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   John Carlos Baez (johncarlosbaez@mathstodon.xyz)'s status on Monday, 11-Nov-2024 05:43:11 JST John Carlos Baez

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   Okay, I hung up the laundry. Imagine an enormous star flinging off its outer layers after it runs out of fuel and its core collapses under its own gravity. If it doesn't become a black hole, the core can shrink down to a ball of neutronium just 20 kilometers across. Just as a ballerina spins faster as she pulls in her arms, this ball spins really fast - like 1000 rotations a second. And since neutronium conducts electricity, it can blast out radio waves as it spins, creating a blinking radio signal, called a pulsar. Pulsars are so precisely periodic that when Jocelyn Bell first spotted one, people thought it was a signal from aliens!

   Like the rest of us, pulsars slow down as they age. But this also means their signal weakens. So we usually don't see pulsars in the gray region of this chart - to the right of the line called the 'pulsar death line'. Pulsars are the gray dots to the left of this line. The pink squares are called 'magnetars'. These are the squalling infants in the world of pulsars: young and highly magnetized neutron stars that do crazy stuff like put out big bursts of X-rays now and then.

   But then there are weirder things. A telescope array called the Australian Square Kilometer Array Pathfinder was searching for radio waves connected to a gamma ray burst in 2022 when it stumbled on something that blasts out radio waves about once an hour. It lost track of this object, so folks brought in the more powerful MeerKAT radio telescope and found it again.

   Now it's called ASKAP J1935+2148. It's well to the right of the pulsar death line. What could it be?

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