Characteristics of Stars Groups of stars that form

Characteristics of Stars • Groups of stars that form patterns in the sky are called constellations – Example: Ursa Major (Big Dipper), Ursa Minor (Little Dipper), and Orion • The last two stars in Ursa Major’s “dipper” can be used to find Polaris (North Star) • Polaris is located directly above the North Pole (90º), and is only visible in the northern hemisphere

Circumpolar Constellations • Because of the Earth’s rotation, the constellations appear to move • If the constellations appear to move around Polaris, they are called circumpolar constellations – The constellations Ursa Major and Minor are both circumpolar constellations • Using time exposure photography, the apparent motion of the stars around Polaris can be recorded as circular trails

• The positions of the constellations as viewed from Earth changes from season to season • This is caused by the change in Earth’s position in its orbit around the sun – Example: Orion the Hunter is a winter constellation

Physical Properties of Stars • Stars differ in size, density, mass, composition, and color • The color of a star is determined by it surface temperature (Reference Tables) – The hotter the star, the bluer the color. The cooler the star, the redder the color. – The sun is a yellow star

Physical Properties of Stars • Most stars are made up of mostly hydrogen and helium (approx. 98%) • The remaining 2% may be other elements • A spectrum analysis of the star can tell us what elements a star is made of, since the radiated spectrum depends on a star’s composition and temperature

Apparent Magnitude • How bright a star appears on to us on Earth • The farther a star is from Earth, the dimmer it will look even though it may actually be a very bright star – Because of this, apparent magnitude does not tell the true brightness of a star

Luminosity • The actual (true) brightness of the star • Depends on the size and temperature of the star • Hotter stars are more luminous (brighter) than cooler stars • If the temperatures are the same, a larger star will be more luminous

Absolute Magnitude • The luminosity of the stars if they all were the same distance from Earth – aka – picture all the stars lined up the same distance from Earth, then compare their brightness • This is the most useful when comparing the brightness of the stars

Distances to the Stars

• The sun is the closest star to Earth • It is approx. 150, 000 km (93, 000 miles) from the Earth – This distance is called an astronomical unit (AU) • The closest star to Earth, after the sun, is Alpha Centuri – It is 300, 000 times farther away from Earth than the sun. Because of the great distances in space, larger units of measure must be used • The light-year is the distance that light travels in one year

Star Formation & Origin

• large clouds of dust and gas in space are the basic materials needed for star formation • the majority of this gas is hydrogen • some outside force causes the cloud to be pushed together • as the gas and dust get closer, friction between the particles causes the temperature to increase • the attraction of gravity between the particles causes them to continue to move together, and density also

• friction increases and temperature increase until the center becomes so hot that nuclear fusion takes place • hydrogen atoms are forced together to form helium atoms, and energy is released • In a nuclear reactor like Indian Point, nuclear fission takes place – This is when radioactive atoms are split apart to release energy

But where does the gas & dust come from? ?

SUPERNOVAS • One of the most energetic explosive events • occur at the end of a star's lifetime, when its nuclear fuel is exhausted and it is no longer supported by the release of nuclear energy • If the star is particularly massive, then its core will collapse and in so doing will release a huge amount of energy • This will cause a blast wave that ejects the star's envelope into interstellar space

Etna Carinae Supernova remnant Supernova rings

SUPERNOVA 1987 – right image is the star that became the left image after going supernova – shone brighter than most galaxies

NEBULA • Clouds of dust & gas (supernova remnants? ) • 2 Main Types: – Diffuse Nebula – nearby star illuminates the gas/dust cloud – Dark Nebula – Dark patch against moredistant stars (dust/gas is blocking the light from stars behind it)

ORION NEBULA VEIL NEBULA HELIX NEBULA KEYHOLE NEBULA

CAT’S EYE NEBULA

ESKIMO NEBULA 5000 LY FROM EARTH - 10, 000 YRS OLD

CRAB NEBULA

HORSEHEAD NEBULA – PART OF ORION

A STAR IS BORN… I WANT MY MOMMY!!

THE BIRTH OF A STAR (OOH IT’S A GIRL!) STELLAR NURSERY A STAR BEGINS TO FORM IN A NEBULA (CLOUD OF GAS & DUST) GLOBULE DUST & GAS COMPRESS DUE TO GRAVITATIONAL FORCES, FORMING A SLOWLY ROTATING GLOBULE COLLAPSE PROTOPLANETARY DISK & CORE GRAVITY BECOMES TOO STRONG & THE GLOBULE COLLAPSES, SPINNING INCREASES SPIN, PRESSURE, & TEMPERATURE INCREASE, PLANETS ARE FORMED, AND CENTRAL CORE (SUN) FORMED

LIFE CYCLE OF STARS • A star’s life cycle is determined by its MASS – The larger the star, the faster it burns out! • A star’s MASS is determined by the MATTER available in the nebula of formation

LIFE CYCLE OF STARS SUN-LIKE STARS STELLAR NURSERY RED GIANT PLANETARY NEBULA WHITE DWARF BLACK DWARF (UP TO 1. 5 X MASS OF OUR SUN) MASSIVE STARS RED SUPERGIANT SUPERNOVA NEUTRON STAR (1. 5 – 3 X OUR SUN) STARS FORM IN A NEBULA OF GAS & DUST SUPERMASSIVE STARS > 3 X OUR SUN RED SUPERGIANT SUPERNOVA BLACKHOLE

