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Nebulas: The Birthplace of Stars • Nebula: – A cloud of gas and dust in outer space – Mostly consist of Hydrogen and Helium • When a nebula reaches a certain density, gravitational forces begin to pull the gas and dust particles close together causing a lump to form inside the main cloud of the nebula. • As more matter collects, more gravity develops creating a protostar (baby star). Crab Nebula M16 Eagle Nebula “Birth” of a Star When the protostar reaches critical density and temperature (~15x107°C), the gravitational forces pulling matter towards the center are so strong that it causes nuclear fusion to begin. This event causes a chain reaction that will continue for the star’s entire lifespan. “Birth” of a Star The star’s size eventually stabilizes when the gravitational force pulling matter inward matches the outward pressure of the fusion reaction. Not all Stars are Alike • A star’s mass determines – Brightness – Colour – Size – Lifespan • In the early 20th century, Ejnar Hertzsprung and Henry Norris Russell organized these variables into the Hertzsprung-Russell diagram. The Hertzsprung-Russell Diagram (H-R Diagram) Can be used to deduce the evolution of stars (how they change over time) ~90% of all stars plotted onto the H-R Diagram fall along a diagonal band called the Main Sequence Our Sun is an example of a Main Sequence Star “Death” of a Star Depending on its initial mass, a star may endure 1 of 4 known fates. Red Giant • • • • After 10 billion years, a main sequence star (like the Sun) has converted most of its hydrogen into helium. With less energy pushing outwards, the helium center starts to contract. This contraction causes the core to heat up. Heat from the core causes any remaining hydrogen in the outer layers to fuse and expand outward (eventually cooling and becoming red) White Dwarf • Small sized stars also convert most of their hydrogen fuel to helium at some point in their life. • Since small stars don’t have as much mass, they do not produce the conditions to reignite nuclear fusion. • The hot core remains and the outer layers simply drift away • When the white dwarf star cools, it looks invisible and is called a black dwarf Supernova Supermassive stars are rare compared to main sequence stars They tend to burn significantly faster than smaller stars Massive stars convert Hydrogen to Helium, then Helium to Carbon, etc, until Iron is formed through nuclear fusion. At this point, fusion cannot continue Supernova The growing force of gravity pulls matter towards the iron core and the star attempts to implode. The iron core prevents this and sends the solar material (nebular gas and dust) flying outwards into space in an awesome explosion called a supernova Neutron Star Massive stars (larger than the Sun) supernova and leave behind a neutron star (an extremely dense star composed of tightly packed neutrons) Neutron stars have immense gravitational force and tend to spin quickly. This spinning creates highfrequency radio waves, which have been detected by astronomers on Earth. Black Hole When a supermassive star dies / supernovas it leaves behind a core that is so massive and so dense that the gravitational force it produces does not let light escape Black holes are surrounded by radiation emitting celestial objects as they are under the influence of the black hole’s gravity (until they are absorbed) The Solar Nebula Theory • • • The Solar system formed ~5 billion years ago from a massive cloud of dust and gas (nebula) that began to contract The contraction caused a protostar to form As the protostar grew in mass it began to spin faster and faster (like a spinning skater pulling their arms and legs close during a twirl) causing the surrounding nebular dust to form a disc The Solar Nebula Theory When the protostar reached critical mass, nuclear fusion began The lighter elements (H and He) were thrown further from the Sun and became the gas giants Heavier elements remained close to the Sun and formed the terrestrial planets Evidence for the Solar Nebula Theory Explains why: All planets orbit in the same direction The planets all revolve around the Sun on the same plane Terrestrial planets are closer to the Sun while gas giants are further from the Sun Edwin Hubble and the Universe • Before 1920, it was established that the Milky Way Galaxy was the Universe. • In 1922-1923, Edwin Hubble observed what was thought to be spiral nebulae (The Andromeda and Triangulum galaxies) • Concluded that these nebula existed outside of the Milky Way and represented other galaxies, implying that the Universe is much larger than the Milky Way Galaxy. Andromeda Galaxy The Expanding Universe Edwin Hubble also observed that each galaxy seems to emit its own spectrum of light. NOTE: Light shifts its wavelength depending on whether it is moving toward an observer or moving away from an observer Hubble’s Law: The light from distant galaxies seems to be redshifted = Moving away = The Universe is expanding Dark Matter • • • Upon further study and with the help of technology, astronomers have found celestial objects moving at a speed that does not seem consistent with their surroundings They have also concluded that there isn’t enough visible mass in galaxies to explain their tremendous gravity This strange matter is unknown and “dark” because we don’t know what it is Dark Energy In 1998, it was observed that the Universe may be expanding at an accelerated rate (the expansion is getting faster and faster) Astronomers acknowledge that there may be an unknown force working against gravity. It is called “Dark” because we don’t know what it is and if it exists. The Big Bang Theory Cosmologists (people who study the physics and evolution of the Universe) believe that all matter, energy, forces and time expanded from a single infinitely small point The Big Bang Theory places the beginning of the Universe and beginning of time ~13.8 billion years ago Evidence for the Big Bang Theory Arno Penzias and Robert Wilson, two physicists, were conducting experiments with a sensitive antenna in Crawford, New Jersey (1965) They picked up radiation from all directions Through experimentation it was included that the energy represented remnant energy from the big bang Red Shift The Future The Big Freeze / Hear Death The Big Rip The Big Crunch The Big Bounce / Multiverse The Future: Large Hadron Collider • The Large Hadron Collider (LHC) is a gigantic scientific instrument near Geneva, where it spans the border between Switzerland and France about 100m underground. It is a particle accelerator used by physicists to study the smallest known particles – the fundamental building blocks of all things. It will revolutionise our understanding, from the minuscule world deep within atoms to the vastness of the Universe. The Future: Large Hadron Collider • The precise circumference of the LHC accelerator is 26 659 m, with a total of 9300 magnets inside. Not only is the LHC the world’s largest particle accelerator, just one-eighth of its cryogenic distribution system would qualify as the world’s largest fridge. • At full power, trillions of protons will race around the LHC accelerator ring 11 245 times a second, travelling at 99.9999991% the speed of light. Space Test Review You are responsible for the following text sections: All of chapter 8 excluding 8.7 All of the chapter 9 excluding 9.4, 9.5, and 9.9 You DO NOT need to review anything from chapter 10