Free Astronomy Magazine May-June 2016

C omposite image of TMC-1A observations. Dense gas seen around the star with ALMA is shown in red. ALMA also spotted outflowing gas from the star, a feature often seen around baby stars; this outflowing gas is shown in white. The position of the star is indicated with a cross. [ALMA (ESO/NAOJ/NRAO), Aso et al.] SPACE CHRONICLES ary between the inner rotating disk and the outer infalling envelope with high accuracy for the first time. Since gas from the outer envelope is continuously falling into the disk, it had been difficult to identify the transition region in pre- vious studies. In particular, the tenuous but high speed gas in rotating disks is not easy to see. But ALMA has enough sensitivity to highlight such a component and illustrate the speed and distribution of gas in the disk very precisely. This enabled the team to distinguish the disk from the infalling envelope. The team found that the boundary between the disk and envelope is located 90 astronomi- cal units from the central baby star. This distance is three times longer than the orbit of Neptune, the outermost planet in the Solar System. The ob- G as motion around TMC-1A. The red color indicates gas is moving away from us while the blue color is coming closer to us. [ALMA (ESO/NAOJ/NRAO), Aso et al.] served disk obeys Keplerian rota- tion: the material orbiting closer to the central star revolves faster than material further out. The high-sensitivity observations provided other important informa- tion about the object. From detailed measurement of the rotation speed, the research team could calculate that the mass of the baby star is 0.68 times the mass of the Sun. The team also determined the gas infall rate to be a millionth of the mass of the Sun per year, with a speed of 1 km per second. Gravity causes gas to fall towards the cen- tral baby star, but the measured speed is much less than the free-fall speed. Something must be slowing the gas down. The researchers sus- pect that a magnetic field around the baby star might be what is slow- ing the gas. “We expect that as the baby star grows, the boundary between the disk and the infall region moves outward,” said Aso. “We are sure that future ALMA observations will reveal such evolution.” n