ALMA spots baby star’s growing blanket
|Artist’s impression of the baby star TMC-1A. The star is located in the center |
and surrounded by a rotating gas disk. Gas is infalling to the disk from
the envelope further out [Credit: NAOJ]
Astrophysical Journal. "To understand the formation mechanism of a disk, we need to differentiate the disk from the outer envelope precisely and pinpoint the location of its boundary."
|Gas motion around TMC-1A. The red color indicates gas is moving away |
from us while the blue color is coming closer to us
[Credit: ALMA (ESO/NAOJ/NRAO)]
The team found that the boundary between the disk and envelope is located 90 astronomical 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 observed disk obeys Keplerian rotation: the material orbiting closer to the central star revolves faster than material further out.
The high-sensitivity observations provided other important information 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 central baby star, but the measured speed is much less than the free-fall speed. Something must be slowing the gas down. The researchers suspect that a magnetic field around the baby star might be what is slowing 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."
Source: National Astronomical Observatory of Japan [March 03, 2016]