Post on 16-Dec-2015
transcript
Chapter 21Chapter 21
STARSSTARS
Characteristics of StarsCharacteristics of Stars• Groups of stars that form patterns in the
sky are called constellations– Example: Ursa Major (Big Bear), Ursa Minor
(Little Bear), and Orion
• The last two stars in Ursa Major’s “dipper” are called the “Pointer Stars” and are be used to find Polaris (North Star)
• Polaris is located directly above the North Pole (90º N), and is only visible in the northern hemisphere (above the Equator)
Circumpolar Circumpolar ConstellationsConstellations
• Because of the Earth’s rotation, the constellations appear to move
• If the constellations 1) appear to move around Polaris and 2) can be seen at all times of year and 3) can be seen at all times of night, they are called circumpolar constellations – The constellations Ursa Major and Ursa
Minor are both circumpolar constellations
• Using time exposure photography, the apparent motion of the stars around Polaris can be recorded as circular trails
VIFVIFThe apparent motion of stars is due to the
Earth’s daily rotation on its axis.
The stars don’t move – WE DO!!!!
Here is a time-lapse photo of circumpolar star movement…
Star trail photos!!!!!
•The positions of the constellations as viewed from Earth changes from season to season
•This is caused by the revolution of the Earth and the change in Earth’s position in its orbit around the sun –Example: Orion the Hunter is a winter constellation
Ex – when the Earth is in this position (Nov 21), the bright sun during the day blocks our view of all of the constellations toward the lower right side of the diagram
Physical Properties of Physical Properties of StarsStars
• Stars differ in size, density, mass, composition, and color
• The color of a star is determined by it surface temperature (ESRT’s P. 15 top) – The hotter the star, the bluer the
color. The cooler the star, the redder the color. (yeah, yeah, I know, it’s backwards….)
– The sun is an AVERAGE SIZE, medium, yellow star
• Most stars are made up of mostly hydrogen and helium (approx. 98%)
• The remaining 2% may be other elements
• A spectral analysis (remember Ch. 20) 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
Physical Properties of Physical Properties of StarsStars
•Some stars may appear to be brighter than others
•The star’s brightness may be described in three ways
1. APPARENT MAGNITUDE2. LUMINOSITY3. ABSOLUTE MAGNITUDE
(See the H-R Diagram in the ESRT’s P.15)
ApparentApparent MagnitudeMagnitude
• How bright a star appears (apparent) to us on Earth
• The farther a star is from Earth (increasing distance), 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
LuminosityLuminosity •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 Absolute MagnitudeMagnitude
•The luminosity of the stars if they all brought to 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
The H-R Diagram
Distances to the Distances to the StarsStars
• The sun is the closest star to Earth• It is approx. 150,000,000 km (93,000,000
miles) from the Earth– This distance is called an astronomical unit
(AU)
• The next closest star to Earth, after the sun, is Proxima Centauri– 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
• Since light can travel 300,000 km/sec (186,000 miles/sec), light travels 9.5 trillion km/year!!! – Proxima Centuri is 4.3 light-years from Earth!
So…
One Astronomical Unit (AU) = 150,000,000 km
And, one light year (LY)= 9.5 trillion km
(9,500,000,000,000 km)
Okay… let’s calculate the Okay… let’s calculate the distances from Earth to each distances from Earth to each planet in Astronomical Units planet in Astronomical Units
(AU)(AU)
Remember – 1 AU = 150,000,000 kmJust divide the distance from the
Sun in km by 150,000,000 km.
Example: Jupiter = 778,300,000 km 150,000,000 kmJupiter is 5.19 AU from the Sun
Star Origin,Star Origin,FormationFormation
& & EvolutionEvolution
• 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
of gas and dust 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 increases
• friction increases and temperature increases until the center becomes so hot that nuclear fusion takes place
• hydrogen atoms are forced together to form helium atoms, and a tremendous amount of 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
OK, so stars form from OK, so stars form from hydrogen gas and dust, hydrogen gas and dust, but where does that gas but where does that gas
& dust come from????& dust come from????
SUPERNOVASSUPERNOVAS• One of the most energetic explosive
eventsoccur 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 gas envelope into interstellar space
Etna Carinae
Supernova ringsSupernova remnant
SUPERNOVA 1987 – right image is the star that became the left image after going supernova – shone brighter
than most galaxies for a few months!
