A star set to explode in 2083 will be the brightest object in Earth's sky as it dies

• V Sagittae is invisible to the naked eye but astronomers predict that it will be the brightest star in the sky in 2083 when it meets its demise.
• The star has slowly been getting brighter at an increasing rate since the 1890s.
• The explosion will be so massive that astronomers forecast that it will shine for an entire month.

V Sagittae is barely visible in the night sky, even if you use a telescope. However, by 2083, this star is set to explode and outshine even Sirius — the brightest star we have right now.



Not only will V Sagittae be the most luminous object in the Earth's skies, but it will also beam brighter than anything else in the Milky Way.

This prediction was presented for the first time during the 235th American Astronomical Society (AAS) meeting on Monday.

"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," said Professor Emeritus Bradley E. Schaefer, LSU Department of Physics & Astronomy.

"In the final days of this death-spiral, all of the mass from the companion star will fall onto the white dwarf, creating a supermassive wind from the merging star, appearing as bright as Sirius, possibly even as bright as Venus," he explained.

V Sagittae is already much brighter than it should be

Although V Sagittae isn't very bright from Earth, it's still much brighter than it should be. It falls into the category of ‘cataclysmic variables' — a type of binary star system. In this case, V Sagittae is an ordinary star in a binary orbit around its white dwarf star.

In most cataclysmic variables, the white dwarf is considerably bigger than this orbiting star. However, V Sagittae is 3.9 times the size of its white dwarf.

Because of this, V Sagittae is the most luminous cataclysmic variable in the known universe. By 2083, it will merge with its companion star in a blaze of glory.

What happens when the star explodes?

When V Sagittae merges will its companion star, it's going to be an explosive event that will shine in the sky for the entire month.

"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-spiralling rapidly," said Schaefer.

Essentially, V Sagittae's neighbour is slowly eating at it. As it continues to chomp off energy, V Sagittae spins faster and faster.

"This falling mass will release a tremendous amount of gravitational potential energy, driving a stellar wind as never before seen, and raise the system luminosity to just short of that of supernovae at the peak," he explains.

And thus, they will merge. The end result will be a single star will a degenerating white dwarf at its core and hydrogen burning layer on the outside — entirely enveloped in gas cloud of hydrogen.

V Sagittae has grown 10 times brighter over the last century

V Sagittae has been getting brighter by the day since the 1890s. The American Association of Variable Star Observers (AAVSO) has been able to confirm that since 1907, the star has grown brighter by a factor of 10.

"V Sge is exponentially gaining luminosity with a doubling time scale of 89 years," said Juhan Frank, co-author of the study.

Using this data, they were able to predict that the star will explode in 2083. The prediction is accurate — give or take 16 years — according to the study.

"Therefore, the merge will be approximately between 2067 and 2099, most likely near the middle of this range," said Frank.

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