E+S chp 29.3

Stars like our sun have enough hydrogen to power itself for

10 billion years

Pulsar

A spinning neutron star that exhibits a pulsing pattern of light.

Supergiant

A star that occurs from being much higher on the main sequence. It starts off more massive than our sun but still starts off by converting hydrogen into helium. Since the star is so massive, it is very luminous and burns up its fuel quickly and undergoes many more reaction phases, which produce many elements inside of the star. The star becomes a red gaintseveral times as it expands after each reaction stage. As more shells are formed from the fusion of all the different elements, the star expands to a larger size and becomes a super giant. Ex. Betelgeuse in the Orion constellation.

Nebula

An interstelar cloud of gas and dust that a star starts out as. Nebulas collapse on themselves because of gravity. Once it gets smaller and denser and hotter it eventually becomes a protostar

Protostar

Center of a nebula that is dense and hot that forms as a nebula gets smaller due to collapse from gravity. This will continue until it gets hot enough for nuclear fusion (hydrogen to helium), eventually reaching hydrostatic equilibrium.

Main sequence to super giant

Main sequence star must be 8x the size of the sun to become a super giant!

Super giant to a black hole

Nuclear fusion stops. Core moves past Carbon to Iron and sheds outer layers. It becomes small and dense until there is Iron in its core.

White dwarfs

Stars plotted at the lower left corner of the HR diagram. They are small dense and hot. They are usually around the size of the earth. Normal stars will never get hot enough to convert carbon so energy production is done. The outer layers are shed from the original star and a white dwarf is whats left behind. White dwarfs still remain stable even though there are no nuclear reactions to counter the gravity. This is because of the electrons being squeezed together. The electron pressure does not require ongoing reactions so it can last indefinitely. Once cooled and undetectable, white dwarfs become black dwarfs.

Planetary nebula

When the outer layers of a star are shed from the star due to nuclear reactions becoming stronger and pushing the star outward against gravity.

Gravity and pressure

balance each other in a star.

Neutron star

collapsed dense core of a star that forms quickly while its outlayers are falling inward. It contains mostly neutrons. It has a radius of about 10 km, a mass of 1.5-3 times that of the sun and becomes neutral.

The mass of a star

determines its internal structure and its other properties like temp, luminosity, and diameter.

Nuclear fusion ='s

hydrogen converting into helium, making it a stable hydrostatic equilibrium star

As a star ages:

its internal composition changes, consequently changing its temp and density

supernova

massive explosion that occurs when the outer layer of a star is blown off. The outliers bounce off the neuron star core, and explode outward. It was formed because its core was too massive to be supported by electron pressure and reactions in the core of the star create iron. Eventually the star becomes a neutron star, forming quickly while the outer layers of the star are still falling inward. The inflating gas rebounds when it strikes the hard surface of the neutron star and explodes outward. Then the entire outer portion of the star is blown off in a massive explosion.

Evolutionary path of a star

nebula, protostar, main sequence

red giant to white dwarf

nuclear fusion stops and the core is made up of carbon. It sheds its outer layers into space and becomes small dense and a hot object. (crushed by gravity!)

Main sequence

point of the life of a star where they are fusing hydrogen in their cores. Large diagonal grouping of stars. ex. the sun.

temperature governs the

rate of nuclear reactions which in turn determines a stars energy output (luminosity).

Black holes

small dense remnant of a star whose gravity is so immense that not even light can escape its gravity field.. A star that begins with a mass more than 20 times the suns will end up above the mass limit and cannot form a neutron star.. The pressure from the resistance of neutrons being squeezed together cannot support the core of a star. The resistance of neutrons to being squeezed is not great enough to stop the core from collapsing, compacting matter into a smaller volume.

Red giants

stars plotted at the upper right of the HR Diagram. These are stars that are cool yet luminous, but emit much less radiation then other stars. 100 times the size of the sun. As a red giant the star loses gases from its outer layers. The core gets hot enough to fuse helium into carbon. Occurs after the main sequence stage (about 10 billion years) The stars luminosity has increased while its surface temperature has decreased due to expansion due to leftover excess hydrogen reacting and forcing the outer layers of the star to expand and cool.

When a star runs our of hydrogen

the core turns to helium because it is no longer balanced. Some hydrogen still converts near the edges of the core causing the star to expand and therefore the nuclear reaction to become stronger and push the star outward against gravity transforming it into a red giant.

The more massive a star

the greater the gravity pushing inwards and the hotter and denser a star must be inside to balance its own gravity.

With a change in a stars core composition

the stars density increases, temperature increases, and luminosity increases,