This end-of-life phase of red giant stars is relatively short, and the celestial structures that form around them are rare, so the Kankan Tobi Nebula is an excellent example of a case study in the evolution of a star.
The luminous nebula IC 2220, known as the Toby Jug because of its resemblance to an English drinking vessel, is a rare astronomical discovery. This return nebula, located about 1,200 light-years away in the direction of the Carina group, is a bipolar cloud of gas and dust created and illuminated by the red giant star at its center. The end-of-life phase of red giants is relatively short, and the structures that form around them are rare, so the Tubi Jug Nebula is an excellent example of a case study in the evolution of a star.
This image, taken by the Gemini South Telescope, showcases the impressive, nearly symmetrical, bipolar structure of the Toby Jug Nebula and its luminous stellar heart. These properties are unique to red giants that change from aging stars to planetary nebulae and therefore provide astronomers with valuable insights into the evolution of low- to medium-mass stars nearing the end of their lives and also into the cosmic structures they create.
The star swells to 400 times its original size
At the heart of the Toby Pitcher Nebula is its creator, the red giant star HR3126. Red giants form when a star exhausts its core's supply of hydrogen. Without the outward fusion force, the star begins to contract. This raises the core temperature and causes the star to swell up to 400 times its original size. That HR3126 is much younger than our Sun - only 50 million years old compared to the age of the Sun which is 4.6 billion years. However, its mass is five times greater. Its mass allowed the star to exhaust its hydrogen supply and become a red giant much faster than the Sun.
As HR 3126 inflated, its atmosphere expanded and it began to shed its outer layers. The ejected stellar material flowed into the surrounding area, creating an impressive structure of gas and dust that reflects the light from the central star. Detailed studies of the Kankan Tobi Nebula in Light AA revealed that nitrogen dioxide (silica) is most likely the compound that reflects the light of HR3126.
Astronomers hypothesize that bipolar structures similar to those seen in the Tobii Jug Nebula are the result of an interaction between the central red giant and a companion binary star. In previous observations, however, no such companion was found for HR3126. Instead, the astronomers observed a very compact disk of material around the central star. This finding suggests that it is possible that a companion to Belantry (the second star in a binary star system) that was previously torn apart into the disk, and this may have caused the formation of the surrounding nebula.
The sun will also become a red giant
In about five billion years, when our Sun has exhausted its supply of hydrogen, it too will become a red giant and eventually develop into a planetary nebula. In the very distant future, all that will be left of our solar system will be a vigorous nebula like the Tobey Jug Nebula with the slowly cooling Sun at its center.
- The term "planetary nebula" is misleading: they are not related to planets. The first to use the name was probably the astronomer William Herschel in the seventies of the 19th century, who noted their rounded, planet-like shape as seen in observations through early telescopes.
Red giants - summary
- Red giants are stars whose mass is only between about 0.3 and about 8 solar masses. More massive stars transform into other types of stars at the end of their lives.
- During their evolution, red giants balance the nuclear fusion process by expanding outward. This causes their surface to cool.
- Red giants spend a long time (hundreds of millions to several billions of years) in the "red giant branch".
- More massive stars undergo faster nuclear fusion and evolve more quickly, and therefore do not reach the red giant stage. Stars with a mass of 8-10 solar masses become supernova at the end of their lives instead of red giants. Stars above 10 solar masses transform straight into other types such as Wolf-ray stars.
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