CHAPTER 28 SECTION 3 AND 4

Stellar Parallax The apparent shift in the position of an object when

viewed from 2 locations. The closer an object is to an observer the greater its

parallax. The measurement of parallax is used directly to find

the distance of the body from the Earth and from the Sun.

The two positions of the observer and the position of the object form a triangle; if the base line between the two observing points is known and the direction of the object as seen from each has been measured, the apex angle (the parallax) and the distance of the object from the observer can be found simply.

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http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::800::600::/sites/dl/free/007299181x/78778/Parallax_Nav.swf::Stellar Parallax Interactive

Life Cycle of Stars Stars are born from great clouds of gas

and dust. They mature, grow old, and die. When they die they can produce new

clouds of dust and new stars can form here.

The more massive a star is the shorter its life will be.

The Hertzsprung-Russell Diagram

The H-R diagram plots the luminosity of the stars against their temperatures.

There are several groups noted on the H-R diagram the groups represent the life cycles of stars.

The majority of the stars (90%) are in the band that crosses the entire diagram. This band is called the main sequence.

The stars in the main sequence are called main-sequence stars.

Main Sequence stars Stars on the main sequence can also be

known as happy, healthy stars. They are all fusing hydrogen to helium. They can differ in size, surface

temperature, and absolute magnitude. Some of them can burn for a million

years, others can last billions of years.

Giant Stars Larger, more luminous stars found above

the main sequence stars on the H-R Diagrams.

They have diameters from 10 to 100 times greater than that of our sun.

Supergiant Are more luminous than the giant stars They are more than 100 times that of the

sun Even thought red super giants are cool,

they are huge and therefore very luminous

Betelgeuse is an example of a red super giant

White Dwarfs A white dwarf is a star that is near the

end of its life. These stars used to be red giants As the star began to die it puffed off its

outer layers to stabilize itself What is now left is the inner core

Dying White Dwarf Star

What dwarf core

Birth of a star A nebula is a nursery for stars, it is where

stars are born A nebula contains gas and dust. 99% of

the nebula is gas, mostly hydrogen. A nebula may begin to condense in on

itself when something like a shock wave from a super nova hits it.

The force compresses regions of the nebula where particles of gas and dust condense, and become denser, and hotter.

If it is a large nebula parts will begin to glow due to the increasing temperature.

These glowing nebula are called protostars They are not stars yet because they are

not producing H to He fusion. Eventually as compression continues the

center gets so hot that fusion begins in the center, and it is officially a star.

Eagle Nebula

Crab Nebula

Eagle Nebula

Death of a Star like the Sun

How do you think the sun will die? Main sequence stars with a mass similar

to the sun will remain the same size for billions of years.

Eventually they will begin to brighten When all of the hydrogen is used the star

begins to shrink. The hydrogen core shrinks and contracts

which causes the star to heat up. This triggers fusion outside the core.

The star begins to die when the temperature of the star is hot enough to fuse helium into heavier elements.

The heaviest elements that can form is Carbon and Oxygen due to the temperature and a Carbon, Oxygen core forms

The outer layers of the star are puffed off, until the only thing that is left is the carbon-oxygen core is left.

Planetary Nebula The halo that surrounds a star that is

dyeing. Eventually the halo dissipates, and the

white dwarf is all that is left.

Planetary Nebula (Eskimo nebula)

Death of a massive star Hydrogen is fused more quickly in larger

stars, and fusion processes continue until iron is formed in the nucleus.

The lifespan is less than a billion years When the star is no longer fusing H to He

the star swells to become a super giant When the core is Fe it no longer releases

energy it absorbs it. The Fe core quickly and suddenly

collapses.

The collapse of the core produces a shock wave that blasts the star’s outer layers into space at thousands of km per seconds and produces a huge burst of light.

The explosion produces a supernova. The supernova is millions of times

brighter than the original star. A single supernova can outshine all of the

stars in its galaxy for a short period of time.

Supernova remnants In 1987 there was a supernova in the

Large Magellanic Cloud which is an irregular galaxy close to us.

When the star produces a supernova elements heavier than iron are produced.

We are star stuff: elements from earth came from stars that long ago exploded.

Populations of Stars Population I: Sun like stars ( fairly young

and recycled) High content of heavy elements. These are the most common.

Population II: Previous generations, less recycling, lower amount of heavy elements. Rare to find these.

Population III: Original generation of stars, no heavy elements in them. None of these have ever been seen.

Why?

