A dying star star just swallowed a planet, granting view to Earth’s future

In SYFY’s 2022 original science fiction series The Ark (streaming now on Peacock!), a crew of colonists is on the last ship off a dying Earth, and on their way to a new home on Proxima Centaur b. There are half-a-hundred reasons we might need to leave Earth in the relatively near future. Catastrophic climate collapse could force us to jump the figurative ship. Nuclear winter, an especially virulent pandemic, super volcano, asteroid, gamma ray burst… the list goes on. The universe has no shortage of ways to sterilize a world, but if you wait around long enough, one way is for certain. One day, the Sun will die and take the whole solar system with it.

The magic of a star happens in its core, where hydrogen atoms are smooshed together through the overwhelming pressure of gravity until they fuse. As stars age and burn through their fuel, they do something rather counterintuitive. Rather than get smaller as they burn their own guts, they grow larger. It’s a counterintuitive behavior of very massive objects, due to the interplay between gravity and internal heat and pressure.

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During the main phase of a star’s life, the inward pull of gravity and the outward push caused by fusion are neatly balanced. Once all of the hydrogen in the core is fused, stars start looking for things to fuse further out, in concentric shells around the core. That new burst of heat overwhelms the inward pull of gravity, and the star expands into a red giant. Eventually, the Sun’s core will collapse into a white dwarf and the rest of its material will be violently expelled into space for the next generation of stars and planets to use. Before that, however, its growth will consume Mercury, Venus, and Earth.

That’s the fate of all inner planets orbiting stars up to about eight times the mass of the Sun. However, try as they might, astronomers have so far come up empty in the search for planet-consuming red giants. Until now. A new paper published in the journal Nature, documents for the first time, a red giant consuming one of its planets.

Prior to this recent discovery, astronomers had seen stars building up to a planetary snack and they had seen stars rubbing their expanding bellies after eating a planet, but they’d never caught one in the act. Using data collected by the Zwicky Transient Facility — an instrument which scans the entirety of the northern sky every two days — astronomers hunted for temporary but dramatic bursts of light and energy from distant stars. They were looking for something called novae, brief bursts from white dwarfs as they gobble up material from a companion star, but they found a planet eater instead.

The signal came from a point in space about 12,000 light-years away, near the constellation Aquila. Over the course of a week, they watched a star increase in brightness 100 fold. Those sorts of spikes in luminosity usually come from the novae they were hunting for or from the collision of two stars, but when astronomers took a closer look, they realized something wasn’t quite right.

If the spike was a nova, then spectral data should reveal the presence of hot gas, but there was none to be found. That got them thinking about a merger of two stars, but that didn’t fit either. Figuring out what they had seen would require time and additional observations. About a year after the initial detection, astronomers used the infrared camera at Palomar to detect near-infrared signals trailing for about six months after the spike. Then they used data from NEOWISE, NASA’s asteroid-hunting telescope, to crunch the numbers on how much energy was released by the star during and after the burst. That’s when everything fell into place.

The amount of energy unleashed was about 1,000 times smaller than we would expect from a stellar merger. Do you know what else is about 1,000 times smaller than a star? A planet. For comparison, our own Sun is approximately 1,048 times the mass of Jupiter. Whatever crashed into the expanding star and caused its miniature outburst must have been a planet-scale object. Researchers estimate that the star in question began with between 0.8 and 1.5 solar masses and the planet it engulfed would have been between 1 and 10 times the mass of Jupiter.

In about 5 billion years, any extraterrestrial astronomers sitting 12,000 light-years from here will be treated to a similar, if slightly smaller, light show when the Sun lets out its last gasp and swallows the inner solar system. If we’re really lucky, those future extraterrestrial astronomers might even be us.

Catch the complete first season of The Ark, streaming now on Peacock!