This lucky planet is only a billionth away from destruction.

Recently, scientists discovered that a gas giant planet orbits a white dwarf, which may be the future of our solar system: what will happen after the sun explodes into a red giant and destroys most of the inner planets. Cartography: Adam makarenko, Keck Observatory

This is a world the size of Jupiter, almost destroyed by the dying expansion of stars-about 5 billion years later, our sun may have the same fate.

Written by nadia Drake.

This is perhaps the luckiest planet in the Milky Way: it is about 6,500 light years away, near the center of the Milky Way, and it is a huge gaseous world, almost destroyed by the dying main star.

Planets and main stars distort the starlight behind them, which is discovered by astronomers. Related descriptions were published in the journal Nature in June 65438+1October 65438+March. Fortunately, this distant world the size of Jupiter is revolving around a tiny star-a dim white dwarf star about the size of the earth, which once looked like the sun. The aging star expands into a red giant and then collapses into a dense white dwarf. In this process, the planets in orbit are easily destroyed.

"This planet is really a narrow escape," said Juliet Becker of California Institute of Technology. "Probably almost ruined." Becker was not involved in the investigation.

If the planet is closer to the star, it may be doomed to a series of bad luck, such as being burned to ashes or torn to pieces; When the dying sun expands into a red giant, the earth will finally usher in one of its destinies. Scientists speculate that this alien planetary system may be similar to the fate of the earth's neighbors in the late life of the sun.

"This system is very similar to the final state of our solar system," said David Bennett of NASA's Goddard Space Flight Center, the author of the study.

This system also helps scientists understand the probability of planet survival after the tragic death of the main star. Scott Gaudi, an astronomer at Ohio State University, said that if complete planets are common around white dwarfs, "there are more planets than we expected".

"This means that so far, we may have underestimated the calculation of the planets in the Milky Way," he said. "There is a joke in the field of exoplanets: you can find new planets by opening every rock."

The fate of the solar system

With the growth of stars' age, the hydrogen needed by the central nuclear furnace is exhausted, which leads to a series of events, which is very dangerous for planets in orbit. In about 5 billion years, the sun will have the same fate, and then the earth will be in trouble.

Without hydrogen, the sun will slowly expand into a red giant. In this process, mercury will be swallowed and burned, and then Venus. It is almost certain that if the earth is not burned, it will be torn by the gravity of the sun. Mars may survive because it is far enough away. In the outer solar system, four giant planets will be pushed around, and it is very likely to enter a farther orbit; But in some special cases, they may be completely thrown out of the solar system or even pushed to the sun.

"As the sun grows older, planets in the solar system will encounter all kinds of strange phenomena," Becker said. "This process is very intense, especially for planets in the solar system."

After the sun expands into a red giant about 1 100 million years, it will collapse into a compact star corpse: a white dwarf, with only half the original mass and the same volume as the earth. This process will also cause serious damage to nearby planets, leaving the world unrecognizable. If the four giant planets can survive, they are likely to disappear for billions of years because they meet passing stars.

Stories of survivors

Although astronomers speculated that planets could survive the chaos after the death of the main star, they did not find many planets that survived the catastrophe. In 20 10, scientists discovered the newly described system with the help of the astrophysical gravitational microlens observation project. The surviving planets and white dwarfs came directly in front of the more distant background stars.

This arrangement leads to the gravitational amplification of two stars, which distorts the distant starlight and produces what astronomers call gravitational microlens phenomenon. So far, through this phenomenon, astronomers have discovered about 90 worlds, including free-floating planets and rogue planets roaming alone in the Milky Way galaxy without a main star.

The way giant planets and white dwarfs distort the starlight behind them shows several key features of the system, including the operation in the sky, the existence of stars and planets, and the large orbits of planets. The observation results also help astronomers to calculate the relative mass of these two celestial bodies. Astronomers are interested in this system named MOA-20 10-BLG-477Lb, but it will take several years to observe it more carefully.

"When the gravitational microlens phenomenon occurs, it is difficult for us to distinguish two stars because they just overlap," Bennett said. "So we have to wait for them to separate."

In 20 15, Bennett and his colleagues used the powerful Keck Telescope II at the top of Mauna Kea Mountain in Hawaii to find this star. Five years later, they knew that the system must have moved a long distance, so they aimed the telescope at the target and searched in the dark, but found no celestial body similar to the star they were looking for-only another star, moving in the wrong direction.

On 20 16 and 20 18, the research team made another observation and found nothing. But according to the distorted starlight, they knew it was there. According to the observation results, Bennett and his colleagues realized that whatever they were looking for, Keck II was too dark to find.

"We know that it is a dark star, slightly lighter than the mass of the sun, so it is obviously a white dwarf," Bennett said.

After several calculations, the research team concluded that the system includes a world the size of Jupiter and a white dwarf with half the mass of the sun. The orbit of this planet is at least 2.8 times as far away from the star as the Earth, which is similar to the position of the asteroid belt in the solar system.

Gaudi said: "This planet is where we expect to form a giant planet." "This suggests that Jupiter-like planets may survive the evolution of stars like the sun."

Somehow, this giant planet is in the right position, avoiding the fatal consequences of star evolution-this distance depends not only on the dying star, but also on the characteristics of the planet and neighboring planets (if any).

Looking for more planets orbiting white dwarfs

Astronomers have found evidence that planets orbit white dwarfs, but they are all different from this one. In 20 19, an international team of astronomers discovered a disk of gas debris around a white dwarf star, and speculated that there might be the remains of a compact asteroid in the debris. This ruined world may be the inevitable fate of the earth. Astronomers also found many other debris disks and judged that they came from unfortunate planets and asteroids.

Last year, another research team used the Tess telescope of NASA's Explorer program to discover a giant planet orbiting a white dwarf in 34 hours. The planet is so close to the main star, "that it will be swallowed up in the red giant stage," Becker said. "This means that when a star becomes a white dwarf, it must move."

In the past 20 years, scientists have detected traces of chemical elements on the surface of white dwarfs-fragments left by the swallowed rock world.

All these observations, together with the newly discovered system, show that some planets can survive, at least for a while, during the evolution of the main star. But the process of determining a planet's life and death is still unclear.

The NASA Nancy Grace Roman Space Telescope is scheduled to be launched from 265438 to the mid-1920s, which will bring us more planets orbiting white dwarfs. Astronomers will find more planets orbiting the dead bodies of stars, so as to further understand how the death of stars changes the structure of planetary systems and predict the future of the solar system.

Bennett said that in the newly discovered system, there may be other planets orbiting white dwarfs. Although the earth can't survive the sudden death of the sun (at least in an identifiable state), maybe other planets can, and the solar system will continue to exist in constant changes.

(Translator: Sky4)