Solar Stars
Types of Stars
Star Evolution
HR Diagrams
Birth of a Star
100
This is the sun's primary source of energy.
What is Nuclear fusion?
Nuclear fusion is the process by which multiple atomic nuclei join together to form a heavier nucleus, releasing a significant amount of energy. It occurs under extreme conditions of high temperature and pressure, like those found in the cores of stars, including the Sun. During fusion in the Sun, hydrogen nuclei combine to form helium, which provides the energy that powers the Sun and subsequently supports life on Earth.
100
Stars with this mass live longer
What is low mass stars?
High mass stars burn up their fuel at a faster rate compared to low mass stars, so they live for a shorter amount of time.
100
This is the final element a star can possibly fuse.
What is iron?
Nuclear fusion stops at iron because attempting to fuse elements beyond iron-56 would actually use up more energy than it releases due to iron having the lowest mass per nuclear particle. This creates an energy deficiency. Once a star can no longer keep up nuclear fusion, the star collapses in on itself until it supernovas and releases energy.
100
This is the type of energy transport mechanism that takes over convection during the course of stage three on the HR diagram. (Image from Pearson text)
What is radiative diffusion?
As gravity continues to contract the protostar, its core increasingly heats and begins to fuse hydrogen into helium. The core begins to stabilize, and the primary form of energy transport switches from convection to radiation.
100
This is the temperature that stars are able to form in.
What is cooler temperatures?
The temperature needs to be low enough for the gas particles to come together and become a dense core.
200
This causes the sun to appear yellow from Earth.
What is the scattering of light from earth's atmosphere?
The Sun appears yellow from Earth because its white light, which contains all colors, is scattered by Earth's atmosphere. The shorter wavelengths of light (like blue and violet) are scattered more than the longer wavelengths (like red, orange, and yellow), making the Sun appear mostly yellow to us.
200
This is the labeled region on an H-R diagram that the majority of the stars fall into.
What is Main Sequence?
A main sequence star is any star that has a hot, dense core which fuses hydrogen into helium to produce energy. This means that the majority of stars fall into this category.
200
A star enters this stage when nuclear fusion begins and it is balanced.
What is the main sequence?
The main sequence stage is the longest phase in a star’s life cycle where the star fuses hydrogen into helium for energy. While in this stage, the mass of a star does not change much, however, as helium accumulates the rate of fusion and temperature accumulates. A star remains in the main sequence until it depletes all the hydrogen in its core.
200
The main sequence appears as a line of stars with increasing temperature and luminosity from the right. Below the main sequence is this type of star, labeled D, with a high surface temperature and a low luminosity.
What is a white dwarf?
A white dwarf has a high temperature and low luminosity because it is the compressed core of a low-mass star supported by electron degeneracy pressure. The core heated as it burned heavier elements and contracted. When the star’s outer layers are blown off, a small, hot white dwarf is born.
200
This is the large cloud of dust and gas that stars are formed in.
What is molecular clouds?
Stars are formed in these clouds of dust and gas that are called molecular clouds.
300
This is the surface layer of the sun.
What is the photosphere?
The photosphere is the outermost layer of the Sun's atmosphere and is the part from which visible light is emitted, making it the layer we see when looking at the Sun. The photosphere is marked by sunspots, which are cooler, darker regions caused by disturbances in the Sun's magnetic field.
300
I have exhausted all of my nuclear fuel and am supported by electron degeneracy pressure. I have a very low luminosity, am small in size and made almost completely of carbon and oxygen.
What is white dwarf star?
White dwarfs are the core left behind after a dying star has exhausted its nuclear fuel and expelled its outer layers. Its low luminosity is due to the emission of residual thermal energy.
300
This is the upper limit of mass a white dwarf star can have.
What is the Chandrasekhar limit?
As a star increases in mass, its electrons move faster. When a star’s mass approaches 1.4 solar masses, the Chandrasekhar limit, the electrons are nearly moving at the speed of light, which means the star cannot grow any larger because nothing can surpass the speed of light.
