The Milky Way is orbited by several dozens of satellites, smaller galaxies much smaller than our own. The biggest of them is called the Large Magellanic Cloud (LMC), and new research suggests that the LMC might have a small satellite of its own.
An international research team, led by Nicolas Martin from the Observatory of Strasbourg in France, found a small stellar system, called SMASH 1, 29 light-years in radius that is likely related to the LMC. The system is quite small and is about 186,000 light-years from the Milky Way.
"It is very likely because its distance from us and position on the sky places it in the sphere of influence of the LMC," Martin told Phys.org. "But it's also possible that its velocity means its orbit is not bound to the LMC. Only follow-up observations would unambiguously confirm the association."
In a study, available online and accepted for publication in the Astrophysical Journal Letters, the researchers discuss how SMASH 1 is similar to another potential satellite of the LMC known as NGC 1841. Both of them are within the potential well of the LMC even though they are found at a significant distance from it, with SMASH being slightly closer at 42,000 light-years away.
The origin of SMASH 1 is unclear. It could be a fragment of the LMC formed during an interaction with the Small Magellanic Cloud (another satellite of the Milky Way), or it might have formed in its current position. While it is very small, it has about 200 times the luminosity of the Sun, and even though it would be very bright if we were close to it, it was a hay-shaped needle in a haystack for the astronomers.
"It isn't trivial to find such a faint stellar system," Martin said. "To discover SMASH 1, it is necessary to remove the contamination of much more numerous foreground stars by selecting only stars with the right color and magnitude."
The discovery is part of the Survey of the Magellanic Stellar History (SMASH), which is trying to understand how the Large and Small Magellanic Clouds have evolved over time.
The team is planning follow-up observations to measure the three-dimensional velocity of the cluster. That should provide enough information to estimate if SMASH 1 does indeed belong to the LMC.