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Astronomers have glimpsed what may be a previously unknown planet encircling one of the stars closest to Earth.
The researchers spotted the bright spot near Alpha Centauri A, one of a pair of stars that sway so closely that they appear as one in the southern constellation Centauri. The stars form what is called a binary system 4.37 light years away, a stone’s throw in cosmic terms.
The sighting is so tentative that scientists only refer to it as a “candidate planet,” aware that the bright spot in the darkness of space may be evidence of alien asteroids, dust trails, or, more prosaically, of an unforeseen problem in their equipment. .
“We have detected something,” said Pete Klupar, chief engineer of Breakthrough Initiatives, which are a series of space projects funded by Yuri Milner, a Silicon Valley-based entrepreneur. “It could be an artifact in the machine or a planet, or it could be asteroids or dust.”
The international team observed the star as part of the Breakthrough Watch-supported “New Earths in the Alpha Centauri Region” experiment, an effort to find and study rocky planets the size of Earth around Alpha Centauri and other nearby stars.
To search for planets around the star, astronomers used the Very Large Telescope, or VLT, operated by the European Southern Observatory at Cerro Paranal in Chile’s Atacama Desert. Scientists were aided by a new coronograph on the instrument that blocks light from Alpha Centauri, making it easier to detect orbiting worlds.
Klupar likens the device to erase the sun with a thumb at hand. The procedure allows unprecedented sensitivity to the direct image of planets beyond the solar system. “We’re trying to see a flashlight right next to a lighthouse,” he says.
In Nature Communications, the team describes how infrared observations over 100 hours in May and June 2019 revealed a bright point they were unable to explain. If confirmed as a planet by further observations, the sighting would be the first to directly image an exoplanet around a nearby star.
“A lot of people say that planets cannot form in this type of binary and that is one of the reasons we are wary of pretending that it is in fact a planet. But if so, it would be roughly the size of Neptune, ”he added. The planet would be in the star’s habitable zone, where temperatures allow liquid water to form, and would take about a decade to complete an orbit.
Neptune is about four times the size of Earth and has no solid surface. Instead, it has an Earth-sized core enveloped in a thick soup of water, ammonia, and methane, the latter gas making it blue like Uranus.
Professor Beth Biller, who studies exoplanets at the University of Edinburgh’s Institute for Astronomy, said the researchers had “an interesting candidate” but were right to be cautious.
“It will take separate, independent detection to really confirm this,” she said. “If this is confirmed, it could be a detection of the dust disk around the star or an actual planet. Both would be very interesting results.
Klupar said the team wanted to look again later this year to see if the candidate planet has moved to where predictions suggest it should be. But he said further observations might not be possible with the still raging coronavirus pandemic.
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