The monster star, known to astronomers as IRAS 17163-3907, has a diameter about a thousand times bigger than our Sun. At a distance of about 13 000 light-years from Earth, it is the closest yellow hypergiant found to date and new observations show it shines some 500 000 times more brightly than the Sun.
"This object was known to glow brightly in the infrared but, surprisingly, nobody had identified it as a yellow hypergiant before," said Eric Lagadec (European Southern Observatory), who led the team that produced the new images.
The observations of the star and the discovery of its surrounding shells were made using the VISIR infrared camera on the Very Large Telescope (VLT). The pictures are the first of this object to clearly show the material around it and reveal two almost perfectly spherical shells.
If the Fried Egg Nebula were placed in the centre of the Solar System the Earth would lie deep within the star itself and the planet Jupiter would be orbiting just above its surface. The much larger surrounding nebula would engulf all the planets and dwarf planets and even some of the comets that orbit far beyond the orbit of Neptune. The outer shell has a radius of 10 000 times the distance from the Earth to the Sun.
Yellow hypergiants are in an extremely active phase of their evolution, undergoing a series of explosive events — this star has ejected four times the mass of the Sun in just a few hundred years. The material flung out during these bursts has formed the extensive double shell of the nebula, which is made of dust rich in silicates and mixed with gas.
This activity also shows that the star is likely to soon die an explosive death — it will be one of the next supernova explosions in our galaxy. Supernovas provide much-needed chemicals to the surrounding interstellar environment and the resulting shock waves can kick start the formation of new stars.
The VLT mid-IR instrument, VISIR, captured this image of the Fried Egg Nebula through three mid-infrared filters that are here coloured blue, green and red.