Nova Vulpeculae 1670 is merely a collision between two dwarf stars.

The term ‘Nova (Novae)’ refers to a transient astronomical event that causes sudden appearance of a bright, apparently new star which gradually fades away over several weeks. In some cases, the fading process may take many months. All the novae, which have been observed to date, involved an interaction between binary stars. These progenitors could either be a pair of red dwarf stars or a white dwarf with a main sequence star (it produces Hydrogen fusion in its core). The latter of these processes is the most common type of nova and is categorized as ‘Classical Nova Eruptions’.

These events are created when both the stars (white dwarf and main sequence) reaches in the vicinity of each other. This allows the white dwarf to start drawing accreted matter from its companion star. This leads to a shallow atmosphere (mostly Hydrogen) which is incredibly dense. Consequently, the fusion reaction is triggered as soon as the pressure and temperature reach their critical levels. This dramatic generation of energy produces an envelope of bright light which was previously considered a new star. However, advanced research has proved otherwise.

In 1670, a famous Nova called Nova Vulpeculae 1670 emerged to the scene after a bright light was observed in the Northern sky. It is one ofthe earliest examples of a well-documented nova but a recent research proves that it was not a nova. Prior to this research, astronomers did challenge its status of being a nova in 2015 when they probed the gas surrounding the object. At that time, they found that this bright light was a result of a collision between two main sequence stars. Having said that, the latest research ruled out that idea, as well.

An international team of researchers used the Atacama Large Millimeter-submillimeter Array (ALMA) to examine the hourglass-shaped debris of the celestial event and concluded that the two objects involved were a white dwarf and a brown dwarf. Brown dwarfs are too small to support hydrogen fusion and rely primarily on deuterium fusion. It is a vital process for newly forming stars as it can take place at a lower temperature. On the other hand, a white dwarf is a dead star which cannot produce hydrogen fusion any longer. The core of these stars is supported by ‘Electron Pressure’. Summer Starrfield, an Astronomer from the Arizona State University, said,

“It now seems what was observed centuries ago was not what we would today describe as a classic ‘nova‘. Instead, it was the merger of two stellar objects, a white dwarf and a brown dwarf. When these two objects collided, they spilled out a cocktail of molecules and unusual isotopes, which gave us new insights into the nature of this object.”

The researching team reconstructed the binary system by analyzing these isotopes and tried to replicate the demise of the star system. This reconstruction showed that the white dwarf was 10 times more massive than its companion despite being significantly smaller in size. Similarly, it had a much greater gravity than the brown dwarf. As both these stars grew closer together in their mutual orbit, the tidal force of the white dwarf ripped apart the brown dwarf.

After that, the white dwarf would have ejected some of the brown dwarf’s material almost instinctively. The remaining material would have fallen into the white dwarf in the form of an accretion disk. This would have led to stellar jets which gave the hourglass shape to this material. Stewart Eyres, an Astronomer at the University of New South Wales, referred to that by saying,

“The presence of lithium, together with unusual isotopic ratios of the elements carbon, nitrogen, and oxygen, point to material from a brown dwarf star being dumped on the surface of a white dwarf.”

In addition to all this, the presence of organic molecules, like Formaldehyde and Formamide, votes against the existence of a nova because these molecules can’t survive in a nuclear fusion environment. Given the fact that nuclear fusion is an essential part of a nova, it is impossible for these molecules to survive all these years if it was a nova. Hence, the researchers concluded it as a collision between a white dwarf and a brown dwarf.