INTEGRATED SCIENCE

Stars & Life Cycle of Stars

Birth of Stars Steps 1st a huge cloud of nebula 2nd as the density of the gas grows so

does gravitational pull (more particles are collected)

3rd the forming star is called a Protostar. 4th Density increases as gravity

continues to crunch the matter together

Birth of Stars 5th When the central temperature reaches

about 10 million Kelvins hydrogen begins to fuse to make helium (This marks the change from a protostar to a star)

6th The pressure from the fusion (outward force) and gravity (inward force) reach equilibrium, A stable star is formed

Stars The material that makes up a star depends upon

how old the universe was when the star formed. Older stars were mostly hydrogen and helium But through the birth and death of stars in the past,

younger stars contain elements heavier than hydrogen and helium

Heavier elements were made inside of a star, basically we are made from those reused and left over elements

High Mass Star

Low Mass Star

LIFE CYCLE OF A STAR

Gamma ray

Hydrogen nuclei collide to form

helium-3

Two helium-3 nuclei collide. Helium-4 and

hydrogen nuclei form.

Nuclear Fusion in Stars

Green particles are protonsPurple particles are neutrons

Large Amount of Energy

Released!

Stars & Life Cycle of Stars

The mass of a star determines the path of its evolution.

Nebula A group of bright

young stars can be seen in the hollowed-out center of the Rosette Nebula.

Supernova The above two photographs are

of the same part of the sky. The photo on the left was taken in 1987 during the supernova explosion of SN 1987A, while the right hand photo was taken beforehand. Supernovae are one of the most energetic explosions in nature, making them like a 1028 megaton bomb (i.e., a few octillion nuclear warheads).

Supernova The Crab Nebula is

the remnant of a supernova explosion that was observed on Earth in A.D. 1054. The supernova was so bright that people could see it in the daytime.

Possible end results for starsNeutron Stars

A neutron star is about 20 km in diameter and has the mass of about 1.4 times that of our Sun. This means that a neutron star is so dense that on Earth, one teaspoonful would weigh a billion tons! Because of its small size and high density, a neutron star possesses a surface gravitational field about 2 x 1011 times that of Earth. Neutron stars can also have magnetic fields a million times stronger than the strongest magnetic fields produced on Earth.

Neutron stars are one of the possible ends for a star. They result from massive stars which have mass greater than 4 to 8 times that of our Sun. After these stars have finished burning their nuclear fuel, they undergo a supernova explosion. This explosion blows off the outer layers of a star into a beautiful supernova remnant.

The central region of the star collapses under gravity. It collapses so much that protons (+) and electrons (-) combine to form neutrons (No charge). Hence the name "neutron star".

Neutron Star The Hubble Space Telescope

succeded in taking an image of a neutron star located less than 400 light-years away from Earth.This star was previously detected by its Xray radiation, indicating a surface temperature around 700,000°.Its diameter is less than 28 km.

28 kilometers = 17.4 milesRoughly Cville to Lebanon

Black Holes Black holes are the end result of a massive star’s

death. The force of gravity is so strong that the escape speed is greater than the speed of light. Hence the name black hole.

Once you cross the event horizon you will continue to be stretched and squeezed until you reach the singularity.

They are detected by X-rays given off by matter entering the black hole and their gravitational effects on neighboring stars.

Betelgeuse, Procyon, and Sirius are three of the brightest stars in the sky. Betelgeuse is a much cooler star than the others.

Properties of Stars

Brightness

Astronomers have discovered that the brightness of stars can vary by a factor of more than a billion.

Stars that look bright may actually be farther away than stars that appear dim.

Properties of Stars

These streetlights all have about the same absolute brightness, but the closer lights appear brighter.

Properties of Stars

The sun appears very bright to us because it is much closer than other stars.

The brightness of a star as it appears from Earth is called its apparent brightness.

The apparent brightness of a star decreases as its distance from you increases.

Properties of Stars

Absolute brightness is how bright a star really is.

A star’s absolute brightness is a characteristic of the star and does not depend on how far it is from Earth.

You can calculate a star’s absolute brightness if you know its distance from Earth and its apparent brightness.

Properties of Stars

Size and Mass

Once astronomers know a star’s temperature and absolute brightness, they can estimate its diameter and then calculate its volume.

The masses of many stars can be determined by observing the gravitational interaction of stars that occur in pairs.

For most stars, there is a relationship between mass and absolute brightness.

Properties of Stars

The Hertzsprung-Russell Diagram

H-R diagrams are used to estimate the sizes of stars and their distances, and to infer how stars change over time.

Stars can be classified by locating them on a graph showing two easily determined characteristics.

Such a graph is called a Hertzsprung-Russell diagram, or H-R diagram.

An H-R diagram is a graph of the surface temperature, or color, and absolute brightness of a sample of stars.

The Hertzsprung-Russell Diagram

The vertical axis of the H-R diagram shows absolute brightness, with the brightest stars at the top and the faintest at the bottom.

