Sometime during the summer or early fall of 2024, astronomers and the public alike will be treated to a sight that may be a once-in-a-lifetime event that happens once every 80 years. T Corona Borealis, also known as “The Blaze Star or T CrB,” ordinarily a 10th magnitude star, will be 1000 times brighter than its normal state and become a nova, not to be confused with a supernova. For what may be several hours to a couple of days, T CrB will increase from magnitude 10.2 to somewhere around magnitude 2, making it visible to the naked eye, and for a couple of days, probably the brightest star in Corona Borealis outshining Alphecca before a slower demise into its quiescent state. It may remain visible to the naked eye for several days, but probably not much longer.
T CrB is a binary system with a white dwarf and a cool M-type star, and the pair is known as a “cataclysmic variable.” As they revolve around the barycenter (center of gravity), the white dwarf is close enough to its larger companion to pull hydrogen off the M-type star as a result of the dwarf’s gravitational pull, which is over 100,000 times the gravitational pull of the earth. Imagine taking a mass equivalent to the sun and compressing it into the size of the earth. A tablespoon of the white dwarf may weigh in at several tons, which explains its tremendous gravitational pull.
During its cycle of roughly 80 years, the white dwarf continues to pull hydrogen from its companion. Eventually, the dwarf’s gravitational pull increases pressure and temperature on the surface of the white dwarf, resulting in a runaway thermonuclear explosion fusing hydrogen into helium, resulting in the forecasted nova. A nova transforms a star from its normal state to maximum brightness in a few hours to a few days. Its return to an obscure quiescent state will normally take several months, and the process will start over again as the world awaits the next T CrB nova in another 80 years.
A nova does not destroy either the progenitor dwarf or its companion. The fusion only occurs on the outer layers of the dwarf which is different from a supernova where temperature and pressure force carbon fusion in the dwarf’s core resulting in a cataclysmic explosion totally destroying the white dwarf. It is probably not a healthy thing for its companion either. However, since it is 2700 light years distant, please don’t station me any closer than 10 light years.
The latest information indicates an eruption around July 3, 2024, but it could happen anytime within the next several months. Let’s hope it happens while Corona Borealis is still high in the evening sky and can be enjoyed by millions. Below is an image of Corona Borealis and the position of T CrB. For you astro photographers, this is also a chance to image an asteroid called Pallas which is near T CrB. It will appear as a cigar shape in a long exposure.
Additional information can be found at the below NASA website:
NASA, Global Astronomers Await Rare Nova Explosion – NASA
~ Stephen Barr
DAS Trustee and Outreach Coordinator