It’s common to see images of astronauts on the International Space Station exercising, running on special treadmills and pedaling cycles designed for tight quarters.

The building blocks of rocky planets may have begun forming just 100 million years after the Big Bang—long before the first galaxies even existed—according to new research from the University of Portsmouth.

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.