• The Blue-Ring Nebula is a result of two stars  merging together thousands of years ago
  • GALEX is the telescope which first spotted the Blue Ring Nebula
  • The Blue Ring Nebula is the first star merger ever to be seen by scientists at its stage

A stellar mystery that's been puzzling scientists for over 16 years has finally been solved.

The Blue Ring Nebula has been a subject of interest for NASA astronomers since 2004 when it was spotted by NASA's Galaxy Evolution Explorer (GALEX). Appearing as a large, faint blob of gas with a star in its center, it has never been seen by astronomers before in the Milky Way. Although it does not emit light that is visible to the human eye, scientists called this discovery the Blue Ring Nebula.

Over the course of studying the mysterious object for 16 years using ground-based and space-based telescopes, scientists have finally cracked the mystery of this elusive blue blob of gas. A study published Wednesday in the journal Nature has reported that the nebula, or the cloud of gas seen surrounding the star, is likely composed of debris from a collision of two stars thousands of years ago. The stars appear to have collided and merged into a single star system.

Although star systems merging together is seen as a common occurrence, they are nearly impossible to study immediately after they form due to the debris that the collision produces. Once the debris clears up after hundreds or thousands of years, however, it is still difficult to study because these merged star systems almost do not differ from non-merged stars. This is where the Blue Ring Nebula is seen as the missing link.

A few thousand years after the merging began, astronomers now are able to observe the nebula while still being able to spot plenty of evidence of the collision and the merger. The Blue Ring Nebula is considered the first known example of a merged star in this particular stage.

"The object's size was similar to that of a supernova remnant, which forms when a massive star runs out of fuel and explodes, or a planetary nebula, the puffed-up remains of a star the size of our Sun. But the Blue Ring Nebula had a living star at its center, " NASA stated in an article it published Wednesday.

"What's more, supernova remnants and planetary nebulas radiate in multiple light wavelengths outside the UV range, while further research showed that the Blue Ring Nebula did not."

Through this discovery, NASA astronomers will be able to work with more information about stars and their origin, providing more answers to the never-ending questions the universe poses.