zacks astronomy presentation outline

8/13/2019 Zacks Astronomy Presentation Outline

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Hertzsprung-Russell Diagram

A Scattergraphing of Stars showing their absolute magnitudes, or luminosities

versus their spectral types, or classifications, and effective temperatures.

It is a compilation of stars, nota map.

The X axis would be the Color and Spectral class, and the Y axis would be the

Luminosity and Absolute Magnitude.

Each star is represented by a dot, possibly colored depending on the intricacy of the

diagram

The diagonal line cutting through the entire graph is known as the main sequence.

This is where the majority of stars fall under.

Luminosity is the amount of energy a star radiates in one second, but its commonlyviewed as how bright or dim the star appears to be, which is also correct.

The X Axis (Color and Spectral class), represents the stars surface temperature, not

the core temperature. The Temperature is measured using the Kelvin scale. Its

worth pointing out that the reference point 0 does not start in the left and increase

as it goes right. The higher/hotter temperatures are on the left and it cools as it goes

right.

The Diagram was created around 1910 by Ejnar Hertzsprung and Henry Norris

Russell. It was an important development toward the understanding of Stellar

Evolution.

The Hertzsprung-Russell Diagram is an way of categorizing Stars by

comparing their Color and Spectral Class (which is given by the surface

temperature) by their Luminosity and Absolute Magnitude (the brightness). It was

important because it highlights a relationship between the two, which is the hotter a

star is, the higher the luminosity will be, and vice versa. The way it is ordered is by

having the Color and Spectral class as the X-axis, and the Luminosity and Absolute

Magnitude as the Y-axis. Its important to know that we assign luminosity based

around the reference point, which is our sun. So anything hotter than our sun will

increase with positive numbers, while anything cooler will be assigned a negative

number. Also, The temperature for the X-axis is measured using the Kelvin scale,and the X-axis does not begin from left to right. 0 Kelvin would actually begin on the

right, with temperatures increasing as it goes left. It also only represents the stars

surface temperature, not the core temperature. The color, as given by the surface

temperature, will change as we look right to left. The coolest stars will be red, and

itll go through orange, yellow, green, white, blue, then violet as its temperature

increases. The human eye cant actually see stars as green or violet so theyll appear

white or blue respectively. Most of the stars plotted on the H-R Diagram fall under


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the Main Sequence. The main sequence is the line of best fit, drawn within the

average of all stars that highlight the relationship between Surface temperature and

Spectral class, and Luminosity. The hot bright stars will be on the top left, while the

cool dim stars will be on the bottom right. Scientists Ejnar Hertzsprung and Henry

Norris Russell created the diagram in 1910 and it was an important step in the right

direction to fully understanding stellar evolution.

source: http://aspire.cosmic-ray.org/labs/star_life/hr_diagram.html

NEUTRON STAR

Neutron star is actually a stellar remnant of a star gone supernova

As the Name might suggest, its composed almost entirely of neutrons, which are

subatomic particles with no electric charge and a higher mass than protons.

They are very hot. Newly formed ones start around 10^11 Kelvin to 10^12 kelvin.But within a few years it drops to around 10^6 Kelvin.

Most of the light emitted is in X-rays. They appear white in visible light because it

emits the same amount of energy in all parts of the visible spectrum.

Neutron stars are impervious to further collapse by quantum degeneracy pressure

due to the Pauli Exclusion Principle, which in very simple terms states that no two

neutrons can occupy the same place and quantum state at the same time.

1 Solar mass is equal to 10^30 kg. Which is about two nonillion kg

Your average neutron star has the mass of about 1.4-3.2 solar masses

The density of a neutron star is comparable to a Boeing 747 condensed to the size of

1 grain of sand, or the entire human population to the size of a sugar cube.

Surface gravity is so high on a neutron star, that any object that is falling on the

surface of the star, is pulled with tremendous force into the star by its gravity, and

the force of impact would be so great, that it would destroy the atoms of whatever

the object is, rendering all of its matter, in most respects, identical to the rest of the

star.

The structure of a neutron star is currently defined by mathematical models. Theatmosphere is hypothesized to be a few, micrometers thick. The crust would be

extremely hard and smooth due to the high surface gravity. The outer part of it

would be composed of ions and electrons, while the inner crust would be of

electrons, neutrons and nuclei. Next would be the outer core which is called the

Neutron Dip, and its full of nuclei, electrons, and neutrons that become smaller and

smaller until the core is reached. There is acutally quite a bit of speculation on what


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exactly the core would be since it would theoretically be full of things so dense and

so small. They range from strange matter, to ultra dense, quark degenerate matter.

