Part 4 Astronomy 4

Astronomy : 

Astronomy Birth, Life, Makeup, and Death of Stars

Birth of Stars : 

Birth of Stars Recall the Nebular Hypothesis The birth of stars begin in dark, cool, interstellar black clouds made up of dust and gases The cloud becomes denser and begins to contract As the nebula shrinks it begins to shrink, heat up, and spin The sun forms in the center, while the planets form in the out reaches of the nebula

Birth of Stars : 

Birth of Stars Birth of stars

Life of Stars : 

Life of Stars Stages of life As time passes, the temperature slowly increases until it is hot enough to radiate energy from its surface in the form of long-wavelength red light This large red object is called a Protostar It is not yet hot enough to engage in Nuclear Fusion

Life of Stars : 

Life of Stars Protostar stage Continued contraction causes core to heat more than the outer layer When the core reaches 10million K, pressure within is so great that nuclear fusion of hydrogen begins The star is now born! Heat from the hydrogen fusion causes gases to increase motion This causes an increase in outward pressure When the outward pressure equals the inward force of gravity, the star becomes a stable main-sequence star

Life of Stars : 

Life of Stars Main-Sequence Stars Now the star spends its life trying to keep the balance of outward pressure equaling inward pressure This continues for a few billion years until the outward pressure is finally overcome by the gravitational force inward

Life of Stars : 

Life of Stars Main-Sequence Stage Different stars age at different rates Hot, massive blue stars radiate energy at such an enormous rate that they deplete their hydrogen in just a few million years Less massive stars can remain stable for billions of years before burning out Our star is a main sequence star with a life expectancy of about 10 billion years The least massive red stars can delay their death by fusing heavier elements and becoming a giant

Life of Stars : 

Life of Stars Red Giant Stage This stage occurs because the zone of hydrogen fusion continually moves outward leaving behind a helium core No fusion is taking place at the core, so there is no outward pressure The core begins to contract As it contracts it grows hotter and radiates energy to the hydrogen in the outer core increasing hydrogen fusion This makes the outer layer increase in size again The result is a Red Giant

Life of Stars : 

Life of Stars Red Giant Stage As the surface expands, it cools This explains the reddish appearance As the core continues to collapse, it reaches 100 million K. This is hot enough to convert helium to carbon So, helium and hydrogen are now used to produce energy Eventually, the fuel is consumed Gravity takes over and squeezes the star into the smallest, most dense piece of matter possible

Life of Stars : 

Life of Stars

Death of Stars : 

Death of Stars Burnout and Death All stars, regardless of their size, eventually run out of fuel and collapse due to gravity Not all stars die the same death. How a star ends up depends on its mass

Death of Stars : 

Death of Stars Death of low-mass stars Are not massive enough to reach the high temperatures and pressure to fuse helium They never reach a red giant stage They stay a main sequence star until they consume their hydrogen fuel and collapse into a white dwarf

Death of Stars : 

Death of Stars Death of medium mass stars Go through the red giant stage During their collapse into a white dwarf, they cast off their bloated outer layer, creating a expanding round layer of gas The remaining hot, central white dwarf heats the gas cloud causing it to glow These are called planetary nebulae

Death of Stars : 

Death of Stars

Death of Stars : 

Death of Stars

Death of Stars : 

Death of Stars Death of Massive Stars Massive stars have relatively short life spans They end their lives in brilliant explosions called Supernova During a supernova the star becomes millions of times brighter than its pre-nova self Supernova are thought to be triggered when a massive star consumes most of its nuclear fuel The star collapses The implosion results in a shock wave which destroys the star and blast the outer shell into space The star then becomes a neutron star or a black hole

Death of stars : 

Death of stars

Death of Stars : 

Death of Stars

After Death : 

After Death Stellar Remnants After all the fuel is consumed, stars collapse into one of three states White Dwarf Neutron Star Black Hole

After Death : 

After Death White Dwarfs The star compacts to the size of Earth Matter is squeezed together so tightly that electrons are displaced much nearer to the nucleus The density is so great that a spoonful of the matter would weigh several tons As it contract the temperature can reach 25,000 k, but the white dwarf has no heat source and so will cool into a small, cold body called a black dwarf

After Death : 

After Death Neutron Stars These are smaller and more massive than white dwarfs Matter is squeezed so tightly that electrons combine with protons to produce neutrons If the Earth was to collapse to the density of a neutron star, it would have the diameter equal to the length of a football field A pea sized sample of this matter would weigh 100 million tons

After Death : 

After Death Supernovae into Neutron Stars After the outer layer is ejected, the core collapses to the size of a very hot neutron star This neutron star has a very strong magnetic field that causes it to rotate fast Radio waves generated by these rotating stars would be concentrated into two narrow zones that align with the star’s magnetic poles These would appear to be rapidly rotating beacons emitting strong radio waves These are called Pulsars. One was found in the early 1970s in the Crab Nebulae

After Death : 

After Death Supernovae Another option is to collapse into something even smaller than a neutron star These are called Black Holes Their gravity is so strong, that even light cannot escape

After Death : 

After Death Finding Black Holes Two methods seem to work Follow the X-rays As matter is pulled into a black hole, it becomes very hot and emits a flood of x-rays before being pulled in Binary systems Gases are pulled from a companion star and spiral into a disk shaped structure around the black hole while giving off x-rays

After Death : 

After Death