Exploding nova T Coronae Borealis may be visible for the first time in 80 years. Here’s how to spot it
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Exploding nova T Coronae Borealis may be visible for the first time in 80 years. Here’s how to spot it

If predictions prove accurate, Australians could witness a star explode in the next few months.

T Coronae Borealis, also known as the “Brilliant Star,” last lit up the sky 80 years ago, and astronomers believe it will soon erupt again.

While scientists disagree on the exact date of the explosion, they agree it will be an exciting event and have pointed their telescopes in its direction.

“You basically have a hydrogen bomb going off on the surface (of the star),” says Tanya Hill, an astronomer and curator at the Melbourne Planetarium.

“I think it’s pretty cool.”

Whether we will be able to see it depends on time.

Here’s what you need to know about this astronomical event, and how to maximise your chances of seeing it in Australia.

How bright will it be?

T Coronae Borealis is a pair of stars in the constellation Corona Borealis that can be seen in the evening sky in Australia from May to late September.

The stars, which are about 3,000 light-years away, are typically too faint to see with the naked eye. At about magnitude +10 — the logarithmic measurement used by astronomers — an amateur telescope is typically needed to spot the pair.

But every 80 years or so, one of the stars lights up in an explosion known as a nova (more on that later), then returns to normal brightness within a few weeks.

When a star explodes, its brightness increases dramatically, eventually reaching magnitude +3 or +2.

According to Dr. Hill, the brightness of the +3 magnitude constellation will be about the same as the brightness of the constellation Delta Crucis, the faintest of the four main constellations stars in the Southern Cross. It is easily visible to the naked eye, even in light polluted areas.

A starry sky with four bright stars in the shape of a cross

When a star explodes, it can be as bright as Delta Crucis, the blue star visible to the right of the Southern Cross. (Getty Images: Haitong Yu)

“It’s very exciting that a star will appear where there hasn’t been one before,” Dr. Hill said.

“But it won’t set the night sky on fire.

“You’ll probably want to go out and do your homework first so you can see what the constellation (Corona Borealis) looks like without the star, and then you’ll be able to see it easily.”

After exploding, T Coronae Borealis may look like a normal star to the naked eye, but astronomers are excited to be able to use high-powered telescopes to observe this stellar explosion for the first time.

“The entire community, space telescopes, everything, will be pointed at this star.”

When will it happen?

Astronomers disagree on whether we will see it in the next few months or whether the explosion will occur in the next few years.

“While it could happen as early as this year, it is more likely to happen between 2025 and 2027.” predicts astronomer Alex Kemp.

The explosion was last observed in early 1946, when it became visible without a telescope. Over the next month, the star gradually faded.

This is the second time in 80 years that this star has been seen with the naked eye from Earth.

According to Dr. Kemp of KU Leuven in Belgium, the next explosion will most likely be seen in 2026 — 80 years after the previous one.

However, there is another group of astronomers who believe that the nova will occur much earlier, potentially between now and September of this year.

This is because of a characteristic dip in brightness that occurs before the star begins to rapidly increase in brightness.

Eighty years is a long time between outbursts, so although a nova was spotted in 1866, we only have detailed information from the 1946 nova. Blaze Star dimmed slightly in May 1945, then rapidly increased in brightness to full brightness in February 1946.

The graph shows a slight drop in brightness in mid-1945, followed by a huge increase in brightness around February 1946.

In 1946, the brightness of the star T Coronae Borealis dropped for several months before it exploded. (Wikimedia: PopePompus/CC BY 4.0 SA)

This time, astronomers observed a dip in brightness in March 2023, suggesting a nova could explode this year, Dr Hill said.

“Of course, a star can decide to do something completely different. That always has to be a caveat.”

While this lack of certainty may seem a bit frustrating for anyone who just wants to see an exploding star, even the rough predictions are exciting for astronomers like her.

“The fact that we can narrow it down to six months when the stars are 3,000 light-years away is, I think, a truly remarkable achievement.”

Is T Coronae Borealis visible from Australia?

The timing of the nova’s appearance will be important in determining whether Australians will be able to see it.

Fortunately, this constellation will be visible from Australia in the evenings for several hours over the next two months.

In the country’s more northerly latitudes, such as Brisbane and Darwin, the constellation will be higher in the sky, but any explosion should be visible across Australia around 20:30-21:00 local time.

A diagram showing the star T ​​Coronae Borealis in the night sky, just west of the North Point.

The star T ​​Coronae Borealis will be visible in Australia’s night sky for the next few months. (Stellarium/ABC)

According to Dr. Hill, the star will remain close to the horizon until the end of September, facing north, between the bright stars Vega and Arcturus.

However, it will disappear over the horizon in October and will not be visible to Australian viewers until next year.

“In late October and November, no one (worldwide) will be able to see it because the sun will be in that part of the sky,” Dr Hill said.

“That would truly be the worst misfortune.”

What is new?

Unlike our Sun, sometimes stars, such as those that make up T Coronae Borealis, they come in pairs.

A large red star surrounded by dust, in one part of which a white explosion occurs

Artist’s impression of the new star shows a red giant and a white dwarf orbiting each other.(NASA: Goddard Space Flight Center)

Dr Kemp explains that new stars consist of a white dwarf – an old star like the Sun that has exhausted its fuel, leaving only its core – and a companion star.

“Even though white dwarfs have a mass similar to a star, they are about the size of Earth, meaning they are incredibly dense and have brutally strong gravity at their surface.”

In the case of T Coronae Borealis, the second star is a red giant, a younger version of a white dwarf, but in a later phase of its life than our Sun.

Normally, stars rotate around each other, bound by gravity.

But sometimes they get too close. The white dwarf pulls material, mostly hydrogen, from its companion, which accumulates on its surface.