Unexplainable: Astronomers Discover Massive Planet Near a White Dwarf Star

Astronomers have discovered, for the first time, proof of a massive planet rotating around a small, lifeless white dwarf star. The planet is similar in size with Neptune, and, to the surprise of the discoverers, it is over four times the diameter of the star it spins around, which is approximately the size of Earth.

In a press release, Boris Gänsicke ​, from the University of Warwick, and study author, said that the planet could not be seen directly. However, because the star is incredibly hot, it is shrinking the planet, making its atmosphere evaporate. As a matter of fact, the searing star is expelling a ray of vaporized material away from the planet at a pace of about 260 million tons per day.

The new finding is great evidence of a giant planet that has survived a star’s change into a white dwarf. It shows that evaporating planets around lifeless stars may be quite normal in the Universe. Moreover, because our Sun, similar to most stars, will also ultimately transition into a white dwarf, the discovery could even help scientists understand what could happen to our Solar System.

A Peculiar Pairing

The white dwarf discovered, now known as WDJ0914+1914​, is located at approximately 1,500 light-years away in the constellation Cancer. Even though the white dwarf is not subjected to a nuclear fusion anymore, similar to the process a normal star goes through, its remaining heat means it is still blazing at 49,500 degrees Fahrenheit (25,000 Celsius)​. 

​When the astronomers examined the unique spectrum of the dwarf star, they identified chemical remains of hydrogen, which is quite bizarre. They also discovered fingerprints of oxygen and sulfur, elements they have never found in a white dwarf before.

“It was one of those chance discoveries,” Gänsicke said in a European Southern Observatory (ESO) press release“We knew that there had to be something exceptional going on in this system, and [we] speculated that it may be related to some type of planetary remnant.”

Therefore, to better understand what is going on in the peculiar array, the team utilized the X-shooter instrument on the ESO’s Very Large Telescope ​located in Chile to perform the needed observations. After a closer examination, the astronomers saw that the weird elements they thought were emitted by the white dwarf were, in fact, coming from a disk of gas swirling around the lifeless star.

“At first, we thought that this was a binary star with an accretion disk formed from mass flowing between the two stars,” Gänsicke explained. “However, our observations show that it is a single white dwarf with a disk around it roughly ten times the size of our Sun, made solely of hydrogen, oxygen, and sulfur. Such a system has never been seen before, and it was immediately clear to me that this was a unique star.”

The Unexplainable Happened

After getting a grasp on how unique the white dwarf really is, the researchers decided to focus on discovering what could birth such a peculiar system.

Using Schreiber’s calculations,​ the dead star’s extreme temperature signifies the fact that it is attacking the closest massive planet with high-energy photons. This is making the planet lose its mass at a pace of over 3,000 tons per second.

“As the white dwarf continues to cool, the mass-loss rate will gradually decrease and become undetectable in [about 350 million years.] And by then, the giant planet only will have lost an insignificant fraction of its total mass,” ​the paper, published in the journal Nature on Wednesday notes.

Due to the fact that the massive planet is located at such close distance to the white dwarf, the astronomers say it should have been eaten during the star’s explosion phase; unless it moved inward after the star shifted into a white dwarf.

“This discovery is major progress because over the past two decades, we had growing evidence that planetary systems survive into the white dwarf stage,” said Gänsicke.

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