships involved in funerals over water," Williams said.

In the epic poem "Beowulf," the funeral of the Danish king Scyld Scefing sees the dead king placed on a ship that drifts off to sea. In the 13th-century Scandinavian book "Heimskringla," by Snorri Sturluson of Iceland, the "sea-king Haki [was] set adrift and set alight so that his body burned with those of his slain retinue," Williams said, and in another story by Sturluson, "the god Baldr is set adrift and his ship set alight by his brother Thor."

The funeral of Baldr has been particularly notable, McGuire said, noting that it inspired J.R.R. Tolkien to include a similar scene in his "Lord of the Rings" books.

Practical problems

Experts noted that this kind of fire-arrow burial might not have even been possible.

"Personally, I consider cremation at sea using a ship set alight from the shore with flaming arrows to be rather unrealistic," Matthias Toplak, head of the archaeology department at the Viking Museum Haithabu in Germany, told Live Science in an email. "My own experiments show that it is not at all easy to set something alight with flaming arrows."

He noted that fire must burn at a high temperature for several hours for cremation to be effective. "At sea, the ship would probably sink before the body had been sufficiently cremated," Toplak said. "Apart from that, there is of course also the danger that a ship ablaze and adrift would be driven by currents or the wind into other ships or harbour facilities."

McGuire also noted that there are practical problems with the idea. "if you send a burning boat out onto the water, how do you stop it from drifting ashore with rather grisly contents?"

Overall, the scholars we spoke with doubted that the Vikings used fire arrows to burn funeral boats set adrift at sea. "However romantic the idea of such a funeral scene may be, I unfortunately consider it highly unlikely," Toplak said.

Instead, Williams suspects 20th-century Hollywood movies played a major role in the creation of this idea. "I strongly suspect this specific trope owes its origin to the 1958 film The Vikings and the concluding scene of Einar's funeral," Williams said.

It "says little about how 'Vikings' treated their dead," Williams added, "but tells us a lot about our valorised ideals of fate, honour and death linked to both fantasy and historical 'Vikings.'"

See how much you know about ancient norsemen with our Viking quiz!

'> Did the Vikings really shoot fiery arrows at funeral boats?

Rather than continuously using energy to force a calculation through a series of processing steps, the DNA computer is designed so that its more "energetically favorable" state is the correct answer. In other words, the computer is built to use less energy than other biological computers, which integrate living cells with traditional hardware, would take to calculate the answer.

"The clever part is that the binding process is competitive: the DNA molecules compete with each other to select a winner, which succeeds in binding to the scaffold; all of the jostling and competition process information and execute a computation," Damien Woods, a professor of computer science at Maynooth University in Ireland and a co-author of the study, told Live Science in an email. "Eventually, the system settles down into its energetically-preferred state which encodes the answer to the computation."

The researchers described their system, called the Scaffolded DNA Computer (SDC), in a study published Sept. 16 in the journal Nature. They tested the SDC on 10 programs, including 100-bit computations. Some calculations, like 10 + 3, took around 30 seconds for the SDC to compute.

There are several possible long-term applications for the SDC, but these are currently speculative, the researchers noted in the study.

DNA-based systems could potentially contribute to molecular data storage, energy-efficient forms of computation, or even devices capable of running inside living cells.

"Molecular computers like this are not trying to replace electronic ones, but they could be used in biological environments, smart materials and archival DNA data storage," Abeer Eshra, an assistant professor of computer science and a co-author of the study, told Live Science via email. "Our work is a new direction for DNA data storage, since any data stored in such a system would have natural built-in error correction properties."

A computer made from DNA

The SDC is made from short strands of DNA that interact with a longer DNA scaffold. The strands are placed into a small amount of salt water, and then heated and cooled.

As the DNA strands interact, they assemble into structures according to a set of programmed rules that make up the "computation." The DNA strands act like tiny molecular puzzle pieces, with their sequences determining which pieces can attach to one another and to different positions on the longer scaffold. By designing these binding rules, the researchers effectively "program" a calculation.

