Prediction: In 2022, two stars will collide into one another. That collision will unleash a massive amount of energy. So massive, the two stars — which are now invisible to the naked eye — will increase in brightness by a factor of 10,000.
And not only will we be able to see this explosion, in real time, with unaided eyes, it will become one of the brightest objects in the entire sky.
Astronomer Larry Molnar of Calvin College is making this prediction today at the meeting of the American Astronomical Society in Grapevine, Texas. If he’s right, it will be the first time an astronomer predicted an explosion of two stars merging.
“We know these things merge, but we really don’t understand what mechanism that causes them to merge,” he told me.
Molnar’s betting that the stars, located some 1,800 light years away, have already exploded. By 2022 (plus or minus a year), the light from the explosion will finally reach Earth.
That year, we should be able to see it slowly getting brighter over the course of a few months in the constellation Cygnus (a cross-shaped constellation that lines up neatly with the Milky Way). If he’s right, you’ll be able to look up at the night sky and see this cataclysmic collision for yourself.
“If the prediction is correct, then for the first time in history, parents will be able to point to a dark spot in the sky and say, ‘Watch, kids, there’s a star hiding in there, but soon it’s going to light up,’” Matt Walhout, a dean at Calvin College, said in a press statement.
That’s cool. And having a time series of data before, during, and after such an explosion will yield new insights about how solar systems form and evolve.
How do astronomers know these stars could collide?
Scientists have never predicted a binary star system collision. (A binary star system is a solar system that has two stars that orbit one another. Think of the double sunset in the original Star Wars.) But they have seen them before, and have partial data on what the systems look like in the years before a collision.
In 2008, Romuald Tylenda, a Polish astronomer, observed such an explosion. Shortly after, Tylenda realized, by coincidence, she had partial data on the stars leading up to the collision. In that data, there was a pattern. The stars — as they got closer to impact — seemed to be growing closer together. The length of time they took to orbit one another was decreasing, like two tether balls getting wrapped up around the same pole. They spun closer and closer, faster and faster, until … bang!
That’s when Molnar began his search. He and his students started looking for stars with that same pattern of accelerating orbits. The hope was to find a star system nearing collision, and then capture an enormous amount of data on it in the years before, during, and after the collision.
In 2013, he and his students found a star system that showed a similar pattern as the 2008 explosion. Since then, the evidence has only grown stronger. Molnar and his colleagues have observed the orbit of the two stars growing faster every year. That suggests it’s nearing a collision. The orbits “get more extreme every year,” he says.
In 2022, he forecasts we’ll see the two stars — one about 40 percent more massive than the sun, the other about a third of its size — get so close that their outer atmospheres will graze one another, and the smaller star will take a dive into the larger one. Most of the energy of the collision will go to forming a new star with an even more massive core.
But a lot of energy will blow off the outer layers of the stars. “And that has to go somewhere.” This type of explosion is called a “red nova” because, well, the light that flashed out of it is red in hue.
And just how confident is Molnar this will happen?
He confident enough to devote a lot of time and resources to the project for the next several years.
“At this point we have now made over 33,000 images of the star with Calvin College telescopes on more than 170 nights of observing,” he says. “In a sense, that investment is my bet that this is going to be worthwhile.” But in the end, he says, the prediction is just a prediction. We’ll just have to wait and see if it becomes true.
In 2022, Molnar will have devoted around a decade to observing this star system. What will he feel if the prediction is correct? “It would be the most satisfying event of my scientific life,” he says.