An international team of astronomers has used the Atacama Large Millimeter/submillimeter Array (ALMA) in the Atacama Desert, northern Chile, to observe a cluster forming clump in the infrared dark cloud G34.43+00.24 and discover a protostar surrounded by a large cloud of hot gas.

Up to 90 percent of stars are born in clusters in large molecular clouds. Thus, understanding the formation mechanism of clusters is one of the most important problems for astronomy. Molecular clumps are thought to be a birthplace of clusters.

Infrared dark clouds – objects dark in the mid-infrared band – are distributed throughout the galactic plane. To date, astronomers have discovered many molecular clumps associated with infrared dark clouds. These cold and dense clumps are thought to host very early stages of cluster and high-mass star formation.

The cluster forming clump MM3 in G34.43+00.24 is located in the constellation Aquila about 5,100 light-years away.

Using ALMA, the team found a young object in MM3 that was emitting the methanol molecular line. A detailed study revealed that the temperature of the methanol is minus 140 degrees Celsius. The astronomers concluded that G34.43+00.24 MM3 harbors a new-born star.

“Thanks to the high sensitivity and spatial resolution, we need only a few hours to discover a previously unknown baby star. This is an important step to understand the star formation process in a cluster forming region,” said Dr Takeshi Sakai from the University of Electro-Communication, Japan, who is a lead author of a paper published in the Astrophysical Journal Letters.

Dr Sakai with colleagues also observed radio emission from carbon sulfide and silicon monoxide to reveal the detailed structure of the molecular outflow from G34.43+00.24 MM3. The speed of the emanated gas is 28 km/s and the extent is 4,400 au.

Based on these values, the team estimates the age of the outflow to be only 740 years. Although molecular outflows are common features around protostars, the outflow as young as the one in G34.43+00.24 MM3 is quite rare. The astronomers also found that the protostar is very young but has a giant, hot core.

“Why the hot core in G34.43+00.24 MM3 is so large? In order to warm up the large volume of gas, the baby star should emit much more energy than typical ones. Protostars produce emission by converting the gravitational energy of infalling material to the thermal energy. The large size of the hot core in G34.43+00.24 MM3 is possibly due to the high mass infalling rate than ever thought. The other possibility is that two or more protostars are embedded in the hot core.”

“ALMA’s spatial resolution improves much more in the near future. Then much detail of the infalling material toward the protostar can be revealed, and it helps us answer to the mystery behind the diversity in star formation,” Dr Sakai said.

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Bibliographic information: Takeshi Sakai et al. 2013. ALMA Observations of the IRDC Clump G34.43+00.24 MM3: Hot Core and Molecular Outflows. ApJ 775, L31; doi: 10.1088/2041-8205/775/1/L31