Remember Mr. Creosote? If you don’t, he’s worth getting to know — but only if you have a very strong stomach. Mr. Creosote was the colossally obese character in Monty Python’s Meaning of Life who gorged himself on buckets of food in a French restaurant, somehow surviving his own gluttony, but only until he capped off the meal with a single “waffer-thin mint.” Then he, um, exploded. Well, Mr. Creosote, meet the Type 1a supernova. You two characters have a lot in common.
Supernovas come in more than just one flavor. The most common variety occurs when a star has exhausted all or most of its hydrogen fuel and its decaying core suddenly collapses, generating a burst of gravitational energy that triggers a massive explosion — one that may briefly appear brighter than an entire galaxy. A somewhat more complex dynamic plays out in what’s known as a Type 1a supernova, which is the eruption of a small, dead carcass of a star known as a white dwarf. In general, white dwarfs don’t have sufficient mass to trigger supernovas, but if they’re part of a binary system with a nearby red giant, the dwarf may suck in enough matter from its much bigger sibling that it eventually blows. The waffer-thin mint on a cosmic scale.
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Type 1a supernovas are rare — typically there are only one or two per century in an average-size galaxy. More common are smaller, garden-variety white-dwarf explosions — novas without the super prefix — sometimes occurring repeatedly as a single white dwarf vacuums up and blasts away red giant material over and over again. The Milky Way itself is home to a recurrent nova called RS Ophiuchi, which is located 5,000 light-years from Earth and erupts roughly once every 20 years. What has never been seen is a recurring nova that eventually reaches the super level. The mere fact of shedding matter in the smaller bursts prevents it from ever attaining the mass for a truly big blow.
Or at least that was always the thinking. But a paper published in the Aug. 24 issue of Science provides evidence of the first ever recurring nova that did go super. The method used to detect the phenomenon is almost as impressive as the fact that it happened at all.
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The exploding star, known as PTF 11kx, is found in the constellation Lynx, 600 million light-years from Earth. It was detected on Jan. 16, 2011, by the Palomar Observatory in California. The light signature pouring into the 48-in. telescope that night was unmistakably that of a supernova, and shortly after its detection, Peter Nugent, a senior scientist at the Lawrence Berkeley National Laboratory, and Jeffrey Silverman, a postdoctoral student at the University of California, Berkeley, began taking spectroscopic measurements of the expanding cloud of gas and other matter, trying to learn more about its chemical signature. They found a great deal of calcium mixed in with the other elements — and that surprised them.
Calcium is a common byproduct of stellar detonations, but this expanding shell of the material was too far away from the freshly exploded star and moving too slowly to be the result of the supernova that had just occurred. It would be easy enough to explain the calcium’s presence if the star had gone nova once before, releasing a burst of the element in all directions and then slowing steadily as it encountered the stellar wind that permeates space. But that would mean that the elusive recurrent nova that goes super would finally have been found. The only way to determine if this was so would be to watch. If the calcium signal faded and slowed further and then lit up explosively when the fresh blast of faster star debris caught up with it and energized it, the deal would be sealed. Exactly 58 days later, that’s what happened.
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“This was the most exciting supernova I’ve ever studied,” postdoctoral researcher Ben Dilday of the University of California at Santa Barbara, who was the lead author of the Science paper, said in a statement. “For several months, almost every new observation showed something we’d never seen before.”
It’s not clear how common recurrent Type 1a novas that eventually go supernova are, th0ugh Silverman suspects that the mere fact that astronomers have been studying novas for so long and never seen one like this before is a sign that they’re pretty rare. It’s not even clear whether many folks outside the astronomy community will care terribly much that a sub-subcategory of the familiar supernova has at last been identified. But the astronomers care deeply, and well they might. Cosmic phenomena do a very good job of concealing themselves from us. Every curtain we part makes the universe a more transparent — and, in this case, literally more dazzling — place.