A Neutron Star is actually a stellar remnant of a star gone supernova. As the

name might suggest, its composed almost entirely of neutrons, which are subatomicparticles with no electric charge and a higher mass than protons. These stars are

very hot. Newly formed ones start around 10^11 Kelvin to 10^12 kelvin. But within

a few years it drops to around 10^6 Kelvin. Most of the light emitted is in X-rays.

They appear white in visible light because it emits the same amount of energy in all

parts of the visible spectrum. Neutron stars are impervious to further collapse by

quantum degeneracy pressure due to the Pauli Exclusion Principle, which in very

simple terms states that no two neutrons can occupy the same place and quantum

state at the same time. 1 Solar mass is equal to 10^30 kg. Which is about two

nonillion kg. Your average neutron star has the mass of about 1.4-3.2 solar masses.

The density of a neutron star is comparable to a Boeing 747 condensed to the size of

1 grain of sand, or the entire human population to the size of a sugar cube. Surfacegravity is so high on a neutron star, that any object that is falling on the surface of

the star, is pulled with tremendous force into the star by its gravity, and the force of

impact would be so great, that it would destroy the atoms of whatever the object is,

rendering all of its matter, in most respects, identical to the rest of the star. The

rotation of newly formed neutron stars can be as fast as several times per second.

The structure of a neutron star is currently defined by mathematical models. The

atmosphere is hypothesized to be a few, micrometers thick. The crust would be

extremely hard and smooth due to the high surface gravity. The outer part of it

would be composed of ions and electrons, while the inner crust would be of

electrons, neutrons and nuclei. Next would be the outer core which is called the

Neutron Dip, and its full of nuclei, electrons, and neutrons that become smaller andsmaller until the core is reached. There is acutally quite a bit of speculation on what

exactly the core would be since it would theoretically be full of things so dense and

so small. They range from strange matter, to ultra dense, quark degenerate matter.

There are 19 known sub-types of Neutron Stars. And we know of 2000 within the

Milky Way and the two Magellanic Clouds.

Source: http://imagine.gsfc.nasa.gov/docs/science/know_l1/pulsars.html

MAIN SEQUENCE STAR

A star that falls within the main band of stars as seen on the Hertzsprung-Russell

diagram.

All main sequence stars are in hydrostatic equilibrium, which is where outward

thermal pressure is balanced by inward gravitational pressure.


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The main sequence is sometimes divded into upper and lower parts, based on the

more dominant processes that stars use to generate energy.

Stars that are below around 1.5 solar masses tend to fuse hydrogen atoms together

to form helium, which is called the Proton-Proton chain.

Stars that are above that mass use a fusion, that uses Carbon, nitrogen, and oxygen,

as a way to fuse helium from hydrogen atoms, called the CNO Cycle.

Stars in the Main Sequence with more than 2 solar masses undergo convection in

their core, which stirs up the newly created helium and maintain the right

conditions for fusion to occur.

Main Sequence stars below 2 solar masses have cores that are entirely radiative

with convection zones near the surface

Usually, the more massive a star is, the shorter the lifespan will be on the mainsequence.

Once the hydrogen fuel at the core as been depleted, the star will evolve away from

the main sequence

After that it can become either a white dwarf, or a red giant, depending on its mass.

The very massive stars can go supernova or collapse in on itself in a black hole.

A Main Sequence Star is a star that falls within the main band of stars as seenon the Hertzsprung-Russell diagram. All main sequence stars are in hydrostatic

equilibrium, which is where outward thermal pressure is balanced by inward

gravitational pressure. The main sequence itself can be divided into upper and

lower parts, based on the more dominant processes that stars use to generate

energy. Stars that are below around 1.5 solar masses tend to fuse hydrogen atoms

together to form helium, which is called the Proton-Proton chain. Stars that are

above that mass use a fusion, that uses Carbon, nitrogen, and oxygen, as a way to

fuse helium from hydrogen atoms, called the CNO Cycle. Stars in the Main Sequence

with more than 2 solar masses undergo convection in their core, which stirs up the

newly created helium and maintain the right conditions for fusion to occur. Main

Sequence stars below 2 solar masses have cores that are entirely radiative withconvection zones near the surface. Usually, the more massive a star is, the shorter

the lifespan will be on the main sequence. Once the hydrogen fuel at the core as

been depleted, the star will evolve away from the main sequence. After that it can

become either a white dwarf, or a red giant, depending on its mass. The very

massive stars can go supernova or collapse in on itself in a black hole.

Source: http://spiff.rit.edu/classes/phys230/lectures/star_age/star_age.html


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