Author: Robert Lea

Scientists are still learning about a cosmic "string of pearls," a unique celestial relic left by a supernova explosion that humanity witnessed around 850 years ago.

That is thanks to the most detailed observation of the dandelion-shaped chains of gas and supernova debris that comprise Pa 30, the only supernova remnant of its type observed in the Milky Way. What makes Pa 30 even more unique is that it has a rare "zombie star" at its heart.

Supernovas like the one that created Pa 30 are called Type Ia supernovas; they happen when a dead star called a white dwarf overfeeds on a companion star like a cosmic vampire. This overfeeding triggers a runaway nuclear explosion that usually destroys the white dwarf. But on rare occasions, the supernova doesn't completely destroy the star, and a shattered stellar body remains, called a zombie star. These events are called Type Iax supernovas.

Pa 30 was first identified in 2013 by a citizen scientist in 2013, but scientists soon linked it to a cosmic explosion recorded independently in the year 1181 in Japanese, Chinese, and Arabic historical documentation. That makes this one of only five supernovas seen before the invention of the telescope.

"Reliable historical records of stellar explosions extend back only about a thousand years. For all we know, there might well be similar remnants still lurking in the dark in our own galaxy," team member Ilaria Caiazzo, assistant professor at the Institute of Science and Technology Austria (ISTA), said in a statement.

"Today, we are lucky to study an intriguing object we know was observed by astronomers who made three independent historical records of the event centuries before the invention of the telescope."

Solar system-sized pearls

Pa 30 is a good laboratory to study supernovas because, at around 7,500 light-years away, it is relatively close to Earth on cosmic scales. For instance, the heart of our galaxy is around 26,000 light-years away. "We can see this much detail because of Pa 30's proximity to Earth," said Caiazzo. "This proximity makes Pa 30 uniquely valuable for study."

It is also an important subject of study because it is the only supernova remnant in which we can see a zombie star.

Using the Gemini North telescope, Caiazzo and colleagues zoomed in on Pa 30, discovering knots along the strands of gas radiating out from the site of the cosmic explosion, like pearls on a string.

These pearls are each wide enough to encompass the orbit of Neptune, the most distant planet from the sun, ten times over.

"The planetary region of our solar system could fit in each knot about ten times with room to spare," said Caiazzo. "The knots are quite strikingly uniform. We are excited to try to model them."

The team also discovered that the zombie star sits almost perfectly at the heart of Pa 30. When these cosmic explosions happen, they should provide any debris, including zombie stars, with a kick. The fact that this "living dead" star still sits dead center of this wreckage suggests that when this explosion happened, it was roughly symmetrical and the kick was relatively light.

"Explosions conserve momentum. If the explosion itself was perfectly symmetric, the ejecta should also be symmetric, and the surviving star should not receive a substantial kick," Caiazzo said. "We were able to measure a precise upper limit of the remnant star's transverse kick speed, showing that it was surprisingly small. We practically don't see the star moving away at all."

While there are still many mysteries surrounding Pa 30 and its zombie occupant, one of the most exciting prospects emerging from this research is the possibility it will help identify the wreckage of other Type Iax supernovas in our galaxy.

"While we can see Type Iax supernovas in distant galaxies as point sources of light, resolving the remnants of such explosions is only possible in our own galaxy and in very few nearby ones," Caiazzo concluded. "Eventually, we plan to use Pa 30's distinctive properties to search the Milky Way and nearby galaxies for similar objects."

The team's research was published in The Astrophysical Journal.

Using NASA’s SPHEREx spacecraft, astronomers have studied a host of "failed stars," also known as brown dwarfs.

These strange cosmic bodies straddle the line between planets and stars, possessing a mass between 13 and 80 times that of Jupiter (0.013 to 0.08 times the mass of the sun). They get the nickname failed stars because they form like stars from collapsing clouds of gas and dust but fail to gather enough mass to trigger the fusion of hydrogen to helium in their cores, the process that powers actual stars.

This formation process also means that brown dwarfs are cosmic loners, wandering the darkness of space alone, bereft of the light of a parent star. That description might sound like lyrics from a Type O Negative song ("Black No. 1," anybody?). And that's apt, according to the leader of the new study, which reveals that, chemically speaking, the atmospheres of these dark and cloudy worlds are not unlike those of our solar system's gas giant planets.

"They’re kind of goth," Zafar Rustamkulov, of the California Institute of Technology (Caltech), said in a statement. "Unlike exoplanets, free-floating brown dwarfs are completely independent celestial objects that will fade into eternity alone. We’re still learning how complex they are."

