A rare celestial event is about to grace the night sky, offering a unique opportunity to witness a “new star” or nova. This phenomenon, while not lighting up the entire sky, promises to be a special sight, typically difficult to predict in advance.
What is T Coronae Borealis?
The star at the center of this event is T Coronae Borealis (T CrB), pronounced “T Cor Bor.” It resides in the constellation of the Northern Crown, visible prominently in the Northern Hemisphere and also observable from Australia and New Zealand over the next few months.
T CrB, located 3,000 light years away, is generally too faint to be seen. However, approximately every 80 years, it erupts brightly, making it visible for a short period before fading back into obscurity.
The life cycle of T CrB
Stars, during their prime, are powered by nuclear fusion in their cores, typically converting hydrogen into helium, which keeps them stable and shining for billions of years. T CrB, however, is a white dwarf, a stellar remnant that has exhausted its nuclear fuel and undergone significant compression due to gravity.
T CrB also has a companion star, a red giant in its old age. The white dwarf attracts gas from the red giant, forming an accretion disc. As matter accumulates on the white dwarf, pressure and temperature rise until a thermonuclear reaction ignites on its surface, causing the star to shine 1,500 times brighter than usual.
Predicting the nova
T CrB is part of a rare class of recurrent novae that erupt within a century, allowing astronomers to observe and predict their cycles. There are only ten known recurrent novae, though others might exist with longer cycles.
Historical records show T CrB’s earliest known eruption in 1217. Its most recent eruptions in 1866 and 1946 followed a predictable pattern: a gradual increase in brightness (high state) about ten years before the eruption, followed by a slight dimming a year before the explosion.
In 2015, T CrB entered its high state again, and a pre-eruption dip was observed in March 2023, indicating an imminent eruption.
How to see the nova
Start stargazing now! It’s a good idea to get used to seeing Corona Borealis as it is now so that you get the full impact of the “new” star.
Corona Borealis currently reaches its best observing position (known as a meridian transit) around 8:30pm to 9pm local time across Australia and Aotearoa. The farther north you are located, the higher the constellation will be in the sky.
A fleeting spectacle
The nova’s maximum brightness will last only a few hours. Within a week, T CrB will have faded, and binoculars will be necessary to see it. Amateur astronomers, who regularly monitor stars, will likely be the first to alert the professional community when T CrB erupts.
The American Association of Variable Star Observers (AAVSO) has over 270,000 observations of T CrB, showcasing the collaborative effort to monitor and document this celestial event.
Astronomers hope the nova will erupt before October, as Corona Borealis will no longer be visible in the Southern Hemisphere’s evening sky after that.