Planet surviving its dying star offers clues to our solar system



How will the solar system die? This is an extremely important question that researchers have speculated a lot about, using our knowledge of physics to create complex theoretical models. We know that the Sun will eventually become a “white dwarf,” a burnt stellar remnant whose faint light gradually fades into darkness. This transformation will involve a violent process that will destroy an unknown number of its planets.

So which planets will survive the death of the Sun? One way to look for the answer is to look at the fate of other similar planetary systems. It turned out to be difficult, however. The weak radiation from white dwarfs makes it difficult to detect exoplanets (planets around stars other than our Sun) that survived this stellar transformation – they are literally in the dark.

In fact, of the more than 4,500 currently known exoplanets, only a handful have been found around white dwarfs – and the location of these planets suggests they got there after the star died.

This lack of data paints an incomplete picture of our own planetary destiny. Fortunately, we are now in the process of filling in the gaps. In our new article, published in Nature, we report the discovery of the first known exoplanet to have survived the death of its star without its orbit being changed by other moving planets – over a distance comparable to that between the Sun and the planets of the solar system. .

A planet similar to Jupiter

This new exoplanet, which we discovered with the Keck Observatory in Hawaii, is particularly similar to Jupiter in terms of mass and orbit separation and provides us with a crucial snapshot of planetary survivors around dying stars. The transformation of a star into a white dwarf involves a violent phase in which it becomes a swollen “red giant”, also known as a “giant branch” star, hundreds of times larger than before. We believe that this exoplanet has barely survived: if it were initially closer to its mother star, it would have been swallowed up by the star’s expansion.

When the Sun finally becomes a red giant, its radius will actually reach Earth’s current orbit. This means the Sun will (likely) engulf Mercury and Venus, and possibly Earth – but we’re not sure.

Jupiter and its moons were expected to survive, although we were not sure before. But with our discovery of this new exoplanet, we can now be more certain that Jupiter will really make it happen. In addition, the margin of error on the position of this exoplanet could mean that it is almost half as close to the white dwarf as Jupiter is currently to the Sun. If so, this is further evidence to assume that Jupiter and Mars will succeed.

So, could a life survive this transformation? A white dwarf could fuel life on moons or planets that end up being very close to it (about a tenth of the distance between the Sun and Mercury) for the first billion years. After that, there wouldn’t be enough radiation to support anything.

Asteroids and white dwarfs

Although the planets orbiting the white dwarfs were difficult to find, which was much easier to detect, it was the asteroids that crash near the surface of the white dwarf. In order for exoasteroids to get so close to a white dwarf, they must have enough momentum from the surviving exoplanets. Therefore, it was long assumed that exoasteroids were evidence that exoplanets were also present.

Our discovery finally confirms it. Although in the system discussed in the paper, current technology does not allow us to see any exo asteroids, at least now we can piece together different parts of the puzzle of planetary fate by merging evidence from different white dwarf systems.

The link between exoasteroids and exoplanets also applies to our own solar system. Individual objects in the Main Asteroid Belt and the Kuiper Belt (a disk in the Outer Solar System) are likely to survive the disappearance of the Sun, but some will be moved by gravity by one of the surviving planets to the surface. of the white dwarf.

Prospects for future discoveries

The new white dwarf exoplanet was discovered with what is called the microlens detection method. This examines how light bends due to a strong gravitational field, which occurs when a star momentarily aligns with a more distant star as seen from Earth.

The gravity of the star in the foreground amplifies the light of the star behind it. All the planets orbiting the foreground star will bend and distort this magnified light, which is how we can detect them. The white dwarf we studied is located a quarter of the way to the center of the Milky Way, about 6500 light years from our solar system, and the farthest star is in the center of the galaxy.

A key feature of the microlens technique is that it is sensitive to planets orbiting stars at the Jupiter-Sun distance. The other known planets that orbit the white dwarfs have been found with different techniques that are sensitive to different star-planet separations. Two examples related to planets that survived a star’s transformation into a white dwarf and ended up closer to it than before. One was found by transit photometry – a method of detecting planets as they pass a white dwarf, which creates a hollow in the light received by Earth – and the other was discovered through detection of the evaporating atmosphere of the planet.

Another detection technique – astrometry, which accurately measures the movement of white dwarfs in the sky – should also work. In a few years, the astrometry of the Gaia mission should find a dozen planets orbiting white dwarfs. Perhaps these could offer better evidence of the exact death of the solar system.

This variety of discovery techniques bodes well for potential future detections, which could offer better insight into the fate of our own planet. But for now, the recently discovered Jupiter-like exoplanet offers the clearest glimpse of our future.

Article by Dimitri Veras, Associate Professor and STFC Astrophysics Fellow Ernest Rutherford, University of Warwick

This article is republished from The Conversation under a Creative Commons license. Read the original article.


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