How big is Ant Nebula? | Scale of the Universe

The Ant Nebula is a cloud of glowing gas thrown off by a dying star, in the southern constellation Norma. Seen through telescopes on the ground, it looks like the head and body of an ant. NASA estimates that it is about 1.6 light-years, or 15 trillion kilometers, long, where a light-year is the distance light travels in one year. Its distance from Earth is uncertain, and so is its true length.

Size

On the sky, the whole nebula is roughly 1 arcminute long, where an arcminute is 1/60 of a degree. Its brightest part is a pair of bubble-shaped lobes, one on each side of the central star, which form the ant's body. They reach about 15 arcseconds, a quarter of an arcminute, from the star in each direction, so together they span about half the nebula's full length. Fainter columns and streaks of gas extend farther out.

Turning that angle into a length needs the nebula's distance, which is hard to measure. Published estimates range from about 3,300 to 8,800 light-years. At those distances, 1 arcminute spans about 1 to 2.6 light-years, and NASA's estimate of 1.6 light-years falls within that range.

Size comparisons

The Boomerang Nebula, another hourglass-shaped cloud around a dying star, is about 2 light-years long. By NASA's estimate, the Ant Nebula is about four-fifths of that length.
NASA's estimate is about half a parsec, a unit of distance equal to about 3.26 light-years.
The nebula is a little more than a third as long as the distance from the Sun to Proxima Centauri, 4.2 light-years.
If the Ant Nebula were shrunk to the height of a person 1.7 meters (5 feet 7 inches) tall, the whole orbit of Neptune would be about 1 millimeter across.

Four outflows

A detailed 2004 study using the Hubble Space Telescope and large telescopes on the ground found at least four separate streams of gas flowing out from the star. They are the bright bubble-shaped lobes, two narrow columns, a cone of faint rays, and a very dim, flattened ring. The team named that ring the chakram, after an ancient disk-shaped throwing weapon from India.

How fast each part is moving suggests that the star threw them off in a series of eruptions. The faint rays came first, at least about 1,500 years ago, and the bright lobes came last. Gas streaming out along the nebula's long axis reaches about 500 kilometers per second. At that speed, it could cross the distance from Earth to the Moon in about 13 minutes.

A puzzling star

Astronomers still do not agree on what kind of object the Ant Nebula is. It has been classed as a planetary nebula, the glowing shell of gas a dying star leaves behind, and also as a type of double star. A flat disk of dust hides the central star, and that star may be a pair of stars.

A companion star close to the dying star could explain the nebula's shape, by pulling the outflowing gas into two lobes. Magnetic fields twisted up by the spinning star are another possible explanation.

In 2018, astronomers using the European Space Agency's Herschel Space Observatory found that hydrogen gas in the core amplifies some of its own light, the same process a laser uses. The astronomer D. H. Menzel, who discovered the nebula in 1922, had been one of the first scientists to suggest that such amplification could happen. The nebula is also called Menzel 3 after him.