"Each program corresponds to a set of DNA strands: to program a different computation, or give a different input, we simply select different DNA strands from the fridge," Woods and Eshra told Live Science in an email.

The approach also exploits thermodynamics — the tendency of physical systems to move toward more energetically favorable states. When the mixture is heated and cooled, the strands compete to form the most stable arrangements, with the correct configuration becoming energetically favored. The final structure encodes the answer, allowing the molecules to "compute" by simply interacting with each other.

While the DNA computer itself is tiny, the number of strands involved in the computing process is enormous.

"A small droplet of liquid contains billions, and sometimes trillions, of DNA strands," Eshra said in a statement. "These strands interact with one another to produce a result."

A reusable molecular computer

Using the SDC, the researchers demonstrated more than 700 computations across their experiments. Their programs included addition; multiplication by 3; division by 2; and eight-bit parity detection, a common type of error correction for computing. Small calculations could be completed in under a minute, which is striking given that the computing has to go through chemical reactions that take the same amount of time or longer.

"They're trivial calculations you could easily do faster yourself, and a silicon computer would finish in an instant," Constantine Evans, a senior research fellow at Maynooth University and a co-author of the study, told Live Science. "Our system uses just a handful of molecules, never really following an organized process of steps, never making irreversible steps, and yet ending up with the right answer. When thinking about computation at a molecular level, reliably making even those seemingly simple computations is very hard."

Larger calculations took considerably longer. A more difficult sum in the range of about 11 million to 34 million took up to 14 hours.

"It demonstrates that the system is programmable, reusable and although slow compared to silicon, it is fast compared to other DNA computers," Woods and Eshra wrote in a joint email to Live Science.

In addition to being fast, the SDC is reusable. Whereas many earlier molecular computers were intended as one-time experiments, the SDC was designed so the molecules could be used repeatedly.

"Many molecular computers to date relied on specially prepared components, or molecular fuels to drive the system forward, or carefully timed reactions," Eshra said. "Our DNA computer instead works by throwing the molecules together and letting it relax towards equilibrium."

Three of the programs were successfully redone up to 24 times. The team even repeated one experiment 1.5 years after the original experiment. The SDC had partially dried out, but the researchers were able to rerun the calculations by adding water.

For now, however, the work is mainly a demonstration that thermodynamics can be used to perform useful calculations.

"There is still a lot more theory to do!" Eshra said. Broader future directions include "designing scaffolds that are better suited to computation, improving the system's read-out, and investigating potential applications in DNA data storage. We are already working on some of these questions."

Can you match these ancient devices to their pictures? Find out with our computing quiz!

'> Scientists build a DNA computer that can perform calculations in a drop of water , such as exploding stars and rapidly spinning neutron stars. But in this case, the signal, dubbed GW231123, originated from a pair of colliding black holes around 2 billion light-years from Earth.

The merger also made waves in the media as the most massive black hole collision to date, with the two parent black holes birthing a singularity around 230 times more massive than the sun. The only problem is that the colliding black holes ‪—‬ which weighed 100 and 130 solar masses, respectively ‪—‬ are too large to be explained by our current understanding of the universe.

The pair dwell in what astronomers call a "mass gap," meaning they are too large to be stellar-mass black holes, created by collapsing stars, but they are smaller than intermediate-mass black holes, which we still do not fully understand. Adding to the strangeness, the black holes were spinning much faster than expected when they smashed into each other.

Researchers have put forward several potential explanations for the black holes' "forbidden" sizes. One study released last year proposed a new pathway by which singularities of this size could form: via the collapse of larger stars that would otherwise explode as supernovas. However, this idea goes against a lot of previous observational evidence.

