In yet another addition to your 2024 skygazing agenda, NASA expects a star system roughly 3,000 light-years from Earth to undergo a rare outburst sometime this year. Known as a nova, this celestial explosion will offer a week-long, unaided view of one of space's most captivating phenomena.
T Coronae Borealis, or T CrB, is a star system named for its location within the Corona Borealis constellation. (If you're familiar with Bootes or Hercules, look for a small, C-shaped arc between those two arrangements.) T CrB is magnitude +10 on a typical day, making it too dim to see without a telescope. But sometime between now and September, the star duo will reach magnitude +2, making it about as visible to the naked eye as Polaris (the North Star).
That's because T CrB is a recurrent nova: a star system that undergoes a vibrant thermonuclear outburst fairly regularly. Like any other recurrent nova, T CrB consists of a primary star (a white dwarf) and a companion star (in this case, a red giant). As the red giant experiences an increase in temperature and pressure, it becomes unstable and sheds the material that comprises its outer layers. This material forms an accretion disk around the white dwarf, increasing that star's temperature and pressure. Eventually, these conditions grow so dire that the white dwarf's hydrogen-rich disk begins to experience "runaway" nuclear fusion reactions, resulting in a dramatic release of energy. This drawn-out release is so brilliant that it makes the primary star appear more luminous.
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T CrB experiences this cycle once every 80 years or so. The last time it exploded was in 1946; after reaching peak brightness on May 12, it faded rapidly, returning to its original magnitude weeks later. This time, NASA expects T CrB to be visible to the naked eye for "just over a week" before it dims again. After that, T CrB likely won't undergo another nova until after the turn of the century.
Astronomers aren't yet sure when T CrB will experience its vibrant outburst this year. Though the recurrent nova appears to occur on a somewhat regular cycle, stars don't operate on the day-by-day schedules we humans prefer. Scientists are also working to understand the science behind the triggers that launch novas' runaway thermonuclear reactions. Should they ever fully understand this process, nova timing might become easier to predict. For now, we can expect T CrB's nova to occur sometime before this fall, with NASA publishing updates on X.
