Black aurora appears in the sky over Alaska

An extremely rare black aurora borealis creates an E-shaped swirl of light in this recent image taken over Alaska.

A strange E-shaped aurora was recently photographed in the skies above Alaska. The unusual light show is caused by a rare black aurora, also known as an antiaurora, which pushes charged particles from the Sun out of Earth's atmosphere and into space, Live Science reported on December 4.

Aurora hunter Todd Salat spotted the unusual aurora on November 22 at a location in south-central Alaska around 4 a.m. local time. The glowing E appeared seemingly out of nowhere and lasted for several minutes while morphing into several shapes, all of which contained dark patches not found in most auroras.

An aurora borealis creates an E floating in the Alaskan sky. (Photo: Todd Salat).

"It came from the northwest and I just went wow. It looked like an E. Within minutes, it transformed and looked like some kind of insect with legs in mid-air," Salat said.

Antiauroras are unusual phenomena that produce dark circular patches that look as if they've been bitten into pieces. As their name suggests, antiauroras are essentially the opposite of auroras. They prevent the gas from releasing its energy in the form of light. The result is dark rings, curls, or globs that are interrupted by bright colors, according to the European Space Agency (ESA).

Auroras are triggered when energetic particles from the Sun, mainly electrons, pass through the Earth's magnetic field or magnetosphere and superheated gas molecules in the upper atmosphere. The excited molecules release energy as light, which combines to form soft, undulating bands across the sky. Their colors vary depending on the excited element and their location in the atmosphere. Auroras usually occur near the poles, where the Earth's magnetic field is weakest. But they are especially prominent and widespread now because of increased solar activity during solar maximum, the peak of the 11-year cycle.

However, antiauroras disrupt the formation of auroras by stripping the gas of its charged particles. " A black aurora is not really an aurora. It's a lack of aurora activity where electrons are pulled out of the ionosphere ," says Göran Marklund, a plasma physicist at the Royal Institute of Technology in Stockholm.

Antiauroras were first identified in the late 1990s. But in 2001, scientists discovered how they work when NASA's four Cluster satellites flew above them. The activity revealed tiny gaps in the upper atmosphere where electrons are ejected back into space. A 2015 study using more than a decade of data from the Cluster mission found that these gaps form when the aurora loses plasma, creating holes in the upper atmosphere.

Anti-auroras can occur during the Northern and Southern Lights, and typically last only about 10 to 20 minutes. Experts predict that aurora activity will continue to be strong for the next few years.