INTRODUCTION TO THE LIFE OF A STAR

Accurate

Even though it’s possible the apple thing never happened.

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Thinking intensifies

THE LIFE OF A STAR: STAR NURSERIES

How did this "star stuff" come to exist? The life of stars is a cycle: a star's birth came from a star's death. When it comes to star birth, the star nebulae reigns supreme.

        A Nebula (take a look at pictures, they're some of the most beautiful things in the universe) is a giant cloud of dust and gas. This is the region where new stars are formed. Nebulae live in the space in between stars and between galaxies - called interstellar space (or the interstellar medium) - and are often formed by dying stars and supernovas (NASA). 

        This cloud of particles and gases is mostly made of hydrogen (remember - stars mostly fuse hydrogen!). These appear as patches of light (emission, reflection, or planetary-types) or a dark region against a brighter background (dark-type). This depends on whether "... it reflects light from nearby stars, emits its own light, or re-emits ultraviolet radiation from nearby stars as visible light. If it absorbs light, the nebula appears as a dark patch ..." (The Free Dictionary). 

        There are four main types of nebulae: emission, reflection, dark, and planetary nebulae.

        Emission nebulae are a high-temperature gathering of particles, of which are energized by a nearby ultra-violent-light-emitting star. These particles release radiation as they fall to lower energy states (for more information on electrons moving to energized states and falling back to lower states, read this). This radiation is red because the spectra/wavelength of photons emitted by hydrogen happens to be shifted to the red-end of the visible light spectrum. There are more particles than hydrogen in the nebulae, but hydrogen is the most abundant.

        Next up is the reflection nebulae - which reflect the light of nearby stars. As opposed to emission nebulae, reflection are blue, because "the size of the dust grains causes blue light to be reflected more efficiently than red light, so these reflection nebulae frequently appear blue in color ...." The Reddening Law of Nebula describes that the interstellar dust which forms nebulae affects shorter wavelength light more than longer-wavelengths (CalTech).

        Then there's the "emo" nebulae: dark nebulae. These are, very simply, nebulae which block light from any nearby sources. The lack of light can cause dark nebulae to be very cold and dark (hence their name), and the heat needed for star formation comes in the form of cosmic rays and gravitational energy as dust gathers. Many stars near dark nebulae emit high levels of infrared light (this type is much more intricate then I've explained, but that summary will do for now. If you're interested in learning more, read this).

        Finally, there are planetary nebulae. And these aren't nebulae made of planets. These nebulae are formed when stars (near the ends of their life) throw out a shell of dust. The result is a small, spherical shape, which looks like a planet (hence their name) (METU).

        Nebulae themselves are essentially formed by gas and dust particles clumping together by the attractive force of gravity. The clumps increase in density until they form areas where the density is great enough to form massive stars. These massive stars emit ultraviolet radiation, which ionizes surrounding gas and causes photon emissions, allowing us to see nebulae (like we discussed in the types of nebulae). Universe Today said, "Even though the interstellar gas is very dispersed, the amount of matter adds up over the vast distances between the stars. And eventually, and with enough gravitational attraction between clouds, this matter can coalesce and collapse to forms stars and planetary systems."

        Britannica notes the structure of nebulae in terms of density and chemical composition: "Various regions exhibit an enormous range of densities and temperatures. Within the Galaxy’s spiral arms about half the mass of the interstellar medium is concentrated in molecular clouds, in which hydrogen occurs in molecular form (H2) and temperatures are as low as 10 kelvins (K). These clouds are inconspicuous optically and are detected principally by their carbon monoxide (CO) emissions in the millimeter wavelength range. Their densities in the regions studied by CO emissions are typically 1,000 H2 molecules per cubic cm. At the other extreme is the gas between the clouds, with a temperature of 10 million K and a density of only 0.001 H+ ion per cubic cm." The composition of nebulae also aligns with what we see with the rest of the universe, mostly being made of hydrogen and the rest being other particles, particularly helium (this matches up with the composition of stars!).

        Fun-fact: supernova can create nebulae, but also destroy them. Possibly the most famous nebulae, the "Pillars of Creation," the Eagle Nebula, is hypothesized to have been destroyed by the shockwave of a supernova 6,000 years ago. Since it takes light 7,000 years to travel from that nebulae to the Earth, we won't know for another 1,000 years (Spitzer). If you're wondering how exactly we could know how far nebulae are, check out this article about a new way to measure that distance using the "surface brightness-radius relation", and other distance measurements (such as the parallax measurement).

