Stargazers around the world should prepare for a dazzling celestial event as the binary star system T Corona Borealis (T CrB) is predicted to undergo a spectacular nova explosion between now and September. The eruption could literally happen at any moment.
This extraordinary explosion will transform T CrB from a star too faint to be seen with the naked eye to one that rivals the brightness of the North Star (Polaris).
Novae, like the one anticipated in T CrB, occur in binary star systems where a white dwarf – the dense remnant of a Sun-like star – orbits closely with a companion star.
"Novae are binary star systems, where two stars closely orbit each other," Dr Darren Baskill, astronomer lecturer at the University of Sussex, tells BBC Science Focus. "Around half the stars in the night sky are binary systems."
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These are not to be confused with supernovae – the dramatic explosions accompanying the death of massive stars, capable of releasing enough energy to briefly outshine entire galaxies.
The white dwarf essentially steals material from its companion through a process called accretion. This material then builds up on the white dwarf's surface until it reaches a critical temperature, igniting a powerful hydrogen fusion.
The result? A dramatic nuclear explosion ejects gas from the white dwarf, significantly increasing the system's brightness.
"This sudden onset of nuclear fusion makes this surface layer of gas even hotter, triggering even more nuclear reactions to take place resulting in a dramatic chain reaction and a dramatic brightening of the star – a nova explosion," Baskill says.
Most novae are unpredictable and observed only once, but T CrB belongs to a special category of recurrent novae, erupting approximately every 80 years. So, if you don’t catch a glimpse this time around, you only have to wait until around the year 2100 – no time at all.
It is the closest such system to Earth, at a distance of about 3,000 light-years, and the only one bright enough to be seen with the naked eye, even in areas with moderate light pollution like towns and some cities.
Because of its distance from us, T CrB's nova explosion is only now reaching us, and it has likely experienced 35-40 more such outbursts since this one, each with light signals yet to arrive.
The last eruptions of T CrB were recorded in 1866 and 1946, with the latter preceded by a noticeable drop in brightness. This same dip was observed earlier this year, indicating that another explosion is imminent.
"Amateur astronomers around the world have been watching the star closely and have noticed a slight variation in brightness every 3-4 months," Baskill explains. "When that happened back in 1945, within a year the gas on the surface of the white dwarf star had dramatically exploded as it became a nova – so could this happen again soon?"
How to see the nova explosion
Currently too dim for unaided observation, T CrB can be seen with a modest amateur telescope. However, once the eruption occurs, no special equipment will be needed to witness the event.
To prepare, stargazers should familiarise themselves with the constellation Corona Borealis using a star chart or a smartphone app (here are our favourites).
This preparation will make the sudden appearance of the nova even more striking when it adds a new star to the familiar constellation.
Dr Mark Hollands, a research fellow at the University of Warwick, advises: "The nova will be visible to the naked eye for a few nights and reach a similar brightness to other stars in the Corona Borealis constellation, but if you miss that window, it’ll still be visible for a few weeks with a good pair of binoculars."
While our Sun will eventually become a white dwarf in 5 to 6 billion years, it will not undergo such nova eruptions as it lacks a stellar companion to accrete material from.
Keep your eyes on the skies for this once-in-a-lifetime astronomical event and enjoy the rare opportunity to witness a nova explosion bright enough to be seen without a telescope.
About our experts
Darren Baskill is an outreach officer and lecturer in the Department of Physics and Astronomy at the University of Sussex. He previously lectured at the Royal Observatory Greenwich, where he also initiated the annual Astronomy Photographer of the Year competition.
Mark Hollands is a postdoc in the Warwick Astronomy and Astrophysics group. His primary research focus is the study of white dwarfs, the dying remnants of Sun-like stars. His work has been published in journals such as Nature Astronomy, Monthly Notices of the Royal Astronomical Society and he has given talks at numerous conferences around the world.
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