Remarkable planet reveals habitable place around dead star

Astronomers are surprised to have a planet found it those around the remainder of his deceased mother star. This discovery offers hope that the planets in our solar system are after the death of the sun will survive. Plus, it creates a whole new kind of place to search for alien life.

In about 5 billion years, our sun will run out of fuel. At that moment it will expand into a red giant. The outside of the sun then reaches approximately the orbit of the earth. This will swallow the inner planets – Mercury, Venus and perhaps Earth itself – by the expanding star. To make matters worse, the red giant then blows its outer gas layers into space. This destructive process will also affect the more distant planets.

It is not clear exactly how that will go. To find out, astronomers study white dwarfs. These are the ultimate remnants of bright stars such as the sun, consisting of the slowly fading core of the former star. In those white dwarfs, astronomers hope to find clues to the fate of the planets that once revolved around them.

Torn planets

Research in recent years has produced a gloomy picture. Astronomers found only remnants of planets around white dwarfs. As a former star core, a white dwarf is small in size, but is still extremely heavy. As a result, planets that move near the dead star experience an extremely strong gravitational force. This causes the planets to be torn to pieces and sometimes even fall on the white dwarf, astronomers observed. Should a planet survive the violent transition of its star, the white dwarf will then ensure that it does not have a long life, the sad conclusion seemed.

However, an unexpected find shines new light on the matter. With observations from planet hunter TESS a team of astronomers discovered an intact object orbiting a short distance around a white dwarf. The discovery was then confirmed by multiple telescopes. Most likely it is a gigantic planet, which is nearly fourteen times heavier than Jupiter.

The only image we have known of planets around white dwarfs: slowly disintegrating by the destructive power of their parent star. Illustration: Harvard Center for Astrophysics / Mark A. Garlick

Cool guy

“ Never before have we found evidence that a planet gets so close to a white dwarf and survives it, ” said astronomer Andrew Vanderburg of the University of Wisconsin-Madison, who led the study. a press release. ‘We used TESS to investigate the destruction of planets around white dwarfs. We did not expect to find a planet that appears to be intact. It’s a pleasant surprise. ‘

Not only has the planet mysteriously resisted the destructive power of the white dwarf, but it also exhibits a number of other unique features. For example, the combination of a gigantic planet and a modest white dwarf creates the curious fact that the planet is many times larger than the star it orbits.

In addition, the giant turns out to be remarkably cool: the mercury does not exceed 17 degrees Celsius. This is unprecedented for a Jupiter-like planet so close to its parent star. So-called ‘hot Jupiters’, of a similar size and distance from their star, can temperatures of thousands of degrees Celsius to achieve.

Livable zone

‘That temperature can be so low because white dwarfs emit very little radiation,’ says astronomer Vincent Van Eylen (University College London), not involved in the study. ‘This means that at a short distance from the star you already have temperatures comparable to those of the Earth, where liquid water can also exist. In white dwarfs, the habitable zone is actually very close to the star. ‘

Because white dwarfs emit very little radiation, the temperature is very low even at a short distance. Illustration: NASA / JPL-Caltech

The discovery thus offers unexpected new places to search for extraterrestrial life. This planet is bigger than Jupiter; there will certainly be no life there, ‘Van Eylen continues. “But an Earth-like planet at a similar distance to a white dwarf is a place where you might expect life.”

Extra interesting is that white dwarfs are very stable: they cool very slowly, emitting a more or less constant amount of light for billions of years. Life on a planet like Earth would not survive the extreme conditions during the red giant phase. But should the Earth survive itself and migrate inward just like the discovered planet, habitable conditions will arise again. Then life might get a second chance. ‘

Miraculous Migration

Do planets like Earth then have a second life in store? That is still the question. “Our discovery suggests that the planet was originally far from the star,” says Vanderburg. “Only after the star became a white dwarf did the planet somehow travel in.” However, it is unclear how unscathed the planet survived the disruptive forces of the white dwarf during this inward migration.

Using computer simulations, the researchers found a possible explanation. The swallowing of the inner planets by the red giant can unbalance the orbits of other planets. The planet in question may have entered an oval orbit, where it came close to the white dwarf on its closest approach. Over a long period of time – the white dwarf in question has existed for 6 billion years – a gradual loss of energy would eventually bring the planet into its current, stable orbit close to the white dwarf.

Planet hunter TESS is extremely suitable for detecting Earth-sized planets around white dwarfs. Image: NASA / Goddard Space Flight Center

A new quest

‘This is the first intact planet to be found. It is therefore difficult to say whether this is a rarity or whether there are more such objects to be found, ‘says Van Eylen. With this one discovery, the fate of our solar system remains uncertain for the time being. But the find does offer hope, according to Vanderburg. “Now that we know that it is possible for planets to survive the journey without being torn by the white dwarf’s gravity, we can look for other, smaller planets near such stars.”

The small size of the white dwarf works to the advantage of astronomers. ‘Unlike with normal stars, you can discover small planets relatively easily here. You can also study their atmosphere better ‘, notes Van Eylen. ‘It is quite possible to use TESS to find Earth-like or even smaller planets around white dwarfs. Although they may be rare, this discovery will make them more actively sought after. ‘

LEESTIP. In Planet Hunters, Lucas Ellerbroek describes the hunt for habitable worlds elsewhere in the universe. Order in our webshop.
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