Image Credit: Gemini Observatory/AURA
Kronberger 61 or Kn 61 (nicknamed the Soccer Ball) is a faint, almost perfectly round, planetary nebula located about 13,000 light-years away in the northern constellation of Cygnus (the Swan). It was only discovered in January 2011 by the amateur astronomer Matthias Kronberger.
Despite their name, planetary nebulae have nothing to do with planets. The name of planetary nebulae arose because of the visual similarity between some round planetary nebulae, like Kronberger 61, and the planets Uranus and Neptune when viewed through early telescopes.
When a star with a mass up to eight times that of the Sun runs out of fuel at the end of its life, it blows off its outer shells and begins to lose mass. This allows the hot, inner core of the star (collapsing from a red giant to a white dwarf) to radiate strongly, causing this outward-moving cocoon of gas to glow brightly as a planetary nebula.
Over the next several thousand years, the nebula will gradually disperse into space, and then the star will cool and fade away for billions of years as a white dwarf. Our own Sun is expected to undergo a similar fate, but fortunately this will not occur until some 5 billion years from now.
However, very few planetary nebulae are this spherical. They’re usually elongated, have complex shapes and often look like butterflies.
This image of Kronberger 61 is showing the ionized shell of expelled gas resembling a soccer ball, hence its nickname. The light of the nebula is primarily due to emission from twice-ionized oxygen, and its central star can be seen as the slightly bluer star very close to the center of the nebula.
How planetary nebulae can form such complex structures is a hot debate among astronomers. One camp suspects a dying star requires the gravitational and/or magnetic “interference” of a celestial partner—perhaps another nearby star or very large planet—to create a planetary nebula’s complex shapes. Another camp thinks that the complex shapes, including butterfly-like clouds, can form without the help of nearby companions.