Now, in a study published Aug. 25 in The Astrophysical Journal Letters, researchers propose a simpler, yet equally intriguing explanation for GW231123. They suggest that the signal from the merger was warped by a strange space-time phenomenon called gravitational lensing, which occurs when distant emissions pass through patches of distorted space-time bent by the gravity of massive foreground objects.

This effect has been shown to magnify, or otherwise warp, distant light sources many times before. However, until now, researchers had found no evidence that gravitational lensing could happen to ripples in space-time.

"Like light, gravitational waves can also be deflected, magnified and split into multiple signals by massive objects," study co-author Miguel Zumalacárregui, an astrophysicist at the Max Planck Institute for Gravitational Physics in Germany, said in a statement. "For gravitational waves, diffraction and interference effects give us an additional way to identify and study lensed signals."

Cosmic magnification

The idea of gravitational lensing was first proposed in 1915 by Albert Einstein's theory of general relativity, which states that the gravity of massive objects, such as galaxies or black holes, warps the space-time surrounding them. If such an object is positioned directly between Earth and another more distant object, then the light from the far-off entity can pass through the distorted space-time, effectively bending around the middle object. As a result, the light can be magnified, diffracted or otherwise altered — just as it might by passing through a glass lens.

This effect can create stunning spectacles, including halos of light known as Einstein rings, unusual cross-shaped structures, and multiple copies of a single light source. By studying these luminous curiosities, researchers can weigh the lensing objects, thus revealing hidden discrepancies caused by invisible dark matter and providing one of our best methods for studying this elusive substance.

In the new study, the researchers modeled how gravitational waves might be altered by a lensing object. They found that the GW231123 signal could have been magnified, which would have greatly exaggerated the masses of the black holes involved.

"If we assume that GW231123 was deflected and distorted by a compact object of about 190 to 850 solar masses — or by an extended structure such as a globular cluster — we can understand the observed high masses," study first author Srashti Goyal, a postdoctoral researcher at the Max Planck Institute for Gravitational Physics, said in the statement. "Moreover, the lensing interpretation does not require unusually high spins."

Taking this into account, the total mass of the newly merged black hole would be around 140 solar masses rather than the 230 solar masses researchers initially measured, meaning the colliding black holes that formed it no longer dwell in the problematic mass gap. It also suggests that the black hole may be even farther from Earth than astronomers thought.

However, while the lensing of gravitational waves is theoretically possible, it has never been seen before. The new study is also purely theoretical ‪—‬ the researchers have no direct evidence of lensing, such as an accompanying Einstein ring ‪—‬ so more work is needed to show this may be what happened here, the researchers noted.

A new mystery

The new theory could finally put the mystery of GW231123 to bed. But in doing so, it raises another intriguing question: What lensed the puzzling signal?

In most cases of gravitationally lensed light, the lensing object is something enormous, like a galaxy, which can be trillions of times more massive than the sun. But the researchers' models suggest that any potential lensing object here must be much smaller, and they have not been able to spot anything that fits the bill in between Earth and the origin point of GW231123.

"The nature of the lens remains a major mystery in our analysis, as individual compact lenses with 100 – 1,000 solar masses should be exceedingly rare," Zumalacárregui said. "Future work will need to establish whether such lenses can form, or whether an ensemble of lighter objects, including stars, can explain this event.

If the team can figure out what may have magnified the signal and prove that the space-time ripples have been warped, it could be transformational for future astronomy. If gravitational waves can be lensed, it opens up the possibility of studying ancient black hole mergers or similar cosmic events that would otherwise be too far away for us to detect. The researchers also think that analyzing the diffraction patterns of such signals could provide more clues to the elusive identity of dark matter.

'> An 'impossible' black hole merger may finally be solved thanks to Einstein's relativity — but it raises an even bigger mystery

So what causes this change?

The short answer is that hair color is controlled by a complex interplay of genes, pigment-producing cells and, later in childhood, hormones. Scientists understand many of the genes involved in hair color, but they are still trying to find out why some blond children's hair darkens while others' locks remain blond for life.

