Your gateway to endless inspiration
Protostar - Blog Posts
Dusty regions like these are often the places where stars form. In fact, there are two notable stars—V633 (top left of center) and V376 Cassiopeiae (bottom left)—in this image from the Hubble Space Telescope.
These stars have yet to start fusing hydrogen in their cores, and continue to accumulate mass. As they do this, much of the material they ingest gets shot back out as energetic jets. For these young stars, these jets can contain as much mass as Earth has.
Credit: ESA/Hubble & NASA; Gilles Chapdelaine.
ALT TEXT: A protostar in the process of forming. Above the center, at 11 o’clock, is a bright, white star. To the bottom right of this star is a large cavity, surrounded by dark brown gas and dust. This surrounding dust fills the image with the exception of another small cavity toward the bottom left. At about 4 o’clock in this cavity, there is another bright, white star. Smaller white stars are spread throughout the image.
Take-aways:
This is a baby star imaged in stunning detail
Stars are born violently - there's hot gas striking the other gas and dust around it, making these amazing patterns
This particular baby star will one day be like the Sun 💖
THE LIFE OF A STAR: A STAR IS BORN
All you need to make a star is dust, gravity, and time.
Stars form from nebulae's molecular clouds - which are "clumpy, with regions containing a wide range of densities—from a few tens of molecules (mostly hydrogen) per cubic centimetre to more than one million." Stars are only made in the densest regions - cloud cores - and larger cloud cores create more massive stars. Stars also form in associations in these cores. Cores with higher percentages of mass used only for star formation will have more stars bound together, while lower percentages will have stars drifting apart.
These cloud cores rotate very slowly and its mass is highly concentrated in its center - while also spinning and flattening into a disk (Britannica: Star Formation). This concentration is caused by gravity. As the mass of the clump increases - it is very cold and close to absolute zero, which increases density and causes atoms to bind together into molecules such as CO and H2 - it's gravity increases and at a certain point, it will collapse under it (Uoregon). The pressure, spinning, and compressing create kinetic energy which continues to heat the gas and increase density.
Finally, there's the last ingredient: time. The process of these molecular clouds clumping, spinning, concentrating, and collapsing takes quite a while. From start (the cloud core-forming) to finish (the birth of a main-sequence star) - the average time is at about a cool 10 million years (yikes). Of course, this differs with density and mass, but this is the time for a typical solar-type star (StackExchange).
The next stage in a star's life - after the nebulae - is a protostar.
After one clump separates from the cloud core, it develops its own identity and gravity, and loose gas falls into the center. This releases more kinetic energy and heats the gas, as well as the pressure. This clump will collapse under gravity, grow in density in the center. and trap infrared light inside (causing it to become opaque) (Uoregon).
A protostar looks like a normal star - emitting light - but it's just a baby star. Protostars' cores are not hot enough to undergo nuclear fusion and the light they emit (instead of coming from the release of photons after the fusion of atoms) comes from the heat of the protostar as it contracts under gravity. By the time this is formed, the spinning and gravity have flattened the dust and gas into a protostellar disk. The rotation also generates a magnetic field - which generates a protostellar wind - and sometimes even streams or jets of gas into space (LCO).
This protostar, which is not much bigger than Jupiter, continues to grow by taking in more dust and gas. The light emitted absorbs dust and is remitted over and over again, resulting in a shift to longer wavelengths and causing the protostar to emit infrared light. The growth of the star is halted as jets of material stream out from the poles - the cause of this has been unidentified, although theories suggest that strong magnetic fields and rotation "act as whirling rotary blades to fling out the nearby gas." (Britannica: Star Formation)
The "infall" of stars stops by pressure, and the protostar becomes more stable. Eventually, the temperature grows so hot (a few million kelvins) that thermonuclear fusion begins - usually in the form of deuterium (a heavier form of hydrogen), lithium, beryllium, and boron - which radiates light and energy. This starts the pre-main-sequence star phase - also called T Tauri stars - which includes lots of surface activity in the form of flares, stellar winds, opaque circumstellar disks, and stellar jets. In this phase, the star begins to contract - it can lose almost 50% of its mass - and the more massive the star, the shorter the T Tauri phase (Uoregon).
Eventually, when the star's core becomes hot enough (in some cases, we'll touch on this later), it will begin to fuse hydrogen. This will produce "an outward pressure that balances with the inward pressure caused by gravity, stabilizing the star." (Space.com)
This will either create an average-sized star or a massive star.
Nuclear fusion marks the beginning of the main sequence star. A star is born.
But it isn't always.
Now that we've discussed the transition from nebulae to main-sequence star, we'll be talking about what happens when hydrogen fusion doesn't occur. Those are called Brown Dwarfs.
Brown Dwarfs are those stars that form much too small - less than 0.08 the sun's mass - and as a result, they cannot undergo hydrogen fusion (Space.com).
Brown Dwarfs, are, bigger than planets. They are roughly between the size of Jupiter and our sun. Like protostars, brown dwarfs start by fusing deuterium, and their cores contract and increase in heat as they do so. Brown Dwarfs, however, cannot contract to the size required to heat the core enough to fuse hydrogen. Their cores are dense enough to hold themselves up with pressure. They are much colder compared to main-sequence stars, ranging from 2,800 K to 300 K (the sun is 5,800 K). They are called "Brown Dwarfs" because objects below 2,200 often cold too much and develop minerals in their atmosphere, turning a brown-red color (Britannica: Brown Dwarf).
Once Brown Dwarfs have fused all of their deuterium, they glow infrared, and the force of gravity overcomes internal pressure (the internal force of nuclear fusion used to keep it stable) as it slowly collapses. They eventually cool down and become dark balls of gas - black dwarfs (NRAO).
Now that we've covered how stars form - and what happens in certain cases where they are not - we'll be moving to the actual life of a star. Before we talk about the end of a star's life (arguably - my favorite part) we need to discuss main-sequence, cycles, mass, heat, pressure, structure, and more. This is to understand how a star died the way it did.
Because - when it comes to the menu of star death - stars have a few options to choose from.
First - Chapter 1: An Introduction
Previous - Chapter 3: Star Nurseries
Next - Chapter 5: A Day in the Life
WANT MORE? GET YOUR HEAD STUCK IN THE STARS AT MY BLOG!
Life cycle of our Sun, from beginning to end~