For almost every star astronomers have ever catalogued, colour tracks temperature with remarkable fidelity. Cool stars glow orange and red, stars like our Sun emit a balanced white light, and the hottest stars shine pale blue, following the same logic that makes a blacksmith’s iron shift from red to orange to white-hot as it heats. This relationship holds because most stars behave as near-perfect thermal radiators, their light distributed across wavelengths in a way determined almost entirely by temperature. White dwarfs were assumed to obey the same rule. The earliest ones discovered were hot and blazed white or pale blue, which is how the class earned its name. The Warwick team asked whether that apparent simplicity was hiding something, and the answer turned out to be a resounding yes.

The key to the anomaly is density. The coolest white dwarf atmospheres can reach around one gram per cubic centimetre, roughly the density of water and millions of times denser than the Sun’s photosphere. In that crushing environment, trace elements such as carbon, calcium and sodium no longer behave as they do in a diffuse gas. They interact with the surrounding dense helium plasma and absorb light across far broader ranges of wavelength than they would under ordinary conditions. Because colour is simply the balance of light remaining after absorption, these broadened absorption features can strip away entire swathes of the spectrum and push a star’s apparent colour far from the orange, white and blue expected of a perfect radiator.

No white dwarf is close enough for its colour to be seen directly through a telescope, so the researchers calculated it from data that astronomers already collect routinely. Every stellar spectrum is a fingerprint, produced when starlight is split by wavelength much as a prism splits sunlight into a rainbow. The team ran these spectra through a model of human colour vision, converting the measured distribution of light into the colour each star would present to an observer standing nearby. The method demonstrates how much information a spectrum carries: not just a star’s temperature or chemical composition, but its true chromaticity, the precise colour quality of its light as the eye would perceive it.

Applying the technique to white dwarfs across the sky, the team found that the colours fall into distinct groups, each tied to atmospheric composition. Carbon-rich white dwarfs typically appear pink or purple. Those polluted by debris from shattered asteroids and comets, the remnants of old planetary systems, tend towards yellow. Cooler white dwarfs with mixed hydrogen and helium atmospheres often take on a cyan or pale blue tinge, caused by hydrogen molecules colliding with helium atoms in their ultra-dense atmospheres. Each group represents a different physical mechanism distorting the starlight, from molecular absorption to the accretion of planetary wreckage, and together they map a chromatic diversity nobody had previously suspected in stellar remnants.

The most striking case is WD J1330+6435, a cool white dwarf of roughly 4,000 degrees Celsius that has accreted rocky material from its own planetary system, enriching its atmosphere with calcium, lithium and sodium. In the team’s models, the sodium absorbs light across broad bands of the yellow, orange and red spectrum, leaving behind a chartreuse green glow. As far as the researchers are aware, no other star, living or dead, has ever been credibly reported as green, making this the first known genuinely green star in the Galaxy. Dr Mark Hollands, the Warwick Prize Fellow who led the work, described the effect in vivid terms: the sodium in the atmosphere absorbs the orange part of the spectrum, leaving a ghostly green star that would look like something out of science fiction to an observer on a nearby planet.

At the opposite end of the colour range, the team identified what may be the reddest star ever recorded. WD J1011+2845, a white dwarf just 48 light years from Earth, possesses a deep convection zone that has dredged carbon up from its core to its surface. The carbon atoms form diatomic molecules that distort the star’s light so severely that almost all of it is squeezed into wavelengths beyond 600 nanometres, at the deep red end of the visible spectrum and beyond. The result is a deep salmon-pink glow unlike anything produced by an ordinary star. A similar process operates in WDJ0902+2010, where convection has lifted interior carbon into a helium-dominated envelope, and the resulting C2 molecules absorb blue, green and yellow light so strongly that the star appears pink.

To establish how common these exotic colours are, the team studied a representative sample: the 151 white dwarfs within 20 parsecs, about 65 light years, of Earth. Five of them showed unusual colouring, two yellow and three pink, suggesting that roughly one in thirty white dwarfs in the Universe shines with an unusually coloured light. For the remaining 146, the researchers measured the colour temperature, a quantity that compares an object’s colour with that of a perfect radiator and is familiar from household light bulbs, where warm white corresponds to about 3,000 Kelvin and cool white to about 6,000 Kelvin. The median colour temperature of the sample came out at approximately 6,800 Kelvin, which the human eye perceives as white.

