The Disco Star

V838 Monocerotis is located in the constellation Monoceros, which is about 20,000 light years from earth, and was at one point considered one of the largest stars in the universe.

In 2002, the brightness of the star shot up suddenly. It was thought to be a simple nova, which is what happens when the remaining core of a dead star (known as a white dwarf) accumulates too much hydrogen gas from a neighboring star, causing a fantastic explosion. The star dimmed after a couple weeks, as expected, and scientists put it in the record books as a nova.

But less than a month later, the star burst into light again. Since the time period between the explosions was too short to be caused as two separate novas, astronomers were puzzled and took a closer look. It was then they discovered their problem: there was no white dwarf. The star had simply erupted by itself – and it repeated this process of brightening and dimming several times over the next few months. During its brighest eruption, the star became a million times brighter than the sun, and one of the brightest lights in the sky.

Typically, stars brighten slightly before their death – but measurements indicated that the star was only a few million years old, a mere toddler in star years. When the Hubble Telescope captured an image of the star after the eruptions, a large cloud of gas and debris was seen accelerating away from the star. One theory is that the star had collided with something unseen, such another star or planet, but scientist are still puzzled by this now decade-old mystery.