The artist's depiction of a Jupiter-sized planet orbiting a white dwarf. It is lamentable that the two objects in the picture are actually of equal size, as the size of the white dwarf is comparable to that of Earth. Source: NASA/JPL
The unprecedented discovery of Jupiter-sized planets orbiting white dwarfs suggests that it is entirely possible for planets to survive the chaotic dying struggles of their parent star.
Imagine an obscure late star about the size of Earth with a Jupiter-sized planet orbiting it every 34 hours. It would be a strange sight: smaller but denser objects appearing to control a combination of objects that visually mismatch. To tell you more vividly how strange this is, you can imagine that white dwarfs can successfully fill Jupiter's Great Red Spot.
Such a system, according to the new research now released, actually exists.
As Ian Crossfield, an associate professor of physics and astronomy at the University of Kansas and co-author of the study, explained in an email, this is "the first clear discovery of planet orbiting a white dwarf." The new study, published in the journal Nature, was led by Astronomer Andrew Vanderburg of the University of Wisconsin-Madison.
In 2015, the study documented a unique discovery, the entire process of a small planet, possibly an asteroid, being crushed by its white dwarf "owner." What makes this new discovery unique is that the planet is large, cohesive, and in a fairly stable orbit.
Students in school are terrified when they learn about the ultimate fate of our solar system. Billions of years from now, our Sun will run out of fuel, causing it to expand into a giant red giant. In the process, all the planets in the solar system— including Earth——, will be swallowed up by our bloated Death Star. When this phase is complete, the red giant will shrink to a white dwarf: an Earth-sized sphere with half the mass of the current Sun. White dwarfs are theoretically stars because they still release light and heat as they cool, even though they can no longer undergo nuclear fusion.
This is, and will be, the fate of all similar stars in the universe. Astronomers aren't sure if planets, especially exoplanets, will survive this extremely destructive process, but new research suggests they can. The study could now inspire astronomers to study similar objects next to other white dwarfs.
The astronomers used a proven transit method and some infrared scans of the galaxy to discover the white dwarf star, called WD 1856b. Through NASA's Transiting Extragalactic Planet Survey Satellite Space Telescope, the team can record the fainting process of white dwarfs every 1.4 days. From our perspective on Earth, this dimming process is a potential signal for an orbiting planet to transform in front of a star. The authors confirmed this with infrared data collected by NASA's Spitzer Cosmetry (the satellite was decommissioned just this past January). By studying the system at infrared wavelengths, the researchers discovered that it was actually a planet, not another star orbiting a white dwarf.
The artist's vision of the white dwarf and the planet. Source: NASA/JPL-Caltech/NASA Goddard Space Flight Center
"The hotter the star will release more infrared, while the cooler planet will release less infrared." Crossfield said, "We didn't see the extra infrared, proving that what we found was really planets." ”
Several above-ground telescopes also joined the necessary validation link for the study, as the TESS data was already obscured by light from neighboring stars.
The authors speculate that WD 1856b survived when its star became a red giant due to the distance between the two objects.
"If it had started where we see it now, it would never have survived; so it must have been moving much farther away from the star." Crossfield explains, "Then, when the star becomes a white dwarf, the planet will get closer and closer to it. ”
The researchers saw from the simulations that this was a possible scenario: when the red giant devoured the inner planet, WD 1856b's orbit would become unstable, causing it to enter a highly elliptical orbit that would allow the planet to be either close to or far away from its dead parent star. This orbit has gradually shrunk during the universe's long evolution, moving the planet into its tight circular orbit.
"We think this star died about 6 billion years ago and became a white dwarf, long before the formation of the sun, Earth, and solar system." Crossfield said.
We asked Crossfield if it was possible for a Death Star to capture a wandering planet, either during its red giant or white dwarf period. A recent study suggests that trillions of wandering planets could be carried away by the Milky Way, perfectly escaping the stars they once orbited today.
"It's possible, but it's not very likely either." He replied, "We'll know after we've measured the planet's atmospheric composition with the James Webb telescope after it launches next year." ”
Indeed, WD 1856b is in a fairly stable and moderately distanced orbit, just 80 light-years away from Earth, so scientists can study it carefully in the near future. All we can know about the planet now is its size (about the size of Jupiter, which may also be larger than Jupiter), its orbital period (34 hours), and its approximate temperature (below freezing point). Future observational studies will "tell us what it is made of, how it came to be, and perhaps why we can see it in our current position." Crossfield said.
An interesting point is that white dwarfs undergo other transformations, becoming fainter brown dwarfs, and finally black dwarfs, no longer hot and glowing. The latest research suggests that the largest black dwarfs will explode like supernovae, but that will be trillions of years from now.
BY: George Dvorsky
FY: Dawn
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