Blazing Star Event First Recorded in a Medieval Manuscript to Return

An astronomical anomaly that was first observed and recorded more than eight centuries ago is about to make a return visit to Earth’s night skies. Sometime between now and September, a double star collectively known as T Coronae Borealis will flare up and make its presence known all over the planet, glowing with a low-level intensity that matches that of the North Star, Polaris. The newly visible star may be observable for up to a week before it dims and once again disappears into the firmament.

Despite being located approximately 3,000 light years from Earth, this variable stellar body (it has been nicknamed ‘the Blaze Star’) will be visible from many locations, emerging like a beacon in a previously empty section of sky inside the hard-to-spot constellation Corona Borealis, not far from the more visible constellations of Boötes and Hercules. This phenomenon will be the result of a violent interaction between the two stars that comprise this double-star system, which will generate a light burst so intense that it will radiate across the Milky Way galaxy undimmed for the equivalent of several Earth days.

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A ‘Wonderful Sign’ Will Be Seen

The first recorded display of T Coronae Borealis (T CrB) occurred in the year 1217, when a German monk known as Abbott Burchard described the appearance of a brightening point of light inside the borders of Corona Borealis.

"A wonderful sign was seen," he noted in a medieval manuscript, in the form of an object that "shone with great light" for "many days."

While it was once believed the Abbott was describing a comet, this theory is no longer considered tenable.

"This event cannot be a report of a comet, because Burchard used the term for a star ('stella') and not for a comet, and because Burchard had the omen being very positive, with such being impossible for comets that are universally the worst of omens,” wrote Bradley Schaefer, a Professor Emeritus in the astronomy department at Louisiana State University, in an article published in 2023 in the Journal for the History of Astronomy. “The reported event is just as expected for a prior eruption of T CrB, and all other possibilities are strongly rejected, so the case for the 1217 eruption of T CrB is strong."

An even better documented sighting of the flaring interstellar object took place in 1787, when British astronomer and Church of England minister Francis Wollaston reported the sudden appearance of a star in precisely the location where T CrB is now known to be. He observed the new star four times through telescopes in late December of that year, before the object vanished completely into the inky black sky.

The last two appearances of the object took place in 1866 and 1946 respectively, indicating that the phenomenon that causes T CrB to flare brightly recurs every 80 years or so. Astronomers are now able to track changes in T CrB despite its great distance, and this is how they know the object will be flaring brightly again soon, just slightly short of its normal 80-year marker.

Estimates are the starburst from T Coronae Borealis will reach a magnitude of +2 during the upcoming event, which puts it in the medium-bright category. If it follows its past pattern it will remain visible for several consecutive nights, peaking in intensity at the mid-point of its appearance before gradually fading away.

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T Coronae Borealis (T CrB) is situated near the Hercules constellation, and will become the the most visible star in the sky for about a week. (BBC/YouTube Screenshot)

A Once—or Maybe Twice—in a Lifetime Event

In astronomical terms, what is happening with T CrB is known as a nova event.

The star is actually a double or binary star system, consisting of a dense white dwarf and a larger red giant that rotate around each other in unsteady orbits. Every eight decades or so when the stars are close the force of the white dwarf’s gravity generates the nova event, which mimics the astounding violence of a star exploding into a supernova at the end of its lifespan.

"The stars are close enough that as the red giant becomes unstable from its increasing temperature and pressure and begins ejecting its outer layers, the white dwarf collects that matter onto its surface," the US space agency NASA explained in a statement about the phenomenon.

"The shallow dense atmosphere of the white dwarf eventually heats enough to cause a runaway thermonuclear [fusion] reaction— which produces the nova we see from Earth." NASA

The atmosphere produced on the white dwarf’s surface is comprised of hydrogen, which is so explosive that when it reaches a critical temperature a chain reaction of simultaneous destruction and creation is set off, converting hydrogen into helium and releasing almost imaginable amounts of excess energy in the process. This is the same chemical reaction that powers the Sun and all other active stars, although the heat and light produced by the periodic nuclear fusion of the T CrB binary star is far more intense.

Before T CrB explodes into view, it always follows the same developmental sequence. In the pre-eruption cycle it jumps in brightness first, before experiencing a sudden dip in intensity. When this happens, its appearance is imminent.

"The T CrB Pre-eruption Dip has already started in March/April of this year," the American Association of Variable Star Observers (AAVSO) explained in a 2023 press release. "If the Dip in 2023 is similar in timing to that in 1945, then the primary eruption should occur roughly 1.1±0.3 years later, or in 2024.4±0.3."

If the timing of these starburst events holds in the future, the next appearance of T CrB will occur just past the turn of the next century. A small percentage of people alive today should be around for that appearance as well, giving them a unique opportunity to experience a rare and unique astronomical phenomenon twice in their lifetimes.

So get ready to experience this rare event soon!

Top image: Conceptual image of T Coronae Borealis outburst predicted for late 2024. Source: NASA’s Goddard Space Flight Center

By Nathan Falde