If you look carefully at the night sky over the coming weeks and months, you might discover something new. It will shine as brightly as the North Star, Polaris, for more than a week before fading back into darkness.
This temporary lighthouse is T Coronae Borealis, often referred to as T CrB. It's a nova, a nuclear explosion exploding from the pale corpse of a long-dead star. Some people may have seen it before. The same fascinating sight lit up our skies nearly 80 years ago, and future generations will see it 80 years from now.
On any nearby world, divinity would be eschatological. But for stargazers in our world, about 3,000 light-years away, this is “an exciting and exciting coming cataclysm,” said Bradley Schaefer, an astrophysicist at Louisiana State University.
Here's everything you need to know about this event: What the event is, when it will appear and where you can catch a glimpse.
What is Nova?
There are over 400 known novae in our galaxy. They are caused by explosive conjunctions between common types of stars (e.g. on the main sequence, such as Earth's Sun or an elephantine red giant) and white dwarfs, which are the smoldering stellar cores left behind after the star dies. The two are gravity-bound companions destined to cause a fiery explosion in space.
White dwarfs are relatively small, but they are so dense that their intense gravity causes them to steal hydrogen-rich material from nearby regular stars. The volatile material fell onto the white dwarf's surface, and after a while it began to pile up, crushing the lower layers and raising their temperature.
Eventually, the compressed material “goes beyond the ignition temperature of hydrogen,” Dr. Schaefer said. This ignites and further increases the temperature of the adhered material. After a certain point, a runaway nuclear reaction begins, causing an apocalyptic explosion.
“These novae are basically hydrogen bombs,” Dr. Schaefer said.
But don't confuse the nova with its more violent sibling, the supernova. A supernova destroys a star permanently, angrily stripping it of its outer layers. When the nova's core embers darken, the cycle begins anew as the white dwarf races toward another explosion.
What is T Coronae Borealis and how do you know when it will explode?
T CrB is a nova that occurs when a white dwarf strips away enough of the outer layers of a red giant star that is about 74 times the size of the Sun.
The nova last exploded in 1946. Astronomers also observed a nova exploding in 1866, and historical reports suggest the nova was discovered in 1787 and 1217.
Most novae have explosion cycles that last for thousands of years. But T CrB is impatient. It is a voracious consumer of the stellar fuel of red giant stars. Past observations have shown that the star erupts once every 80 years, suggesting it is a recurrent nova, meaning it explodes at least once every 100 years.
Previous observations of T CrB have also shown the nova flaring and twitching in a particularly erratic way in the years leading up to the explosion, and things appear to be no different this time around. If we look at activity over the past 10 years, we're bracing for an explosion that could happen any time between now and September.
Where can you see it in the night sky?
T CrB appears in the constellation Corona Borealis, bordering Hercules and Bootes. “When it explodes, it will be as bright as the North Star and will be visible for several days,” said Bill Cooke, director of the Meteoroid Environment Office at NASA's Marshall Space Flight Center in Huntsville, Alabama.
“You will notice that there is a new star in the sky,” he said, adding that it can be seen with the naked eye.
Don't miss it. “It’s a once-in-a-lifetime event,” Dr. Cooke said. “How often can people say they’ve seen a star explode?”