“C’mon, Sy, LIGO detects those black hole collisions by tracking how its mirrors move when a gravitational wave passes by. How can NANOGrav detect those waves from pulsar twinkles?”

“Not twinkles, Vinnie, definitely not twinkles. Astronomers hate twinkles. That shifting, wavering light we find so charming messes up the precise measurements they want to make. We didn’t get really good astrometry and light curves until we lifted observatories into orbit where atmospheric turbulence can’t distort the starlight. Fortunately there’s less twinkling at longer wavelengths down in the radio range. When a grad student named Jocelyn Bell discovered pulsars glinting in the radio range half a century ago everyone panicked.”

“What’s so scary about stars acting funny? They’re a long way away.”

“True, but it was how they acted funny. The glints were so regular that everyone first thought they were man‑made signals and probably from Russia or one of their allies. This was back in the 1960s, during the Cold War, a decade after Sputnik and right after the Cuban Missile Crisis. Lots of paranoia. But then Bell and her thesis adviser found that the first two signals were definitely coming from two different but consistent points up in the sky and that ruled out Earth‑centered sources.”

“Aliens?”

“Yeah, that was one of the hypotheses. In fact, the researchers even called the first source LGM‑1 for ‘Little Green Men.'”

“HAW!”

“Hey, astronomers make jokes, too. But when they found the second source that idea pretty much went away except that the conspiracy crowd still loves it.”

“What do the signals look like?”

“Just the question I’d expect from a telescope hobbyist like you, Al. They look like flashes from an airport beacon — nothing, then a blink then more nothing until another blink. Typically the blink intervals for different sources range between milliseconds and tens of seconds. Early researchers determined that each star’s blinks are regular to well within a millisecond which was the best we could do for accurate timing back then. Until we got really good laser clock tech, the pulsars were the steadiest timepieces we knew of.”

“What’s a blink look like?”

“That was a critical question. Bell had to scan literally miles of high‑speed strip‑chart paper to get a good handle on it. In general the plots of signal strength against time were triangles, about 40 milliseconds wide at half‑height. Bell’s first pulsar’s triangles used 3% of her strip‑chart recorder’s output, which meant that 97% of the paper was wasted space but research works that way sometimes.”

“Couldn’t be something with a bright side and a dark side, then, or you’d get half and half.”

“Exactly, Vinnie. The pulsar’s shiny spot must be a small fraction of its circumference. Another number from Bell’s charts gave us an additional clue to the spot’s size. LGM-1 blinks every 1.3373 seconds, regular as clockwork. That’s about a million times faster than the Sun spins, but suppose LGM-1 is a star about the Sun’s size. If the spot’s at the star’s equator, it’d have to be moving eleven times faster than light.”

“Not likely.”

“Mm-hm. So this pulsar and all the others that blink at anything near that rate must be made of collapsed matter, probably a neutron star.”

“Wait, why can’t it be something smaller like a shiny planet or something?”

“Gyroscopes, Al. The heavier the spinner, the better it maintains a constant spin. Earth’s pretty big, by our standards, but we need to adjust civil time by a leap second every few years to match our planet’s speed‑ups and slow‑downs. These guys don’t do that, they just slow a few nanoseconds or less per year. Rapid rotation says that pulsars must have small geometry but nanosecond regularity says they must have enormous mass. Neutron stars meet both qualifications because they pack a solar mass into the volume of a small planet.”

“Okay, but why do they spin so fast?”

“Angular momentum, Vinnie, radius times speed — always conserved, right? Say a star with a month‑long rotational period collapses. Its radius shrinks about a million‑fold. Every atom in that collapsing star now runs a tighter travel radius and must speed up to compensate. The whole star spins up.”

~~ Rich Olcott