The universe simply doesn't operate on a human timescale. Events that are right about to happen in the cosmic sense could still be centuries away. But an extensive search discovered a star that really was right about to explode.
Researchers from Ohio State conducted a survey of twenty-five nearby galaxies, hoping to discover a giant star in its final death throes before it went supernova. It's taken them three years, but they have found a star in a binary system in the Whirlpool Galaxy that got noticeably dimmer right before its partner went supernova. This is the first of the many systems they've cataloged that has produced a supernova.
Unfortunately, it appears that they weren't able to directly observe the explosion itself, which happened this past summer. But there may be some data on its much brighter partner star, and the fact that they were able to observe a noticeable change in the binary system right before the supernova occurred is a promising sign. The astronomers hope to figure out how to predict imminent supernovas based on these sorts of minor changes.
Principal investigator Christopher Kochanek says this near miss isn't considered a disappointment. In fact, they see it as confirmation that they're on the right track:
"Our underlying goal is to look for any kind of signature behavior that will enable us to identify stars before they explode. It's a speculative goal at this point, but at least now we know that it's possible."
We know about lots of giant stars in our galaxy and beyond that are on the verge of going supernova, but the problem is that "on the verge" can mean anything from next week to a hundred thousand years from now. We also observe a fair number of supernova explosions, but since they come unexpectedly we can't get optimal observations. It's basically the old adage about how a watched pot never boils, only on the largest scale imaginable.
Fellow researcher Dorota Szczygiel adds:
"The odds are extremely low that we would just happen to be observing a star for several years before it went supernova. We would have to be extremely lucky. With this galaxy survey, we're making our own luck. We're studying all the variable stars in 25 galaxies, so that when one of them happens go supernova, we've already compiled data on it."
This particular system was composed of a very bright blue star and an extremely bright red star. The red star appears to be the one that dimmed over the past three years, while the blue star is the one that went supernova. The red star appeared to dim about three percent each year for a total of roughly ten percent. This companion star likely survived the supernova, but it's too soon to tell.
This research, and hopefully future finds like it, should allow for astronomers to create a litmus test that can tell us when a star really is right about to go supernova on a human timescale. It may also be possible to predict before the explosion even occurs whether the remnants of the supernova will form a dense neutron star or collapse into an even denser black hole.