Rustamkulov added that, from Earth orbit, SPHEREx — short for Spectro-Photometer for the History of the Universe, Epoch of Reionization, and Ices Explorer — sees wavelengths of light that are nigh-impossible to see with telescopes on the ground because water in Earth’s atmosphere absorbs them. That is important for bringing brown dwarfs into the light.

"We are picking up light from the deep, red clouds of brown dwarfs all over the sky," he said.

A forest (of brown dwarfs)

Brown dwarfs have been somewhat mysterious since their discovery in the 1990s, due to the fact that the small amount of nuclear fusion that occurs within them causes them to emit no more than a faint glow. That means that our understanding of their makeup, their storms, and their evolution really only comes from theory.

To help lift this observational darkness, the team turned to data from SPHEREx. They studied 37 nearby brown dwarfs in a spectrum of light including 102 wavelengths, from the deepest red our eyes can see to the invisible infrared light. These local failed stars spanned the full temperature range for brown dwarfs — from 4,000 degrees Fahrenheit to minus 10 degrees Fahrenheit (2,200 to minus 20 degrees Celsius).

Considering that the temperature of the sun is about 10,000 degrees Fahrenheit (5,500 degrees Celsius), you could definitely say brown dwarfs run cold.

The spectra of brown dwarfs seen by SPHEREx allowed the team to determine that their atmospheres are chemically rich in water, carbon dioxide, carbon monoxide and methane.

"We’re seeing the signatures of these molecules and how they change from object to object across the entire temperature regime," said team member J. Davy Kirkpatrick, also of Caltech. "Our paper concentrated on just three dozen, but we have thousands more that we are in the process of analyzing.

"I really want to see what bounds the universe places on the variety of brown dwarfs."

All my colors

Brown dwarfs have been routinely observed by other telescopes, including NASA's James Webb Space Telescope and the agency's now-retired Spitzer Space Telescope, but the wide wavelength coverage of SPHEREx has made it particularly useful in observing these failed stars. That's good news for astronomers waiting for change in the atmospheres of brown dwarfs as they age and grow cold.

The researchers found that some brown dwarfs observed by SPHEREx are at a stage of extreme change in which their clouds are clearing, creating atmospheres rich in methane.

The team may have discovered significant new details about brown dwarfs, but they are still on the proverbial mystery street when it comes to these strange celestial objects,

"The state-of-the-art models are capturing the general chemical trend, but when it comes to these cloudy transitions, the models are struggling to match the data," said Rustamkulov. "No two brown dwarfs are alike. Even at the same temperature, their spectra look quite distinct."

"This journey has turned many of us into accidental meteorologists. We know how hard it is to predict weather on our own planet, and we realize it's going to be just as challenging to explain the phenomena we see in these bizarre, cold objects," Kirkpatrick said. "The findings are a call to action to explore even more of these dark worlds."

As astronomers resond to that call to action, I will ponder how I could have worked Bauhaus' Goth classic "Bela Lugosi is Dead" into this article.

The team's research was published on Sept. 28 in The Astrophysical Journal.

How awesome would it be if the sun could take on a spooky green glow for Halloween? It turns out that scientists have discovered that our star may indeed go green, but only billions of years from now after its death  — and only if it then starts eating planets like a cosmic zombie.

That's possible because scientists have discovered that white dwarfs, the type of stellar remnants sun-sized stars leave behind when they die, can actually take on a range of colors including green if they snack on their rocky planets like cosmic cannibals.

For stellar scientists, the colors of stars have always been indicative of their temperatures. Cool stars look orange, while stars like the sun look white, and the hottest stars glow pale blue. This is akin to a blacksmith's iron glowing red, then orange, then white-hot as it heats up. Researchers have always assumed that white dwarfs follow the same rule. However, new research suggests that these stellar corpses could glow in a range of colors including green, pink, cyan, yellow, and purple. That means the universe is far more colorful than we suspected.

"Most stars, including most white dwarfs, behave like 'perfect radiators,' so their color is set almost entirely by temperature. But nobody had really looked into what else might be possible for white dwarfs," team leader Mark Hollands of the University of Warwick said in a statement sent to Space.com.

"It turns out these incredibly dense stars caaaaan produce colors nobody expected, and some of them genuinely surprised me."

How white dwarfs break stellar color rules

White dwarfs get their name because when they were discovered, they appeared surprisingly hot and glowed white or pale blue. However, this new research suggests that this slightly bland and uniform appearance is because no white dwarf is close enough for Earthbound astronomers to see their true colors.

The key to the rainbow-like array of colors this team suggests white dwarfs could possess is their density. White dwarfs form when stars with a mass roughly that of the sun run out of fuel and can no longer support themselves against their own gravity, causing their cores to collapse. As a result, the matter that makes up white dwarfs is around the density of water, millions of times denser than the sun's surface, the photosphere.

