What will happen after the sun dies? ‘Serendipitous’ discovery gives clues

A distant gas giant found orbiting a white dwarf star suggests outer planets in our solar system might survive the sun’s demise


A Jupiter-sized planet has been found orbiting a white dwarf star in the Milky Way, providing clues as to what will happen in our solar system when the sun eventually dies.

An international team of astronomers observed the phenomenon, which forms when a star runs out of nuclear fuel to burn, and dies.

The distant planet, a gas giant with a mass 1.4 times that of Jupiter, was able to survive the death of its host star.

The scientists say the discovery is in keeping with previous calculations that more than half of white dwarf stars may have similar giant planets orbiting them. Though the phenomenon had been predicted, it had never been observed before.

The study’s first author, Joshua Blackman of the University of Tasmania, said: “We predict this planet has a distance [from the white dwarf] of between 2.5 and six times the distance of the Earth from the sun, which is similar to that of Jupiter.”

Blackman said the discovery shed light on what will happen when the sun runs out of fuel. “This is the first time we’ve found … a system which resembles what we expect to happen to our solar system in five or six billion years’ time.”

In five billion years, the sun is expected to expand, becoming what is known as a red giant. “In this process of the sun becoming a red giant, it’s likely going to obliterate the inner planets … likely Mercury and Venus will be destroyed,” Blackman said. Earth may survive the event, but will not be habitable.

Once the sun completely runs out fuel, it will contract into a cold corpse of a star – a white dwarf.

Themiya Nanayakkara, an astronomer at the Swinburne University of Technology who was not involved in the research, said the discovery suggested outer gas giant planets like Jupiter and Saturn could survive the death of the sun.

“It rules out theories in the past … that say you can’t have planets around white dwarfs,” Nanayakkara said.

The size of a star determines what it eventually turns into: bigger, heavier stars may end up as black holes or neutron stars instead.

In the Milky Way, about 95% of all stars are destined to eventually become white dwarfs, Blackman said. “The universe is not old enough for that to have happened yet.”

White dwarfs give off only faint light, which makes them virtually impossible to observe directly from ground-based telescopes. Instead, the team found the dead star using a technique known as gravitational microlensing, where the light from a distant planet – the Jupiter-sized gas giant – is bent by the gravity of a closer star – in this case, the white dwarf.

The discovery was “completely serendipitous”, Blackman said. “We expected to see a normal star like our sun. So we spent quite a few years toiling over the data trying to determine if we made a mistake.”

Based on their observations, the team were able to rule out other possibilities for the dead star, such as a black hole or neutron star.

The study was published in the journal Nature.

Contributor

Donna Lu

The GuardianTramp

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