DEATH OF A SUN-LIKE STAR RED GIANT LONGEST, MOST STABLE PERIOD OF A STAR’S LIFE – CONVERTS HYDROGEN TO HELIUM, RADIATING HEAT & LIGHT NUCLEAR FUEL DEPLETES, CORE CONTRACTS, SHELL EXPANDS PLANETARY NEBULA WHITE DWARF BLACK DWARF STAR COOLS ARE STAR SHRINKS LOSES BECOMING ONLY A FEW ALL HEAT OUTER LAYERS DRIFT THOUSAND TO SPACE AND MILES OFF INTO BECOMES ACROSS! SPACE IN COLD AND SPHERE-LIKE NO DARK PATTERN NUCLEAR REACTION

Handy Dandy Earth Science Reference Tables Page 15

H-R DIAGRAM

Properties of the Sun • average size yellow star • fairly cool compared to other stars • diameter is approx. 110 times larger than Earth’s, with a volume that hold more than 1, 000 Earths. • Light traveling from the sun takes approx. 8 minutes 20 seconds to reach Earth! • surface temperature is approx. 5, 500 C and its interior temperature is

Sunspots & Prominences • Sunspots are regions of intense magnetic fields • Sunspot temperatures are cooler than the photosphere, which makes them appear as dark spots • Prominences are regions along a magnetic field line where conditions are right for light to be emitted • Huge, arching columns of gas often

Solar Flares • Occasionally, kinks and stresses occur on magnetic field lines discharging amounts of energy (known as Solar Flares) • The amount of energy released is equivalent to a 2 billion megaton bomb • Flares release large numbers of particles into the corona

Source of the Sun’s Energy • The process of NUCLEAR FUSION • Einstein explained this process as E = MC² (matter can be converted into energy) • The hydrogen molecules that the sun is made of fuse together to form a helium atom. When this occurs, energy is given off! • **It is estimated that the sun has enough mass for nuclear fusion to

GIANTS/SUPERGIANTS • the brightest & largest kind of star • luminosities of 10, 000 to 100, 000 • radii of 20 to several hundred solar radii (about the size of Jupiter's orbit) • two types are red supergiants (Betelgeuse and Antares) and blue supergiants (Rigel)

Betelgeuse a red supergiant, with about 20 times the mass and 800 times the radius of the Sun, so huge that it could easily contain the orbits of Mercury, Venus, Earth, and Mars. It will probably explode as a supernova at some point within the next 100, 000 years. Even at its relatively remote distance, it normally ranks as the tenth brightest star in the sky. Rigel, a blue supergiant, has a diameter of about 100 million kilometers, some seventy times that of the Sun. Within a few million years, it will probably evolve to become a red supergiant like its neighbor in Orion (though not in physical

Dwarf Stars • A term used, oddly enough, to describe any star that is of normal size for its mass • The Sun, for example, is classified as a yellow dwarf • In general, dwarf stars lie on the main sequence and are in the process of converting hydrogen to helium by nuclear fusion in their cores

White Dwarfs • A medium sized star that has exhausted most or all of its nuclear fuel and has collapsed to a very small size • Typically part of a planetary nebula • Eventually cools into a BLACK dwarf (lump of carbon) – This takes BILLIONS of years! – This is the fate of OUR SUN!

Neutron Star • The imploded core of a massive star produced by a supernova explosion • The most dense known objects in the universe! – A sugar cube of neutron star material weighs 100 million tons! (think Mt. Everest)

BLACKHOLES • A supermassive star that undergoes supernova and the core of the star is “swallowed” by its own gravity • readily attracts any matter and energy that comes near it

Blackholes cont… • It is an area where the escape velocity is greater than the speed of light. • The more massive an object is, the faster you have to travel to escape its gravity. • This is known as the escape velocity. • Black holes are so massive that their escape velocity is faster than the speed of light. • Since nothing can travel faster than light, nothing can escape the gravity of a black

3, 700 LY wide dust-disk encircling a 300 million solar mass blackhole in the center of an elliptical galaxy. The disk is a remnant of an ancient galaxy collision and could be “swallowed” up by the blackhole in a few billion years.

Galaxies & the Universe

Galaxies • system containing millions to billions of stars – Ex. the Milky Way galaxy contains over 100 billion stars • Milky Way galaxy is a spiral shaped galaxy with a large central cluster of stars, and thinner “arms” radiating out from the center – The solar system is located on one of the arms of the Milky Way galaxy

Origin of the Milky Way • Formed 10 -12 billion years ago • Possibly collided with smaller galaxies • Globular star clusters formed • Stars and solar systems formed roughly 5 billions years ago

Milky Way

Andromeda Galaxy – 2. 9 million LY from earth

Sombrero Galaxy – 50 million LY from earth – 100, 000 LY across

Hoag’s Galaxy – 120, 000 LY wide – perfect ring of blue stars surrounding older nucleus of yellow stars

When galaxies collide…

Galaxy Formation • The formation of all the galaxies is explained by the Big Bang Theory • Simply put, it states that the universe was a big ball of hydrogen gas that exploded outward • The expanding cloud had areas that condensed into galaxies that are still expanding out from the center (the universe is getting larger) – We can see this with RED SHIFT!

Space is BIG. Really BIG. You just won’t believe how vastly hugely mind-bogglingly big it is.