Astronomers discover Earth-sized diamond-encrusted white dwarf

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Stars are usually unfathomably hot objects fueled by a nuclear inferno that can only be extinguished when it runs its course, but astronomers have detected an elusive object that doesn’t come close to fitting that description. A white dwarf star 900 light years away might be the coldest star ever found in the cosmos. Hovering near a much larger pulsar, this ancient stellar remnant has a temperature of less than 3,000 K, or about 2,700 degrees Celsius. That’s cooler than an industrial acetylene torch. It’s so old that it has crystallized into what is essentially a Earth-sized diamond, and it was surprisingly difficult to spot.

A white dwarf like the one found near the pulsar is what’s left over after a star about the size of the Sun runs through all its nuclear fuel. The outer layers are thrown off, and all that’s left is a tiny, super-dense core of elements like carbon and oxygen. They burn at an excruciatingly slow pace, taking billions and billions of years to finally go out, and even newly transformed white dwarfs are incredibly hard to spot compared to active stars. This one was only discovered because it happens to be nestled right up next to a pulsar.

In the same way a white dwarf is what’s left after a sun-sized star runs out of fuel, a neutron star is what’s left after a slightly larger one runs its course. A spinning neutron star is known as a pulsar because it appears to pulse as it strobes the universe with beams of radio waves while whirring around. The pulsar partnered up with our diamond-encrusted white dwarf goes by the catchy name PSR J2222-0137, and is 1.2 times the mass of our sun, but even smaller than the white dwarf. Astronomers were tipped off to the presence of something near the pulsar by distortions in its radio waves. An old-fashioned space hunt was on for the culprit.

The low mass made a white dwarf the most likely cause, but astronomers couldn’t see it. For a star of that size to be completely invisible, it would have to be an incredibly old white dwarf 10 times dimmer than any previously discovered. The team estimated the age of this object to be upward of 11 billion years, the same age as the Milky Way. This object was already old when our galaxy was just beginning to coalesce. After all those eons to cool off, the star has likely collapsed into a crystallized chunk of carbon mixed with oxygen and some other elements — a somewhat dirty diamond (though it’s not the first). It could actually be possible, though extremely difficult, to land a spacecraft on an object like this.

There may be many more stars in the sky with diamonds, perhaps some even older than this one. Spotting this white dwarf was a bit of a fluke, though. Until more powerful instruments are devised that can see an incredibly dim, burnt out star, they’ll remain shrouded in the inky black of space.

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