That median result corrects a persistent misconception in astronomy: that white dwarfs are typically blue. Hotter, bluer white dwarfs are brighter and can be seen from greater distances, so they are over-represented in surveys that select stars by brightness alone. A properly representative sample shows that the average white dwarf really is white, even though a substantial minority deviates dramatically. Professor Boris Gänsicke of the University of Warwick’s Department of Physics noted that while one in thirty might not sound like a large fraction, across the entire population of white dwarfs in the Universe it amounts to a great many oddly coloured stars, even as the median across a representative population confirms the class’s traditional name.

The study, titled ‘Any colour you like: The diverse chromaticities of white dwarfs’, opens a new observational window on stellar remnants and the planetary systems that surround them. Because unusual colours flag specific chemistry, sodium from accreted rocky debris, carbon dredged from degenerate cores, or molecular hydrogen colliding with helium, colour becomes a rapid diagnostic of what a white dwarf is made of and what it has been eating. With large surveys cataloguing hundreds of thousands of white dwarfs, the Warwick method could soon turn up many more green, pink and purple stars, each one a dense laboratory where extreme physics bends light into colours that the rest of the cosmos reserves for nebulae and aurorae rather than stars.

Subject of Research: The diverse visible colours of white dwarf stars caused by dense atmospheric chemistry and planetary debris accretion

Article Title: Green, pink and purple: astronomers reveal the surprising true colors of white dwarf stars

Article References: Green, pink and purple: astronomers reveal the surprising true colors of white dwarf stars. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: white dwarfs, stellar colour, University of Warwick, sodium absorption, carbon dredge-up, planetary debris, stellar spectra, colour temperature, astrophysics, green star, RAS Techniques and Instruments, stellar remnants

The study drew on the Norwegian Mother, Father and Child Cohort Study, known as MoBa, and included 92,551 children who were all born at term, between 37 and 41 weeks of pregnancy. By focusing exclusively on term births, the researchers were able to separate two factors that are often entangled in birth records: the timing of delivery within the term window and the size of the baby relative to that timing. Information collected through MoBa was linked with records from the Medical Birth Registry of Norway and with national education records, allowing the team to trace each child from the delivery ward to the classroom.

Size at birth was assessed in a specific and clinically meaningful way. Children counted as smaller than expected, or small for gestational age, were those who weighed less than most babies of the same sex born at the same stage of pregnancy. This definition matters because it distinguishes babies who are simply small but growing appropriately from those whose weight falls below the expected range for how far the pregnancy had progressed, a pattern that can signal that the intrauterine environment did not fully support the fetus’s growth.

The developmental picture was built from repeated assessments across childhood. Researchers examined the children’s language and motor skills at around six months, 18 months, three years and five years of age. They then analysed results from national school tests in mathematics, reading and English, including tests taken at around 10 to 11, 13 to 14 and 14 to 15 years of age. This longitudinal design, spanning from early infancy into adolescence, is what gives the study its power: rather than a single snapshot, it captures how early differences emerge, whether they persist, and at what point they fade or consolidate.

The headline finding concerns persistence. Children who were smaller than expected at birth tended to achieve lower scores in some school subjects, particularly mathematics and reading, and those differences were still apparent in adolescence. In other words, the association between size at birth and academic performance did not disappear once children entered school or accumulated years of formal teaching; it was still detectable in national test results at 14 to 15 years of age. For a field in which many early-life disadvantages attenuate over time, the durability of this link is notable.

By contrast, the second pattern the team examined told a more reassuring story. When the researchers looked at when within the 37 to 41 week term period babies were born, they found that babies delivered at 37 or 38 weeks tended to have slightly poorer language and movement skills in early childhood than those born at 39 to 41 weeks. Yet those early differences had become minimal by the time the children started school. Being born a week or two before the due date, while still fully term, appeared to carry only a transient developmental cost that was washed out within the first five years of life.

Xuan Zhao, a researcher from the University of Warwick’s Department of Psychology, described the contrast between the two patterns as the most surprising element of the results. According to Zhao, differences linked to being born slightly earlier within the term period largely washed out by age five, while those linked to being smaller than expected were still apparent in school performance at 14 to 15 years of age. The comparison suggests that the two measures, gestational timing and fetal size, are not interchangeable indicators, and that fetal growth restriction may reflect processes with longer-lasting consequences for the developing brain than modest variation in delivery timing among term births.

