|
We searched on "death of a star," uncertain what would turn up. We received a mixed bag of results -- celebrities vying with celestial bodies for prominence in the "web site matches." However, near the top of the page we spied a link to the NASA Observatorium essay on Stellar Evolution and Death and clicked on it. Basically, what happens when a star dies depends on its size at birth. Fueled by the burning of their own hydrogen/helium cores, all stars evolve, age, and eventually explode or expire, leaving behind stellar remains. "White dwarfs, neutron stars, and black holes are the dead cinders of former stars." The longevity
of stars is measured in millions or billions of years, and star size is measured in units of solar mass -- equal to that of our sun (or about 330,000 Earth masses). Stars that are greater than eight solar masses when they are born usually end their lives in a gigantic supernova, one of the brightest events in the universe. After this violent and dramatic death, they leave behind a neutron star or black hole. Smaller stars shed layers over thousands of years, ejecting planetary nebula as they run out of nuclear fuel and enter their red giant phase. The
ejected nebula is an expanding shell of gas that leaves behind a burnt-out, highly compact star known as a white dwarf. Understanding the evolution of stars helps us discover more about the size and age of the universe. It also enables us to predict the future of our Sun. Earth's Sun is approximately 4.5 billion years old, and has converted about half the hydrogen originally present in its core into the element helium, releasing life-sustaining light and heat into our home solar system.
|
