This year could be a once in a lifetime opportunity to see a nova

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Astronomers are running regular checks on a star system that currently requires a telescope to see because they expect it will soon be bright enough to view with the naked eye.
According to one prediction, this could happen any time from now until September, although there’s reason to think we might need to wait another year.
One of the wonders of astronomy is the way, very occasionally, stars suddenly brighten spectacularly.
When the star in question was previously too faint to see it can seem as if a new star has appeared, and before the invention of the telescope these became known as novae from “De nova stella”, Latin for new star.
Advertisement AdvertisementTwo and a half thousand light-years away in the direction of the constellation Coronae Borealis, such a brightening is anticipated.
The event will occur because what is known as T Coronae Borealis (T CrB) is not one star, but two.
Although binaries are the most common star arrangement, this pair are a dangerous combination of red giant and white dwarf, both modestly more massive than the Sun.
Over time the white dwarf’s intense gravity is pulling material off the red giant, creating an accretion disk a little like one circling a black hole.
When some of this material gets close enough to the white dwarf it becomes heated to the point where fusion ignites, leading to a surge in brightness.
Most such brightenings are like those of an ordinary variable star.
For example, in 2016, the T CrB system roughly tripled in brightness.
However, since it was still barely visible in binoculars, few people cared.
In 1866 and 1946, on the other hand, the surge was something quite different, increasing several thousand-fold so that it was easily visible with the naked eye.
It’s an event like this that astronomers are eagerly awaiting.
Advertisement AdvertisementSome white dwarfs that are pulling material off their companions do so erratically, brightening only once in our observations.
Others, known as recurrent novae, keep to a regular schedule.
You may not have heard of them, because most recurrent novae are so far away that even when they brighten we can’t see them unaided, which makes T CrB is almost unique.
At its peak in 1866 and 1946 it was almost as bright as Polaris, exceeding all but a few hundred stars.
Only one other recurrent nova is visible with the naked eye at its brightest, and that one barely so.
The gap between T CrB’s two well-studied events was a little under 80 years.
If that were to be repeated precisely, we’d expect the next event in late 2025.
You can’t set your watch by a recurrent nova, unfortunately, so a few years either side would not be surprising.
Last year however, Professor Bradley Schaefer of Louisiana State University noted that prior to the 1946 event T CrB underwent some notable dimming, and has now done something very similar.
Based on the timing from dip to peak, Schaefer predicted we should expect a show between February and September this year.
Schaefer also did some impressive sleuthing to find evidence of what appear to be previous sightings in 1787 and 1217.
Although either previous report could be of something else that happened to be in the same part of the sky, Schaefer makes a strong case that these were most likely previous eruptions of T CrB, in which case we can be more confident to expect it soon.
Full sequence of how T Coronae Borealis might look as it goes from the system’s light being dominated by the red giant to the white dwarf’s explosion.
Image credit: NASA/Conceptual Image Lab/Goddard Space Flight CenterNevertheless, Schaefer’s predictions on timing came with a dose of uncertainty, which seems to have been lost in some recent reports announcing we should be spotting the next peak by September.
T CrB is at a declination of 25 north, which means its visible for most of the year from Europe and North America.
The exception is around September-November, when the Sun is annoyingly close to it in the sky, so we’d really rather it didn’t time its explosion then.
Southern hemisphere observers have a considerably narrower viewing window.
When the explosion comes, NASA predicts T CrB should be visible to the naked eye for a few days, followed by a week or so where binoculars should still be sufficient.
To find it, look between the very bright stars Vega and Arcturus, a little closer to the latter, and about seven degrees from Alphecca, which should be of similar or slightly greater brightness.

Astronomers anticipate that a star system that is currently only visible through a telescope will soon become bright enough to be seen with the unaided eye, so they are monitoring it on a regular basis. One prediction states that this could occur between now and September, but there’s a chance we’ll have to wait another year.

Occasionally, stars can brighten dramatically all of a sudden, which is one of astronomy’s wonders. Prior to the development of telescopes, these stars were referred to as novae from the Latin phrase “De nova stella,” which means new star, when the star in question was too faint to see.

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Such a brightening is expected to occur 2.5 thousand light-years away in the direction of the constellation Coronae Borealis.

T Coronae Borealis (T CrB) is actually two stars, not just one, which is why the event will happen. Despite being the most frequent star configuration, this pair of slightly more massive than the Sun red giant and white dwarf stars is dangerous. An accretion disk resembling the one encircling a black hole is being created over time as a result of material being pulled off the red giant by the white dwarf’s strong gravity.

A burst of brightness results from the heating of some of this material to the point where fusion ignites when it approaches the white dwarf closely enough. The majority of these brightenings resemble those of a typical variable star. One example is the roughly threefold brightness increase of the T CrB system in 2016. Few people seemed to care, though, as it was still hardly visible through binoculars.

This was not the case in 1866 and 1946, when the surge increased thousands of times to the point where it was clearly visible to the unaided eye. Astronomers are excitedly anticipating an occurrence similar to this.

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Certain white dwarfs that are absorbing material from their companions behave erratically, brightening just once in our observations. Some, referred to as recurrent novae, adhere to a set timetable. Though most recurrent novae are so far away that we cannot see them without assistance, T CrB is nearly unique in that regard. This is why you may not have heard of them. It surpassed all stars except for a few hundred at its brightest in 1866 and 1946, when it was nearly as bright as Polaris. When a recurrent nova reaches its peak brightness, only one other one is visible to the unaided eye, and even then, it’s rather faint.

A little less than 80 years elapsed between T CrB’s two thoroughly investigated events. Assuming that exact repetition holds true, the next event is anticipated to occur in late 2025. Unfortunately, you cannot time a recurrent nova, so a few years either way would not be shocking.

But Louisiana State University Professor Bradley Schaefer pointed out last year that T CrB had experienced some significant dimming before the 1946 incident, and it has since done something extremely similar. Schaefer estimated that we should anticipate a show sometime in February or September of this year, based on the timing of the peak to dip. Schaefer additionally performed some amazing detective work to uncover proof of what seem to be earlier sightings in 1787 and 1217.

Schaefer makes a compelling case that these were most likely earlier eruptions of T CrB, in which case we can be more certain to expect it soon—even though either of the earlier reports could have been of something else that happened to be in the same part of the sky.

Whole sequence of possible visuals for T Coronae Borealis from the red giant-dominated light in the system to the explosion of the white dwarf. Image courtesy of Goddard Space Flight Center/Conceptual Image Lab/NASA.

Though some recent reports seem to have lost sight of the fact that we should be able to spot the next peak by September, Schaefer’s timing predictions came with a degree of uncertainty.

T CrB can be seen from Europe and North America for the majority of the year due to its declination of 25 degrees north. We would really prefer that it not time its explosion to occur between September and November, when the Sun is obtrusively close to it in the sky. Those in the southern hemisphere have a much smaller viewing window.

In the event of the explosion, NASA estimates that T CrB will be visible for a few days without the aid of binoculars, and then for about a week after that. It can be located by comparing the brightness of Arcturus and Vega, which are both very bright stars, and by looking about seven degrees away from Alphecca, which is supposed to be similarly or slightly brighter.

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