Professor Dieter Wolke, Professor of Developmental Psychology and Individual Differences at the University of Warwick, offered a possible interpretation of the mechanism. For babies born at term, being small for their stage of pregnancy may indicate adverse effects on the brain that affect learning and last into adolescence, he noted. Crucially, however, Wolke also emphasised that the long-term effects of being born small may be altered by parenting, home stimulation and school support for term-born children. That framing positions the finding not as a deterministic verdict on any child’s future but as a signal about where support can be targeted most effectively.

Professor Siobhan Quenby MBE, from the University of Warwick’s Medical School, highlighted the practical implications for maternity care and for families. Because the study shows that babies who are normal size or large for their stage of pregnancy show no long-term effects of being delivered a few weeks before the due date, she argued that the results should reassure parents whose term babies arrive slightly early. At the same time, she cautioned that not every baby born smaller than expected will experience difficulties, but said the study underlines the importance of monitoring a baby’s growth during pregnancy and ensuring that children receive appropriate support as they develop.

Taken together, the findings carry weight for clinicians, educators and policymakers alike. For obstetric care, they reinforce the value of fetal growth monitoring as a tool that identifies not just immediate perinatal risk but a group of children who may benefit from extended developmental follow-up. For schools and families, they suggest that children born small for gestational age at term represent a population in which early awareness, stimulating home environments and targeted educational support could meaningfully shape trajectories that might otherwise show up as lower mathematics and reading scores years later. With more than 92,000 children tracked from the first months of life to the middle of secondary school, the study provides one of the clearest demonstrations yet that what happens before birth, particularly whether a fetus reaches its expected size, can echo quietly through a child’s academic life well into the teenage years.

Subject of Research: The association between fetal size and gestational age at term birth and neurodevelopmental and academic outcomes from infancy to adolescence

Article Title: Babies who are smaller than expected at birth tend to have poorer school performance as teenagers

Article References: Babies who are smaller than expected at birth tend to have poorer school performance as teenagers. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: birth weight, gestational age, fetal growth, school performance, mathematics scores, reading scores, neurodevelopment, MoBa cohort, Norway, University of Warwick, term birth, adolescence

White dwarfs are the end state of the vast majority of stars, including our own Sun. When a star exhausts the nuclear fuel in its core, it sheds its outer layers into space and leaves behind an Earth-sized ember of dense matter that slowly cools over billions of years. These remnants are not quiet in a chemical sense. Because white dwarfs have intense surface gravities, any heavy elements in their atmospheres should rapidly sink out of view, settling into the dense interior within a relatively short astronomical timescale. When astronomers detect metals such as silicon, iron, or magnesium in a white dwarf’s spectrum, they know the star must be actively accreting material — almost always debris torn from asteroids or minor planets in the surrounding system that wandered too close and were shredded by tidal forces.

That is precisely why the atmosphere of HS 0209+0832 stood out. In a typical polluted white dwarf, the accreted material is dominated by rock-forming elements, reflecting the composition of ordinary terrestrial planets and asteroids that condensed from the original protoplanetary disc. But HS 0209+0832 displays an extraordinary abundance pattern featuring unusually high levels of heavy elements, including zinc, copper, and — most strikingly — niobium, detected at concentrations more than one thousand times higher than those measured in the Sun. This marks the first time niobium has ever been identified in the atmosphere of a white dwarf, and the anomaly demanded an explanation that conventional models of planetary debris could not provide.

The key to the puzzle lies in how those elements were forged. Dr Nicholas Stone of the University of Wisconsin-Madison explained that the pattern is a telltale sign of the s-process, a slow neutron-capture nuclear reaction that builds heavy elements inside dying stars during their bloated red giant phase. As an aging star swells and burns helium and other fuels in shells around its core, it manufactures elements far heavier than those produced during its long stable lifetime, then dredges them up and eventually expels them into space. A planet formed from pristine interstellar material — a so-called first-generation planet — simply should not carry this chemical signature. The presence of s-process products in the material raining onto the white dwarf told the team that whatever is feeding the star was made from the star’s own death ejecta.

