STARS

The Stars Life Begins From a Nebula:

THE    NEBULA STARTS TO SHRINK FROM THE INTERSTELLAR MEDIUM Gravitational forces cause nebula to shrink The interstellar medium (Nebula) is the gas and dust that is found between many stars. It is mostly hydrogen and some other trace elements. Some areas have heavier gases than other regions. Within the mixture there are large clouds of denser gases than other areas of the mixture. Spheres of matter build with in the clouds As the cloud shrinks the nebular sphere begins to rotate more rapidly. Kind of like when a skater spins and pulls in their arms to go fast With this Nebula collapsing: The clouds center collapses further and concentrates into a gas/solid mass (ball) the temperatures really increases to form a PROTOSTAR Temperature increase due to: Collision between atoms creating friction Increased pressure due to increased density Incredible Detail  Image by NASA/STSCI/Nolan Walborn/Hubble Heritage Team  This beautiful image of the Keyhole Nebula, located within the larger Carina Nebula, illustrates Hubble's unprecedented power to resolve fine detail. Space images take on the vibrancy of family snapshots, with none of the grainy, two-dimensional quality often seen in telescope images of the past. "You have enough information that you can actually perceive 3-D structures in the nebulae," says Space Telescope Science Institute (STSCI) astronomer Nolan Walborn. "That is one of the advantages of Hubble that I don't think was necessarily foreseen."  Credit - National Geographic Magazinehttp://magma.nationalgeographic.com/ngm/0312/feature3/index.html

PROTOSTAR: 1st stage of a stars life As the protostars core reaches 10,000 degrees Celsius NUCLEAR FUSION BEGINS: Nuclear Fusion:  Nuclear Fusion is when small atomic nuclei combine to form large atomic nuclei, which releases a lot of energy. Example of energy released: 1 gram of hydrogen converts to helium, which makes enough energy to light 100-watt light bulb for 3000 (thousand) years. Review 1st Stage of stars life: PROTOSTAR Atoms attract to each other Gravity makes atoms collapse into a sphere Temperature and pressure increases Nuclear fusion begins

MAIN SEQUENCE STAR 2nd Stage of Stars Life When this happens the star is called a Main Sequence Star: This is the stage that our sun is currently experiencing.  (Z.A.M.S = Zero Age Main Sequence) Longest life stage of a star Energy generated in core of star Hydrogen (H) atoms fuse to become Helium (He) atoms Energy radiating away from star which balances gravitational pull inward Maintains a stable size as long as there is ample supply of hydrogen atoms When the H runs out it changes star type

3rd Stage of Stars Evolution: Giants and Supergiants Happens when almost all of the hydrogen atoms inside of the core have fused into Helium atoms. Without H as a source of fuel the core contracts under the force of the stars gravity. Stars core temperature increases as the core contracts  The stars shell of gas expands and cools  The increased core temperature causes the mainly He left to change into carbon atoms. SIZE Giants: 10X bigger than our sun Supergiants: 100 X bigger than our sun The star changes yet again towards a White Dwarf Star

4 th stage of Stars Evolution:  White Dwarf Star This Hubble Space Telescope image shows Sirius A, the brightest star in our nighttime sky, along with its faint, tiny stellar companion, Sirius B. Astronomers overexposed the image of Sirius A [at center] so that the dim Sirius B [tiny dot at lower left] could be seen. Image Credit: NASA, ESA, H. Bond (STScI), and M. Barstow (University of Leicester) Very little H or He energy available for the Red Giant or Super giant star so it changes into a WHITE DWARF STAR Gravity causes the core to collapse inwards Leaves a hot really dense core of matter Really hot in temperature but the star is dim in brightness due to its decrease in size A white dwarf star begins its life by casting off a cocoon that enclosed its former self.  In this analogy, however, the Sun would be a caterpillar and the ejected shell of gas would become the prettiest of all! The above cocoon, the planetary nebula designated NGC 2440, contains one of the hottest white dwarf stars known. The white dwarf can be seen as the bright dot near the  photo's center. Credit: H. Bond (STScI), R. Ciardullo (PSU), WFPC2, HST, NASA  Credit - www.fcaglp.unlp.edu.ar/evolgroup/ White dwarf either dies out into a dead star  Black Dwarf which would be the end of stars life: Or during the cooling process it might explode which is called a NOVA.

NOVA: Nova Cygni 1992 http://hubblesite.org/newscenter/newsdesk/archive/releases/category/star/nova/ a star that suddenly increases dramatically in brightness and then fades to its original luminosity over a short period of months or years.  May repeat process repeatedly

or it might SUPERNOVA The Star needs a really large size to supernova Stars with 10 to 100 X the size of our SUN  Due to the large amount of Carbon Atoms in the Core it fused again to form heavier element like Fe (iron)  Iron core absorbs huge amounts of energy and collapses. Causes the outer part of star to VIOLENTLY explode 100X brighter flash than a nova In 1054 China records show flash that lasted over 3 week

5 TH Stage of Stars Evolution After major explosion of a SUPERNOVA  NEUTRON STAR It may contract into a very small dense ball of NEUTRONS called a Neutron Star 1 teaspoon of this would be approximately 100 million tons of Earth Due to the great density it rotates very rapidly It might have a diameter of only 30 kilometers Some Neutron stars emit 2 beams of radiation.  These kind of stars are called  PULSAR Stars.  What is a Pulsar? Pulsars are rapidly-spinning neutron stars. These stars have very strong magnetic fields. Jets of charged particles are ejected from the magnetic poles of the star. This material is accelerated, producing beams of radiation (light) of all wavelengths from the magnetic poles. The "north" and "south" poles of the magnetic field may not coincide with the star's rotational poles, as shown in the image below. This means that the beams of light sweep around as the star rotates. We see a pulsar when one of its beams of radiation crosses our line-of-sight. A pulsar is like a lighthouse. The light from a lighthouse appears to be "pulsing" because it only crosses our line-of-sight once each time it spins. Similarly, a pulsar "pulses" because we see bright flashes every time the star spins. This is illustrated below. Credit Information / Photos - www.airynothing.com/.../sources/pulsars.html

SOME STARS ARE SO MASSIVE IN SIZE THAT THEY ARE TO BIG TO BE NEUTRON STARS : These form  BLACKHOLES Credit: Margaret Masetti (GSFC) Galactic (stellar sized) black holes are often found in a binary system. This artist's conception shows how the accretion disk forms as material is pulled from the companion star and swirls into the black hole.  credit - NASA imagine.gsfc.nasa.gov/.../black-holes.html Due to their massive size after the star supernovas: The stars core contracts with even greater force.  The huge amount of contraction even crushes the dense core of the star Matter is continued to be pulled in and even traps light energy A Chandra image of the supermassive blackhole at the center of our Galaxy. Credit NASA/CXC/MIT.F. K. Baganoff et al.  Astronomers have finally confirmed something they had long suspected: there is a super-massive black hole in the center of our Milky Way galaxy. The evidence? A star near the galactic center orbits something unseen at a top speed of 5000 kilometers per second. Only a black hole 3 million times more massive than our Sun could cause the star to move so fast. Still, a key mystery remains. Where did the black hole come from? For that matter, where do any super-massive black holes come from? There is mounting evidence that such "monsters" lurk in the middles of most galaxies, yet their origin is unknown. Do they start out as tiny black holes that grow slowly, attracting material piecemeal from passing stars and clouds? Or are they born big, their mass increasing in large gulps when their host galaxy collides with another galaxy? STAR CHART