Stellar Classification and Evolution

What is a star?

A cloud of gas and ______, mainly hydrogen and helium

The core is so hot and dense that nuclear ______can occur.

The fusion converts light elements into ______ones

Every star is different

______:

Tells us how much ______is being produced in the core

Can be calculated using ______and distance

Color:

Tells us the surface ______of the star

Determined by analyzing the ______of starlight

Mass:

Determines the life cycle of a star and how ______it will last

Measuring Temperature

The temperature of a star is indicated by its ______

Blue stars are ______, and red stars are ______

Star Classification

Spectral Class

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Determined by anazlyzing a star’s ______

O stars are the ______and______

M stars are the ______and ______

Our Sun is a ______ star

Hertzprung-Russell Diagram

What information is plotted on the H-R Diagram?

______

What are the main stages of stars?

______

Do stars always stay in the same stage?

______

The Life of Stars

Origins of stars

Solar systems are created in giant molecular clouds of cosmic dust and ______

When ______causes intense heat and pressure in the core of the proto-star, it triggers ______and a star is “born

Mass and Stellar Evolution

The life cycle of a star is determined by its ______

More massive stars have greater gravity, and this ______the rate of fusion

O and B stars can consume all of their core hydrogen in a few ______years, while stars with very low mass (red dwarfs) can take hundreds of ______of years.

Brown Dwarf– a “Failed Star”

If a proto-star does not have enough ______, gravity will not be strong enough to compress and heat its core to the temperatures that trigger ______

If the mass is less than 0.08 x solar mass, it will form a Brown Dwarf (not actually a star)

Brown Dwarfs are ______, but they do give off small amounts of ______as they cool

The Main Sequence

______life stage of a star

Energy radiating away from star ______gravitational pull inward (hydrostatic equilibrium)

Main-sequence stars fuse ______into helium at a constant rate

Star maintains a stable size as long as there is ample supply of hydrogen atoms

The Sun will spend a total of ~10 billion years on the main sequence

When hydrogen in the core starts to run low…

In stars with masses more than 0.4 x solar mass, fusion slows down

Outer layers of the star begin to ______and surface temperatures fall

The ______surrounding the core begins to fuse hydrogen

Stars move out of the ______Sequence

Red Giants and Supergiants

______stars

______produced through shell fusion becomes part of the core

Star’s core temperature ______as the more massive core contracts

The increased core temperature causes the helium left to fuse into ______atoms (triple-alpha process)

The “Death” of stars

Depends on ______

“Low mass stars” are less than 8 solar masses

“High mass stars” are greater than 8 solar masses

The Death ofLow-Mass Giants and Supergiants

In ______mass stars (0.4 – 8.0 x solar mass) strong solar winds and energy bursts from helium fusion ______much of their mass

The ejected material expands and cools, becoming a planetary ______(which actually has nothing to do with planets, but we didn’t know that in the 18th century when Herschel coined the term)

The core ______to form a White Dwarf

White Dwarf Stars

The burned-out ______of a star less than 8 x solar mass becomes a white dwarf

The carbon-oxygen core that remains is about the size of earth, but much more ______

Theoretically, after all of the stored ______radiates out into space, these stars will become giant crystals of carbon and Oxygen (Black Dwarfs)

The Death ofHigh-Mass Stars: Massive stars continue ______

Massive stars (> 8 x solar mass) have more ______than low-mass stars

When helium fusion ends, gravity______the core and the temperature rises beyond 600 million K

Fusion of the atoms from ______elements begins, and the star becomes a luminous supergiant

These stars produce neon, magnesium, oxygen, sulfur, silicon, phosphorous, and iron

Supernova explosions

The ______-rich core signals the impending violent death of the massive star

The core collapses in seconds, and the resulting temp. exceeds 5 billion K

Intense ______breaks apart the atomic nuclei in the core, causing a shock wave

After a few hours, the shockwave reaches the star’s ______, blasting away the outer layers in a ______

Supernova remnants are strong sources ______and ______waves

Neutron Stars

The ______left over after Supernovae can become Neutron Stars-- very small, ______balls of NEUTRONS

1 teaspoon of this would be approximately 1 billion tons on Earth

Due to the great ______it rotates very rapidly, and some become PULSARS

Pulsars

Rapidly-spinning neutron stars with very strong ______fields.

Jets of charged particles are ejected from the magnetic poles of the star.

This material is accelerated, producing beams of ______in all wavelengths from the magnetic poles.

We can see this “lighthouse effect” many times per second

Black Holes

______stars (>25 x solar mass) collapse into neutron stars too massive to be stable

They collapse in on themselves, forming a region of infinite density and zero volume– a SINGULARITY at the center of a Black Hole

Space “curves inward” and ______all matter and electromagnetic radiation