ALMA Reveals How Massive Stars are Born

Scientists have taken a closer look at the massive star-forming region, IRAS 16547-4247, and have learned a little bit more about how monstrous stars are born.

All stars in the sky vary in their masses. While some stars have masses that are smaller than one tenth of solar masses, others have masses that are larger than 100 solar masses. Exactly how these large stars come to be, though, has long remained a mystery.

In order to find out, the researchers turned to the Atacama Large Millimeter/submillimeter array (ALMA). The researchers used ALMA to look at IRAS 16547-4247, which is an object emitting strong radiation with about 60 times solar luminosity and is surrounded by a high-density molecular cloud with a mass of about 1,300 solar masses.

"Even though many of the astronomers assumed that this would be a fertile high-mass star forming region, we couldn't probe the kinematics of gas around high-mass protostars at the level of resolution provided by existing telescopes," said Aya Higuchi, one of the researchers, in a news release.

In order to get a better glimpse of the structure, the researchers observed molecular line emission of dust, CO and methanol. They found that the center of the region contains two high-density compact gas clouds with masses that are 10 to 20 times that of our own sun. It's thought that these gas clouds surround a newly forming high-mass star like a cocoon.

The scientists also found two pairs of outflows aligned with the north-south and east-west direction, respectively. The researchers were able to see the details of complex structure and kinematics of gas.

The researchers also found  that methanol molecule is spreading from the center of the object in the form of an hourglass structure. Methanol is usually produced on the surface of dust, but when the temperature increases by some process, it will be released from the dust surface and turn into gas which emits radio waves.

"We conducted radio observations of carbon monoxide and methanol to explore the details of the distribution and kinematics of gas in the region where high-mass stars are forming in clusters," said Higuchi. "A typical example of a high-mass star forming region is the Orion Nebula, but ALMA enabled us to see the complex formation environment of star clusters which is even 7 times farther away than the Orion Nebula with the highest imaging resolution ever achieved. ALMA will become indispensable for the future research on the high-mass star forming region."

The findings are published in The Astrophysical Journal.

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