Move over Judy Garland, a new star has just been born (or at least discovered). On March 15, Australian astronomer Adriano Valvasori discovered a brightening white dwarf star in the midst of a nova and was able to capture it on film before it began to fade. It's big news too: The nova is the brightest one in the constellation Sagittarius since 1898, and the brightest in the entire sky since the Delphini nova in 2013. The newest nova is so bright, in fact, that it can be seen with the naked eye, but astronomers advise viewers to grab those binoculars quickly — it won't be around for long.
Despite its newer reveal, Nova Sagittarii 2015 No. 2, (or PNV J18365700-2855420, as it's so lovingly called in scientific circles) is likely billions of years old. Because white dwarf stars are formed after the death of low- to medium-mass stars like our own sun, it usually takes years for them to ever reach the point of Nova Sagittarii No. 2. As the star's core begins to run out of fuel, it starts to swell into a Red Giant. At that point, the star's internal fuel completely runs dry, and it collapses to the comparable size of the earth — but with the same mass as before, leaving behind a super-dense, compacted version of its former self. The outer layers it sheds and leaves behind are called a nebula.
Explained Bing Quock, assistant director of Morrison Planetarium at the California Academy of Sciences, in a statement:
As the white dwarf’s gravity siphons off—or accretes—hydrogen gas from the atmosphere of its companion, the material piles up on the white dwarf’s surface and starts fusing, triggering a runaway chain reaction that releases a tremendous amount of energy—and up to 100,000 times as much light as the Sun.
In layman's terms, the material ejected from the star as it collapses into a white dwarf state can be seen with the naked eye as a short pulse of bright light in the night sky. Unfortunately, the light from Nova Sagittarii No. 2 won't be around for much longer, warn astronomers. On Monday, Sky and Telescope reported that the white dwarf's brightness had dropped significantly overnight, leaving only a short window of time before its light is diffused completely from our sight.
Novas and white dwarf stars have been making the headlines more than usual lately, it seems. Monday, Tomasz Kaminski and his colleagues from the European Southern Observatory, the Max Planck Institute for Radio Astronomy, and the Onsala Space Observatory published an article in the journal Nature that one of the oldest known novas, CK Vulpeculae, was actually the remnant observation of a violent merging of two bright stars, referred to as a "red nova" or a red transient.
In the summer of 1670, in the constellation Cygnus, a bright shock of light appeared and remained in the night sky until it began to fade away that fall. According to historical records, it reappeared once again in the spring of 1671 and began to increase in brightness throughout the rest of the year, reports National Geographic. Both lunar cartographer Hevelius and Giovanni Domenico Cassini, the astronomer after whom the Cassini spacecraft is named, tracked the nova for the next year before it vanished for good.
But the long-accepted idea that CK Vulpeculae was a nova began to bother study author Kaminski, who now says that it was the "star's" chemical composition and isotopic breakdown that caused the group to rethink its categorization altogether. In the study, they explained:
It is most tempting to consider that CK Vulpeculae underwent its 17th century cataclysm owing to a merger of stars, given that such events have now been proved to explain the explosions of [novas like this one]. The explosion could have been violent enough to penetrate and eject inner parts of the merging stars, exposing material that was active in nuclear burning.
"For many years, this object was thought to be a nova, but the more it was studied, the less it looked like an ordinary nova, or indeed any other kind of exploding star," added Kaminski in a later statement to the magazine Astronomy. Said study co-author Karl Menten, "This kind of discovery is the most fun — something that is completely unexpected."