In these conditions, elements like carbon, calcium, and sodium can interact with the surrounding dense helium plasma and absorb light across a wider range of colors than they would at lower densities. That shifts the colors of white dwarfs away from the white/light blue seen for a perfect radiator of heat.

The researchers found that the colors of white dwarfs would fit into distinct groups tied to the individual chemical makeup of the stellar remnant's atmosphere.

White dwarfs abundant in carbon should be pink or purple, while those that have been enriched with debris from consumed asteroids and comets, and the remains of old planetary systems, would take a more yellow hue. Cooler white dwarfs with mixed hydrogen and helium atmospheres often would glow cyan or pale blue, caused as hydrogen molecules collide with helium atoms in their dense atmospheres.

One of the most striking examples of white dwarf coloration, however, would arise when one of these living dead stars starts feeding on the planets around it like a horror movie zombie.

Zombie white dwarfs go green

The researchers found that some dead star white dwarfs can go a little green around the gills after snacking on orbiting planets.

An example of this is WD J1330+6435, a cool white dwarf located around 326 light-years away, which has been accreting rocky material from a planetary companion. This has enriched its atmosphere with calcium, lithium, and sodium, and the team's model suggests this would have led WD J1330+6435 to adopt a green hue.

But unlike the green-tinged zombies of George Romero's classic Dawn of the Dead, there are no hordes of these green-faced cosmic zombies ... yet.

The researchers think that no other star, living or dead, has ever been credibly reported as green. That makes WD J1330+6435 the first known genuinely green star.

"The traces of sodium in the atmosphere of this white dwarf absorb the orange part of the spectrum, leaving behind a ghostly green glow," Hollands said. "Imagine standing on a planet and looking up at a green star. It feels like something out of science fiction."

Scientists see red

The team didn't just discover that a known white dwarf is the first-ever green star; they also discovered what could be the reddest star ever in the form of the white dwarf WD J1011+2845.

Located just 48 light-years from Earth, this white dwarf has a deep convection zone that carries carbon from its core to its surface. These carbon molecules distort light from the white dwarf, causing a deep salmon-pink glow unlike anything seen in any other star.

Despite this rainbow of white dwarfs, the team theorizes that white is still the most common color for these stellar corpses. Only five of the 151 white dwarfs within around 65 light-years of Earth have extraordinary coloring. Extrapolating this to the total population of white dwarfs, the team estimates that only one in 30 of these dead stars has an unusual color.

"One in thirty might not sound like a huge fraction, but across the entire population of white dwarfs in the universe, that is still a lot of oddly colored stars out there," Boris Gänsicke, Department of Physics, University of Warwick, said. "Yet if we take the median across a representative population of white dwarfs, we found that the average white dwarf really is white."

The team's research was published on Thursday (Oct. 14) in the journal RAS Techniques and Instruments.

Now you see them, now you don't. Scientists have discovered that some of the universe's most powerful explosions, hypernovas, may not happen at all.

These explosions, known as hypernovas, were first proposed to explain unusual stars in the halo of our galaxy, the Milky Way, and in a neighboring dwarf galaxy. It was suggested that these stars could only form from the debris of an explosion 10 times more powerful than the 'average' supernovas.

The team behind these new findings suggests that ordinary supernovas could actually account for these stars when the uneven or non-spherical way they fling out matter is considered.

"If we look at a supernova today, the star's materials are not spread evenly. Oxygen might predominantly fly in one direction, sulphur in another. New stars might form from a mix of pieces of the supernova, not its overall mix of elements," team leader Anmol Aggarwal of University College London (UCL) said in a statement. "We developed mathematical models that took account of this and found in all cases that stars with a very unusual mix of ingredients were most likely formed from ordinary supernovas.

"All the evidence we see for hypernovae is suddenly gone."

Hypernova vs. supernova: What's the difference?

Supernovas occur when massive stars run out of fuel for nuclear fusion, effectively ending their lives. This results in the star's core collapsing, sending shockwaves rippling through its outer layers, causing explosions we call supernovas.

Hypernovas are proposed to occur in a similar way, but for an even more massive and rapidly spinning star. This results in a vastly more energetic explosion.

When supernovas or hypernovas happen, they fling elements that the dying star has forged throughout its lifetime into their surrounding cosmic environments. These elements eventually become the building blocks of the next generation of stars.

That means analyzing the chemical signatures of stars can tell stellar scientists about their family histories.

"Just before a star goes supernova, it has layers like an onion, with heavier elements at the center and lighter ones further out. Our model looks at how much material from each layer or each region would be needed to fit the observed star," Ralph Schoenrich of Mullard Space Science Laboratory at UCL said. "We still don’t know how well the supernova material gets mixed before it forms new stars. That is despite decades of work in this area. Our research suggests some mixing goes on, but incomplete mixing.

