Astronomers have witnessed the intense burst of light from a planet being swallowed by its host star, the same dramatic fate that awaits Earth when the sun expands rapidly near the end of its life.
It is the first time researchers have captured the moment when an ageing star swells so much that a nearby planet starts to skim the surface, sending streams of gas and dust into space, before finally plunging into the fiery depths.
“Like a lot of discoveries in science, this happened to be an accidental discovery that really opened our eyes to a new type of phenomenon,” said Kishalay De, a postdoctoral fellow at MIT in Cambridge, Massachusetts. “This is going to be the final fate of Earth.”
The first hint of the cosmic catastrophe came in 2020 when De spotted a burst of light amid observations taken by the Zwicky Transient Facility at the Palomar Observatory in California. The flash was traced to a star 12,000 light years away, near the constellation of Aquila, which became a few hundred times brighter over a mere 10 days.
Researchers on the team suspected a stellar merger, where one star absorbs another in its orbit, but follow-up observations from the Keck Observatory in Hawaii cast doubt on the idea. Most stellar merges spew out hydrogen and helium, as one star erodes the other, but the May event showed no signs of either element.
Further observations with an infrared camera at the Palomar Observatory showed that the star was “insanely bright” in the near-infrared, said De, suggesting that after the initial white hot flash, the star spewed cooler gas into space that condensed into dust visible at infrared wavelengths.
The scientists still suspected a merger of sorts but the details were unclear until the team analysed yet more data from Nasa’s infrared space telescope, Neowise. This showed that the outburst was so faint, whatever fell into the host star was about 1,000 times smaller than a star. “That’s when we realised this was a planet crashing into its star,” said De.
Piecing together the data, De believes the event involved a planet the size of Jupiter, which circled its star incredibly fast, completing an orbit in less than one day. It started to skim the star’s surface about nine months before the burst of light and continued for a few hundred orbits before eventually plunging into the star, causing it to brighten rapidly and then fade.
“The star today looks very similar to what it was before the outburst, except it’s surrounded by this shell of dust that was ejected during the outburst itself,” said De. Details are published in Nature.
When a star runs out of fuel at the end of its life, it expands up to 1m times its original size, engulfing nearby planets in the process. When the sun reaches this point in the distant future, it will swell enough to consume Mercury, Venus and Earth.
“If it’s any consolation, this will happen in about 5bn years,” said Morgan MacLeod, an astrophysicist on the team at Harvard. “We think the planets will be quite inhospitable by that time because the sun increases in power output as well, so all of the water will be evaporated off of Earth and it won’t be such a nice place to live.”