Today, the star V Sagittae (V Sge) is nothing special. You’ll need a good telescope to even see it. But a team of astronomers from LSU believe it could soon, cosmologically speaking, temporarily become the brightest star in the sky and rival Venus’ brightness.
V Sge sits in a star system called Cataclysmic Variables, or CVs. Each CV is home to a regular star in a binary orbit with a white dwarf star. But V Sge is no typical CV. First, it’s 100 times more luminous than every other CV astronomers know about. Where it really stands out, though, is how much more massive the regular star is compared to the white dwarf.
In all CVs but V Sge, the white dwarf is more massive. But in V Sge, the regular star clocks in at 3.9 times more massive than the white dwarf.
“V Sge is utterly unique,” said Professor Emeritus Bradley E. Schaefer (from LSU’s Department of Physics & Astronomy).
Schaefer describes what will happen in the coming decades.
“Over the next few decades, the star will brighten rapidly. Around the year 2083, its accretion rate will rise catastrophically, spilling mass at incredibly high rates onto the white dwarf, with this material blazing away. In the final days of this death-spiral, all of the mass from the companion star will fall onto the white dwarf, creating a super-massive wind from the merging star, appearing as bright as Sirius, possibly even as bright as Venus.”
It won’t be as bright as a supernova at its peak, but it’ll be close, according to Schaefer.
But 2083 seems pretty specific when we usually hear about space stuff talked about in hundreds of thousands, or even millions of years. How did the astronomers get to this date?
Thanks to old sky photos now at the Harvard College Observatory, they were able to get a detailed history going back to 1890. What they found was that V Sge was showing an increase in brightness by a factor of 10X. Data dating back to 1907 from the American Association of Variable Star Observers showed the same increase.
“V Sge is exponentially gaining luminosity with a doubling time scale of 89 years,” said astronomer Juhan Frank. “This brightening can only result with the rate of mass falling off the normal companion star increasing exponentially, ultimately because the binary orbit is in-spiraling rapidly.”
When the pair of stars finally merge into one, it’ll produce a stellar wind that’ll cause the star system to flare in brightness for over a month. According to Schaefer, it’ll be the brightest ‘guest star’ since Kepler’s Supernova in the year 1604.
The prediction does come with a ± of 16 years (2067 and 2099, with the merger most likely to happen in the middle). Hopefully, it’s a little closer to 2067. I’ll be pushing 96 years old if Schaefer’s 2083 prediction is right. Maybe Betelgeuse is finally getting ready to go supernova.