A Small Galaxy Orbiting The Milky Way Might Not Be What We Thought

Astronomers have made a shocking discovery about the Small Magellanic Cloud, suggesting that it is not one tiny galaxy, but two.


Unexpected Double Nature

Distances in space can be challenging to measure, and knowing the intrinsic brightness of an object is crucial for determining its distance. Recently, astronomers have made a surprising revelation about the Small Magellanic Cloud, a well-known object in Earth's sky. New analysis suggests that it is not just one tiny galaxy orbiting the Milky Way, but actually two.

According to a team led by astronomer Claire Murray, the two distinct stellar populations observed in the Small Magellanic Cloud are superimposed along our line of sight. The data indicates that the rearmost group of stars is located approximately 16,000 light-years behind the other population. This finding has been accepted into The Astrophysical Journal and uploaded to the preprint resource arXiv.

Background of the Small Magellanic Cloud

The Small Magellanic Cloud is one of several dwarf galaxies that are orbiting the Milky Way. It is approximately 200,000 light-years away and has a mass of about 3 billion Suns. Interestingly, it is accompanied by another galaxy called the Large Magellanic Cloud, which is about twice the size of the Small Magellanic Cloud. Both galaxies orbit each other while also orbiting the Milky Way.

Since the 1980s, there have been indications that the Small Magellanic Cloud may not be what it seems. The movement of its stars and the environment of interstellar gas have shown inconsistencies with the properties typically associated with dwarf galaxies. Additionally, there have been observations of at least two distinct populations of stars within the cloud.

Thorough Investigation Reveals the Truth

To unravel the mystery surrounding the Small Magellanic Cloud, Murray and her colleagues conducted an extensive study. They analyzed data from the Gaia survey, which maps the positions and velocities of stars in the Milky Way with high precision. Additionally, they utilized data from a galactic survey conducted using the Australian Square Kilometer Array Pathfinder radio telescope to study the composition of the interstellar gas within the cloud.

The study revealed that the Small Magellanic Cloud consists of two separate populations of stars with similar gas mass. These populations are located at a significant distance from each other and exhibit distinct interstellar gas signatures and star movement. The closer population is estimated to be around 199,000 light-years away, while the more distant one is approximately 215,000 light-years away. This new evidence strongly supports the double nature of the Small Magellanic Cloud, reinforcing previous estimates of its line-of-sight structure.


The Fate of the Small Magellanic Cloud

The Small Magellanic Cloud has long been admired in the southern sky by Indigenous astronomers from Australia, South America, and Africa. However, despite its celestial beauty, the Small Magellanic Cloud is gradually being absorbed by the Milky Way, a fate shared by many other galaxies throughout history. This process of galactic assimilation is an integral part of how galaxies grow over billions of years.

By studying the Small Magellanic Cloud and its larger companion, the Large Magellanic Cloud, astronomers gain valuable insights into the ongoing process of galactic evolution. The research findings have been accepted into The Astrophysical Journal and are accessible on arXiv.