300
This is the name for the violent end a star found in area C will undergo.(https://www.atnf.csiro.au/outreach/education/senior/cosmicengine/stars_hrdiagram.html)
What is a supernova?
The objects found in region C are classified as supergiants, high-mass stars which will eventually fuse silicon into iron in their cores. A star that runs out of fuel in this region will begin to collapse due to the lack of a sufficient outward force from the star. The outer shells bounce off the inner shell and explode into space as a supernova.
300
These are specific regions in a spiral galaxy with the most star formation.
What are its arms?
The arms of a spiral galaxy are density waves containing the highest amount of gas and number of molecular clouds in the galaxy. Therefore, this is the region with the most star formation.
400
This is the temperature of the sun's core.
What is 15 million degrees Celsius or 27 million degrees Fahrenheit?
The core of the sun is where nuclear fusion occurs and is therefore the hottest layer of the sun. The immense pressure gravity exerts downward is balanced by the radiation pressure which results in an equilibrium. Nuclear fusion can only occur in circumstances where there are sufficient levels of pressure and heat.
400
This is rapidly rotating neutron stars.
What is pulsars?
A pulsar is a highly magnetized rotating neutron star that emits beams of electromagnetic radiation out of its magnetic poles.
400
This stage occurs in a low to medium mass star when it exhausts its fuel and leaves behind a hot and dense core surrounded by a glowing shell of gas.
What is the planetary nebula stage?
The planetary nebula stage is near the end of a low to medium mass star’s life and occurs after the red giant phase. The star expels its outer layers into space which forms a glowing shell of gas around a hot core; this core eventually becomes a white dwarf.
400
The following image is an HR diagram of low-mass stars at varying stages of their death. This is the name of the region indicated by the yellow grouping of stars. (https://en.wikipedia.org/wiki/Horizontal_branch)
What is the horizontal branch?
As a star exhausts its hydrogen in its core, the core contracts. Gravitational pressure heats the core until the star undergoes a helium flash. The star will stabilize in this region, called the horizontal branch, where it will fuse helium into carbon for a period of time.
400
This is the minimum mass a star can have to still be considered a star.
What is 0.08 solar masses?
A starlike object that is below 0.08 solar masses cannot be considered a star, it would then be considered a brown dwarf. This is because below this mass, hydrogen fusion isn’t possible and that is the quality that distinguishes stars from planets.
500
This is what would happen to Earth's orbit if the sun became a black hole.
What is no real effect?
The orbit is based on the respective masses and distances of the objects. If the sun became a black hole, its mass would not change, only its density. Due to this, the earth would not have any significant change to its orbit.
500
This is the primary source of energy for a star as it grows in size to become a red giant.
What is hydrogen fusion in a shell surrounding the central core?
A red giant is a star that has exhausted the supply of hydrogen in its core and has begun thermonuclear fusion of hydrogen in a shell surrounding the central core.
500
This process occurs in the core of low mass stars as it contracts and heats up, triggering a series of shell burning stages.
What is Helium flash?
A Helium flash occurs in low mass stars as they are transitioning from the red giant phase to the horizontal branch. As the star’s core contracts, there is a rapid increase in temperature in the core and helium fusion can occur. This rapid increase in temperature and subsequent helium fusion leads to a large amount of energy being released which is referred to as a helium flash.
500
This is the name for the star in region B.
What is a red giant?
This is a low-mass star that has reached the end of its life. It is now “burning” heavier elements instead of hydrogen and has left the main sequence as it expanded. Consequently, its surface temperature decreased and luminosity increased, thus making it a red giant.
500
This is the primary molecular makeup of a star born in the earliest times of the universe.
What are Hydrogen and Helium?
Heavier elements, or "metals," are synthesized in the cores of stars through nuclear fusion processes and spread into the universe via supernovae, which hadn't yet occurred in the early stages of the universe. Consequently, these first stars formed from the pristine gas clouds that lacked any elements heavier than helium, reflecting the elemental makeup of the universe shortly after its inception.