How big is Stingray Nebula? | Scale of the Universe

The Stingray Nebula is a planetary nebula: a shell of glowing gas thrown off by a dying star and lit up by the hot star left behind. NASA described it in 1998 as the youngest planetary nebula known. By the most recent estimate, it is about 1.1 trillion kilometers across. Its distance from Earth is uncertain, so published estimates of its width range from about 0.56 to 1.5 trillion kilometers.

Size

Ordinary stars like the Sun are expected to end their lives by making planetary nebulae. From Earth the Stingray looks tiny: its bright inner ring is only about 1.6 arcseconds long, where an arcsecond is 1/3,600 of a degree. No details of it could be seen until the Hubble Space Telescope observed it.

Turning that angle into a true size needs the distance, and estimates of the distance range from about 2,700 to 19,000 light-years. A light-year is the distance light travels in a year, about 9.46 trillion kilometers. A 1998 Hubble study used 18,000 light-years, which made the nebula about 1.5 trillion kilometers across.

Later studies put the star closer. A 2014 study found about 5,200 light-years and a width of about 0.56 trillion kilometers. A 2017 study adopted about 8,200 light-years, and its model of the glowing gas is about 1.1 trillion kilometers, or 0.12 light-years, across.

Size comparisons

At 1.1 trillion kilometers, the nebula is about eight times as wide as the distance from the Sun to the farthest point of Sedna's orbit.
It is about 120 times as wide as the orbit of Neptune, the outermost planet.
If Neptune's orbit were shrunk to the width of a basketball, the nebula would be about 30 meters (100 feet) across.
It is about 43 light-days wide: light takes about 43 days to cross it.

A nebula that switched on

Between 1971 and 2002, the nebula's central star, called SAO 244567, heated up from less than 22,000 to about 60,000 degrees Celsius. The gas around it began to glow as a planetary nebula, probably in the early 1980s. Its shape, which resembles a stingray, gave the nebula its name.

Hubble's images show a bright ring of gas around the star, with bubbles of gas blown out above and below the ring. A second star, a companion to the central one, lies within the nebula.

Fading fast

Hubble images taken 20 years apart, in 1996 and 2016, show the nebula fading and changing shape. The light given off by its oxygen dropped by a factor of nearly 1,000. The wavy edges that suggested a stingray have almost disappeared, and the once-bright inner ring seems to be shrinking as it fades.

The fading reflects changes in the central star, which has been cooling and giving off less of the radiation that makes the gas glow. One suggestion is that its earlier heating came from a brief flash of helium fusion, the joining of helium nuclei that releases energy, in a shell around the star's core. In 2020, astronomers estimated that at its rate of fading, the nebula would barely be detectable in 20 or 30 years.