Astronomers may have for the first time witnessed a sun-like Death Star devouring a planet, shedding light on the fate that will befall Earth in about four billion years when our dying sun swells to engulf our world, a new study finds.
That’s no moon! At least not anymore. A white dwarf that scientists are playfully comparing to The Death Star — a spacecraft in the “Star Wars” franchise capable of planetary destruction — has been caught in the act of chewing up a small, rocky world.
By analyzing countless stars during various stages of their evolution, astronomers have discovered that as our sun and stars like it near the ends of their lives, they begin to exhaust their primary source of fuel, the hydrogen near their cores. This leads their cores to contract and their outer shells to expand and cool. During this “red giant” phase, these stars may billow out anywhere from 100 to 1,000 times their original diameter, swallowing closely orbiting planets.
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This real-life Death Star is actually a dead star. White dwarfs are the dense, dead remnants of stars that were once like our own sun. One day, the sun will expand into a huge, cool red giant — then lose its outer layers and shrink into a shriveled white dwarf, its mass cut in half.
“Honestly, one of the biggest surprises for me was that we found it in the first place,” De said in an email. “Planetary engulfment has been a fundamental prediction in our understanding of stars and planets, but their frequency have been very uncertain. So finding a potentially rare event for the first time is always exciting.”
In a study published Wednesday in Nature, researchers report the first ever “planet” (it’s really only about the size of an asteroid) found orbiting a white dwarf some 570 light years away from Earth. It’s very close to its dead host — about twice the distance that the Earth is from the moon — and orbits once every 4.5 hours. According to the scientists studying the object, this proximity has been its undoing.
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In the new study, De and his colleagues made their breakthrough after examining a burst of radiation dubbed ZTF SLRN-2020, which took place in 2020 in the Milky Way’s disk about 12,000 light-years away, near the constellation Aquila. During the event, a star brightened by a factor of 100 over the course of a week.
The initial discovery was made by analyzing data collected by the Zwicky Transient Facility, run at the California Institute of Technology’s Palomar Observatory. The Zwicky Transient Facility scans the sky for stars that rapidly change in brightness, which could be events such as novas.
By observing the passage of the planetoid in front of its host star using the Kepler telescope, the researchers found signs of a rocky world torn asunder. Kepler (now called K2) works by showing scientists variations in the brightness of stars, which can reveal the transit of planets between the stars and the telescope.
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Cool gas from such bursts often results from merging stars, De explained. When he followed up by looking at data from the same star collected by the Keck Observatory in Hawaii, he also found molecules that can only exist at very cold temperatures.
Cold gas can condense to form dust over time. About a year after the initial discovery, De and his colleagues analyzed data from the same star, this time collected using an infrared camera at the Palomar Observatory. Infrared data can yield signals of colder material, in contrast to bright visible light signals that often come from novas and other powerful events.
The pattern of this white dwarf’s dimming indicated an irregular shaped object, like a comet with a trailing tail. The researchers believe this unusual signature is caused by a cloud of dusty debris from the disintegrating object, which is being pulled apart by the dense star’s strong gravity.
The scientists found the brief outburst of visible light from the star was accompanied by extraordinarily bright near-infrared light signals that slowly faded over the course of six months. This confirmed De’s suspicion “that this source had indeed formed a lot of dust,” he said.
The final piece of the puzzle came when the researchers examined data collected by NASA’s infrared space telescope, NEOWISE. This suggested the total amount of energy the star released since its initial outburst was surprisingly small — about a thousandth the magnitude of any stellar merger observed in the past.