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The second-generation planet orbiting the white dwarf star HS 0209+0832, the first planet discovered orbiting a white dwarf, is shown in this image released on October 5th. Photo: Reuters . |
Astronomers have discovered an exoplanet that may have formed from material ejected by its host star before it died. This is the first evidence of a planet forming around a white dwarf, the dense core left behind after a star runs out of fuel, Reuters reports.
Researchers call this a “second-generation” planet. Earth and most planets in the Solar System formed from disks of matter surrounding a newly formed star. In this case, the planet is thought to have formed from the leftover matter after the death of its host star.
"This is the first example of a planet forming around a white dwarf," said Jamie Williams, an astrophysicist at the University of Warwick (UK) and lead author of the study published in Nature Astronomy .
This exoplanet is located about 250 light-years from Earth, near the constellation Cetus. It is a gas giant, possibly slightly more massive than Jupiter, and orbits a white dwarf in just 4.4 days.
Because it is so close to the remnant star, the planet is subjected to intense ultraviolet radiation, causing its outer atmosphere to gradually evaporate. Some of the material then falls back into the white dwarf.
The planet's chemical composition also supports the hypothesis of this particular origin. It contains high levels of niobium, copper, and zinc, elements often released by some stars in the final stages of their lifecycles. This suggests the planet may have formed from a disk of material surrounding the core of a dead star.
“In mythology, the phoenix rises from its own ashes. With this planet, it was born from the ashes of its dead host star, so the entire planetary system is reborn,” Williams said.
White dwarfs are more common than pulsars, a type of stellar remnant that has been found to contain several second-generation planetary candidates. According to Williams, more than 95% of the stars in the Milky Way will eventually evolve into white dwarfs, so there could be many second-generation planets orbiting these objects.
The newly discovered planet is not suitable for life. However, scientists believe that other second-generation rocky planets could exist in regions with suitable conditions. As the white dwarf cools, a rocky planet at the right distance could maintain a habitable environment for billions of years.
Also in Nature Astronomy , another study describes a star system located about 300-500 light-years from Earth, in the constellation Taurus.
Scientists have discovered a red dwarf with a mass only about 8% that of the Sun orbiting a brown dwarf. This celestial body is larger than a planet but too small to be a star, with a mass about 30 times that of Jupiter.
The two celestial bodies orbit each other in just 87 minutes, at a distance slightly greater than half the distance between Earth and the Moon. The red dwarf's gravitational pull appears to be drawing matter from the brown dwarf.
"This is the first time this phenomenon has been observed," said Aaron Householder, an astrophysics graduate student at MIT and lead author of the study.
According to Householder, the two celestial bodies are so close together that their entire orbits could fit inside the Sun.