They find the first planet orbiting a dead star

An artist’s recreation of a white dwarf with its core exposed. DR MARK A. GARLICK / SPL

Within about a few 5000 million years our closest star, the Sun, it will go out, turning into a red giant. Actually the sun is half its age as a star with enough hydrogen fuel to double the time you have.

But, from that moment on, in the core, Helium will melt to form oxygen and carbon, while hydrogen will continue to fuel nuclear fusion reactions that will grow the star around the exhausted interior. When it turns into a red giant it will begin to devour everything in its path, which includes the planets of Mercury, Venus and surely the Earth. After that period of expansion, it will slowly begin to shrink and dissolve in space, until it becomes a super dense object called a white dwarf, a stellar corpse with a mass not much less than that of the Sun and a size like that of our planet.

Today, international astronomers published an investigation in the Nature magazine, where for the first time, it is possible that have discovered an intact world around a white dwarf, which suggests that even after the stars die, your solar system may still host some planets.

Previous investigations have found the remains of worlds that disintegrated when the progenitor stars of the white dwarfs engulfed nearby planets during their red giant phase. This raised the question of whether any world could avoid this destruction and end up orbiting the resulting white dwarfs. That is, to survive the collapse of a star.

Astronomers used NASA's Transiting Exoplanet Study Satellite (TESS)

Astronomers used NASA’s Transiting Exoplanet Study Satellite (TESS)

In the new study, astronomers investigated a white dwarf in the constellation Draco, about 81.5 light years from Earth. Using NASA’s Transiting Exoplanet Study Satellite (TESS) and other telescopes, they discovered that the dead star was orbited by a body about the size of a planet called WD 1586 b, which has a mass like maximum 14 times that of Jupiter and a diameter approximately 10 times that of Jupiter. of the white dwarf.

The researchers suggest that to avoid destruction when the progenitor star evolved into a red giant, WD 1586 b must have originally orbited its star further afield than the distance between the Earth and the sun. Later, gravitational interactions with other worlds in the remnant planetary system threw WD 1586 b into a closer orbit. It is now nearly 20 times closer to the white dwarf than Mercury is to the sun, completing one orbit every 34 hours.

“If a giant planet survived the trip near a white dwarf, then it means that smaller planets could also”Said the study’s lead author, Andrew Vanderburg, an astronomer at the University of Wisconsin-Madison.

09/16/2020 In this illustration, WD 1856b, a potential planet the size of Jupiter, orbits its faint white dwarf star every day and a half.  POLICY RESEARCH AND TECHNOLOGY NASA GODDARD SPACE FLIGHT CENTER

09/16/2020 In this illustration, WD 1856b, a Jupiter-sized potential planet, orbits its faint white dwarf star every day and a half. POLICY RESEARCH AND TECHNOLOGY NASA GODDARD SPACE FLIGHT CENTER

Although white dwarfs no longer burn fuel, they can still stay hot for billions of years. Vanderburg noted that “if a rocky planet were to take a similar journey to the planet we discovered, it could end up in the white dwarf’s habitable zone,” the area around a star warm enough to harbor water and potentially life such as we know.

Still, these findings “could offer a way for a white dwarf to give rise to a second generation of life in a planetary system, long after the star ran out of hydrogen fuel and died,” Vanderburg completed.

“This planet is roughly the size of Jupiter, but it also has a very short orbital period: a year on this planet lasts only 1.4 days, so it rotates rapidly around its white dwarf star, “explained Ian Crossfield, assistant professor of Physics and Astronomy at the University of Kansas.

At first, WD 1856 b caught the interest of astronomers when they noticed a possible object in transit with the NASA TESS Space Telescope survey. “TESS finds a planet by looking at a star and measures its brightness continuously for weeks,” she says. If a planet is orbiting the star, and if the planet passes between you and the star, some of the light from that star will be blocked. Then the star will get brighter again as the planet passes; We call this the ‘transit’ of the planet. TESS then searches for transiting exoplanet satellites. It warns that there is something there, but it does not necessarily say what it is because it could be another faint star passing in front of it instead of a planet ”.

  Illustration of a carbon-rich planet with diamonds and silica as the main minerals.  SHIM / ASU / VECTEEZ

Illustration of a carbon-rich planet with diamonds and silica as the main minerals. SHIM / ASU / VECTEEZ

To help the international team of scientists confirm whether WD 1856 b was in fact a planet orbiting the white dwarf, Crossfield studied the object’s infrared emissions with NASA’s now-defunct Spitzer Space Telescope in the months before the satellite telescope was dismantled. .

“For this white dwarf object, it is difficult to measure its mass, so we knew how big it was, but not how heavy it was,” he pointed out. This new object could have been a small star or a large planet. The way we could tell the difference was to look and see: Does this thing also emit infrared light? If it is a star, stars are generally hotter than planets and it should glow in the infrared. “

“But if it’s just a planet, planets are generally cooler than stars, so there should be little or no infrared light,” he continues. What our Spitzer data showed is that there is basically no infrared light. And the depths of these transits are identical between the TESS data and our Spitzer data sets. That really put the final nail in the coffin that this thing is almost certainly a planet, rather than a star. “

In about 5 billion years, our Sun will turn into a white dwarf. There are many open questions as to whether planets can survive the process of inflating a star into a red giant, swallowing some of the inner planets, and then shrinking again and becoming the white dwarf again. Can planets really survive that … or is it impossible? And until now, there were no known planets around the white dwarfs, “he concluded.


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