A bizarre "zombie star" is expected to come back from the dead and light up the night sky in the coming months—but scientists don't know exactly when.
The star, named T Coronae Borealis or T CrB, is located around 3,000 light years away from our solar system, and is usually much too dim to be seen with the naked eye.
Any time soon, however, the star is expected to become brighter than the North Star in the night sky, exploding in a giant "nova" for the first time since 1946.
What is the "zombie star"?
Elizabeth Hays, chief of the Astroparticle Physics Laboratory at NASA Goddard, told ABC7 in a live interview that this "zombie star" explodes in a blaze of light every 80 years or so, due to it sucking the life out of a stellar companion.
"This is a star that is dead—it's no longer burning like our sun. It's called a white dwarf, it's gotten all packed down and is just kind of sitting there, radiating," she said.
"It has a companion—this is a red giant star, and it's kind of feeding it. This is where it gets its zombie nickname, it's feeding on this material, and it's built up this layer on the outside. We're excited because it's going to blow this layer off, sometime in the near future."
White dwarves are the tiny, dense remains of stars after they have used up all their fuel and collapsed under their own gravity, while red giants are stars in their death throes, having expanded out much larger than their usual size as they run out of hydrogen.
Sometimes called the "Blaze Star," the Earth-sized white dwarf T CrB is in a binary star system with a red giant, and slowly strips away the outer layers of its companion over many years, getting larger and hotter as it does. Eventually, it heats up enough that it explodes in a "nova," which doesn't destroy the star—unlike a supernova—but makes it shine incredibly brightly.
During the nova, the star shines much brighter than usual. Normally, T CrB has a magnitude of +10, much too dim to be seen with the naked eye. When the star explodes, it suddenly becomes as bright as magnitude +2, and is visible shining as a new star in the night sky. Smaller positive and larger negative magnitudes represent brighter objects: Venus has a magnitude of around -4, and the full moon hits a magnitude of -13.
The star stays visible for around a week, before fading back into nothingness for the best part of the next century.
After the nova, the white dwarf returns to its normal size, and starts the process all over again. T CrB tends to go nova once every 80 or so years—having last exploded in 1946, and before that, in 1866. There are only five known recurring novae like this one in our galaxy.
When will the "zombie star" explode?
"We very rarely know ahead of time when these are going to happen, there are only a handful of stars that we know do this every so many years. This one went off last time 80 years ago," Hays said.
T CrB was initially forecast to explode in September this year, due to the star's behavior appearing similar to how it acted just before the last eruption. However, the star is holding on for now.
"It's really hard to predict down to the day when this is going to happen. We know within a few years, and we wanted to make sure to get the word out," Hays said. "There's a really big uncertainty on that, and it could be sometime within the next couple of years."
How to see the "zombie star"
When it eventually does go nova, the new star will be situated in the constellation Corona Borealis or the Northern Crown, which is a horseshoe-shaped curve of stars located to the west of the Hercules constellation. The best view of the star will be from the Northern Hemisphere, far away from the light pollution of cities or street lights.
Having passed the initial September 2024 due date, it's still unclear when T CrB will eventually explode.
"Recurrent novae are unpredictable and contrarian," Koji Mukai, an astrophysics researcher at NASA Goddard, said in a statement earlier this year. "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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