Physical Science the Universe Notes 01/2014
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Physical Science The Universe Notes 01/2014
What Are Stars?
• ______: a large celestial body that is composed of gas and that emits light; the sun is a typical star
• ______: the distance that light travels in one year; about 9.5 trillion kilometers
• Stars are huge spheres of hot ______.
• The nearest star to the Earth is ______.
• We use the unit light-year to describe a star’s ______from Earth.
• Stars are driven by ______
• The ______of a star is extremely hot, extremely dense, and under extreme pressure.
• Nuclear ______takes place in the core of a star.
• Fusion combines the nuclei of ______atoms into ______.
• When two particles ______, energy is released.
• Energy moves slowly through the layers of a star.
• Energy moves through the layers of a star by convection and radiation.
• ______: rising hot gas moves upward, away from the star’s center, and cooler gas sinks toward the center
• ______: atoms absorb energy and transfer it to other atoms in random directions; atoms near the star’s surface radiate energy into space.
Studying Stars
• Why do some stars appear brighter than others?
• The brightness of a star depends on the star’s ______, ______, and ______from Earth.
• The brightest star in the night sky, Sirius, appears so bright because it is relatively ______to Earth.
• We learn about stars by studying ______.
• Stars produce a full range of ______, from high-energy X-rays to low-energy radio waves.
• Scientists use optical telescopes to study visible light and radio telescopes to study radio waves emitted from astronomical objects.
• Earth’s atmosphere blocks some wavelengths, so telescopes in space can study a wider range of the spectrum. • A star’s color is related to its ______.
• ______objects glow with light that has shorter wavelengths (closer to the blue end of the spectrum).
• ______objects glow with light that has longer wavelengths (closer to the red end of the spectrum.)
• Spectral lines reveal the composition of stars.
• The spectra of most stars have dark lines caused by gases in the outer layers that absorb light at that wavelength.
• Each element produces a unique pattern of ______
• Astronomers can match the dark lines in starlight to the known lines of elements found on Earth.
The Fate of Stars
• The sun formed from a cloud of gas and dust.
• Stars are born, go through different stages of development, and eventually die.
• The sun formed about ______years ago.
• Stars appear different from one another in part because they are at different stages in their life cycles.
• The sun now has a balance of inward and outward forces
• The fusion reactions in the core of the sun produce an outward force that balances the inward force due to gravity.
• Over time, the percentage of the sun’s core that is helium becomes larger.
• Eventually the core will run out of hydrogen and the sun will begin to die.
• Scientists estimate that the sun can continue nuclear fusion for another ______years.
• The sun will become a ______before it dies.
• As fusion slows, the outer layers of the sun will expand.
• The sun will become a red giant.
• ______: a large, reddish star late in its life cycle
• When the sun runs out of helium, the outer layers will expand and eventually leave the sun’s orbit.
• The sun will become a white dwarf.
• ______: a small, hot dim star that is the leftover center of an old star.
• ______stars explode in supernovas.
• Massive stars evolve faster, develop hotter cores, and create heavier elements through fusion.
• A supergiant forms ______at it’s core. • Eventually the core collapses and then explodes in a Type II supernova.
• ______: a gigantic explosion in which a massive star collapses and throws its outer layers into space, plural supernovae
• A Type I supernova occurs when a white dwarf in a binary system (a system composed of two stars) collects enough mass from its companion to exceed 1.4 solar masses.
• After a Type II supernova, either a neutron star or a black hole forms.
• If the core that remains after a supernova has a mass of 1.4 to 3 solar masses, the remnant can become a ______
• If the leftover core has a mass that is greater than ______solar masses, it will collapse to form a black hole.
• ______: an object so massive and dense that not even light can escape its gravity
• The ______shows how stars evolve. (Hertzsprung-Russell)
• The vertical line on an H-R diagram indicates brightness in absolute ______.
• The horizontal line on the H-R diagram indicates ______.
• Most stars appear in a diagonal line called the ______
• As stars age and pass through different stages, their positions on the H-R diagram change.
Galaxies
• Galaxies contain millions or billions of stars.
• ______: a collection of stars, dust, and gas bound together by gravity
• Because stars age at different rates, a galaxy may contain many types of stars.
• Gravity holds galaxies together in clusters.
• Galaxies are not spread evenly throughout space.
• ______: a group of stars or galaxies bound by gravity
• The Milky Way galaxy and the Andromeda galaxy are two of the largest members of the Local Group, a cluster of more than 30 galaxies.
