The night sky might be on the brink of gaining a brand-new star for a few weeks.
T Coronae Borealis, also known as the "Blaze Star" or T CrB, is a binary star system located about 3,000 light-years from Earth. It is due to explode in a spectacular manner any day now.
Usually too dim to see with the naked eye, T CrB is expected to shine brighter than the North Star Polaris temporarily during its explosion, known as a "nova."
T CrB is one of only five known recurring novae in our galaxy. It is comprised of a white dwarf and a red giant orbiting each other in a binary system, with the white dwarf undergoing a strange regular nova explosion every 80 years or so—the last of which was observed in 1946. Researchers have noted that the star's recent behavior is strikingly similar to the period leading up to its last eruption, suggesting that another outburst is imminent before September this year.
How to spot T CrB
To locate T CrB, skywatchers should look towards the Northern Hemisphere's summer sky. T CrB is located in the constellation Corona Borealis, a distinct horseshoe-shaped pattern of stars situated between the Hercules and Boötes constellations. To find it, draw a straight line between the two brightest stars in the Northern Hemisphere—Arcturus and Vega—and then look between them to locate the arc-shaped Corona Borealis. You can pinpoint the reddish-colored Arcturus by following the handle of the Big Dipper constellation.
The explosion, once it occurs, will be visible for less than a week. Observers should look up at the night sky shortly after sunset for the best chance to see the nova. The precise timing is unpredictable, but astronomers are confident that the event will take place by September 2024. Hopeful stargazers will get the best view of the star far away from light pollution.
Normally, T CrB has a magnitude of +10, making it invisible to the naked eye. Magnitudes in astronomy are measured backward, with a lower number or higher negative number meaning an object is brighter—the full moon has a magnitude of -13, while the stars Sirius and Arcturus have magnitudes of -1.5 and -0.05, respectively. If an object has a magnitude of +6 or less, it will be visible to the naked eye. T CrB is expected to reach a magnitude of around +2 at its brightest, shining about as strongly as Polaris, the 48th-brightest star in our skies.
"It's a once-in-a-lifetime event that will create a lot of new astronomers out there, giving young people a cosmic event they can observe for themselves, ask their own questions, and collect their own data," Rebekah Hounsell, an assistant research scientist specializing in nova events at NASA's Goddard Space Flight Center in Greenbelt, Maryland, said in a NASA statement. "It'll fuel the next generation of scientists."
T CrB goes nova every 80 or so years due to a strange property of the white dwarf-red giant binary system. The white dwarf, which is the remnant core of a star that has collapsed, slowly steals the hydrogen gases from the atmosphere of the red giant, getting larger and hotter, until eventually it explodes in a thermonuclear explosion known as a nova. These novae are less powerful than supernovae, which completely destroy a star at the end of its life.
After this explosion, the process starts again from scratch. This is why T CrB explodes around once every 80 years. The star system has been behaving in a very similar way to how it was just before the last explosion, making astronomers pretty sure a nova will occur before September this year.
"There are a few recurrent novae with very short cycles, but typically, we don't often see a repeated outburst in a human lifetime, and rarely one so relatively close to our own system," Hounsell said. "It's incredibly exciting to have this front-row seat."
Astronomers hope to study the upcoming nova in detail using a variety of telescopes around the globe, including NASA's Fermi Gamma-ray Space Telescope and NASA's James Webb Space Telescope.
"Typically, nova events are so faint and far away that it's hard to clearly identify where the erupting energy is concentrated," Elizabeth Hays, chief of the Astroparticle Physics Laboratory at NASA Goddard, said in the statement. "This one will be really close, with a lot of eyes on it, studying the various wavelengths and hopefully giving us data to start unlocking the structure and specific processes involved. We can't wait to get the full picture of what's going on."
There is a small possibility that the nova doesn't occur before September at all, however.
"Recurrent novae are unpredictable and contrarian," Koji Mukai, an astrophysics researcher at NASA Goddard, said in the statement. "When you think there can't possibly be a reason they follow a certain set pattern, they do—and as soon as you start to rely on them repeating the same pattern, they deviate from it completely. We'll see how T CrB behaves."
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