Life Cycle of Stars Mr. Weaver

Birth of a Star Nebula- A cloud of gas and dust where stars are born. Composed mostly of Hydrogen, with a little bit of Helium

Horsehead Nebula

Hourglass Nebula

Carina Nebula

Pillars of Creation Eagle Nebula

Birth of a Star Dust and gas pulled together by gravity, forming a disk. Center gets hotter as it gets compacted Massive jets of matter shoot out perpendicular to the disk When core reaches 15 million K, fusion starts and the star is born Leftover matter in disk forms planets

Formation of Star and Planets

Main Sequence Hydrogen converted to Helium in core through Nuclear Fusion Star is made up almost entirely of Hydrogen and Helium Our Sun is in the Main Sequence 90% of a Star’s total lifetime

Death Depends on Size Up to 12 Solar Masses: Red Giant, then White Dwarf 12-25 Solar Masses: Supernova/Neutron Star 25+ Solar Masses: Supernova/Black Hole

Sun Sized Stars As Hydrogen runs out, core collapses inwards and gets hotter Outer layers of Star expand outward Star swells into a Red Giant

Our Sun as a Red Giant in ~5 Billion Years

Sun Sized (continued) As Hydrogen runs out, Helium starts fusing into heavier elements When fuel runs out, the Red Dwarf sheds its outer layers, forming a Planetary Nebula Remaining Core is called a White Dwarf

Planetary Nebula White Dwarf

For Much Larger Stars As Hydrogen runs out, expands into a Red Supergiant. Helium fuses into increasingly larger elements. After Iron, fusion ceases to create energy (This is why Nuclear Fission of larger elements gives off energy) Once the core turns to Iron, the star ceases to produce energy and collapses inward

Supernova! When a giant star collapses in on itself, it rebounds back outwards in a tremendous explosion known as a supernova. These supernovas are incredibly bright, outshining their entire galaxy for a brief time. All elements heavier than Iron are created during these tremendous explosions

400 Year Old Supernova Remnant

12-25 Solar Masses Stars 12-25x the mass of our sun leave behind a super dense core known as a neutron star. A neutron star is made up entirely of neutrons Only about the size of one human city Incredibly dense: one thimble’s worth of neutron star would weigh 100 million tons

Neutron Stars Continued Neutron Stars spin extremely fast, rotating several times per second This is because stars rotate, and as the star shrinks its speed of rotation increases Neutron stars give off powerful beams of radiation. Every time they spin, we get a burst, like a lighthouse. We call these bursts Pulsars.

Escape Velocity The takeoff speed required to fully escape the gravitational pull of an object Mass and Radius of an object determine escape velocity Escape Velocity of Earth: 25,000 mph Escape Velocity of the Sun: 1.4 Million mph!

Stars >25 Solar Masses When the largest stars collapse, their cores implode into something even more dense than neutron stars These objects are so dense that the escape velocity is even higher than the speed of light This means, light cannot escape the pull of gravity We call these Black Holes

Black Holes Nothing can travel faster than the speed of light, so if light cannot escape a black hole, nothing can. We cannot observe black holes directly; they give off no light. We can only see their effects, for instance when they bend the light of other stars, or when large stars revolve around them

Event Horizon The boundary of a black hole, past which nothing will ever escape, is called the Event Horizon. Physicists are still trying to understand the complex warping of space-time that occurs within a black hole.

Black Holes (Continued) Astrophysicists have found evidence of many black holes throughout our observable universe. In fact, there is evidence that a super large black hole lives in the center of our own galaxy!