Astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) have spotted aluminum monoxide (AlO) molecules in the gas surrounding Orion Source I, the 10-solar-mass protostar about 1,500 light-years away.
An artist’s impression of Orion Source I, a young, massive star about 1,500 light-years away. Image credit: NRAO / AUI / NSF / S. Dagnello.
“Disks of gas surround young stars,” said team leader Professor Shogo Tachibana from the University of Tokyo and JAXA and colleagues.
“Some of the gas condenses into dust grains which then stick together to form more substantial objects, building up to form meteors, planetesimals, and eventually planets.”
“Understanding the formation of these solid objects is essential for understanding everything which follows.”
The researchers analyzed ALMA data for Orion Source I and found distinctive radio emissions from AlO molecules.
“Aluminum oxide played a significant role in the formation of the oldest material in the Solar System,” Professor Tachibana said.
“Our discovery will contribute to the understanding of material evolution in the early Solar System.”
“Interestingly, the radio emissions from the AlO molecules are concentrated in the launching points of the outflows from the rotating disk around the protostar.”
“In contrast, other molecules such as silicon monoxide (SiO) were detected in a broader area in the outflow.”
Typically, the temperature is higher at the base of the outflows and lower in the downstream gas.
ALMA image of the distributions of AlO molecules (color) and warm dust particles (contours); the molecular outflow (not shown in this image) extends from the center to the top-left and bottom-right. Image credit: ALMA / ESO / NAOJ / NRAO / Tachibana et al.
“Non-detection of gas-phase AlO downstream indicates that the molecules condensed into solid dust particles in the colder regions,” Professor Tachibana said.
“Molecules can emit their distinctive radio signals in gas-phase, but not in solid-phase.”
ALMA’s detection of AlO in the hot base of the outflow suggests that the molecules are formed in hot regions close to Orion Source I.
“Once moved to colder areas, AlO would be captured in dust particles which can become aluminum-rich dust, like the oldest solid in the Solar System, and further the building blocks for planets,” the astronomers said.
Their findings were published in the Astrophysical Journal Letters.
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Shogo Tachibana et al. 2019. Spatial Distribution of AlO in a High-mass Protostar Candidate Orion Source I. ApJL 875, L29; doi: 10.3847/2041-8213/ab1653
