Protostars discovered near the supermassive black hole at the center of the Milky Way

The protostars detected by ALMA (Image ALMA (ESO/NAOJ/NRAO), Yusef-Zadeh et al.; B. Saxton (NRAO/AUI/NSF))
The protostars detected by ALMA (Image ALMA (ESO/NAOJ/NRAO), Yusef-Zadeh et al.; B. Saxton (NRAO/AUI/NSF))

An article published in the “Astrophysical Journal Letters” describes the discovery of protostars near the center of the Milky Way, near the supermassive black hole known as Sagittarius A* (or Sgr A*). A team of astronomers made this discovery using the ALMA radio telescope, a surprising result because the conditions in that area were considered too hostile due to the gravitational tides caused by Sgr A* and the intense electromagnetic emissions from the heated gas and dust ring around it.

With its estimated mass of 4.3 million times the Sun’s, Sgr A* has a force of gravity that’s supposed to cause devastation for a radius of a few light years, destroying the clouds of gas and dust from which stars form. When those gas and dust approach the supermassive black hole not so much to be swallowed, they can heat up enough to emit even X-rays that flood the neighborhood. In short, these are very harsh conditions, yet apparently not impossible for star formation.

Astronomer Farhad Yusef-Zadeh of Northwestern University in Evanston, Illinois, USA, had already led a team that observed the area around Sgr A* with ALMA (Atacama Large Millimeter/submillimeter Array), inaugurated in March 2013, discovering massive stars very young from an astronomical point of view, with an estimated age of about 6 million years. It was already a remarkable discovery, but the subsequent one made by these astronomers with new observations is far more extraordinary because they found the signs of 11 small protostars less than 3 light years away from the supermassive black hole.

This discovery was made thanks to the fact that radio waves are among the electromagnetic radiation that pass through interstellar dust that make the area invisible at frequencies such as those of visible light. The ALMA radio telescope detected the emissions from the protostars, which have a shape similar to an hourglass.

This shape, also called double-lobed, is due to the fact that large amounts of gas and dust from the cloud a star is forming from are collapsing due to their gravity, causing the growth of what will become stars but a part is ejected in a double high speed jet at its poles.

The astronomers tried to offer some hypothesis to explain such an astonishing phenomenon, particularly what forces can compensate for the destructive ones of Sgr A*. Perhaps high-speed gas and dust clouds move across the area causing a compression that determines the birth of stars. Perhaps the jets of materials coming from the supermassive black hole compress those clouds.

The effects of these enormous objects with a powerful force of gravity are object of discussion and according to a research published in February 2017 they can favor the formation of new stars. The controversy exists particularly in the cases of supermassive black holes with a remarkable activity around them that forms a quasar and will likely continue until it becomes clear when these objects can favor star formation and when they inhibit it.

As for research on the protostars near Sagittarius A*, the astronomers intend to keep on observing them with the ALMA radio telescope. There’s the opportunity to study the formation of stars, but also the hope to find dust and gas disks around them, from which planets could form. That too would be surprising.

A protostar's double-lobed shape (Image ALMA (ESO/NAOJ/NRAO), Yusef-Zadeh et al.; B. Saxton (NRAO/AUI/NSF))
A protostar’s double-lobed shape (Image ALMA (ESO/NAOJ/NRAO), Yusef-Zadeh et al.; B. Saxton (NRAO/AUI/NSF))

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