A mystery explosion in space observed by astronomers 350 years ago has been explained by scientists as an extremely rare violent breed of stellar collision.
Seventeenth century astronomers, including Hevelius and Cassini, observed and documented the appearance of a new star in the sky in 1670.
Hevelius described it as nova sub capite Cygni but astronomers today know it as Nova Vulpeculae 1670. It was so spectacular it could easily be seen with the naked eye during its initial outburst. However, the traces it left were so faint that scientists could not unravel its secrets until hundreds of years later with submillimetre telescopes.
Published in the journal Nature, the authors said scientists had believed the object to be a nova (an exploding white dwarf) but the more it was studied, the less certain they became.
Nova Vul 1670 was visible at varying brightness for about two years. It then disappeared and reappeared twice, before finally vanishing a few years later.
Twentieth century astronomers came to understand that most novae could be explained by the explosive behaviour of close binary stars, but the enigmatic Nova Vul 1670 did not fit this model.
Furthermore, researchers lacked the equipment to observe it – they caught a glimpse in the 1980s of a faint nebula in the suspected location, but this sighting did not provide any new information about the event.
However, using new telescopes, including the Apex and Effelsberg radio telescope, researchers were able to find out the chemical composition and the ratios of different isotopes in the gas – providing a detailed account of the makeup of the area and giving clues as to where the material might have come from.
Lead author Tomasz Kaminski said: "We have now probed the area with submillimetre and radio wavelengths. We have found that the surroundings of the remnant are bathed in a cool gas rich in molecules, with a very unusual chemical composition."
Findings showed the mass of the cool material was too great to be the result of a nova explosion, while the isotope ratios were different to what is expected.
Instead, astronomers believe there was a huge collision between two stars – extremely rare events where a star explodes because of a merger with another star. Material is spewed from the stellar interiors into space, leaving behind a faint remnant in a cool environment, rich in dust and molecules.
Study co-author Karl Mentensaid: "This kind of discovery is the most fun: something that is completely unexpected."