T HE E VOLUTIONARY C YCLE OF S TARS

C YCLE OF S TARS The 3 major interests (or parameters) of astronomers are their mass, luminosity, their surface temperature & distance they are away from us. They are also used to place stars into an evolutionary sequence which describes their formation, life & death. “Luminosity” of a star is a function of its radius & effective temperature.

T HE H ERTZSPRUNG -R USSELL D IAGRAM

F OUR MAIN G ROUPINGS “M AIN S EQUENCE S TARS ” It is a defined curved trend across the center of the diagram which displays a relationship between mass & luminosity

F OUR MAIN G ROUPINGS “R ED G IANTS ” They are stars which are cooler, but more luminous than stars on the main trend.

F OUR MAIN G ROUPINGS “S UPER G IANTS ” Most massive of all stars. Short life spans.

F OUR MAIN G ROUPINGS “W HITE D WARFS ” This is the last stage of stellar evolution.

B IRTH -L IFE -D EATH A giant molecular cloud contains H at low temperatures. This is a NEBULA(e) that contains gas & dust from the beginnings of a star. Cosmic cloud of gas & dust, basic building blocks of the universe, & the largest objects in the universe. Temperatures rise, driven by gravitational collapse, and a PROTOSTAR forms. It is the early stage in star formation. The star evolves & becomes part of the Main sequence of stars. The star eventually converts into a Red Giant & expands to up to 100 times the diameter of the original star. Red Giants develop as the hydrogen in the core is depleted. White Dwarf The final evolutionary state whose mass is not too high. This is the last stage of stellar evolution.

Super Nova  is a stellar explosion that creates an extremely luminous object. A supernova causes a burst of radiation that may briefly outshine its entire host galaxy before fading from view over several weeks or months.  The explosion expels much or all of a star's material  is a stellar explosion that creates an extremely luminous object. A supernova causes a burst of radiation that may briefly outshine its entire host galaxy before fading from view over several weeks or months.  The explosion expels much or all of a star's material

Black Hole FThey are formed from the cores of super massive stars and can best be described as regions of space where so much mass is concentrated that nothing, not even light, can escape the gravitational pull.

Dark Matter  Scientists estimate that what we do see may only account for 10% of the mass of the universe. That means that 90% of the matter is invisible. Some estimates even place this number as high as 99%. Astronomers refer to this invisible mass as dark matter.