The article, “Hubble Space Telescope Spots ‘Cosmic Calabash,’” explains that the new image from Hubble captured a once-normal star going through a rapid transformation from a red giant to a planetary nebula. When this happens, it blows its outer layers of gas and dust out into the surrounding space. This phase of a stars evolution happens so quickly that it is extremely rare for astronomers to capture. The object is known as the Calabash Nebula located in the constellation of Puppis, about 5,000 light years away from us. It will likely develop into a fully bipolar planetary nebula over the next 1,000 years.
Our objective was to be able to describe how stars evolve and die. This article relates to the objective because it discusses a star that was captured transitioning from a red giant into a planetary nebula. We know that this star must have been a low-mass star because only low-mass stars produce planetary nebulas. The textbook states that a low-mass star spends most of its life generating energy by fusing hydrogen in its core. When core hydrogen is exhausted, the core begins to shrink while the star as a whole expands to become a red giant, with hydrogen shell fusion around an inert helium core. When the core becomes hot enough, a helium flash initiates helium fusion in the core, which fuses helium into carbon. The core shrinks again when helium core fusion ceases, while both helium and hydrogen fusion occur in shells around the inert carbon core and cause the outer layers to expand once more. A low-mass star like the Sun never gets hot enough to fuse carbon in its core, because degeneracy pressure stops the gravitational collapse of the core. The lecture tutorial, “Stellar Evolution,” states that a low-mass star, less than about eight times the mass of our Sun, eventually ejects its outer layers to produce a planetary nebula just like what is happening in this article. The stellar core remaining in the middle of this planetary nebula is called a white dwarf.
I liked this objective a lot because I did not know much about stars and the phases that they go through throughout their life cycle. I had always thought that every star took the same course, but I now know that stars can take different courses based on many different elements. I thought that this article related well to the objective and it gave a good brief explanation about what a planetary nebula is and why it is so rare for astronomers to capture.