PORTLAND, Maine — A long-anticipated midnight sky show slated to take place in the darkened heavens over Maine is late and nobody knows for sure when — or if — it will happen.
The binary star system T Coronae Borealis, or T CrB, is not normally visible with the naked eye. Every 80 years, the two stars tangle with each other, producing a runaway thermonuclear reaction bright enough to see from Maine, some 3,000 light years away.
It’s basically a once-in-a-lifetime cosmic exhibition. Astronomers last observed the phenomenon in 1946. It was predicted to reappear between February and September last year but nothing happened. Experts can only guess why, while Maine star gazers can only watch and wait.
“As time has passed with no eruption, I’ve become a bit lazy about checking on it,” said Alan Seamans of the Central Maine Astronomical Society. “I was jolted back to paying attention by a scientific paper that came out this fall, in which a new, tentative prediction was made.”
The paper, written by French astronomer Jean Schneider and supported by other scientists, now predicts the phenomenon will occur between March and November. But the nova is hard to pin down.
First recorded in the Middle Ages, astronomers finally studied it closely in 1888 but didn’t really understand it was a regular-recurring phenomenon until the same thing happened again, in the same sky location, in 1946. Since 80 years elapsed between those two well-documented events, experts are now making an educated guess as to when it will happen next.
Why it happens is well understood. The two sister stars are a white dwarf and a red giant. They’re so close to each other — about the same distance Earth lies from the sun — that the red giant becomes unstable from the ever-increasing temperature and pressure.
When that happens, it begins ejecting outer layers, which the white dwarf collects. That star’s dense atmosphere then eventually heats enough to set off a thermonuclear reaction, which produces the bright nova light we can see from here. When it’s all burned off, the process begins to repeat itself.
The big, hot, cosmic mess won’t last long. Once it appears, it will only be visible to the unaided eye for a few days and for just over a week with binoculars, according to NASA. Then it will vanish for another 80 years. When it goes nova, T CrB will shine about as bright as Polaris, the North Star.
To appreciate T CrB when it goes nova, first go look at what you can’t see now. Use a star chart or phone app, along with an ordinary pair of binoculars, to find the U-shaped, five-star constellation Corona Borealis — or Northern Crown — between Hercules and Bootes.
You likely won’t see a dim sixth star — T CrB — dangling off the left end. That’s where the binary system will appear when it goes nova, probably sometime later this year.
Dwight Lanpher, a member of DarkSky International from Northeast Harbor, said he’s definitely looking forward to seeing the star appear but he’s putting it in context, especially after the full solar eclipse last fall.
He called it an interesting event but one in the same class as a meteor shower that barely meets expectations or a comet that never gets too bright. It’ll still be worth a look, he said.
“No doubt, the universe is an interesting place,” Lanpher said.
