Using the Atacama Large Millimeter/submillimeter Array (ALMA) collection of radio telescopes in Chile, astronomers have caught a glimpse of a water snowline around a star for the first time.
Heat from young stars typically prevents freezing of water molecules within a radius of about 450 million kilometers, but beyond this point, water condenses and forms layers of ice on particles. This region is known as the snowline.
Because the snowline normally huddles too close to the star, astronomers have not been able to observe it directly until now. A violent burst of brightness and heat in a young star superheated its disk, pushing the water snowline out farther than normal, allowing scientists to image it with ALMA.
The young star V883 Orionis, which lies 1,350 light-years away from Earth in the constellation Orion, experienced a burst of heat and brightness due to a sudden influx of new material. This allowed the star to vaporize ice out to 3.7 billion miles, which is comparable to the average distance from where Pluto orbits the sun.
Although this sun-like star is only 30 percent more massive compared with the Solar System's sun, the outburst set off by material coming from the disk that fall into the star's surface made V883 Orionis 400 times more luminous and hotter.
Scientists are excited to have spied a stellar snowline for the first time because it may contribute to the understanding of how planets form around young stars. The rocky section of the disk forms planets such as Mars and Earth, while gaseous worlds similar to Jupiter and Saturn form in the snowy outskirts.
Study researcher and Princeton University astronomer Zhaohuan Zhu said the observation provided direct evidence that a frosty region with conducive conditions for the formation of planets exists around other stars.
"Since water ice is more abundant than dust itself beyond the snowline, planets can aggregate more solid material and form bigger and faster there. In this way, giant planets like Jupiter and Saturn can form before the protoplanetary disk is gone," Zhu said.
The observation shows that ALMA can shed more light on how planets form and evolve and that studying water snowlines can contribute to a better understanding of planet formation.
"As most planetary systems are expected to experience outbursts caused by accretion during their formation, our results imply that highly dynamical water snow-lines must be considered when developing models of disk evolution and planet formation," Zhu and colleagues reported in their study, which was published in Nature on July 13.