"We need to take this into account in our models of how chemicals evolve in galaxies and of how the interstellar medium works."

The team began their investigation by observing four stars that are suspected to have been forged from material ejected in a hypernova explosion. Three of those stars were more likely to have been created after supernovas, the team concluded.

The scientists then studied a single red giant star in the halo of the Milky Way with an odd chemical composition, including an overabundance of heavy elements like silver and uranium. These are too heavy to be forged in the cores of all but the most massive stars, the kind of stars that go hypernova.

Such elements could also be created when two massive and dense stellar remnants called neutron stars collide and merge. However, this star doesn't have certain other heavy elements that would be present after a neutron star collision.

This team considered the origins of this star using a model of the Milky Way that has been rapidly enriched with elements heavier than hydrogen and helium, which astronomers call metals, via the death of the first generation of stars.

The rapid speed at which the star spins and the fact it exists at the outskirts of the Milky Way led the team to conclude that this star escaped a metal-poor dwarf galaxy and was eventually dragged into our galaxy. The event that created it, they concluded, was the combination of a neutron star merger and an ordinary supernova.

No hypernova required. An asymmetrical supernova would be enough, the scientists found.

The team's research was published as two papers in the journal Monthly Notices of the Royal Astronomical Society.

Astronomers investigating mysterious flashes of X-rays believe that these blasts could stem from collisions between neutron stars, the events that forge elements like gold, silver, and platinum.

The event designated EP250704a, was first seen on July 4, 2025, as a blast of gamma rays lasting half a second followed by a bright X-ray emission lasting 10 minutes. After receiving an alert from the joint European-Chinese Einstein probe that witnessed the blast, a team of astronomers started to hunt for its cause by studying the aftermath of the explosion using the European Southern Observatory's Very Large Telescope (VLT), the Very Large Array (VLA), and other telescopes.

According to astronomer Niccolò Passaleva who led the observations of the X-ray flash with the VLT, this cosmic outburst was unlike any scientists had seen before. "This is the longest-lasting prompt X-ray flash ever observed from a neutron star merger," Passaleva said in a statement. "It is an opportunity to have a front-row seat to the most extreme forces of the universe and discover more of its secrets."

Neutron stars are created when massive stars die in supernova explosions, cramming one or two the mass of the sun into a width akin to a city on Earth and creating material so dense that a single teaspoon of neutron star matter brought to Earth would weigh 10 million tons. When these extreme dead stars slam together, they create environments so turbulent and violent they are capable of forging elements so heavy that even the hearts of stars can't do it. Elements like the gold on your finger.

These collision and merger events, marked by flashes of light called kilonovas, have long been associated with flashes of high-energy gamma-rays that disappear within two seconds, but new research suggests some neutron star mergers could reveal themselves via blasts of X-rays lasting minutes.

In particular, scientists have wondered if neutron star mergers could be the cause of hundreds of X-ray flashes in distant galaxies discovered by the Einstein probe since its launch in 2024. While some of these have been linked to the supernova-explosive death of massive stars that can create a neutron star or a black hole, others have defied explanation. EP250704a is one such X-ray flash.

"When I saw the X-ray data from this new event, I realized something was up," team member Eleonora Troja, part of the Einstein Probe European collaboration, said in the statement.

The team believes that there is something special in the neutron star merger mix that results in these X-ray bursts.

Merging with a magnetar

All neutron stars are created the same way from the collapsing core of a massive star, but not all neutron stars are equal.

Just as an ice skater pulls in their arms to increase the speed of a spin, the rapid reduction in radius of a collapsing stellar core can "spin up" the rotation of a neutron star to 'over 700 times per second. This collapse can have another consequence too.

It turns out that magnetic fields get stronger when magnetic field lines are pushed closer together. That means the collapse of a stellar core with an already powerful magnetic field can create a neutron star with the strongest magnetic field in the universe. Those neutron stars have a special name: magnetars.

The team behind this research thinks that the neutron star merger in question involved at least one magnetar.

"If the remnant of the collision is a magnetar, it could keep bursting for longer," Troja said. "Magnetars are rapidly spinning neutron stars with huge magnetic fields. When they dump their magnetic power into the surroundings, they can make any explosion brighter and longer-lasting."

The researchers ruled out a supernova as the cause of the X-ray burst and were also able to determine that the light from this collision has been travelling to Earth for 6 billion years.

Discovering more of these extreme X-ray flashes could help astronomers determine how often magnetars are formed through these neutron star mergers, Passaleva said in the statement.

The team's research was published in the journal Science Bulletin.