The absolute brightnesses of stars vary even more than temperature, ranging from about one ten-thousandth to a million times that of the sun.

The Hertzsprung-Russell Diagram

A star’s placement on an H-R diagram indicates its absolute brightness and surface temperature (or color).

The Hertzsprung-Russell Diagram

Polaris was used for navigation because it is located above the 23.5O tilted rotational axis of the earth.

Main-Sequence Stars

Stars occur only in certain places on the H-R diagram.

Most stars are found along a diagonal band running from the bright hot stars on the upper left to the dim cool stars on the lower right. Astronomers call this diagonal band on the H-R diagram the main sequence.

About 90% of all stars are found on the main sequence. The sun lies near the middle of this band.

The Hertzsprung-Russell Diagram

Giants and Dwarfs

In general, two factors determine a star’s absolute brightness: its size and its surface temperature.

An H-R diagram shows a star’s absolute brightness and surface temperature.

• If you compare two stars at the same temperature, the brighter one must be larger.

• Hotter stars are brighter than cooler stars of the same size.

The Hertzsprung-Russell Diagram

The very bright stars at the upper right of the H-R diagram are called supergiants.

Supergiants are much brighter than main-sequence stars of the same temperature, so they must be very large compared with main-sequence stars.

The Hertzsprung-Russell Diagram

Supergiants range in size from 100 to 1000 times the diameter of the sun.

Just below the supergiants on the H-R diagram are the giants—large, bright stars that are smaller and fainter than supergiants.

The Hertzsprung-Russell Diagram

Supergiants range in size from 100 to 1000 times the diameter of the sun.

Just below the supergiants on the H-R diagram are the giants—large, bright stars that are smaller and fainter than supergiants.

The Hertzsprung-Russell Diagram

Below the main sequence in the lower part of the H-R diagram are white dwarfs.

• A white dwarf is the small, dense remains of a low- or medium-mass star.

• White dwarfs are hot but dimmer than main-sequence stars of the same temperature.

The Hertzsprung-Russell Diagram

The diameter of a red giant is typically 10–100 times that of the sun and more than 1000 times that of a white dwarf.

The Hertzsprung-Russell Diagram

Galaxies

Astronomers classify galaxies into four main types: spiral, barred-spiral, elliptical, and irregular.

A galaxy is a huge group of individual stars, star systems, star clusters, dust, and gas bound together by gravity.

• There are billions of galaxies in the universe. • The largest galaxies consist of more than a

trillion stars. Galaxies vary widely in size and shape.

Galaxies

Spiral and Barred-Spiral Galaxies

Spiral galaxies have a bulge of stars at the center, with arms extending outward like a pinwheel.

• These spiral arms contain gas, dust, and many bright young stars.

• The Milky Way is a spiral galaxy.

Galaxies

Some spiral galaxies have a bar through the center with the arms extending outward from the bar on either side. These are called barred-spiral galaxies.

Galaxies

Elliptical Galaxies

Elliptical galaxies are spherical or oval, with no trace of spiral arms.

• Elliptical galaxies come in a wide range of sizes. • Elliptical galaxies have very little gas or dust between

stars. They contain only old stars.

Galaxies

Irregular Galaxies

A small fraction of all galaxies are known as irregular galaxies.

Irregular galaxies have a disorganized appearance. They have many young stars and large amounts of gas and dust.

Irregular galaxies come in many shapes, are typically smaller than other types of galaxies, and are often located near larger galaxies.

Galaxies

A. A spiral galaxy in the constellation Coma Berenices

B. A barred-spiral galaxy in the Fornax cluster

Galaxies

C. Elliptical galaxy M87

D. An irregular galaxy with many areas of star formation

Galaxies

The Milky Way Galaxy

The Milky Way galaxy has an estimated 200 to 400 billion stars and a diameter of more than 100,000 light years.

Every individual star that you can see with the unaided eye is in our galaxy.

The solar system lies in the Milky Way’s disk within a spiral arm, about two thirds of the way from the center.

Galaxies

In a side view, the Milky Way appears as a flat disk with a central bulge. An overhead view of the Milky Way shows its spiral shape.

Galaxies

Location of solar system Central bulge

Nucleus

Overhead View of Our Galaxy

About 100,000 light-years

Disk of spiral arms containing mainly

young stars

Central bulge containing mainly

older stars

NucleusHalo containing oldest stars

Side View of Our Galaxy

The Milky Way’s flattened disk shape is caused by its rotation.

The sun takes about 220 million years to complete one orbit around the galaxy’s center.

Recent evidence suggests that there is a massive black hole at our galaxy’s center.

Stars are forming in the galaxy's spiral arms.

Galaxies

Are we made of star remains? The elements themselves (carbon, nitrogen, oxygen, etc.) were synthesized, cooked up as it were, in the nuclear furnaces that are the deep interior of stars (The elements were fused together to make heavier elements). These elements are then released at the end of a star's lifetime when it explodes (supernova), and subsequently used to make a new generation of stars -- and into the planets that form around the stars, and the life forms that originate on the planets.