        Now, why did I just explain the intricacies of nebulae in 900 words when this series is supposed to be about stars? Well, when we talk about the birth of a star (and the death sometimes, too), nebulae become important. Take note of what we've discussed in this article: formation, chemical composition, and density. It'll be important in our next chapter (and nuclear fusion, but when is that not important?).

First -  Chapter 1: An Introduction

Previous -  Chapter 2: Classification

Next -  Chapter 4: A Star is Born

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Looks like I’m getting a new wallpaper

It’s so beautiful ;(

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Sunset in the Kananaskis Valley, Alberta. [2853 x 3566] [oc] - Author: ProjectOxide on reddit

Yeah, Mercury did kinda kick Newton in the balls, didn’t it?

Guess that’s why it’s my favorite planet

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Ah yes, the science

THE LIFE OF A STAR: WHAT GOES AROUND, COMES AROUND

Previously on The Life of a Star, Chapter 6 ...

"But what happens after the shell is fused? We'll get back to that in Chapter 7, where we'll discuss White Dwarfs and Planetary Nebulae."

        After a low-mass star loses its hydrogen core, it becomes a mighty Red Giant - the star contracts and then heats up again, igniting hydrogen shell fusion and swelling the star to epic proportions. That is, until the hydrogen shell and the helium core and all fused up, in which the helium shell will begin to fuse. Remember the last chapter, when I said that these stars don't have enough pressure to fuse the results of the triple-alpha process? Well, I wasn't lying.

        And unlike the end of hydrogen fusion - where low-mass stars have a "2nd life" and continue fusing the elements - this means the end for our star.  Now, due to the build-up of carbon and oxygen in the core (and the lack of enough pressure to fuse these elements), the star has run out of fuel. This cancels out gas pressure, which breaks the hydrostatic equilibrium. Gravity wins the constant battle within the star, and the core collapses.

        The leftover core - tiny and hot - is called a Wolf-Rayet type star and squeezed into a volume one-millionth the size of the original star (Harvard). Now, why does the star stop here? If gravity overpowers the pressure inside the star, why does it not completely collapse into a black hole? Well, that's due to a little thing called electron degeneracy pressure.  Basically, the Pauli exclusion principle states that "no two electrons with the same spin can occupy the same energy state in the same volume." Due to the core collapse, electrons are forced together. The Pauli exclusion principle predicts that these electrons, once having filled a lower energy state, will move to a higher one and begin to speed up. This creates pressure and prevents the core from further collapse. However, at a certain mass, this becomes impossible to maintain. White dwarfs have something called the Chandrasekhar limit, which states that white dwarfs cannot exist if their original mass is over 1.44 times the mass of the Sun. This is due to mass-radius relationships, something we'll discuss in the next chapter.

        One of my favorite things about stars is the fact that they're a cycle - the death of some stars causes the birth of others. White dwarfs do this, too, by creating something we talked about in Chapter 3: Planetary Nebulae.

        The collapsed Wolf-Rayet type star is extremely small, with high density and temperature. Streams of photons/energy/heat - stellar winds - push out the cooler outer layers of the dead star (Astronomy Notes). The core emits UV radiation, which ionizes the hydrogen and causes it to emit light, forming fluorescent and spherical clouds of gas and dust surrounding the hot white dwarf. These are Planetary Nebulae, which can later be clumped by gravity and spun to create a new star. The cycle continues (Uoregon).

        The leftover core, the White Dwarf, is characterized by a low luminosity (due to the lack of new photons, which the star will start to lose by radiation) and a mass under about 1.44 times that of the Sun.

        Due to the intense gravity, the White Dwarf (despite being very large in mass) has a radius comparable to that of the Earth. If you consult the density equation (d=m/v, which basically means that if you enlarge or shrink either the mass or the volume that the density will increase), White Dwarfs have enormous densities. The core is a compact of carbon and oxygen. Because the star is unable to fuse these elements, they kind of just ... sit there. Surrounding this is a shell of helium and a small hydrogen envelope. Some even have a very thin layer of carbon (Britannica).

        However, the White Dwarf isn't the end for the star. There's one more stage for the star to go through before completely "dying": becoming a Black Dwarf.

        After the core is left behind, there Is no fuel left to burn. That means no new energy production. However, the leftover heat from the contraction remains, and the star will begin to cool down. Higher mass White Dwarfs, due to having a smaller radius, radiate this away slower than the low-mass ones. There are two types of cooling: radiative and neutrino. Radiative cooling is simple: as the star gives off light and energy outward, it loses heat. Neutrino cooling is a bit more complex: at extremely hot temperatures, gamma radiation passes electrons, and this reaction creates a pair of neutrinos. Because neutrinos interact very weakly with matter, they escape the White Dwarf quickly, taking energy with them. It's also possible to have a hunch of crystal in the center of a Black Dwarf: "On the other hand, as a white dwarf cools, the ions can arrange themselves in an organized lattice structure when their temperature falls below a certain point. This is called crystallization and will release energy that delays the cooling time up to 30%." (Uoregon).

