Stars Found in Mysterious River of Hydrogen Gas Flowing in Milky Way’s Outskirts

Astronomers have been wondering for decades what's in the Milky Way's mysterious river of hydrogen gas. A team of researchers found out it contains stars for the first time.

Magellanic Stream Contains Stars

A river of hydrogen gas flows from the large and small Magellanic clouds on the Milky Way's outskirts. Astronomers have been baffled by the contents of this river, known as the Magellanic Stream, for decades. However, a group of scientists has now successfully identified stars amid the gaseous clouds of the stream for the first time.

Scientists from the Harvard-Smithsonian Center for Astrophysics used the 21-foot (6.5-meter) Magellan Baade Telescope at Las Campanas Observatory in Chile to locate the stars. The researchers focused on 200 stars in the outermost regions of our galaxy, towards the Magellanic Stream, using a comprehensive map of the Milky Way produced by the European Space Agency's Gaia space telescope.

Thirteen of the subjects had chemical compositions similar to the Magellanic Clouds, according to the light spectrum analysis of those stars. The 13 stars had to be located roughly where the Magellanic Stream is estimated to reside, between 150,000 and 400,000 light-years from Earth.

Researchers believe that the Milky Way's gravitational pull tore apart the gas that forms the stream from the dwarf galaxies. Scientists trying to understand the nature of the stream and how it interacts with our galaxy may benefit from the additional observations. According to astronomers, the stream currently looks to be falling toward the Milky Way.

Charlie Conroy, a professor of astronomy at the Harvard-Smithsonian Center for Astrophysics (CfA) and co-author of the research, said in a statement that they hoped to learn more about the Magellanic Stream and the Magellanic Clouds after the recent study. They also wished to understand their formation, including their past and future interaction with the Milky Way galaxy.

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What Is Magellanic Stream?

The Magellanic Stream is a long gas ribbon stretching nearly halfway around our galaxy. Hubblesite shared a radio and visible-light image of the gaseous stream, shown in pink, while the Milky Way is depicted in a light blue band in the center.

Hubble's Cosmic Origins Spectrograph (COS) was used to detect the concentration of heavy elements, such as sulfur and oxygen, at six points (marked with an "x") along the Magellanic Stream to identify the chemistry of the gas filament. By observing distant quasars whose light travels through the stream, COS could identify these elements' spectral signatures by their absorption of ultraviolet radiation. The dazzling centers of active galaxies are known as quasars.

The astronomers discovered low sulfur and oxygen concentrations for most of the stream. The Small Magellanic Cloud (SMC) levels roughly 2 billion years ago correspond to the formation theory for the gaseous ribbon. Ram-pressure and tidal stripping are two mechanisms that pull off the gas from the SMC as it crashes through the galactic halo. The main source of wasted gas in the stream is determined to be the SMC.