Astronomers have solved a half-century-old scientific mystery, identifying the star associated with a stream of cosmic gas emanating from a pair of nearby galaxies. For nearly fifty years, astronomers searching for stars in the Magellanic Stream came up empty-handed. The Magellanic Stream is a vast band of gas that spans nearly 300 lunar visual diameters across the southern hemisphere sky, trailing behind the Magellanic Clouds, our Milky Way's two closest cosmic neighbors.

Artist's rendering of the Magellanic Stream. Shown on the right side of the image are the Milky Way's closest neighboring galaxies, the Small Magellanic Cloud and the Large Magellanic Cloud. As these galaxies move to the right, the gaseous Magellanic Stream surges behind them, intertwining across the southern sky. Also shown are the 13 red giant stars found in the Magellanic Stream. Photo credit: CfA/MelissaWeiss

Now, the long search for stars is finally over. Researchers at Harvard University and the Smithsonian Center for Astrophysics (CfA) and their colleagues have identified the locations of 13 stars whose distances, motions, and chemical compositions place them within the mysterious star stream.

Positioning these stars has now determined the true distance of the Magellanic Stream, revealing that it extends from 150,000 to more than 400,000 light-years away. These findings pave the way for mapping and modeling the Magellanic Stream in unprecedented detail, providing new insights into the history and characteristics of our galaxy and its neighbors.

"The Magellanic Stream dominates the skies of the Southern Hemisphere, and our work has finally uncovered a stellar structure that people have been searching for for decades," said Vedant Chandra, a doctoral student in Astronomy and Astrophysics at the CfA and first author of a new study published in The Astrophysical Journal.

"The formation of the Magellanic Streams and Magellanic Clouds, and their past and future interactions with our galaxy," said co-author Charlie Conroy, the Magellanic Professor of Astronomy and Chandra's mentor. "With these results and more like them, we hope to gain a deeper understanding of the formation of the Magellanic Streams and Magellanic Clouds, and their past and future interactions with our galaxy."

Insights into the Magellanic Clouds

The Large Magellanic Cloud and the Small Magellanic Cloud are dwarf satellite galaxies of the Milky Way. The Large Magellanic Cloud and the Small Magellanic Cloud are dwarf satellite galaxies of the Milky Way. Their hazy bright lights can be seen with the naked eye and have been known to people since ancient times. As increasingly powerful telescopes became available, astronomers were able to detect phenomena too faint to see with our naked eyes, and in the early 1970s they discovered a huge stream of hydrogen gas apparently ejected from the Magellanic Clouds.

Studies of the gases within the Magellanic Stream have further shown that the Magellanic Stream consists of two intertwined filaments, each originating from a Magellanic Cloud. These features suggest that the Milky Way's gravity may have pulled the Magellanic Stream out of the clouds. However, exactly how the Magellanic Stream formed has been elusive, in large part because its putative stellar composition remains elusive.

Solve the Mystery of the Stars

Chandra is approaching this problem through an ambitious project, which started in 2021 while he was studying for his PhD at the CfA. Chandra consulted Conroy on some interesting research topic areas, and Conroy directed Chandra to the uncharted territory of the Milky Way. Since our solar system lies squarely in the disk of the Milky Way itself, the sparse stars in the Milky Way's outer reaches have been poorly studied, like an audience member near the stage at a concert trying to see someone on the periphery of the crowd.

Over the past decade, however, deep catalogs compiled by new instruments - notably the European Space Agency's Gaia spacecraft - have begun to spy on stellar objects that may be these elusive frontier stars. The Chandra telescope, through CfA and MIT, accessed the 6.5-meter Magellanbad Telescope at Las Campanas Observatory in Chile and conducted a project to perform spectral analysis of 200 distant Milky Way stars.

Spectral analysis of the Magellanic Stream

Spectroscopy is the practice of collecting enough light from celestial objects to detect certain features imprinted in the light's color bands, which, like fingerprints, can uniquely identify individual chemical elements. Therefore, these features reveal the chemical makeup of the celestial body and explain its origin. Additionally, these features change depending on the object's distance, allowing astronomers to discern where an object (such as a star) is going, and where it came from.

In Chandra's study, spectral analysis identified a group of 13 stars whose distances and velocities were well within the expected range of the Magellanic Stream. What's more, the stars' chemical abundances match those of the Magellanic Clouds, such as a distinct lack of heavier elements that astronomers call metals. "These 13 stars just fell out of our data set," said study co-author Rohan Naidu, a former CfA graduate student and now a Hubble postdoctoral fellow at MIT.

Using these stars, researchers obtained reliable distance and range measurements of the Magellanic Stream, confirming that its origin is the gravitational grab of the Milky Way. Additionally, the researchers were able to calculate the overall gas distribution of the Magellanic Flow with greater confidence than previous estimates. The gas distribution suggests that the stream is actually twice as massive as generally estimated.

This result in turn predicts that the Milky Way will be filled with new star formation in the future, because according to previous observations, star streams are actively falling into our galaxy. Therefore, the galactic stream is the main supplier of cold neutral gas needed to create new stars in the Milky Way.

The future of galaxy research

"The Magellanic Stream is the primary source of stellar heat in the Milky Way—it's our breakfast, lunch and supper," said study co-author Ana Bonaca, a former ITC postdoctoral fellow at the CfA and now a staff scientist at Carnegie Observatories. "The Milky Way may end up being fatter than first thought, according to new, higher mass estimates of the Magellanic Stream."

Further study of the Magellanic Stream could also help astronomers learn more about the makeup of the Milky Way. Because the Magellanic Streams are thought to trace the past trajectories of the Magellanic Clouds, simulating the evolution of the relatively massive Large Magellanic Cloud through the Magellanic Streams will help improve measurements of the mass distribution of the Milky Way. Much of this mass is in the form of dark matter - a little-understood substance that has gravitational properties. Better measurements of the Milky Way's mass in its distant hinterland will help calculate the amounts of ordinary and dark matter, constraining the latter's possible properties.

"The great thing about having such a huge stream of stars like the Magellanic Stream is that we can now use it to do a lot of astrophysics studies," said Chandra. "As our spectroscopic surveys continue and we discover more stars, we're excited to see what else the outer reaches of the Milky Way has to offer us."

Reference: "Discovery of the Magellanic Stream as Far as 100kpc", author: Vedant Chandra, Rohan P. Naidu, Charlie Conroy, Ana Bonaca, Dennis Zaritsky, Phillip A. Cargile, Nelson Caldwell, Benjamin D. Johnson, Jiwon Jesse Han and Yuan-Sen Ting, October 13, 2023, "The Astrophysical Journal".

DOI:10.3847/1538-4357/acf7bf

Compiled source: ScitechDaily