STARS A Life and Death Production

Nebula A very large diffuse mass of interstellar dust and gas (mostly Hydrogen). This material starts to collapse in on itself due to gravitational forces. Eventually enough material gathers together to form a gas clump called a protostar.

Examples of Star Forming Nebula Cone NebulaEagle Nebula

Protostar As a gas clump collapses, it heats up because the gas particles collide more often and it starts to spin (counterclockwise) The gas clump forms a disk with the protostar in the center. Extra material in the disk may form planets.

Protostars in Infrared Light Visible Light Infrared Light Dust clouds block visible light whereas infrared light can pass through the dust clouds and be seen as bright spots where new stars are forming.

Nuclear Fusion When enough material collapses the temperature and pressure can build until nuclear fusion starts in the core. 4 H  He The star settles down to spend about 90% of its life as a main sequence star.

Main Sequence Stars Depending on the size of the protostar a small or medium sized star may be created such as our sun. Small sized stars may last for 100 billion years. Medium sized stars may last for 10 billion years. Large stars (10 times the mass of our sun) use their hydrogen fuel faster and may only last a few million years. However they are 5000 times brighter than our sun. Extremely large stars (30 times the mass of our sun) may only last for one million years and are extremely bright (and are very rare).

Old Age Eventually all the H 2 is converted to He and the nuclear reactions stop. Gravity causes the core to shrink. As the layers collapse, fusion may start again using Helium as the fuel and the outside layers puff out to form a RED GIANT.

When our Sun expands and becomes a red giant, Mercury, Venus and possibly Earth will be swallowed up by the Sun. If Earth is not swallowed up, the Sun will heat the Earth's surface so that the oceans will boil and the atmosphere will evaporate away. Main Sequence Star

Final Farewell When the core fuel runs out again, the outer layers are ejected and a planetary nebula forms.

Supernova The largest stars shed their layers in a massive explosion called a Supernova. The end result is also a planetary nebula. Supernova are so bright that they can outshine an entire galaxy for a period of time.

Planetary Nebula from a Supernova

Supernova 1987A In February 1987, a supernova exploded in a nearby galaxy. It was the first supernova to be clearly visible to the unaided eye in over 400 years. BEFOREAFTER

Supernova 1987a Remnants

Death What remains after the outer layers of a star are blown off depends on the mass of the core. 1. Small and medium stars will shrink down to a white dwarf. 2. Large stars form a neutron star. 3.The largest of the large will collapse to a point called a black hole.

White Dwarf The last stage of a small to medium sized star. After losing its outer layers of gas as a planetary nebula the rest of the star collapes to about an Earth-sized object and will remain hot enough so that it appears as white light. These celestial objects are extremely dense (a lot of matter in a very small volume).

Neutron Star The last stage of a large sized star (10 solar masses). After losing its outer layers of gas as a planetary nebula the rest of the star collapes to about 10 to 20 km in size and is even more dense than a white dwarf. One teaspoonful of a neutron star weighs about 2 billion tons.

Black Hole This collapsed core is so dense that not even light can escape it’s gravitational pull! The last stage of a very large sized star (30 solar masses). It may only be a few kilometers in size.

Star Colour The colour of a star is dependent on its temperature. The order of colours from hottest to coolest is: Blue Bluish-white White Yellowish-white Yellow (our sun) Orange Red

Star Brightness The brightness of a star as we see it from Earth is dependent on two things: 1. How big/hot the star is. 2. How far away the star is.

The brightness of stars are split into six categories of magnitudes. The brightest stars are called first-magnitude and the faintest stars visible with the unaided eye are called sixth magnitude. The rest of the stars are ranked in between. Magnitude

Apparent Magnitude This is the brightness of a star as it appears to someone looking at the night sky. This is not an indication of how bright the star actually is since the observed brightness is affected by how far away the star is.

Brightness is affected by distance If two stars of equal size and brightness were observed, the closer of the two stars would appear brighter to us and the further star would appear dimmer.

Absolute Magnitude This discrepancy in measuring the brightness of stars led to a new measurement called absolute magnitude. This is an actual measurement of the brightness of a star if it were located 3.26 light years from Earth (1 parsec).

An example of Absolute Magnitude Stars as they actually appear in the sky. The same stars as they would appear if they were all 3.26 light years from Earth.