Stars Discovered Within the Previously Enigmatic Gas Stream Entering the Milky Way

Stars, contrary to previous assumptions, exist within the gas stream originating from two small galaxies on the outskirts of the Milky Way.

A stream of hydrogen gas, emanating from the Large and Small Magellanic Clouds—two dwarf galaxies situated on the outskirts of the Milky Way—has long intrigued astronomers. Known as the Magellanic Stream, this gaseous river has now revealed a surprising secret: stars exist within its clouds. In a groundbreaking discovery, a team of researchers from the Harvard–Smithsonian Center for Astrophysics utilized the Magellan Baade Telescope at Las Campanas Observatory in Chile and the detailed Milky Way map generated by the European Space Agency’s Gaia space telescope to identify 200 stars within the farthest reaches of our galaxy, aligned with the direction of the Magellanic Stream.

The team scrutinized the spectrum of light emitted by these stars, finding that the chemical composition of 13 stars matched that of the Magellanic Clouds. These stars were estimated to be positioned between 150,000 and 400,000 light-years from Earth, aligning with the expected distance of the Magellanic Stream. The Magellanic Stream, discovered in the 1970s, spans a vast region of the Southern Sky equivalent to the size of 300 full moons but requires sophisticated equipment for observation.

Astronomers believe that gravitational forces from the Milky Way caused the gas constituting the stream to be torn from the dwarf galaxies. The newfound stars within the stream present an opportunity to gain insights into its nature and its interaction with our galaxy, suggesting a dynamic relationship where the stream appears to be entering the Milky Way.

Professor Charlie Conroy from the Harvard-Smithsonian Center for Astrophysics expressed optimism about the potential for these observations to enhance our understanding of the Magellanic Stream and Clouds, shedding light on their formation, past interactions, and future dynamics with the Milky Way. The Magellanic Stream, with its abundant stellar content, provides a unique opportunity for astrophysical investigations, offering surprises and discoveries as researchers continue their spectroscopic survey.

The findings also challenge previous estimations, revealing that the Magellanic Stream is about twice as massive as initially thought. This implies a greater amount of gas being absorbed by the Milky Way, influencing star formation and contributing to the galaxy’s mass. By refining the mass calculations of the stream and deepening our understanding of the Magellanic Clouds, astronomers aim to better ascertain the mass distribution of the entire Milky Way. This comprehensive approach contributes to the ongoing quest to unravel the mysteries of dark matter—a crucial factor in the galaxy’s composition and gravitational dynamics.

The study was published in October in the Astrophysical Journal.  

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