Blaze Star Nova Could Flash Brighter Than Polaris, Then Fade in Days

Astronomers say a star system nicknamed the Blaze Star is very likely to erupt soon, but none can say exactly when. According to Space.com, skywatchers have waited about two years for the nova, and when it comes it will make a faint, normally invisible star briefly outshine Polaris.

The system, T Coronae Borealis (T CrB), last erupted in 1946. Two researchers told Space.com the eruption could come within a few years, but they stressed that the exact timing is unknown.

What the Blaze Star is and why it erupts

T CrB is not a single star. It is a binary system made up of a dense white dwarf and a bloated red giant. Over a period of around 80 years, the white dwarf's gravity pulls material off its companion. When the gas that has piled up reaches a critical threshold, a nova explosion follows, and the system flares to 1,000 times its usual brightness. It then settles down and starts the cycle again.

Why no one can name a date

Bradley Schaefer of the Louisiana State University Department of Physics and Astronomy told Space.com that experts are confident of the outcome. In his words, T CrB "will erupt sometime soon." The difficulty, he said, is that astronomers cannot measure precisely how fast gas is falling onto the white dwarf. They also lack an accurate figure for the trigger mass, the amount of gas that sets off the explosion.

Elizabeth Hays, lab chief at NASA's Astroparticle Physics Laboratory at Goddard, said the glare of the red giant swamps the dimmer white dwarf, which makes detailed observation hard. She added that there is no way to precisely measure the temperature and pressure of matter near the white dwarf's surface. She compared nova forecasting to predicting the weather: conditions can be right while the timing of the storm stays uncertain.

Astronomers have tried to forecast the eruption by comparing a recent change in the system's light with a similar change before the 1946 event. Hays told Space.com that earlier dimming and brightening episodes caused excitement but did not turn into the main event. She said she would be a little surprised if the eruption had not happened by 2030, which would be 84 years after the last one, though she could not offer a guaranteed prediction.

What the eruption will look like

According to Space.com, the system normally sits at magnitude +10, beyond what the naked eye can see. In the nova it is expected to jump to magnitude +1.7. That would look as if a star brighter than Polaris had suddenly appeared in the sky.

The rise will be fast. Schaefer said that once the runaway nuclear process starts, it will peak in less than a day. Hays said the glow should drop below naked-eye visibility in dark places within a couple of days and become too faint for binoculars in about a week. Radio, X-ray and gamma-ray light from the eruption could be detectable for months or even years.

What this means for stargazers

Do not expect a visible warning. Hays said there will be none in ordinary light before the eruption reaches Earth, although an early flash could show up in X-rays. Amateur astronomers around the world are watching the system about every minute or two, Schaefer said. When it has brightened by around one magnitude, alerts should spread worldwide within minutes. Observatories and telescopes will then start observing programs they have prepared in advance.

For anyone hoping to see it, the window is short. Because the naked-eye glow lasts only a couple of days, people who want to catch it will need to act quickly once an alert goes out.

Space.com said T CrB sits near Epsilon Coronae Borealis, a star of magnitude +4.28, in the constellation Corona Borealis. In November it can be found in the early evening, with Hercules and Bootes on either side. For viewers in the U.S., it dips below the horizon a few hours after sunset and reappears in the northeastern sky before dawn.

Around Prague, based on reporting by Space.com

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