Got a crush

Crab Pulsar Wind Nebula (NASA)

The wild concept of a crushed sun started in 1783 with the British natural philosopher John Mitchell. He proposed the seemingly preposterous idea of an object collapsing to infinity and occupying no space at all. The invisible puppeteer would be gravity, a universal force with a patience that transcends time itself.

Our Sun has a stable size and shape. But always waiting in the wings, like a greedy relative hovering over a deathbed, is gravity. Its inheritance can’t be denied, and the mere matter of waiting ten billion years presents not the slightest obstacle.

Only by consuming four million tons of itself every second, and converting this into energy via Einstein’s E = MC2, can the Sun produce enough outward pushing force to forestall gravity’s foreclosure. Each clump of solar material the size of a person is converted into an H-bomb of energy each second. Given the Sun’s mass in tons (2 followed by 27 zeroes), there is plenty of fodder for a mass-into-energy lifespan of billions of years. Eventually, however, the Sun loses its gravity battle and shrinks to our planet’s size while still weighing the same as 300,000 Earths. It’s crushed down to be 40,000 times denser than steel.

There are stars with ten times the Sun’s mass. This puts tremendous pressure on their cores, forcing their nuclear fuel to be squandered in explosive frenzies. So much heat bursts from their centers that these stars always shine with an arc-welder blue/white intensity. Instead of a stable ten-billion-year sabbatical of leisurely hydrogen-burning like the Sun, massive blue/white stars have longevities measured in the mere millions of years: the cosmic equivalent of mayflies. Then gravity steps in with a true vengeance.

The melodramatic details of giant suns imploding were first set down by the Indian astrophysicist Subrahmanyan Chandrasekhar in 1930. His surprising calculations described how high-mass objects behave under enormous pressure. For when stars have more than 1.4 times the mass of the Sun, their collapse becomes so overwhelming that gravity is not satiated when atoms are merely pushed into a crowded state of contact, like a subway car. Instead, atoms are pushed into each other, and the star keeps collapsing like a spherical avalanche. The smaller it gets, the stronger the gravity at its new surface becomes, which pulls it yet smaller – and on it goes. This is runaway collapse.

The collapse stops when the star is only ten miles across. Such freakish curiosities are neutron stars. If their fast spin aims beams of energy our way like a lighthouse, it’s called a pulsar. Harder than a zircon, smaller than Tokyo and spinning dozens or even hundreds of times a second, hundreds of such objects have been catalogued.

The most famous, the Crab Pulsar, is now up at midnight in the east. It’s easily located because it lurks just below the sky’s brightest “star” at that hour: the planet Jupiter.

You wouldn’t want to visit one. Anyone reaching a neutron star’s solid surface would experience such awesome gravity that their body would be crushed down to the height of a single atom, their organs promptly spreading themselves evenly, like a thin film of lubricating oil, over the entire surface. This isn’t good for you.

These crushed suns make excellent clocks. So precise are their rhythmic spins that several pulsars were graphically charted as “locator beacons” and placed on the “cover” of the famous videodisc attached to the Voyager spacecraft launched in 1977. It was designed to let any aliens who find it know exactly where Earth is located. Whether this proves to be an excellent or a poor idea depends on whether these creatures come bearing gifts or destroy us in our tracks.

Actually, the tiny Voyagers are extremely unlikely to be detected at all when one of them pays its first star a visit 40,000 years from now, even if aliens live there. Its nearest approach of 1.6 light-years to that star in Camelopardalis would be like us spotting a silent school-bus-sized object 100,000 times farther away from us than the Sun. Like the teensy pulsars whose diagrams they bear, the Voyagers will almost certainly remain eternally out of sight – almost certainly.

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