Black hole stars, dementia exercise, and shrinking shrews top science news

Three discoveries from the latest science news cycle reveal how much we still have to learn about the universe, our own bodies, and the creatures sharing the planet with us.

When the James Webb Space Telescope began transmitting images from the earliest reaches of space, astronomers noticed something that shouldn't have been there: tiny red dots scattered across the cosmic distance. Nobody could say for certain what they were looking at. Galaxies, perhaps. Massive stars. Black holes. The mystery lingered until a recent study published in Nature offered an answer for at least some of them. These objects are black hole stars—a type of celestial body no one had definitively identified before. A black hole star is fundamentally different from what we think of as a star. It consists of a black hole surrounded by an extraordinarily dense envelope of gas and dust, something like a stellar atmosphere. But where a regular star generates light through nuclear fusion at its core, a black hole star produces its glow from a rapidly feeding black hole at the center, holding the entire structure together. Astronomer Rohan Naidu, the lead author of the study at the University of Hawaii, describes it as a glowing black hole sustaining a massive cloud of material—not technically a star, but luminous in a star-like way. The discovery may solve a puzzle that has troubled astrophysicists for decades: how do supermassive black holes, like the one anchoring the Milky Way and weighing millions of times what our sun does, grow to such enormous proportions? These little red dots could represent an early growth phase, or possibly even the birth moment of a supermassive black hole itself.

Back on Earth, a new analysis examining 74 studies involving more than four million participants has upended conventional wisdom about exercise and brain health. The research, published in The Lancet Public Health, found that not all physical activity offers equal protection against dementia. People who exercise by choice during their free time—biking, hiking, swimming—showed significantly lower dementia risk than those whose physical exertion comes from work or commuting. The finding is counterintuitive and troubling. People in physically demanding jobs, such as construction or warehouse work, actually showed higher dementia risk despite their constant movement. Lead researcher Natan Feter at the University of Southern California notes that this contradicts the widespread assumption that any exercise counts equally. The difference appears to hinge on context and circumstance. People who labor physically for income tend to have lower socioeconomic status, which correlates with higher chronic stress, greater exposure to air and noise pollution, and other risk factors known to increase dementia likelihood. These stressors may undermine whatever cognitive benefits their physical exertion might otherwise provide. The study suggests that health inequities run deeper than previously understood—that the same activity can protect one person's brain while leaving another vulnerable, depending on the circumstances surrounding it. Feter offers one small reassurance: even five additional minutes of leisure-time physical activity daily shows measurable benefit.

Perhaps the most remarkable adaptation uncovered by recent science belongs to the long-clawed shrew, a tiny mammal that has evolved an extraordinary strategy for surviving winter. Rather than fattening up like bears or groundhogs to store energy through the cold months, these shrews reduce their energy needs by literally shrinking. The process is dramatic. Their brains contract by a quarter. Their skulls compress. Organs throughout their bodies diminish in size. Then, when spring arrives, they regrow the tissue they shed, restoring themselves to full size. Scientists have known about this phenomenon, called Dehnel's phenomenon, since the 1950s, but serious research into the mechanism only accelerated over the past decade, driven partly by biomedical interest. Researchers studying osteoporosis, bone regeneration, and tissue repair see potential applications in understanding how these animals accomplish what human medicine still struggles with. A new study published by the Royal Society, conducted by researchers in Japan, uncovered an additional wrinkle: while most of the shrew's body shrinks in winter, its snout actually grows longer. Scientists remain uncertain why this counterintuitive change occurs—perhaps it enhances the animal's ability to regulate its body temperature—but it demonstrates just how finely tuned these creatures are to seasonal shifts. Other small mammals with high metabolisms, including moles and weasels, can perform similar shrinking acts, though much remains to be learned about how widespread and variable the process is across species.