Free Astronomy Magazine May-June 2019

58 MAY-JUNE 2019 N ew ALMA observations show there is ordinary table salt in a not-so-ordinary location: 1,500 light-years from Earth in the disk surrounding a massive young star. [ALMA (NRAO/ESO/NAOJ); NRAO/AUI/NSF; Gemini Observatory/AURA] “Usually when we study protostars in this manner, the signals from the disk and the out- flow from the star get muddled, mak- ing it difficult to distinguish one from the other,” said Ginsburg. “Since we can now isolate just the disk, we can learn how it is moving and how much mass it contains. It also may tell us new things about the star.” The detection of salts around a young star is also of interest to as- tronomers and astrochemists be- cause some of constituent atoms of salts are metals – sodium and potas- sium. This suggests there may be other metal-containing molecules in this environment. If so, it may be possible to use similar observations to measure the amount of metals in star-forming regions. “This type of study is not available to us at all presently. Free-floating metallic compounds are generally invisible to radio astronomy,” noted McGuire. A LMA image of the salty disk sur- rounding the young, massive star Orion Source I (blue ring). It is shown in relation to the Orion Molecular Cloud 1, a region of explosive starbirth. The background near infrared image was taken with the Gemini Observatory. [ALMA (NRAO/ESO/NAOJ); NRAO/AUI/ NSF; Gemini Observatory/AURA] The salty signa- tures were found about 30 to 60 as- tronomical units (AU, or the aver- age distance be- tween the Earth and the Sun) from the host stars. Based on their ob- servations, the as- tronomers infer that there may be as much as one sextillion (a one with 21 zeros after it) kilograms of salt in this region, which is roughly equivalent to the entire mass of Earth’s oceans. “Our next step in this research is to look for salts and metallic molecules in other regions. This will help us un- derstand if these chemical finger- prints are a powerful tool to study a wide range of protoplanetary disks, or if this detection is unique to this source,” said Ginsburg. “In looking to the future, the planned Next Gener- ation VLA would have the right mix of sensitivity and wavelength cover- age to study these molecules and perhaps use them as tracers for planet-forming disks.” Orion Source I formed in the Orion Molecular Cloud I, a region of explo- sive starbirth previously observed with ALMA. “This star was ejected from its parent cloud with a speed of about 10 kilometers per second around 550 years ago,” said John Bally, an astronomer at the University of Colorado and co-author on the paper. “It is possible that solid grains of salt were vaporized by shock waves as the star and its disk were abruptly accelerated by a close en- counter or collision with another star. It remains to be seen if salt vapor is present in all disks surround- ing massive protostars, or if such vapor traces violent events like the one we observed with ALMA.” !