Last chance to join our Costa Rica Star Party! Learn about the Moon in a great new book New book chronicles the space program. Dave's Universe Year of Pluto. Groups Why Join? Astronomy Day. The Complete Star Atlas. Two neutron stars merge in this illustration.
These elements become the basis of gas clouds that eventually form stars and planets. Q: Since the heaviest element produced by nuclear fusion is iron, how are elements like gold and uranium formed? Brandon Chang. Neutron stars: A cosmic gold mine. Cosmic ingredients: How the universe forges elements. Magnetic star born from a colossal collision of stellar corpses.
Does all the gold in the universe come from stars? Hubble captures the beating heart of the Crab Nebula. New model could help find gravitational waves in binary pulsars. Cosmos: Origin and Fate of the Universe.
Astronomy's Moon Globe. Galaxies by David Eicher. Argumentative Essay On Galaxies After the Big Bang the universe started to cool of, starting protons and neutrons, hydrogen, helium, lithium and more. Shuffle Toggle On. Card Range To Study through. What is the diameter of the disk of the Milky Way? What kinds of objects lie in the halo of our galaxy? What kinds of objects lie in the disk of our galaxy? What makes up the interstellar medium? How does the interstellar medium obscure our view of most of the galaxy?
It produces so much visible light that it is opaque and blocks our view of anything beyond it. It reflects most light from far distances of the galaxy away from our line of sight. It absorbs visible, ultraviolet, and some infrared light.
It absorbs all wavelengths of light. Harlow Shapley concluded that the Sun was not in the center of the Milky Way Galaxy by mapping the distribution of stars in the galaxy. Approximately how far is the Sun from the center of the galaxy? What do astronomers consider heavy elements? Where are most heavy elements made? How are interstellar bubbles made? What can cause a galactic fountain? What produces the cm line that we use to map out the Milky Way Galaxy? Compared with our Sun, most stars in the halo are young, blue, and bright and have much more heavy element material old, red, and dim and have much more heavy element material old, red, and bright and have fewer heavy elements young, red, and dim and have fewer heavy elements old, red, and dim and have fewer heavy elements.
Compared with stars in the disk, orbits of stars in the halo are relatively uniform to each other. Where does most star formation occur in the Milky Way today? Which constellation lies in the direction toward the galactic center?
How do we learn about what is going on in the center of our own galaxy the Milky Way? We must look at the centers of other galaxies and hope that ours is just like others. Which of the following does not accurately describe what we observe toward the Galactic center? What evidence supports the theory that there is a black hole at the center of our galaxy? We observe an extremely bright X-ray source at the center of our galaxy. Population II stars formed when the abundance of elements heavier than hydrogen and helium was low.
Population I stars formed later, after mass lost by dying members of the first generations of stars had seeded the interstellar medium with elements heavier than hydrogen and helium. Some are still forming now, when further generations have added to the supply of heavier elements available to new stars. With rare exceptions, we should never trust any theory that divides the world into just two categories. While they can provide a starting point for hypotheses and experiments, they are often oversimplifications that need refinement a research continue.
The idea of two populations helped organize our initial thoughts about the Galaxy, but we now know it cannot explain everything we observe. Even the different structures of the Galaxy—disk, halo, central bulge—are not so cleanly separated in terms of their locations, ages, and the heavy element content of the stars within them. The hottest young stars and their associated gas and dust clouds are mostly in a region about light-years thick. Older stars define a thicker disk that is about light-years thick.
Halo stars spend most of their time high above or below the disk but pass through it on their highly elliptical orbits and so are sometimes found relatively near the Sun. The highest density of stars is found in the central bulge, that bar-shaped inner region of the Galaxy. There are a few hot, young stars in the bulge, but most of the bulge stars are more than 10 billion years old. Yet unlike the halo stars of similar age, the abundance of heavy elements in the bulge stars is about the same as in the Sun.
Why would that be? Astronomers think that star formation in the crowded nuclear bulge occurred very rapidly just after the Milky Way Galaxy formed. After a few million years, the first generation of massive and short-lived stars then expelled heavy elements in supernova explosions and thereby enriched subsequent generations of stars. Thus, even stars that formed in the bulge more than 10 billion years ago started with a good supply of heavy elements.
Even the youngest stars in this galaxy are deficient in heavy elements. We think this is because the little galaxy is not especially crowded, and star formation has occurred quite slowly.
As a result there have been, so far, relatively few supernova explosions. Smaller galaxies also have more trouble holding onto the gas expelled by supernova explosions in order to recycle it. Low-mass galaxies exert only a modest gravitational force, and the high-speed gas ejected by supernovae can easily escape from them.
Which elements a star is endowed with thus depends not only on when the star formed in the history of its galaxy, but also on how many stars in its part of the galaxy had already completed their lives by the time the star is ready to form.
We can roughly divide the stars in the Galaxy into two categories.
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