Question

In your own words (imagine trying to explain this to your family members), explain the life stages of a low mass star (use the Sun as an example)? Now explain the life stages of a high mass star. How are massive stars (mass > 8 solar masses) like onions? Why are cepheid variable stars important to astronomers? How did Cepheids variables help Edwin Hubble discover the universe was larger than we thought? Google the term Ring Nebula. What is the Ring Nebula? What surprises you about it? Google the term Butterfly Nebula. What is the Butterfly Nebula? What surprises you about it when you compare it to the Ring Nebula? Where does the carbon in your body comes from? Where does the iron in your body come from? Why did Carl Sagan say: "We are made of star stuff."?

Answer 1

Small stars like our sun will fuse most of its hydrogen into helium which will form an inert core. Gravity starts to compress the star so the core temperature reaches 100million Kelvin and its outer hydrogen layers starts to expand. This makes the star much larger than its original size and its outer layer stays cool so it appear as a big red star called Red Giant. It becomes very luminescent during this phase and the radiation pressure shreds off most of the stellar atmosphere into space over time - this gas and dust from star form a cloud around the star, shaped by the star's radiation pressure - this cloud is known as the Planetary nebula. At the center of it remains of the star form a small but very dense star called white dwarf, consisting mostly of electron degenerate matter. This is the last stage of the star where it spends a long 12Billion years before becoming a black dwarf

Bigger stars, having mass more than 8 times of sun will first evolve into a Red Super-giant by the same causes as before. But later in this stage the radiation pressure is not enough to fight off the gravity which tries to implode the star. Due to this instability the star explodes with massive energy, approximately 10⁴⁴ joules. The core of the remains either is a dense sphere of neutron - called a neutron star or a Black Hole - a singularity in space-time with gravity so immense that even light cannot escape from it. Black hole singularities are covered with a plane of event horizon, past it no object can ever return back. Not even light, that's why its black.

Massive star's core undergo many stages of nuclear fission - making the star filled with many different atomic nuclei. According to their density they start to form layers. Heavy elements in the core like iron and silicon. And lighter layers in the outside layers, like Helium and Hydrogen. This layered structure looks like an Onion with many shell like layers.

Cepheid Variable stars are stars with a predictable periodic pattern of luminosity. Its maximum luminosity is directly proportional to its period of brightness. Accurately knowing a stars absolute luminosity helps accurately measure its distance.

Before Hubble's time people thought that all stars were in the milky way and Andromeda galaxy was a part of it. But Hubble discovered that this was not true, Andromeda is a distance of 1,500,000 light-years from our milky way. And he measured several other galaxy's distance, increasing the presumed size of the universe.

Ring nebula is a planetary nebula created by a past red giant star.

Butterfly nebula is also a Planetary nebula.

Butterfly nebula has this bipolar shape where the ring nebula is circular. spherical shape is natural out of the radial pressure but it it interesting how the central star forms a bipolar gas cloud with nothing in the equatorial plane for the butterfly nebula.

In red giants helium atoms fuse together to make large amount of carbon atoms. ⁴He → ¹²C

Carbon and helium together makes oxygen. ¹²C + ⁴He → ¹⁶O

All elements are formed within a star, the universe started with only hydrogen. all other elements are formed by stars in their core. In our body carbon and oxygen are the two most abundant material, this all came to be within a star and ending up on Earth during the creation of solar system. That's why Sagan's quote is relevant.