LMC

Remnants of Massive Stars Neutron star: The core of a supernova,

which is trillion times more dense than our sun, and only 20 km in diameter!

Pulsar: when a neutron star is first born it gives off bursts of radio waves, and it spins rapidly.

Black hole: a remnant of a star that is 15 times more massive than the sun. The black hole the mass of 10 suns condensed in and area that is 30 km wide.

Neutron Star

Image of a pulsar

Black Holes The gravitational force inside a black hole

is so strong that even light can’t escape. How can we find them? They give off immense X-rays. When atoms are pulled into the black

hole they are ripped apart by the gravity of the back hole and give off x-rays.

Many scientists think that at the center of most galaxies is a super massive black hole.

Spaghettification from a black hole

Diagram of a black hole

Galaxies and the Universe What is a galaxy? A group of millions to billions of stars held

together by gravity. How many are there in our observable

universe? 50-100 billion

What is a universe? The Universe comprises everything we

perceive to physically exist, the entirety of space and time, all forms of matter and energy, and the physical laws that govern them.

The Milky Way Galaxy (our home)

Every star that you see in the sky is in the milky way galaxy

It is a spiral galaxy It is shaped like a think disk with a central

bulge The diameter of the milky way is 100,000

light years. Its greatest thickness is about 10,000

light years

The sun is about 26,000 light years from the center.

We see a hazy band of light we call the milky way, but the whole galaxy is the milky way.

Most spiral galaxies are larger than us. The milky way belongs to a group of more

than 30 galaxies known as the local group. 2 Megallanic clouds, and Andromeda are

the largest galaxies in the local group.

Center of our galaxy Scientists know at the center of our

galaxy must be: An intense energy source Motion of very heavy high mass stars The center must be very small (smaller than

our solar system: (9 billion km radius)Could be a super massive black hole.

Types of Galaxies No two galaxies are the same, but they

can be classified by shape. Spiral Elliptical Irregular lenticular

Spiral galaxies Spiral galaxies come in a range of shapes Some have large, bright nuclei of stars and

tightly wound spiral arms. Some have very small, dim nuclei, and

open arms. Two types: Spiral, barred spiral. A: Large bulge, tightly wound B: medium bulge, medium wound C: small bulge, loose wound Must look face on to see spirals!!!

Elliptical Galaxies Range from nearly spherical to lens

shaped. Their stars are concentrated in their

centers They have no arms They contain less gas and dust than

spiral galaxies They contain few, if any young stars.

Why?

M87: Elliptical Galaxy

Irregular Galaxies Much smaller and fainter Stars are spread out unevenly Weird shape is due to contact with other galaxies, they were not “born” this way.

Lenticular Galaxy A cross between an elliptical galaxy and a

spiral galaxy. It is a spiral galaxy with no arms.

Hubble Tuning Fork Diagram

Active Galaxies (aka abnormal or hyperactive)

Many galaxies total energy output is from their stars, others put off far more energy.

Any galaxy that gives off more energy than it should is considered an active galaxy.

Some emit large amounts of radiation (radio, infrared, UV, x-rays, and gamma ray wavelength)

Some change in brightness over short periods of time, and are highly variable.

Current model of active galaxies

Powered by a super massive black hole in the center.

The black hole puts forth jets of hot gas in opposite directions at nearly the speed of light.

The black hole is surrounded by a disk of gas that is spiraling into it.

As the gas is being pulled into the black hole it gives off radiation.

Quasars: an active galaxy Very distant objects Very luminous Giving off too much of all wavelengths Couldn’t identify spectral lines scientists

thought it was a new elemetns turned out that it was Hydrogen but were

very red shifted (moving really, really fast away from us, also very far away to begin with)

Blazars An active galaxy that has one jet pointed

toward earth. We are looking directly at the jet so it

looks different to us.

One possible explanation for the origin of the Universe

The big band model: An explanation that scientists use to explain the origin of the universe.

The universe began as a small, hot, dense state billions of years ago and has expanded and cooled every since.

Evolution of space and time as a whole, did not occur at one single point.

Knew that it had to be expanding, early universe was 75% H, and 25% He, and there was left over radiation from the hot, dense, state. It should now be cool and faint and be everywhere in the universe.

Scientists knew that the first two were true, but thought that the third could never be proven.

Then in 1964 In New Jersey Bell labs (aka bell telephone company) was testing a new microwave telephone system when they got tremendous interference.

It was static from outside our planet. They found cosmic microwave

background (CMB) which was thought to be radiation from the big bang.