T Coronae Borealis is a binary star system 3,000 light-years away from Earth, a ticking time bomb waiting to explode. If recurring novae follow their usual pattern, we could see a new star appear (albeit temporarily) in our night sky at any time.
The moderator of a citizen scientist group I belong to recently emphasized that “T CrB remains our number one target every night.” His sense of urgency is understandable. Our Cataclysm team needs to search for the expected nova, collecting data before, during and after the explosion. It can appear at any time, providing astronomers (both amateur and professional) with the opportunity to witness and study rare and spectacular events in real time.
The data collected from this event is intended to improve our understanding of binary system dynamics and the complex life cycles of stars. Very cool. But just as cool, the new star is expected to be incredibly bright. In fact, it’s so bright that it will be visible to the naked eye and will appear in the sky like a new star for at least a few days.
Once it becomes visible, and if you get the chance to see it, you can claim to have witnessed a runaway thermonuclear reaction from a distance of 3,000 light-years. That’s the plan to add this to my recent naked eye accomplishments – the most recent of which occurred during the total solar eclipse on April 8th. Like millions of people, I spotted prominences, which look like bright red dots, during totality.
rising stars
T Coronae Borealis (T CrB), also known as the Flaming Star, last exploded in 1946 and explodes approximately every 79 years. The current window opened last February and will run until late summer. The star could explode in August, but given the uncertainties involved, it could happen later this fall. We simply don’t know. The system experienced a pre-eruptive dip last year, alerting astronomers that an explosion was imminent.
T CrB is one of only five known recurring novae in the Milky Way, a binary star system consisting of a heavy white dwarf and a red giant. The distance between them is only 0.54 AU, about the distance from the Sun to Venus, and their close encounter turns T CrB into a ticking time bomb.
White dwarfs are the final stage of medium-sized stars, but this special white dwarf has a mass of about 1.37 times that of the sun and is heading towards the Chandrasekhar limit – an astronomical limit of about 1.4 solar masses, beyond which white dwarfs become will become unstable.
The red giant, about 1.12 times the mass of the Sun, orbits the white dwarf every 227 days, placing it within the Roche lobe, the boundary where its material begins to spill out into a nearby companion star. This process creates an accretion disk – a vortex of stellar material – around the white dwarf.
When enough hydrogen from a red giant accumulates on the surface of a white dwarf, it heats up to extreme temperatures. This intense heat can trigger runaway thermonuclear reactions that turn accumulated hydrogen gas into cosmic fireworks called novae. In the case of T CrB, such explosive events repeat approximately every 79 years. This is…look at the watch…right now.
How to spot the flaming star
At magnitude +10, T Corona Borealis is currently invisible to the naked eye. However, the impending explosion will boost the star system to magnitude +2, with a brightness similar to Polaris, also known as Polaris. The system is located in the constellation Corona Borealis and is visible to observers in the Northern Hemisphere. This constellation forms an arc, and once visible, T CrB will temporarily appear in this part of the night sky.
In the days and weeks following the expected outburst, T CrB will gradually dim, returning to low brightness. It was visible to the naked eye for several days after the explosion, and visible through telescopes and binoculars for more than a week. After this period, the star system will return to its quiet phase. Rinse, repeat, explode again, most likely in 2103.
A previous version of this article was originally published on April 10, 2024.
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