"It depends on their genetic inheritance," Desmond Tobin, a professor of dermatological science at University College Dublin, told Live Science in an email.

Hair gets its color from a pigment called melanin, which is produced by specialized cells called melanocytes in hair follicles. There are two main types of melanin: eumelanin, which produces brown and black shades, and pheomelanin, which contributes yellow and red tones to hair. The amount and type of melanin produced by a follicle largely determine the color of the hair that grows from it.

In general, more eumelanin means darker hair. For example, during pregnancy, high levels of estrogen and progesterone can encourage hair darkening as more eumelanin is produced.

The activity of hair follicles isn't necessarily fixed throughout childhood. As children grow, the biological signals controlling pigment production can change, too.

From blond to brown

For many blond children, the most noticeable darkening happens around puberty, typically between about 10 and 13 years old, Tobin said.

It is likely the hormonal changes during puberty, such as estrogens and androgens that stimulate an increased production of eumelanin, that gradually turn blond hair darker over time, he said. "Those that remain blond typically have a genetically determined reduction in eumelanin pigment formation," Tobin added.

Exactly how hormones might cause this change, however, is still something of a mystery.

One clue comes from a group of hormones called melanocortins. One of these, alpha-melanocyte-stimulating hormone (alpha-MSH), is involved in telling pigment-producing cells to make more melanin. In our skin, alpha-MSH is triggered by ultraviolet (UV) light. UV light can damage DNA in skin cells that, via a cellular signaling pathway, encourages the release of alpha-MSH to make the skin tan.

But in hair, things get, well, hairy. Scientists haven't shown that a rise in alpha-MSH, testosterone, estrogen or any particular hormone is what makes blond hair darken.

The melanocortin system shows that hormones can tell pigment-producing cells to make more eumelanin. What remains unclear is whether changes in this system are actually responsible for blond hair darkening during puberty.

"We haven't yet identified the genes that control this process," Wojciech Branicki, a researcher who studies the genetics of human pigmentation at Jagiellonian University in Poland, told Live Science in an email.

One possibility Branicki suggested is that hormones may affect children's hair follicles differently depending on their genetic background. For now, researchers don't know which genes are involved or how they interact with hormonal changes during puberty, as more research is needed.

Branicki posits that in some children, the hormones could induce the production of melanin or the transport of pigment within the hair follicle. In other words, two children could start out with similarly blond hair but respond differently to the hormonal changes as their bodies develop. One might continue producing relatively little eumelanin and stay blond, while the other's follicles might gradually ramp up pigment production, causing new batches of hair to grow darker.

"Research on human genome variation is quite advanced, but not all aspects have been explained yet," Branicki said.

'> Why does blond hair tend to darken with age? experts suggested.

With the U.S.' recent deployment of these technologies, Live Science ran a poll to see how readers felt about the possible threat of weapons in space. The results reveal just how worrying this topic is.

More than 280 readers voted in the poll, with 80% choosing the option "Yes, I'm worried that space will become the next frontier for weapons."

The comments reflect this general trend. "Of course I am worried that the US have put weapons in space," one reader wrote, adding that they're worried by anything the administration in Washington is currently doing.

Other readers echoed this sentiment, with one commenter saying, "Peace in space depends on the calibre and wisdom of world leaders which currently is simply not up to the necessary standard to be unlegislated."

The next-largest voting group, 14% of readers, picked this option: "This is a bit premature, and I'm waiting to see how other countries will react."

One comment opined that the presence of weapons in space doesn't necessarily mean they are intended to set off a major conflict, with one reader writing, "I think the observation 'if you want peace, prepare for war' is most relevant here. There is no suggestion these weapons were put there to start a war, but if one eventuates one day we will be glad defensive measures are already in place."

'> 'Of course I am worried': Live Science readers react to US weapons in space