The planetary nebula in the scattered star cluster M37 has been expanding for about 75 000 years, many times longer than these short-lived objects normally exist.
Towards the end of their evolution, small and intermediate-sized stars become swollen red giants and then shed their outer shells. A cloud of material will fly away from the white dwarf that remains in the centre and will emit a bright light to form a planetary nebula. These objects have nothing to do with planets and are so called because of their outward resemblance to planetary systems. They look spectacular and some pictures of planetary nebulae have become famous astrophotographic masterpieces.
The planetary nebula IPHASX J055226.2+323724 is the subject of a new article published in The Astrophysical Journal Letters. The main reason for its interest lies in its rarity: the nebula is located in the scattered cluster M37 (NGC 2099), a small group of about 1,500 stars in the constellation of Ascendant. Several thousand planetary nebulae are known to exist in our Galaxy, but only a few are associated with scattered clusters.
When Quentin Parker and his colleagues at Hong Kong University analysed these spectra, they found J055226.2+323724 to be exceptionally long-lived. Clouds that form planetary nebulae tend to disperse quickly and last from five thousand to 25 thousand years. However, this nebula has been expanding slowly for about 70 thousand years, according to astronomers, reaching an exceptional magnitude of 3.2 parsecs - more than 10 light years.
The nebula's relatively peaceful surroundings have revealed the size of the original star, which gained about 2.8 solar masses before shedding its outer shell. Scientists hope that their work will make it possible to estimate more accurately the ratio of the initial mass to the final mass of stars which transform from red giants to white dwarfs. It will be our Sun someday, and understanding its mechanisms will determine how well we understand the future of our Solar System.
