IRAS 17163-3907 is a yellow hypergiant star

Yellow hypergiant

Generally speaking, a yellow hypergiant is a massive star with an extended atmosphere, which can be classified as spectral class from late A to K, with a mass of as much as 20-50 solar masses...

 located 13,000 light years from Earth in the constellation of Scorpius, making it the closest-known yellow hypergiant to Earth. The star is embedded in thick shells of expelled gases and dust, and owing to its appearance has been nicknamed by astronomers the "Fried Egg Nebula". Yellow hypergiants are in an extremely active phase of their evolution, undergoing a series of explosive events.

Discovery

The star was discovered in 1976. At the time of discovery, the star was thought to be much less massive and four times farther than it was discovered to be recently. The star was cataloged in 1983. Though the star was known to glow very brightly, it was not known until recently that it belongs to the yellow hypergiant class of stars.

Features

The star has a diameter about 1000 times larger than the Sun, and would almost reach Jupiter

Jupiter

Jupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with mass one-thousandth that of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn,...

's orbit if placed at the center of our solar system. The star resembles a fried egg when viewed from Earth, with its outer shell measuring 6000 astronomical unit

Astronomical unit

An astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance....

s. Hence it is dubbed Fried Egg Nebula. The picture of the star causing it to be dubbed the Fried Egg Nebula was taken in the mid infrared spectrum using red, blue and green filters by the VISIR instrument in the Very Large Telescope

Very Large Telescope

The Very Large Telescope is a telescope operated by the European Southern Observatory on Cerro Paranal in the Atacama Desert of northern Chile. The VLT consists of four individual telescopes, each with a primary mirror 8.2m across, which are generally used separately but can be used together to...

 in the Atacama Desert

Atacama Desert

The Atacama Desert is a plateau in South America, covering a strip of land on the Pacific coast, west of the Andes mountains. It is, according to NASA, National Geographic and many other publications, the driest desert in the world...

 in northern Chile

Chile

Chile ,officially the Republic of Chile , is a country in South America occupying a long, narrow coastal strip between the Andes mountains to the east and the Pacific Ocean to the west. It borders Peru to the north, Bolivia to the northeast, Argentina to the east, and the Drake Passage in the far...

. The filters used in the instrument passed light of frequencies 12,810 nm (corresponding to red), 8590 nm (corresponding to blue) and 11,850 nm (corresponding to green). The star is also 500,000 times brighter than the Sun in the infrared range. If this was visible light, the apparent magnitude

Apparent magnitude

The apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere...

would be approximately −4 to −5. Located 13,000 light years from Earth, it is the closest yellow hypergiant ever found. The photograph pictured is one of the best ever taken of a yellow hypergiant. The star is eventually expected to end its life in a supernova.

Outer shells

The star is characterized by two outer shells. The source of materials for the dusty shells is material ejected from the star during ejection events common in yellow hypergiants. The star ejects materials which equal the mass of our Sun in a few hundred years. The shells are also discovered to be rich in oxygen. The mass of the outer shell alone is 4 times the mass of our Sun. The time period between expulsion of materials causing the first and the second outer shells is estimated to be 400 years. The star also may contain more outer shells but they were not detected by the VISIR instrument as the field of view of the instrument is insufficient.