• Clusters of galaxies can form even larger groups, called ______.
Types of Galaxies
• We live in the ______galaxy.
• Edwin Hubble divided all galaxies into three major types:
______.
• Most of the objects visible in the night sky are part of the Milky Way galaxy. • Scientists use astronomical data to piece together a picture of the Milky Way galaxy.
• The Milky Way is a ______galaxy.
• Our galaxy is a huge spiraling disk of stars, gas, and dust.
• Our solar system is located within a spiral arm.
• The nucleus of the galaxy is dense and has many old stars.
• The gas and dust is called interstellar matter.
• ______: the gas and dust located between the stars in a galaxy.
• ______galaxies have no spiral arms.
• Elliptical galaxies are ______or ______shaped.
• They contain mostly older stars and have little interstellar matter.
• Because older stars are red, elliptical galaxies often have a ______color.
• All other galaxies are ______galaxies.
• Irregular galaxies lack regular ______and do not have a well-defined ______
• Some irregular galaxies may be oddly shaped because the gravitational influence of nearby galaxies distorts their spiral arms.
How Galaxies Evolve
• Quasars may be ______galaxies.
• In 1960, a faint object was matched with a strong radio signal. This object was called a quasar.
• ______: quasi-stellar radio sources; very luminous objects that produce energy at a high rate and that are thought to be the most distant objects in the universe
• Each quasar has a huge central ______and a large disk of gas and dust around it.
• Galaxies change over ______.
• Galaxies change as they use up their stores of gas and dust
• Galaxies also change as a result of ______.
• As galaxies approach each other, mutual gravitational attraction changes their shape.
• Collisions of gas and dust may cause new stars to begin forming.
What Is the Universe?
• ______: the sum of all space, matter, and energy that exist, that have existed in the past, and that will exist in the future.
• You are part of the universe, as is Earth and everything on it. • We see the universe now as it was in the past.
• It takes time for light to travel in space.
• The farther away an object is, the older the light that we receive from that object.
• Most of the universe is ______space
• Space is a vacuum with no air and no air pressure.
What Happened at the Beginning?
• The universe is ______.
• Observations of spectral lines from other galaxies indicated that they were moving away from us
• ______: an apparent shift toward longer wavelengths of light caused when a luminous object moves away from the observer
• ______: an apparent shift toward shorter wavelengths of light caused when a luminous object moves toward the observer
• Expansion implies that the universe was once smaller.
• Long ago, the entire universe might have been contained in an extremely small space.
• All of the matter in the universe appears to expand rapidly outward, like a gigantic explosion
• Scientists call this hypothetical explosion the big bang.
• Did the universe start with a big bang?
• Scientists have proposed several different theories to explain the expansion of the universe.
• The most complete and widely accepted theory is the big bang theory.
• ______: the theory that all matter and energy in the universe was compressed into an extremely small volume that 10 to 20 billion years ago exploded and began expanding in all directions
• Cosmic background radiation supports the big bang theory.
• ______is a steady but very dim signal from all over the sky in the form of radiation at microwave wavelengths.
• Many scientists believe that the microwaves are dim remnants of the radiation produced during the big bang.
• Radiation dominated the early universe.
• According to the big bang theory, expansion cooled the universe enough for matter such as protons, neutrons, and electrons to form.
• Processes in stars lead to bigger atoms.
• Once hydrogen atoms formed, stars and galaxies began to form, too. • All elements other than hydrogen and helium form in stars.
Predicting the Future of the Universe
• The future of the universe is ______.
• The universe is expanding, but the combined gravity of all the mass in the universe is also pulling the universe inward.
• The competition between these forces leaves three possibilities:
1.
2.
3.
• The fate of the universe depends on ______.
• If there is not enough mass, the gravitational pull will be too small to stop the expansion.
• If there is just the right amount of mass, the expansion will continually slow down, but will never stop completely.
• If there is too much mass, gravity will eventually overcome expansion and the universe will contract.
• New technology helps scientists test theories.
• Powerful telescopes and other sensitive equipment help scientists study the universe.
• Scientists make observations to test theories and develop new explanations.
• There is a debate about ______
• There is more matter in the universe than what is visible.
• Scientists call this dark matter.
• Dark matter may be ______, ______, or
______(starlike objects that lack enough mass to begin fusion.)
• Scientists use ______to build better models.
• ______can be expressed in mathematical form.
• Mathematical models can be used to help test theories that are not easily observed.