Most astronomers think the “Blaze Star” is about to do its thing -- any day now! A star invisible to the naked eye could become conspicuous enough to attract attention worldwide. But it will not last long.
All you have to do to witness the phenomenon is gaze upward, but you must do so during a short window of opportunity. The star is expected to flare for only a few days, adding a new gem to the Northern Crown. Corona Borealis is high overhead in our late summer skies, not far from ruddy colored Arcturus, one of the brightest stars currently visible. In autumn the lovely “C” shaped constellation drifts to the west, but it remains visible in the evening sky until late in the year.
That is good because if predictions are correct, T Coronae Borealis (T CrB for short) could flare yet this year. It is being intently monitored through telescopes worldwide, and initial signs of an imminent eruption have been detected. When it does so, T CrB could briefly rival the constellation’s only prominent star, Alphecca, which matches in brightness the stars of the Big Dipper.
The word Nova can be translated to “New Star,” but of course T CrB (as are all novas) is really a star too faint to be seen without a telescope, which rapidly increases in brightness and becomes a new addition to its resident constellation. “New Star” discoveries are sprinkled throughout the history of observational astronomy since ancient times. Only with the advent of modern telescopes have astronomers come to understand their true nature.
Do not confuse a nova with a supernova. The far more dramatic--and rare--supernova is truly an exploding star, a massive supergiant undergoing a cataclysmic dying act. Instead, novas are of more modest size and mass. Astronomers have found that all observed novas are in fact binary or two-star systems where the components whirl around each other in very close proximity. Most are too distant to be seen with the naked eye until they erupt. One component is an ordinary star, often a giant, while the second (the one that erupts) is a collapsed dwarf not much larger than earth.
White dwarfs are considered “dead weight” among the stellar population. Their component matter is highly compressed and is no longer capable of supporting the thermonuclear activity that sustains stars. But they still exert enormous gravitational force. Because of the close proximity of one star to the other, only half the distance from the earth to the sun in the case of T CrB, there is a complex gravitational interaction in which the tiny star essentially feeds off material drawn from its much larger and more active companion.
In the case of the dwarf in the T CrB system, as matter drawn from the stellar companion piles up, a brief period of runaway thermonuclear activity is awakened, resulting in a stellar pressure cooker that essentially blows its top. Energy and matter are spilled out, producing a brief period of significant brightening. As excess matter is dispersed, relieving the pent up pressure, the star settles back into obscurity over a period of days to several weeks depending on the system’s dynamics. Then in some (but not all) cases, the whole cycle begins anew.
T CrB is one of those reoccurring novas, one of few that are not one-act events, and in fact there are well-documented flares from the past. One happened in 1866, and another in 1946. There is less conclusive evidence for flares in 1787, and maybe as far back as 1217. Nothing stands out in scant observational records predating 1217.
What do these appearance have in common? The nova always emerged at the same position among the stars of the constellation Corona Borealis, rose to a brightness about matching its brightest star (Alphecca), and flared at roughly 79-80 year intervals.
When the 1946 apparition confirmed that T CrB was indeed a recurring nova, research intensified to find out why. Astronomers using big telescopes, and the latest research instruments could now study T CrB over decades as it hovered near minimum brightness, looking for clues to explain why one star in the system brightens so dramatically every eight decades. All of this is happening as they anxiously anticipate an expected replay in 2024.
Its stature as the most well-known and studied of recurrent novas contributes to its nickname, “Blaze Star.” It gives rise to a confident prediction that an additional jewel in the celestial crown could be coming soon. T CrB has done this before, and in a consistent way.
Remarkably, there is precursor evidence when the star is about to blow. It comes from observations of T CrB attained prior to its last eruption. What astronomers have been seeing over the past decade is the same pattern of flickering and slight spasms in its behavior documented when that 1946 eruption was eminent.
While professional astronomers provide the scientific expertise and insight to predict that T CrB will “blaze" (and soon), they cannot nail down exactly when. That is where their amateur astronomer counterparts come in. Amateurs around the world, including right here in West Michigan, are keeping a continuous eye on T CrB. It is important to catch the earliest possible stage of its outburst for maximum scientific return.
Many stars in the sky exhibit erratic behavior, and in 1911 the American Association of Variable Star Observers was formed to study them. One notable member is GRAAA’s Gary Ross, who regularly keeps predawn vigils at Veen Observatory, estimating the brightness of a select list of known variable stars during all sorts of seasonal conditions. Professionals depend on their amateur counterparts to provide scientifically useful data to establish light curves for a long list of restless stars using little more than sky charts, modest telescopes, the human eye, and lots of patience.
The information gathered by the AAVSO over more than a century, continuing unabated today, is of critical scientific value. The organization is among the best of a number of examples of a fruitful research partnership between career astronomers and their backyard counterparts.
The collaboration is illustrated by what happened in 1946, when AAVSO members placed T CrB near the top of their list of stars to keep a close eye on. In February of that year, their diligence paid off. T CrB was caught early in a brightness rise, when maximum scientific return could be realized. Could that happen again in coming weeks or months? If an amateur somewhere, even here in West Michigan, happens to be the first to sound the alarm to the professionals that T CrB is “blazing,” they would attain instant notoriety.
Observatories throughout the world are already on “alert” mode. Even those with the really big telescopes and tight research priorities, and those orbiting high above (think Hubble) are in “drop everything” mode when word comes that T CrB is on the rise. We know from previous episodes that it will happen fast and will not last long, maybe only a few days. The word that the “Blaze Star” has returned will likely be spread worldwide with far greater efficiency than just about any previous transient astronomical event.
So, be sure you know where Corona Borealis is in the night sky, and take a glance to that location whenever we have a clear night. The alert that T CrB is once again “blazing” could come any day now.
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