The night sky is expected to soon light up with a spectacular phenomenon – the explosion of a star that only happens once every 80 years.

We spoke with Tony Piro, a theoretical astrophysicist at Carnegie Science Observatories, to learn more about T Coronae Borealis, the star system at the center of this rare event.

Q: What exactly is T Coronae Borealis and why is this explosion so special?

Tony Piro: T Coronae Borealis is a binary star system, meaning it has two stars orbiting each other. One star is a white dwarf, which is the dense core left after a star like our Sun has burned through its fuel.

The second star is a red giant, which is a large, older star. The white dwarf has a mass about 40% greater than our Sun and orbits the red giant every 227 days.

The red giant is so large that its outer layers are pulled in by the white dwarf’s gravity. This material forms a disk around the white dwarf and, over time, accumulates on the white dwarf’s surface.

When enough material accumulates, it triggers a thermonuclear explosion, known as a nova, on the white dwarf’s surface. This explosion is incredibly bright and can last for weeks or even months.

Q: When was the last time the T Coronae Borealis satellite exploded?

The last nova from the constellation T Coronae Borealis occurred in 1946, and before that in 1866. Based on this pattern, we expect it to erupt about every 80 years, meaning we could be expecting another explosion soon.

Interestingly, before each of these explosions, the white dwarf went through distinct phases.

About 10 years before an explosion, the star system tends to brighten, probably because the disk becomes more active and directs more material toward the white dwarf. We’ve seen T Coronae Borealis brighten again in the past decade, just as it did before previous explosions.

In addition, about a year before each explosion, the white dwarf dims. This dimming began again in March 2023, which leads us to believe that the next explosion could occur at any time in the next few months.

Q: Why are these repeating nova patterns important to astronomers?

There are several reasons why T Coronae Borealis is particularly interesting. First, it is the closest of all the recurring novae, located only about 2,600 light-years away. This proximity allows us to study it in more detail than other similar systems. Because it erupts relatively often, we can also predict when it will happen and prepare for it.

T Coronae Borealis is also intriguing because its white dwarf is close to the maximum mass a white dwarf can have, known as the Chandrasekhar limit. If the white dwarf exceeds this limit, it could collapse and trigger a much larger explosion called a Type Ia supernova. These supernovae are crucial to understanding the universe because they produce many of the heavy elements essential to life and serve as important tools for measuring cosmic distances.

In addition, in recent years we have discovered that novae can emit high-energy gamma rays, something we did not expect. These emissions are probably caused by shocks generated when exploding material from the white dwarf interacts with surrounding material from the red giant. Observing T Coronae Borealis will help us learn more about these surprising gamma-ray emissions.

Q: Will non-professional astronomers be able to see this phenomenon?

Of course! When T Coronae Borealis explodes, the white dwarf will brighten for about five days, reaching a brightness similar to that of the North Star.

It will be visible to the naked eye for a few hours, then gradually fade over the following weeks. You should still be able to see it with binoculars for about five days after its peak.

Interestingly, T Coronae Borealis is unique in that it brightens again about 100 days after the first explosion. This second brightening will not be visible to the naked eye, but astronomers with powerful telescopes will be able to study it in detail.

It is a rare and exciting event that connects us with the awe that astronomers have felt for centuries when observing the wonders of the night sky. While we do not know the exact time, it will certainly be a spectacular sight when it happens.

Source: Carnegie Institution for Science.