A river of hydrogen gas is flowing outward from the Large and Small Magellanic Clouds, two dwarf galaxies located in the outskirts of the Milky Way. Astronomers have been confounded by the contents of this river, referred to as the Magellanic Stream, for many years. However, a team of researchers has, for the first time, successfully located stars within the stream’s gaseous clouds. This discovery will not only aid in comprehending the evolution of the stream’s home galaxies but also in understanding the distribution of matter in the Milky Way itself.
The Harvard–Smithsonian Center for Astrophysics astronomers located the stars using the 21-foot (6.5 meters) Magellan Baade Telescope at the Las Campanas Observatory in Chile. Leveraging a detailed Milky Way map created by the European Space Agency’s Gaia space telescope, the team zeroed-in on 200 stars situated in the farthest reaches of our galaxy, located in the direction of the Magellanic Stream.
Upon analyzing the spectrum of light emanating from these stars, the researchers discovered that the chemical composition of 13 subjects matched that of the Magellanic Clouds. The measurements also suggested that these stars must be situated between 150,000 and 400,000 light-years from Earth, which is approximately the expected distance of the Magellanic Stream.
The stream, originally discovered in the 1970s, spans an area of the Southern Sky equivalent to the size of 300 full moons as seen from Earth. Despite its enormity, it requires a sophisticated equipment to spot it.
Astronomers speculate that the gas forming the stream was pulled from the dwarf galaxies by the Milky Way’s gravitational pull. The new observations may offer insights into the stream’s nature and assist scientists in understanding how it interacts with our galaxy. Scientists believe that the stream seems to be somewhat falling into the Milky Way.
Charlie Conroy, a Professor of Astronomy at the Harvard-Smithsonian Center for Astrophysics (CfA), and co-author of the research, expressed that with these results, they hope to gain a more comprehensive understanding of the formation of the Magellanic Stream and the Magellanic Clouds, as well as their past and future interactions with our galaxy.
As of now, the Magellanic Stream is considered to be sort of falling into the Milky Way.
The Magellanic Clouds have been known to humankind since antiquity, as they are visible with the naked eye. However, astronomers have several questions about the origin and history of these two galaxies, which appear to be colliding with the Milky Way. Mapping and modeling the Magellanic Stream will assist astronomers in advancing the understanding of its source galaxies, whose past trajectory it is believed to trace.
“The beauty of having a vast stellar stream like the Magellanic Stream is that we can now perform so many astrophysical investigations with it,” said Vedant Chandra, a Ph.D. student in astronomy and astrophysics at the CfA, and lead author of the study. “As our spectroscopic survey continues and we find more stars, we’re excited to see what other surprises the galactic outskirts have in store for us.”
Scientists believe that as hydrogen gas from the stream falls into the Milky Way, it creates the right conditions for star formation. By analyzing the data, the researchers also discovered that the stream is about twice as massive than they thought, which means that much more gas must be getting devoured by the Milky Way than previous calculations had suggested.
“The Magellanic Stream is the dominant source of stellar calories for the Milky Way — it’s our breakfast, lunch, and dinner,” said Ana Bonaca, co-author on the study and former postdoctoral fellow at the CfA, now staff scientist at Carnegie Observatories.
The study indicates that by better constraining the mass of the stream and by gaining a better understanding of the Magellanic Clouds, astronomers will be able to better estimate the mass distribution of the entire Milky Way. The study was published in October in the Astrophysical Journal.
