In about 60 years, the people of Earth are in for a rather spectacular stellar show. As we near the end of the 21st century, astronomers predict a distant star called V Sagittae will flare up, becoming one of the brightest objects in the sky. It may even end up brighter than the planet Venus as seen from Earth. The effect will be temporary, but V Sagittae will get plenty of attention during that time.
V Sagittae is actually a binary system sitting about 1,100 light-years away, but it’s not your run-of-the-mill binary like Sirius or Alpha Centauri A-B. This is what’s known as a cataclysmic variable, a class of binary systems where a white dwarf slowly siphons stellar material away from a red dwarf partner. Over time, material builds up in an accretion disk around the white dwarf until it collapses inward and releases a burst of energy. V Sagittae isn’t even your typical cataclysmic variable — it’s the only known system in which the companion star is more massive than the white dwarf, which is a stellar remnant from a dead star that has lost most of its mass. Because of this, the next V Sagittae event is going to be a real doozy.
Astronomers announced the fate of V Sagittae this week at the 235th meeting of the American Astronomical Society in Honolulu. Currently, V Sagittae is a dim object that you can only see with a moderately powerful telescope, but it used to be even dimmer. Astronomers recently analyzed old sky photos archived by the Harvard College Observatory. Comparing those to more recent observations, the team found that V Sagittae doubles in luminosity every 89 years. That means the companion star is spiraling in toward the white dwarf much faster than anyone expected, and the two will collide in 60 years, plus or minus 16.
In the coming decades, V Sagittae will get progressively brighter as more material flows into the white dwarf. Eventually, the stars will merge and almost all the gas from the companion star will form a hydrogen-fusing layer around the white dwarf. Scientists expect V Sagittae will outshine the aforementioned Sirius, which is currently the brightest star in the sky and only 8.6 light-years away. Astronomers think V Sagittae will be almost as luminous as a supernova at its peak, but that will only last for about a month. You can bet every telescope in the world will be watching the show, though.
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