Once-in-a-Lifetime Viewing Opportunity: Nova Explosion, ‘New’ Star in Northern Crown

The upcoming nova outburst of T Coronae Borealis, visible without telescopes, promises a spectacular sky show in 2024, as it brightens to match the North Star in luminosity, a phenomenon resulting from a cosmic dance between a white dwarf and a red giant.

A star system, located 3,000 light-years away from Earth, is predicted to become visible to the unaided eye soon. This could be a once-in-a-lifetime viewing opportunity as the nova outburst only occurs about every 80 years. T Coronae Borealis, or T CrB, last exploded in 1946 and astronomers believe it will do so again between February and September 2024.

The star system, normally magnitude +10, which is far too dim to see with the unaided eye, will jump to magnitude +2 during the event. This will be of similar brightness to the North Star, Polaris.

Once its brightness peaks, it should be visible to the unaided eye for several days and just over a week with binoculars before it dims again, possibly for another 80 years.

As we wait for the nova, become familiar with the constellation Corona Borealis, or the Northern Crown — a small, semicircular arc near Bootes and Hercules. This is where the outburst will appear as a “new” bright star.

This recurring nova is only one of five in our galaxy. This happens because T CrB is a binary system with a white dwarf and red giant. The stars are close enough that as the red giant becomes unstable from its increasing temperature and pressure and begins ejecting its outer layers, the white dwarf collects that matter onto its surface. The shallow dense atmosphere of the white dwarf eventually heats enough to cause a runaway thermonuclear reaction – which produces the nova we see from Earth.

Red Giants

When a main sequence star less than eight times the Sun’s mass runs out of hydrogen in its core, it starts to collapse because the energy produced by fusion is the only force fighting gravity’s tendency to pull matter together. But squeezing the core also increases its temperature and pressure, so much so that its helium starts to fuse into carbon, which also releases energy. Hydrogen fusion begins moving into the star’s outer layers, causing them to expand. The result is a red giant, which would appear more orange than red.

Eventually, the red giant becomes unstable and begins pulsating, periodically expanding and ejecting some of its atmosphere. Eventually, all of its outer layers blow away, creating an expanding cloud of dust and gas called a planetary nebula. The Sun will become a red giant in about 5 billion years.

White Dwarfs

After a red giant has shed all its atmosphere, only the core remains. Scientists call this kind of stellar remnant a white dwarf. A white dwarf is usually Earth-size but hundreds of thousands of times more massive. A teaspoon of its material would weigh more than a pickup truck. A white dwarf produces no new heat of its own, so it gradually cools over billions of years.

Despite the name, white dwarfs can emit visible light that ranges from blue white to red. Scientists sometimes find that white dwarfs are surrounded by dusty disks of material, debris, and even planets – leftovers from the original star’s red giant phase. In about 10 billion years, after its time as a red giant, the Sun will become a white dwarf.

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