The researchers’ conclusion is remarkable: the white dwarf is most likely consuming a newly formed, second-generation giant planet that condensed out of a fresh disc of material created during the star’s demise. When the dying star cast off its outer layers, that expelled matter did not simply vanish into interstellar space. Instead, some of it apparently settled into an orbiting disc around the remnant, and from that disc a new Jupiter-sized gas giant coalesced — a phoenix world rising from the ashes of the star it now circles. Because the disc was composed of the star’s own processed material, it was naturally enriched in the unusual heavy elements now visible in the white dwarf’s atmosphere, providing a coherent explanation for every chemical oddity the team observed.

First author Jamie Williams, a PhD student in the Department of Physics at the University of Warwick, emphasized how unexpected the find was. Second-generation planets are worlds that form out of the material a star casts off as it dies, he noted, and they are incredibly rare — finding one around a white dwarf was completely unexpected. He described the discovery as being a bit like finding a planet that has risen from the ashes of the very star it once orbited, an image that captures both the scientific novelty and the poetic resonance of the result. Similar reborn worlds have long been suspected around pulsars, the rapidly spinning neutron stars that can also acquire discs from stellar debris, but this is the first evidence that a second generation of planets can form around a white dwarf, a far more common type of stellar remnant.

The rarity itself is informative. Forming a protoplanetary disc in this situation is not easy, Williams explained, and that difficulty helps account for why such planets have never been seen before. A single, isolated star dies and sheds its mass in a roughly symmetrical way, sending material streaming outward in all directions with no preferred plane in which it could gather and collapse. For a disc to form — the necessary cradle for planet birth — HS 0209+0832 likely required a companion star whose gravitational influence pulled the ejected material back into orbit around the remnant rather than letting it escape into the galaxy. This requirement for a stellar partner in the system’s past adds a crucial constraint to models of how planets can form in post-main-sequence environments and suggests that searches for similar worlds should focus on white dwarfs with the right evolutionary history.

Independent support for the planet hypothesis came from NASA’s TESS satellite, which monitors the brightness of hundreds of thousands of stars in search of transits and other variability. In the TESS data, the researchers detected a faint but regular brightness signal repeating every 4.4 days, originating directly from the planet itself rather than from an eclipse or transit. Such a periodic modulation is consistent with a Jupiter-sized gas giant tidally locked in a tight orbit around the white dwarf, with one hemisphere perpetually facing the star. At that close distance, the planet’s outer atmosphere is expected to be boiling away under the intense radiation, and the escaping material — rich in the s-process elements inherited from the dead star — rains down onto the white dwarf’s surface, producing exactly the unusual chemical signature observed in its spectrum.

If the second-generation planet candidate is confirmed through follow-up observations, HS 0209+0832 would become the first white dwarf known to host a reborn world, and the discovery would open an entirely new search strategy. Rather than hunting for planets directly around dead stars, which is observationally extremely challenging, astronomers could look for the same carbon and heavy-element signature in the light of other polluted white dwarfs. Any white dwarf whose accreted debris carries s-process enrichment would be a promising candidate for hosting its own second-generation planet, turning atmospheric chemistry into a detection tool for a previously hidden population of exotic worlds.

Professor Boris Gänsicke of the University of Warwick, an ERC grantee and co-author of the study, captured the significance of the result. What is remarkable about the planet around HS 0209+0832, he said, is that it is not a planet from somewhere else, nor a survivor from the system’s birth — it looks like it was built from the very material its own star cast off as it died. In a sense, he observed, the system has given birth to a new world using the foundations of the old one. The discovery also raises a question that extends to our own cosmic doorstep: how many more such phoenix planets might be scattered across the galaxy, and could our own Solar System one day host a second-generation planet formed from the ashes of the Sun? In roughly five billion years, when the Sun becomes a white dwarf and sheds its outer layers, the same physics documented around HS 0209+0832 will play out in our neighborhood — and any worlds that condense from that ejecta will carry the Sun’s own chemical legacy, a final, luminous act of stellar recycling written into the atmospheres of the dead.

Subject of Research: Discovery of a second-generation planet candidate accreting onto the white dwarf HS 0209+0832

Article Title: The phoenix planet: astronomers find a world reborn from its star's ashes

Article References: The phoenix planet: astronomers find a world reborn from its star's ashes. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: white dwarf, second-generation planet, exoplanet, s-process elements, niobium, stellar evolution, planetary formation, HS 0209+0832, TESS, accretion, Nature Astronomy, University of Warwick