Free Astronomy Magazine September-October 2016

SPACE CHRONICLES T his image of the planet- forming disc around the young star V883 Orionis was obtained by ALMA in long-baseline mode. This star is currently in outburst, which has pushed the water snow line further from the star and allowed it to be detected for the first time. The dark ring midway through the disc is the water snow line, the point from the star where the temperature and pres- sure dip low enough for water ice to form. [ALMA (ESO/NAOJ/NRAO)/L. Cieza] transferred from the disk to the star. (Stars are believed to acquire most of their mass during these short but intense accretion events.) This explains the displaced location of its water snow line: the disk has been flash-heated by the stellar out- burst. Lead author Lucas Cieza, from the Proto- planetary Disks Nu- cleus (MAD) and Uni- versity Diego Portales (Santiago, Chile), ex- plains: “The ALMA discovery came as a surprise to us. Our observations were designed to look for disk fragmentation leading to planet for- mation. We saw none T his video shows a three-dimensional view of V883 Orionis. [ALMA (ESO/NAOJ/NRAO)/L. Cieza] of that; instead, we found what looks like a ring at 40 au. This illus- trates well the transformational power of ALMA, which delivers ex- citing results even if they are not the ones we were looking for.” The discovery that these outbursts may blast the water snow line to about 10 times its typical radius is very significant for the develop- ment of good planetary formation models. Such outbursts are believed to be a stage in the evolution of most planetary systems, so this may be the first observation of a common occurrence. In that case, this observation from ALMA could contribute significant- ly to a better understanding of how planets form and evolve through- out the Universe. ly at more than 40 au of the central star (beyond the Neptune's orbit in our sys- tem), greatly facilitating its detection. (The resolu- tion of ALMA at the dis- tance of V883 Orionis is about 12 au — enough to resolve the water snow line at 40 au in this outbursting system, but not for a typi- cal young star.) This star is only thirty percent more massive than the Sun, but its luminosity is 400 times brighter as it’s currently experiencing what is known as a FU Ori outburst, a sudden increase in temperature and luminosity due to large amounts of material being n