NGC 6826 – The Blinking Planetary Nebula

NGC 6826 is 2,200 light-years away and boasts one of the brightest stars ever found to have created a planetary nebula. The nebula doesn’t actually blink. The name comes from the effect of viewing it through the eyepiece of a telescope using averted vision.

Opposing each other astride the central region of the nebula, you can find fast low-ionization emission regions (FLIERS). These are blobs of gas moving at high speed away from the center.

This planetary nebula has a relatively odd structure. It has a spherical outer halo, but the central region is more elliptical in shape. One theory is that interaction with a small companion star caused the inner ellipse. Because that star is no longer present, scientists think it may have collided with the white-dwarf star in the center.

The name “planetary nebula” is a misnomer. Planetary nebulas have nothing to do with planets. Astronomers in the 18th century thought these objects were planets, but now we know differently. When a star with 80% to 800% of the sun’s mass begins to run out of hydrogen fuel, it starts fusing helium into heavier elements such as carbon and oxygen. As it does this, the additional energy from those stepped-up levels of fusion cause it to expel its outer layers.

Ultimately, the star expels all its outer layers from its core, leaving the core exposed in sort of a cosmic burp. Once all the helium is burned up, fusion ceases in the core and what is left is a giant, dense ball of carbon (about the size of the earth, but with the mass of the sun)—a diamond in the sky called a “white dwarf.” That core no longer produces new energy, but it’s still extremely hot and gives off copious amounts of radiation, ionizing the gas it expelled earlier. That cloud of gas then eventually dissipates. But before it does, the ionized gas gives off light we can record here on earth with our cameras (if the star is close enough to us).