Astronomers have discovered a planet that survived the death of its star
A giant gas planet orbiting a dead star provides a glimpse into the future of the sun and solar system 5 billion years from now. An international team of researchers discovered a planet near a white dwarf using the Keck II observatory, located at the top of the extinct Mauna Kea volcano in Hawaii, using the method of gravitational microlensing, in which a previously invisible planet for some time acts as a gravitational lens that amplifies the light of a background star. thereby betraying their own presence. This event, observed in the near infrared range using adaptive optics, was designated MOA-2010-BLG-477Lb. The corresponding article was published in the journal Nature.
The system contains a white dwarf of 0.53 ± 0.11 solar masses and a planet of 1.4 ± 0.3 masses of Jupiter revolving around it at a distance of 2.8 ± 0.5 astronomical units from the star. All this serves as evidence that white dwarf planets can survive the extreme final phase of stellar evolution of such stars similar to the Sun, during which the star, having exhausted its nuclear fuel, swells to the stage of a red giant, sheds its outer shells and burns nearby planets.
The MOA-2010-BLG-477Lb system is located about 6.5 thousand light-years from Earth in the direction to the center of the Galaxy and represents an analogue of how the Sun with Jupiter will look at the final stages of stellar evolution. Perhaps more than half of white dwarfs retain distant planets comparable in mass to the mass of Jupiter, but the fate of inner planets like Earth remains rather uncertain.
After 5 billion years, the Earth will most likely find itself inside the swollen stellar shell and be absorbed by the Sun, although it may survive. However, long before that, life on it will become impossible. For some time, estimated in millions of years, satellites of giant planets like Jupiter and Saturn can become inhabited, but by the time the star turns into a shrunken white dwarf, they will also inevitably cool down, and the entire star system will be dead.
“Our study confirms that planets orbiting a sufficiently large distance from a star can survive its death,” explains Joshua Blackman of the University of Tasmania in Australia, the lead author of this article. “Given that this system is analogous to our own solar system, it can be assumed that Jupiter and Saturn can survive the death of the Sun when it runs out of nuclear fuel and it passes through the red giant phase.”
“The future of the Earth may not be so bright because it is located much closer to the Sun,” said co-author David Bennett of the University of Maryland and NASA's Goddard Space Flight Center. – Humanity could have moved to some moon of Jupiter or Saturn before the Sun burns the Earth during its red giant phase, but we will still remain in circumsolar orbit and will eventually lose heat from the Sun when it collapses into a white dwarf “.
A white dwarf is what the stars of the so-called Main Sequence become after their death, comparable in mass to the Sun. In the last stages of its stellar cycle, the star burns all the hydrogen in its core and swells strongly, then collapses, the star contracts into a white dwarf, all that remains of it is a hot, dense core the size of the Earth, half as much in mass as the former The sun. Since these compact stellar corpses are very small in size and, in the absence of nuclear fuel, can no longer glow brightly, they are rather difficult to detect. It is even more difficult to find the surviving white dwarf planets in distant orbits.
“This is the first gravitational microlensing detection of a planet orbiting a white dwarf,” explains Joshua Blackman, “but surely not the last.”
The white dwarf itself, due to the fact that its luminosity is too negligible, has not yet been detected, but astronomers were able to exclude alternative options – that the planet revolves around an invisible black hole or neutron star.
In 2020, another group of astronomers using a different method – tracking the passage of an object against the background of the parent star (transit method) – when observing with the TESS (Transiting Exoplanet Survey Satellite) space telescope, also discovered a Jupiter-like exoplanet in the white dwarf WD 1856+ 534 in the constellation Draco, over 80 light-years from the Sun. However, the planet WD 1856 b is located quite close to the white dwarf, and this case can hardly be called typical, although the planet's proximity to the white dwarf, of course, contributed to its detection. MOA-2010-BLG-477Lb sits nearly three times the distance between the Earth and the Sun from the white dwarf, making it the first known planet to occupy a Jupiter-like orbit for a white dwarf. In contrast, WD 1856 b orbits its white dwarf in 1.4 days, suggesting that the planet migrated to its current position after the death of its star – although the exact mechanism for such a movement has yet to be unraveled.
Andrew Vanderburg of the Massachusetts Institute of Technology, who led the team that discovered WD 1856 b, told the New York Times that the findings of the new study seemed compelling to him. He also noted that planets with distant orbits near white dwarfs are probably more numerous than objects with close orbits, but the latter type of exoplanets are easier to detect.
New discoveries also allow speculating about the search for extraterrestrial life in such places and assess the potential habitability of white dwarf systems. Lisa Kaltenegger, director of the Carl Sagan Institute at Cornell University, who was also part of the group of astronomers who discovered WD 1856 b, suggested that some stellar systems on which life once arose could go through a new stage of life revival already in white dwarf systems. “I find this study exciting because it adds more and more evidence to support the survival of planets when a star dies, and this allows us to think about the future of the cosmos. If the planets can survive the death of their stars, can they survive? “
Dying stars in the red giant stage emit dangerous radiation, stellar winds, and their systems experience unprecedented turbulence that can destroy life. However, some speculative scenarios that allow for the preservation of habitability of white dwarf systems do exist.
“If humanity somehow survives five billion years from now, then we will probably have a better chance of surviving the red giant phase of the Sun on the moons of Jupiter rather than on Earth,” says Joshua Blackman.
You can imagine a planet far enough away from a star that for some time has become a red giant, which, already at the time when the parent star turns into a white dwarf, will gradually approach it and receive enough heat so that it can exist there again. liquid water. And if life arose on Jupiter's moon Europa, which may contain an under-ice ocean warmed by the tidal forces of the giant planet, it could potentially survive at a greater distance from the star.