Astronomers have found several “cows” in the cosmic meadows — including an especially loud one. They’re a powerful form of supernova — the titanic explosion of a star. They’re named for the first one seen, AT2018cow — the Cow. Only five have been discovered, suggesting that they’re uncommon. But they shine brilliantly at all wavelengths. The most recent discovery was the brightest of all. A month after the explosion, AT2020mrf was producing 20 times more X-rays than the Cow had a month after it went off. And almost a year after the explosion, it was 200 times brighter than the Cow. A possible explanation is that we’re seeing parts of the explosion that had never been seen before. When a supergiant star reaches the end of its life, its core collapses to form a black hole or a neutron star. Its outer layers then blast out into space as a supernova. Most of the time, the exploding star is surrounded by a cocoon of gas and dust. That blocks our view of what’s happening in the core. In the
