I have the feeling tomorrow’s Doctor Who episode, “Face the Raven”, is gonna be pretty massive, and I’ve heard of some critical spoilers having been leaked, so I am deliberately steering clear of all the Doctor Who sites until after I’ve seen it. Which, since I have family coming for an early Thanksgiving tomorrow, will likely not be until Sunday. Ack! Too long to go without Internet! 😛
So today I’m going to talk about something else. A supernova.
In 2016, astronomers are absolutely certain they will see a supernova. This isn’t a nearby one, so don’t worry; it’s in a distant galaxy. So how do they know it will happen next year? We can’t even predict when Betelgeuse will go, and its practically on our doorstep. Or Eta Carinae, for that matter, which always looks kinda scarily unstable. So if we can’t predict to within the nearest 10,000 years when one of *those* will go, how can anyone be so sure of this one? A crystal ball? A TARDIS?
Well . . . in way, time travel actually is the answer. It’s just not us doing the traveling. The supernova actually happened a very long time ago, of course, and as it happens, the galaxy containing the supernova is behind a really massive foreground galaxy as seen from Earth. This foreground galaxy is acting as a gravitational lens, producing one of the few known examples of an Einstein Cross — a formation in the sky where the same distant object appears four times, as images surrounding a central, massive object. The massive galaxy isn’t precisely in front of the background galaxy, so light to each of the four images takes different amounts of time to travel. As a result, we see this supernova more than once. Supernova Refsdal, as its known, has been observed before, in 2014, where it became the first supernova to appear as an Einstein Cross. After observing slight differences in how quickly each of the images faded, scientists predict that it will be visible again next year, as another packet of the light from the same supernova makes its way to us. The Hubble Space Telescope is already tasked with taking looks in the various predicted timeframes where the supernova might reappear.
Pretty cool. 😉