Planets may form in a blaze of radiation

 作者:伏辛     |      日期:2019-02-27 03:14:02
By Kelly Young (Image: C R O'Dell/Rice U/NASA) Some stars blasted by searing radiation still hold on to enough surrounding material to form solar systems like our own, new observations reveal. In the 1990s, astronomers using the Hubble Space Telescope discovered dusty discs around several hundred stars in the Orion Nebula, the nearest large star-forming region to Earth. But massive stars in the nebula appeared to be boiling gas off the discs, leading some astronomers to doubt planets could take shape in such harsh environments. Now, researchers led by Jonathan Williams of the University of Hawaii in Honolulu, US, have used sensitive radio observations to measure the amount of dust in 23 of these protoplanetary discs (shortened to proplyds). Four contained enough dust – weighing about 1% of the Sun’s mass – to build future planetary systems. The proplyds held onto their dust despite being near a set of giant stars known as the Trapezium Cluster. Ultraviolet radiation from these behemoths – one of which is 40 times the Sun’s mass – ionises the gas around smaller stars and boils it off into space. “The question is how much dust will be eroded and how much stays around the star,” says team member David Wilner of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, US. Most stars are born in dense clusters such as Orion’s. But the blistering radiation they face from colossal neighbours lasts only a short time. “The massive stars burn themselves out. That really harsh environment doesn’t last very long,” Wilner told New Scientist. But previous work by John Bally, an astronomer at the University of Colorado in Boulder, US, suggests the intense radiation may actually spur planet formation. He and colleagues calculated the UV light blows away gas – but not dust, which helps seed planet formation. The pressure created by too much gas in the proplyds could stop the dust’s weak gravity from pulling together into clumps. Bally says better observational technologies could turn up many more proplyds dusty enough to form planets. “My gut tells me the team is just seeing the tip of the iceberg,” he told New Scientist. The team will present the observations, made with the eight 6-metre dishes of the Submillimeter Array in Hawaii,