If the calculations are correct, anyone who often looks at the night sky will soon see something special in the constellation Corona Borealis (or the Northern Crown). Astronomers calculated that a ‘new bright star’ will temporarily be visible here with the naked eye. The ‘star’ appears for a few days as brightly in the sky as the North Star Polaris, NASA wrote. After that, ‘the star’ will disappear into darkness again for decades.
What is going on here? Why does a ‘new star’ temporarily appear in the sky? And why is this special?
The apparent new star is actually a flash in an explosion in a system of two stars.
About 3,000 light-years from Earth, a red giant and a white dwarf orbit each other in a star system T Coronae Borealis (T CrB). A white dwarf is a small, compact remnant of a burned-out Sun-like star that has blown away its outer layers, leaving only the compact core that gradually cools. Before a Sun-like star becomes a white dwarf, it swells to hundreds of times its original size. In that phase a star is called a red giant. While in T CrB the large red giant and the small white dwarf orbit each other closely, gas flows from the red giant to the white dwarf.
Normally, T CrB is much too faint to see with the naked eye. T CrB has a brightness of magnitude +10, a measure astronomers use to describe the brightness of a celestial body. The higher the magnitude, the fainter. For comparison, the full moon has a magnitude of about -13.
Flash
But when the white dwarf has collected enough gas, its temperature rises due to the accumulation of matter. Ultimately, a thermonuclear explosion occurs on the white dwarf: a nova (Latin for new). The flash caused by the explosion is bright enough to be seen with the naked eye. From Earth, the flash will appear as a star in the sky with a magnitude of +2 (about the same magnitude as the North Star).
The nova of T CrB is a recurring phenomenon. The last time T CrB exploded was in 1946. There are also indications that this star system exploded in the years 1217, 1787, 1866. This year the explosion will take place sometime between now and September, astronomers from Louisiana State University estimate. Most star systems dim slightly before the nova occurs. This has also been measured at T CrB since March last year.
The bright flash should be visible with the naked eye for several days and with binoculars for just over a week.
Enthusiasts should look at the arc-shaped constellation Corona Borealis (a difficult constellation to find). That constellation is located between the constellations Boötes and Hercules.
T CrB is one of five recurring novas in the Milky Way, but most star systems explode once every few millennia or are so far away that the flash cannot be seen with the naked eye from Earth.
The explosion at T CrB “could be a once-in-a-lifetime opportunity” to see a nova with the naked eye, according to NASA. For most of us, an opportunity like this only comes along once.