Bridge of Stars


By Robert Marshall

Magellanic Clouds

The term satellite came long before mankind started building rockets to put machines in space. The word is derived from the Latin root satelles, meaning companion, and in the science of astronomy it’s used to describe the moons of planets as well as smaller galaxies found in clusters. Similar to the way moons orbit their parent planets, satellite galaxies follow a gravitational path towards their host galaxies. The Large and Small Magellanic Clouds (named after explorer Ferdinand Magellan and abbreviated LMC and SMC) are two of dozens of dwarf galaxies that surround our Milky Way Galaxy. The Magellanic Clouds are visible to the naked eye, but only in the southern hemisphere. 

RR Lyrae Stars

Astronomers still do not know exactly how or when the Milky Way and all of its satellite galaxies formed. To answer such an ambitious question, scientists must fully understand the mass and velocities of the LMC and SMC. Using the European Space Agency’s (ESA) Gaia, a highly sensitive space-based telescope, a team of international astronomers observed prehistoric, variable-type stars. These RR Lyrae stars have a unique identifiable luminous pulse (like a beacon) that can be seen over time using a detector like that onboard Gaia. 

Pieces of the Cosmic Pie

Researchers were hoping to use RR Lyrae stars to determine precise distances to help answer when the galaxy was formed, but were surprised to discover halos of previously undetected stars surrounding the satellite galaxies. This indicates that the clouds have greater masses than anticipated. Even more exciting, they discovered a stream of stars that bridge the 43,000 light-year gap between the clouds and their halos. Though this bridge was thought to exist based on the satellites’ known interactions with each other, it had never been observed. This discovery is another step closer to answering the bigger questions of how and when the Milky Way formed.

Discussion Questions

  • Planets in our solar system orbit the sun and can be seen in both hemispheres from season to season. Why are the LMC and SMC, which orbit the Milky Way, only visible in the southern hemisphere?
  • Satellite
  • Galaxy
  • Astronomy