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

A star system 3,000 light-years away, known as T Coronae Borealis, is expected to become visible to the naked eye between February and September 2024, due to a nova outburst. This rare event, occurring roughly every 80 years, will brighten the star from magnitude +10 to +2, making it as luminous as the North Star. The phenomenon is a result of a thermonuclear reaction within a binary star system, involving a white dwarf and a red giant, and represents a unique opportunity for skywatchers to witness a once-in-a-lifetime celestial event. Credit: NASA/Conceptual Image Lab/Goddard Space Flight Center

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.

A red giant star and white dwarf orbit each other in this animation of a nova. The red giant is a large sphere in shades of red, orange, and white, with the side facing the white dwarf the lightest shades. The white dwarf is hidden in a bright glow of white and yellows, which represent an accretion disk around the star. A stream of material, shown as a diffuse cloud of red, flows from the red giant to the white dwarf. The animation opens with the red giant on the right side of the screen, co-orbiting the white dwarf. When the red giant moves behind the white dwarf, a nova explosion on the white dwarf ignites, filling the screen with white light. After the light fades, a ball of ejected nova material is shown in pale orange. A small white spot remains after the fog of material clears, indicating that the white dwarf has survived the explosion. Credit: NASA’s Goddard Space Flight Center

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.

A conceptual image of how to find Hercules and his mighty globular clusters in the sky created using a planetarium software. Look up after sunset during summer months to find Hercules! Scan between Vega and Arcturus, near the distinct pattern of Corona Borealis. Once you find its stars, use binoculars or a telescope to hunt down the globular clusters M13 and M92. If you enjoy your views of these globular clusters, you’re in luck – look for another great globular, M3, in the nearby constellation of Boötes. Credit: NASA

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.

This illustration depicts a red giant star, like Betelgeuse or Antares. Credit: NASA’s Goddard Space Flight Center/Chris Smith (KBRwyle)

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.

In this illustration, an asteroid (bottom left) breaks apart under the powerful gravity of LSPM J0207+3331, the oldest, coldest white dwarf known to be surrounded by a ring of dusty debris. Credit: NASA’s Goddard Space Flight Center/Scott Wiessinger

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.