In January 2002, astronomers discovered a massive explosion coming from V838 Monocerotis. They initially thought they were witnessing a supernova, but after the initial flash of light began to dim (as expected), it began to brighten again in infrared wavelengths at the beginning of March. After that brightening faded, another one happened in April. While astronomers were certain they weren’t witnessing a supernova, they weren’t quite sure what it actually was.
Now the Hubble team have released an absolutely extraordinary time-lapse video of the event. Check it out here, and make sure you go full screen.
Nothing like this has ever been observed before, making it hard to rule out many of the possible explanations. There are five hypotheses put forward in the literature about what is causing the event, and they really don’t have much in common.
Some scientists believe V838 Monocerotis was a supernova, just a fairly unique one. This idea doesn’t have much support, since the stars in that area are too young and too massive to have caused this type of event. Another unlikely explanation is that a dying star’s core exploded into a helium flash, like what happened in Sakurai’s Object. Again, this star is too young for a thermal pulse to be the most likely scenario.
Another model proposes the helium flash, but as a thermonuclear event in which a massive star would have been able to survive. While this does fit within the necessary age of the star, the star’s mass might not support this idea.
In planetary capture events, stars begin to consume planets in their system. For a very large planet, getting pulled apart would increase friction between the solar atmosphere and the planet. There could be enough energy generated to spark deuterium fusion, which releases large amounts of energy, such as was seen in the explosion. These types of events are predicted to be about five times more common for stars like V838 Monocerotis than for stars like our Sun.
Another possible explanation is an event known as a mergeburst, in which two main sequence stars collide. This hypothesis is supported by computer modeling, and the youth of the star systems in that region could provide the unstable orbits required for stars to merge in that fashion.