Astronomers have used the Atacama Large Millimeter/submillimeter array (ALMA) in Chile to view the largest stellar womb ever observed in the Milky Way. The gigantic object, which resides within the Spitzer Dark Cloud (SDC), is some 500 times the size of the Sun, and is still experiencing growth.

The formation of massive stars (those with a mass 10 or more times the size of the Sun) is a process that is still regarded as mysterious by astronomers. The giant bodies form within huge clouds of dust that make detailed study and observation a problematic process.

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The SDC, which resides some 11,000 light-years away, was first revealed by NASA's Spitzer Space Telescope and the ESA's Herschel Space Observatory, but the unique sensitivity of ALMA's equipment has allowed for a much closer look at the amount of dust present and the motion of the gas moving within the giant cloud.

A composite image of Spitzer Space Telescope and ALMA observations of the SDC (Image: ESO)

The ALMA team performed a microwave scan of the SDC at wavelengths around three millimeters, resulting in the discovery of the largest protostellar core ever found in the Milky Way. Though it was thought likely that the SDC would contain a large stellar womb, the sheer scale of the discovery was unexpected.

“Even though we already believed that the region was a good candidate for being a massive star forming cloud, we were not expecting to find such a massive embryonic star at its center,” said team member Gary Fuller from the University of Manchester, UK.

The mass of the embryonic core is already around 500 times that of the Sun, and the observations show that more material is still flowing into the formation area. When the material eventually collapses, the resulting star could be anything up to 100 times as massive as the Sun.

A dust-obscured wide-field view of the SDC's location in the constellation of Norma (Image: ESO)

NASA's airborne Stratospheric Observatory for Infrared Astronomy (SOFIA) was recently used to shed a little light on the formation process of massive stars, observing G35, a star around 20 times the size of the Sun. The study found that the formation process was more akin to the symmetrical collapse of interstellar clouds seen in the formation of smaller stars than had been expected.

Though the ALMA telescope was officially completed earlier this year, the observations made in this study were carried out using just a quarter of the facility's full array of antennas. ALMA's recent project to obtain a clearer image of star-forming galaxies was also carried out using around a quarter of the facility's potential.

The future is bright for the array, with the team lead on the SDC study, Nicolas Peretto of CEA/AIM Paris-Saclay, France and Cardiff University, UK stating that ALMA will “revolutionise our knowledge of star formation, solving some current problems, and certainly raising new ones.”

Source: ESO

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