Go Outside (to watch the T Coronae Borealis Nova Explosion)

Ethan Wong

June 28, 2024

The T Coronae Borealis (T CrB) is a binary star system of a red giant and white dwarf which orbit each other over 3000 light years away in our Milky Way galaxy. Every 80 years, the T CrB experiences a nova explosion, and one will be constant for around a week between now (sometimes in the next few days or weeks) and September, located just near the Corona Borealis constellation in the Northern Hemisphere. The last thermonuclear explosion that took place between these two stars was in 1946, and given that the next one will likely follow the consistent 80-year time pattern, this is a one-time astronomical sight visible with the naked eye.

In stars, the core experiences a nuclear fusion of hydrogen and helium which produces energy (a fuel, essentially) that neutralizes the gravitational forces that are all around the star, protecting it from collapsing. Once all the energy in the star has been depleted, the forces of gravity overpower the body, causing the star to give way. However, some stars experience a red giant phase where the star expands with the help of heat caused by its collapsing core. The star is transformed into a giant mass that eventually collapses into a white dwarf, neutron star or black hole depending on its size. White dwarfs can be the product of red giants, yet also small stars that do not experience the red giant phase. White dwarfs are dead stars that have run out of energy to withstand the forces of gravity; as a result, they exist, cooling down until they become black dwarfs. T CrB, as stated above, involves a red giant star and a white dwarf star.

The white dwarf in T CrB has around the same mass as our Sun, yet has a strong gravitational pull that strips the hydrogen from the red giant, building pressure and heat as it “layers” the red giant’s hydrogen material around its body. When this material piles up on the white dwarf, a nuclear fusion occurs similar to the reaction that normal stars have in their cores; however, the energy created by the white dwarf’s nuclear fusion travels much faster than the white dwarf can repel the energy away from it, resulting in a gradual expansion of the white dwarf star. This builds up heat, pressure and energy that it has failed to transport away from itself, eventually resulting in a giant explosion that releases all accreted material into space while presenting a bright light visible on Earth. Both stars remain intact, allowing the cycle to continue where another thermonuclear explosion will take place in around 80 years. 

T CrB is expected to hit a magnitude of +2 (any magnitude of +6 or less will be visible to the naked eye). For reference, the Sun has an apparent magnitude of -26.7. So although it won’t be super bright or resemble a bomb explosion from thousands of light years away, it is still a cool event to check out given it will not happen again in your lifetime (probably).