        The White Dwarf will become a Black Dwarf after it radiates away all of its heat and becomes a cold, dark shell of its former self. Because it's radiated away all of its heat, it emits no light, hence the name. However, according to theoretical physics, there isn't a single Black Dwarf in the universe. Why? Because it should take at least a hundred million, billion years for a White Dwarf to cool down into a Black Dwarf. Because the universe is predicted to be around 13.7 billion years old, there hasn't been enough time for a single White Dwarf to completely cool down (space.com).

        However, there's one last thing that can happen to a White Dwarf. And that's where things in this book will start to get explosive.

        White Dwarfs in binary star systems (where two stars orbit around a center of mass, we'll touch on it more in Additional Topics) can undergo a Classical Nova. These supernovae occur in systems with one White Dwarf and one main-sequence star. If they orbit close enough, the White Dwarf will begin to pull the hydrogen and helium from the other star in what is called an Accretion Disk, what is to say a disk of plasma and particles which spiral inwards due to gravity and feeds one body off of another. The accretion of this plasma onto the surface of the White Dwarf increases pressure and temperature so much that fusion reactions spark and the outburst of energy ejects the shell in a burst of light - a nova (Cosmos).

        This process doesn't end, however. It can repeat itself again and again in what is called a Recurrent Nova. We know the existence of these based on pictures of the same star system with expanding shells, the aftermath of recurrent novae. Because White Dwarfs are the most common star death in the universe, and most stars are in binary or multiple star systems, novae are fairly common (Uoregon).

        Our discussion of novae will be an excellent transition into our next topic: supernovae! This will be the beginning of the end for the High-mass stars we talked about in Chapter 6, and we’ll even talk a little bit more about White Dwarf collisions and how they are related to supernovae, neutron stars, and more!

        From here on out, stars are going to become much more dramatic - and all the cooler (well, not really)!

First -  Chapter 1: An Introduction

Previous -  Chapter 6: The End (But Not Really)

Next - Chapter 8: Why We’re Literally Made of Star-stuff (unpublished)

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How do I constantly forget how beautiful the universe is?

Also, this is true, Jewels DEFINITELY aren’t as bright as stars!

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A Stellar Jewel Box: Open Cluster NGC 290 : Jewels don’t shine this bright – only stars do. Like gems in a jewel box, though, the stars of open cluster NGC 290 glitter in a beautiful display of brightness and color. The photogenic cluster, pictured here, was captured in 2006 by the orbiting Hubble Space Telescope. Open clusters of stars are younger, contain few stars, and contain a much higher fraction of blue stars than do globular clusters of stars. NGC 290 lies about 200,000 light-years distant in a neighboring galaxy called the Small Cloud of Magellan (SMC). The open cluster contains hundreds of stars and spans about 65 light years across. NGC 290 and other open clusters are good laboratories for studying how stars of different masses evolve, since all the open cluster’s stars were born at about the same time. via NASA

Okay I know that I love black holes but buddy why don’t you not come here?

I wonder if falling into a black hole would hurt? If I could choose any way to go out, it’d probably be by black holes. Might as well be killed by the love of my life.

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OJ287 is one of the largest black holes in the known universe. If it were placed at the center of our solar system, its event horizon would swallow nearly everything is our Sun’s sphere of influence. All the planets, the asteroid belt, and (obviously) us. This beast is an estimated 18 billion solar masses and drifts through the cosmos some.

Image credit: Jaime Trosper/FQTQ

Goregous :O

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Comet Swan

Pass the happy! 🌌✨ When you receive this, list 5 things that make you happy and send this to 10 of the last people in your notifications!

1. Being reminded to think of happy things xD

2. Space (literally anything, you guys can tell how obsessed I am)

3. Writing Sci-Fi stories

4. Wearing a sweater on a cold day

5. Having lemon cookies to go with my coffee

Remember to all: especially in times like these, it’s nice to take a minute and think about the things that make you happy. They don’t have to be super obvious and sappy, like your family or your pet dog, they can be the little things that brighten your day. Like stars, and lemon cookies. Think about happy little things.

I’m so hype for this telescope though

They say it might be able to see back to when the first stars were born - how exciting!

Eat shit Hubble telescope

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The launch of the James Webb Telescope – the successor of the Hubble Telescope – has been delayed until 2021 but damn it’s going to be awesome.