Berkeley CA (SPX) Aug 15, 2022 Over the last 25 years, astronomers have found thousands of...
Over the last 25 years, astronomers have found thousands of exoplanets around stars in our galaxy, but more than 99% of them orbit smaller stars - from red dwarfs to stars slightly more massive than our sun, which is considered an average-sized star.
Few have been discovered around even more massive stars, such as A-type stars - bright blue stars twice as large as the sun - and most of the exoplanets that have been observed are the size of Jupiter or larger.
Some of the brightest stars in the night sky, such as Sirius and Vega, are A-type stars.
University of California, Berkeley, astronomers now report a new, Neptune-sized planet - called HD 56414 b - around one of these hot-burning, but short-lived, A-type stars and provide a hint about why so few gas giants smaller than Jupiter have been seen around the brightest 1% of stars in our galaxy.
While this theory has been proposed to explain so-called hot Neptune deserts around redder stars, whether this extended to hotter stars - A-type stars are about 1.5 to 2 times hotter than the sun - was unknown because of the dearth of planets known around some of the galaxy's brightest stars.
Hot Neptune desert The discovery of what the researchers term a "Warm Neptune" just outside the zone where the planet would have been stripped of its gas suggests that bright, A-type stars may have numerous unseen cores within the hot Neptune zone that are waiting to be discovered through more sensitive techniques.
According to Dressing, it's well-established that highly-irradiated, Neptune-sized planets orbiting less massive, sun-like stars are rarer than expected.
Whether this holds for planets orbiting A-type stars is not known because those planets are challenging to detect.
Close-in planets orbiting sun-like stars receive high amounts of both X-ray and ultraviolet radiation, but close-in planets orbiting A-type stars experience much more near-ultraviolet radiation than X-ray radiation or extreme ultraviolet radiation.
"Determining whether the hot Neptune desert also extends to A-type stars provides insight into the importance of near-ultraviolet radiation in governing atmospheric escape," she said.