Unusual Star Looks Older Than it Should
Like a pesky child can appear to rapidly age their tiring parent, a star about 330 light years away is looking a lot worse for wear, thanks to the giant exoplanet that constantly encircles it.
The star known as WASP-18 is estimated to only be between 500 million and two billion years old. That may sound pretty old, but our Sun is about five billion years old and it's thought to only be middle-aged. In that sense, WASP-18 would only be in its 20s if it were a person.
Like most younger stars, it was thought that WASP-18 would be active and spritely, with strong magnetic fields, large solar flares, and intense X-ray emissions - factors all linked to a faster rotation, compared to older balls of fiery matter.
However, when astronomers used NASA's Chandra X-ray Observatory to take a closer look at the young star, they didn't detect any X-rays at all. Using nearby emissions to measure the magnetic activity of WASP-18, researchers quickly concluded that the star is a whopping 100 times less active than it should be.
So what's to blame? According to Ignazio Pillitteri of the Istituto Nazionale di Astrofisica (INAF)-Osservatorio Astronomico di Palermo in Italy, the star's orbiting exoplanet WASP-18b it taking a big toll.
"WASP-18b is an extreme exoplanet," said Pillitteri, who recently led a study of the unusual WASP-18 solar system. "It is one of the most massive hot Jupiters known and one of the closest to its host star, and these characteristics lead to unexpected behavior. This planet is causing its host star to act old before its time."
According to Pillitteri and his colleagues, who published their work in the journal Astronomy and Astrophysics, WASP-18b's significant mass is wreaking havoc on its host star's innards.
"The planet's gravity may cause motions of gas in the interior of the star that weaken the convection," explained co-author Salvatore Sciortino. "This has a domino effect that results in the magnetic field becoming weaker and the star to age prematurely."
Much like a parent with a larger-than-life overbearing child, the constant circling of WASP-18b was just too stressful for the star. However, the experts are quick to point out that this is a rather unusual case, in which WASP-18's convection zone - the range in which energy is transported about - is narrower than most. This made it particularly vulnerable to the tidal forces that tug and churn its innards.
The star just really wasn't cut out for parenting, so to speak.