Over the past 25 years, astronomers have discovered thousands of exoplanets around stars in our galaxy, but more than 99 percent of them orbit smaller stars—from red dwarfs to ones slightly more massive than our sun. A star, the sun is considered a medium-sized star.
Few are found around more massive stars, such as A-type stars—bright blue stars twice the size of the Sun—and most observed exoplanets 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.
UC Berkeley astronomers now report a new, Neptune-sized planet — dubbed HD 56414 b — orbiting one of these hot but short-lived A-type stars and providing insight into why there is so little gas Smaller giant stars suggest Jupiter is visible around the brightest 1% of stars in our galaxy.
Current exoplanet detection methods are most likely to find planets with short and fast orbital periods around their stars, but this newly discovered planet has a longer orbital period than most planets discovered so far. The researchers believe that easier-to-find Neptune-sized planets close to bright A-type stars will be rapidly stripped of their gas by intense stellar radiation and shrunk to undetectable cores.
While this theory has been proposed to explain the so-called hot Neptune desert surrounding redder stars, whether this extends to hotter stars — A-type stars are about 1.5 to 2 times hotter than the sun — is unknown because the surrounding known The planets lack some of the brightest stars in the Milky Way.
“This is one of the smallest planets we know of orbiting these really massive stars,” said UC Berkeley graduate student Steven Giacalone. “In fact, it’s the hottest star we know of, and it has a bigger planet than Jupiter. Still small. This planet is interesting in the first place because these types of planets are really hard to find, and we probably won’t find many of them on Earth.” For the foreseeable future. “
hot neptune desert
The researchers found what the researchers dubbed “warm Neptune” outside the gas-stripped region of the planet, suggesting that bright A-type stars may have many unseen cores within the warm Neptune region waiting to be discovered by the more sensitive technology.
“We might expect to see a cluster of Neptune remnant cores in short orbital periods around these stars,” the researchers concluded in their paper.
The discovery also adds to our understanding of how planetary atmospheres evolve, said Courtney Dering, an assistant professor of astronomy at UC Berkeley.
“How the planet maintains its atmosphere over time is a big question,” Dressing said. “When we look at a smaller planet, are we looking at the atmosphere that formed when it was initially formed from an accretion disk? Are we looking at the atmosphere being expelled from the planet over time? If we could look at the atmosphere the planets shed from their accretion disks? Stars receive different amounts of light, especially different wavelengths of light, which is what A star allows us to do – it allows us to change the ratio of X-rays to UV – and then we can try to see how a planet changes with The passage of time preserves its atmosphere.”
Giacalone and Dressing report their findings in an accepted paper astrophysical journal letters and published online.
According to Dressing, highly radiant, Neptune-sized planets are known to orbit less massive Sun-like stars than expected. But whether this applies to planets orbiting A-type stars, which are difficult to detect, is unclear.
A-type stars are different animals from the smaller F, G, K, and M dwarfs. Close planets orbiting Sun-like stars receive large amounts of X-ray and ultraviolet radiation, but close planets orbiting A-type stars receive more near-ultraviolet radiation than either X-ray radiation or extreme ultraviolet radiation.
“Determining whether the hot Neptune desert also extends to A-type stars can provide insight into the importance of near-ultraviolet radiation in controlling atmospheric escape,” she said. “This result is important for understanding the physics of atmospheric mass loss and for studying the formation and evolution of asteroids.”
Planet HD 56414 b was detected by NASA’s TESS mission as it passed its star HD 56414. Dressing, Giacalone and their colleagues used the Medium Aperture Research Telescope System (SMARTS) Consortium by Small and Chilean Cerro Tololo.
The planet has a radius 3.7 times that of Earth and orbits its star every 29 days at a distance of about a quarter of the distance between Earth and the sun. The system is about 420 million years old, much younger than our sun’s 4.5 billion years.
The researchers simulated the effect of radiation from the star on Earth and concluded that, while the star’s atmosphere may be slowly receding, it could live for a billion years—more than the expected lifetime of the star. Burn up and collapse, producing a supernova.
Jupiter-sized planets are less susceptible to photoevaporation because their cores are large enough to hold hydrogen gas, Giacalone said.
“There’s this balance between the Earth’s central mass and how much the atmosphere expands,” he said. “For Jupiter or larger planets, the planet is massive enough to hold its expanding atmosphere through gravity. When you move down to a Neptune-sized planet, the atmosphere is still expanding, but the planets aren’t that big, so they’re more likely to lose atmosphere.”
Giacalone and Dressing continue to search for more Neptune-sized exoplanets around A-type stars, hoping to find other planets in or near the hot Neptune desert to understand where these planets form in the accretion disk during star formation, Whether they move in or out over time, and how their atmosphere evolves.
As stars eat their planets, carnage could be seen billions of years later
Steven Giacalone et al., HD 56414 b: A warm Neptune transiting A-type star, astrophysical journal letters (2022). DOI: 10.3847/2041-8213/ac80f4, iopscience.iop.org/article/10. … 847/2041-8213/ac80f4
Courtesy of UC Berkeley
Citation: Brightest stars in the night sky could strip Neptune-sized planets to their rocky cores (12 Aug 2022), Retrieved 13 Aug 2022 from https://phys.org/news/2022-08- brightest-stars-night-sky – Neptune-sized .html retrieved
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