Nicknamed "the Cow" -- after its official name, AT2018cow -- it was so bright that initially astronomers thought it must be a nearer (and dimmer) phenomenon, possibly a flare-up of a white dwarf star after having engulfed material from a nearby companion star. But analysis of the red shift of the light coming from the explosion shows that it's 200 million light years away -- so lies in a distant galaxy that at first was thought to be behind it.
This means that it was phenomenally bright. Its peak luminosity was equivalent to a hundred billion Suns -- a good ten times brighter than the brightest supernova ever observed.
"The Cow" -- initial appearance (left), peak brightness (middle), and waning (right)
This is despite intensive study. "When we saw that, we thought, 'let's get on with it,'" said Daniel Perley, astronomer at Liverpool John Moores University in the United Kingdom. "We dropped everything in the first two weeks, observing it seven times a night."
Even more curious is that the phenomenon, whatever it is, produced radiation across the electromagnetic spectrum, including a strong signal in the ultraviolet and x-ray regions. But after three weeks, the x-ray emissions started to fluctuate wildly, and the intensity across the entire spectrum started to weaken. Within six weeks, it was back to being entirely invisible.
One possibility is that it was a supernova surrounded by a thick gas cloud. The initial brightening after the supernova's first burst of emissions was augmented when the shock wave hit the gas cloud, warming it up and causing it to glow. The brightening continued as the shock wave plunged through, only diminishing when it reached the outer edges.
But that's only a speculative solution. Other possibilities include the birth of a black hole or a white dwarf being swallowed by a neutron star. But none of these align perfectly with the data. "All of our explanations have problems," said Liliana Rivera Sandoval, astronomer at Texas Tech University. "It's super weird."
The problem, of course, is these one-off phenomena -- events that occur so rarely that the chance of another one happening in our lifetime is small indeed -- give scientists scanty information at best, and no repeated data set with which to compare the initial measurements. "I hope there are more Cows," Sandoval said, but the likelihood of that is pretty slim. So now what we have is one six-week data set, with no way to test any theories against subsequent observations.
"The bright transient AT2018cow has been unlike any other known type of transient," write the research team in a paper published in arXiv last August. "Its large brightness, rapid rise and decay and initially nearly featureless spectrum are unprecedented and difficult to explain using models for similar burst sources."
Frustrating, but that's the way science is, especially with the realms of science that do not allow for replication, such as astronomy, paleontology, and geology. All you can do is use what information you have to generate hypotheses about what is going on, and see which one fits best. After that, nothing much can be done except for waiting and hoping for more data.
So that's this week's puzzle. A colossal explosion in a distant galaxy that is proving to have no easy explanation. I don't know about you, but when I read stuff like this, it makes me feel awfully small and insignificant. Not that this is necessarily a bad thing; there's nothing wrong with a good dose of humility. But the idea that we have observed a mysterious unexplained phenomenon shining with the light of a hundred billion Suns, from a distance of two hundred million light years, boggles my mind with the sheer scale.
Such a big universe, and so much still to learn.
This week's Skeptophilia book recommendation is a little on the dark side.
The Radium Girls, by Kate Moore, tells the story of how the element radium -- discovered in 1898 by Pierre and Marie Curie -- went from being the early 20th century's miracle cure, put in everything from jockstraps to toothpaste, to being recognized as a deadly poison and carcinogen. At first, it was innocent enough, if scarily unscientific. The stuff gives off a beautiful greenish glow in the dark; how could that be dangerous? But then the girls who worked in the factories of Radium Luminous Materials Corporation, which processed most of the radium-laced paints and dyes that were used not only in the crazy commodities I mentioned but in glow-in-the-dark clock and watch dials, started falling ill. Their hair fell out, their bones ached... and they died.
But capitalism being what it is, the owners of the company couldn't, or wouldn't, consider the possibility that their precious element was what was causing the problem. It didn't help that the girls themselves were mostly poor, not to mention the fact that back then, women's voices were routinely ignored in just about every realm. Eventually it was stopped, and radium only processed by people using significant protective equipment, but only after the deaths of hundreds of young women.
The story is fascinating and horrifying. Moore's prose is captivating -- and if you don't feel enraged while you're reading it, you have a heart of stone.
[If you purchase the book from Amazon using the image/link below, part of the proceeds goes to supporting Skeptophilia!]