To date, close to 30,000 satellites have been launched into Earth’s orbit, leading to mounting concerns over the debris created when they collide. In a new analysis posted to the preprint server arXiv, Hugh Lewis of the University of Birmingham shows that satellite constellations can grow so large that they cross a critical size beyond which they generate unstable, runaway amounts of debris. The findings point to an urgent need for tougher rules on which satellites are allowed into orbit in the first place.

More than 70% of massive stars are born in close binary systems, where gravitational tugs and mass transfer between companions dramatically alter their evolution. Yet once the interaction ends—whether through mass transfer, merger or the supernova explosion of one partner—the surviving star often appears as a solitary object, hiding its turbulent past. For decades, astronomers have struggled to detect these hidden histories.

There is a question that often comes up at every public talk I do, and I have never had a good answer to it—well, not an entirely confident one. What’s inside a black hole? The textbook reply is a singularity. Cross the event horizon, and everything falls inward to a point of infinite density where our equations return nonsense. It isn’t so much an answer as an admission that we’ve run out of physics.

Most people underestimate how much light a pair of sunglasses blocks out. A typical dark pair removes around 80% to 90% of the visible light reaching the eye.

Little red dots have puzzled astronomers since their discovery in James Webb Space Telescope (JWST) data from the universe’s deep past. Their “powering engines” might resemble a newly discovered phenomenon dubbed a “black hole star”—an early, rapidly growing black hole wrapped in dense gas. This object, described in a study published today in Nature by researchers at the Institute of Science and Technology Austria (ISTA) and international collaborators, may help explain how billion-solar-mass black holes formed so soon after the Big Bang.