The Star Lifecycle

The Beginnings The development of a star begins with the nebula, a swirling cloud of interstellar gas and dust molecules Because of gravitational attraction, dense parts of the nebula become more dense. These high density areas can unite into a tightly packed object called a protostar Gravitational collapse (in between stars)

Eagle Nebula – 95 light years across

The pillars of creation – in eagle nebula (towers are over 4 light years tall). About 7000 light years from earth.

Protostar As the protostar collects more material and becomes denser the temperature and pressure of it’s core increases. When the inner temperature reaches ~ 10 million degrees Celsius, a nuclear reaction ensues The fusion of Hydrogen atoms into an atom of Helium

Star Continued The fusion of H into He releases a vast amount of energy. This energy is radiated in many forms (visible light and heat!) https://www.youtube.com/watch?v=dg_DOM1OQoo This fusion causes the accretion process to stop, and the accretion disk will coalesce into planets https://www.youtube.com/watch?v=encWo_Jf6Ik (adding of material)

The bright spot is a new star igniting

Main Sequence Star The newly formed star will “burn” hydrogen for billions of years Our sun is in this phase (our sun is 4.5 billion years old, about halfway through its main sequence) https://www.youtube.com/watch?v=2U3ucaVzRqQ

Balancing act The incredible weight of all the gas and gravity try to collapse the star on its core. As long as there is a nuclear reaction taking place, the internal forces will balance the external gravitational forces.

Red Giant When a star is low on hydrogen, fusion slows, and the stars core begins to collapse The collapse causes the core to heat up, eventually reaching a temperature hot enough to start fusing He atoms together into Carbon. Increased temp causes increased fusion rates, thus the outer layers will experience more pressure and GREATLY expand as a result Luminosity 10000x

1 AU = 150 million km

Death of Stars Like the Sun When the He fuel runs out the core begins to collapse, and increase in temperature, causing the fusion of some heavier elements. Star has expanded so much that it doesn’t have the gravity to hold it’s outer layers – becomes planetary nebula The core expands and cools, no longer undergoing fusion (but is still extremely hot). It glows white white dwarf.

97% of stars in the Milky Way will “die” in this manner The White Dwarf will eventually cool down to the temperature of the surrounding space Black dwarf

Death of a Massive Star When He runs out the star begins to fuse heavier elements The heavier the element the less energy produced. Iron is the heaviest element that produces energy

Supernova Once the core becomes iron, the star has no more fuel, and can no longer support it’s own weight, thus collapsing on itself The core becomes so tightly packed that protons and electrons merge to form neutrons. The outer layers of the star fall inward on the neutron core, thereby crushing it further. In less than a second, the iron core, which is about the size of the Earth, shrinks to a neutron core with a radius of about 6 miles (10 kilometers).

Supernova The core heats to billions of degrees and explodes (supernova), thereby releasing large amounts of energy and material into space. The energy of the collapse and explosion is great enough to cause fusion of heavier elements! (Heavier then Iron) https://www.youtube.com/watch?v=44BwqpthXBg

Aftermath The remains of the core can form a neutron star or a black hole depending upon the mass of the original star. Neutron stars are the densest and smallest stars known to exist in the universe; with a radius of only about 10–13 km, they can have a mass of two Suns! (there is no more fusion)

Neutron Stars https://www.youtube.com/watch?v=ZW3aV7U-aik

99.9999999999996%

Black Hole With some SUPER massive stars the gravitational force can be so high that the core of the star can collapse into a singularity, a point of near infinite mass and gravity, known as a black hole The gravity surrounding a black hole is so great that light can’t even escape! (how we know they exist) – why its called black hole

https://www.youtube.com/watch?v=80HkL3EF2tc https://www.youtube.com/watch?v=pTHnesICCmY https://www.youtube.com/watch?v=sNXelB6gIzQ