NEBULAENEBULAE• Clouds of dust & gas (supernova
remnants?)• 2 Main Types:
– Diffuse Nebula – nearby star illuminates the gas/dust cloud
– Dark Nebula – Dark patch against more-distant stars (dust/gas is blocking the light from stars behind it)
Here are some images of nebulae, courtesy of our friend Hubble…
ORION NEBULA
KEYHOLE NEBULA
HELIX NEBULA
VEIL NEBULA
CAT’S EYE NEBULA
CARINA NEBULA
8000 LY FROM EARTH – 200 LY ACROSS
ESKIMO NEBULA
5000 LY FROM EARTH - 10,000 YRS OLD
EAGLE NEBULA
7,000 LY AWAY FROM EARTH
STINGRAY NEBULA
YOUNGEST KNOWN NEBULA – 130 SOLAR SYSTEMS ACROSS – 18,000 LY AWAY FROM EARTH
CRAB NEBULA
HORSEHEAD NEBULA – PART OF THE ORION NEBULA
SNAKE NEBULA – a Black Nebula!!!
A STAR IS A STAR IS BORN…BORN…
I WANT MY MOMMY!!
LIFE CYCLE OF STARSLIFE CYCLE OF STARS
• VIF!!!! - 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
STELLAR NURSERY
STARS FORM IN A NEBULA OF
GAS & DUST
SUN-LIKE STARS
(UP TO 1.5 X MASS OF OUR
SUN)
RED GIANT WHITE DWARF
BLACK DWARF
MASSIVE STARS
(1.5 – 3 X OUR SUN)
SUPERMASSIVE STARS
> 3 X OUR SUN
RED SUPERGIANT
RED SUPERGIANT
SUPERNOVA
SUPERNOVA
NEUTRON STAR
BLACKHOLE
PLANETARY NEBULA(NOVA)
DEATH OF A SUN-LIKE STAR
SUN-LIKE STAR RED GIANT NEBULA WHITE DWARF
BLACK DWARF
LONGEST, MOST STABLE PERIOD OF A STAR’S LIFE –
CONVERTS HYDROGEN TO HELIUM, RADIATING
HEAT & LIGHT
NUCLEAR FUEL
DEPLETES, CORE
CONTRACTS, SHELL
EXPANDS
OUTER LAYERS DRIFT
OFF INTO SPACE IN
SPHERE-LIKE PATTERN
STAR COOLS ARE
SHRINKS BECOMING
ONLY A FEW
THOUSAND MILES
ACROSS!
NO NUCLEAR REACTION
STAR LOSES
ALL HEAT TO SPACE
AND BECOMES
COLD AND DARK
CARBON BALL
GIANTS/GIANTS/SUPERGIANTSSUPERGIANTS
• the brightest & largest kind of star
• luminosities of 10,000 to 100,000 • radii of 20 to several hundred
solar radii (they are 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, Mars & Jupiter. 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 space), Betelgeuse.
Dwarf StarsDwarf 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 DwarfsWhite 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 StarNeutron Star•The imploded core of a
massive star produced by a supernova explosion
•The most dense known objects in the universe!–A sugar cube size of neutron star material weighs 100 million tons!!!!!!!
BLACK HOLESBLACK HOLES•A supermassive star that
undergoes supernova and the core is when the star is “swallowed” by its own gravity
•readily attracts any matter and energy that comes near it - including light…
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 Galaxies & the UniverseUniverse
Big Bang TheoryBig Bang Theory
• The Big Bang Theory is the dominant scientific theory about the origin of the universe
• According to the big bang, the universe was created sometime between 10 billion and 20 billion years ago from a cosmic explosion that hurled matter and in all directions
Galaxy FormationGalaxy 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 via RED SHIFT!
The Solar System
GalaxiesGalaxies• system containing millions to billions of
stars – Ex. the Milky Way galaxy contains over
500,000 million 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 about 2/3 away from the center
Origin of the Milky WayOrigin 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 billion years ago
Milky Way
Andromeda Galaxy – 2.9 million LY from earth
Our CLOSEST neighbor!!!
Ursa Major’s galaxy (a galaxy that we can see within the constellation) –
50 million LY from earth!
Sombrero Galaxy – 50 million LY from earth – 100,000 LY across
Overlapping Spiral galaxies – 140 million LY from earth – within the constellation HYDRA
Whirlpool Galaxy – 37 million LY from earth – 60,000 LY across
Hoag’s Galaxy – 120,000 LY wide – perfect ring of blue stars surrounding older nucleus
of yellow stars
When galaxies collide…