25: The Milky Way Galaxy Flashcards
the central (round) part of the Milky Way or a similar galaxy
central bulge
non-luminous mass, whose presence can be inferred only because of its gravitational influence on luminous matter - composition is not known
dark matter
the mass in the Milky Way that extends well beyond the boundary of the luminous stars to a distance of at least 200,000 light-years from the center of the Galaxy - although we deduce its existence from its gravity, the composition of this matter remains a mystery
dark matter halo
the idea that different parts of the Galaxy turn at different rates, since the parts of the Galaxy follow Kepler’s third law: more distant objects take longer to complete one full orbit around the center of the Galaxy
differential galactic rotation
the outermost extent of our Galaxy (or another galaxy), containing a sparse distribution of stars and globular clusters in a more or less spherical distribution
halo
the band of light encircling the sky, which is due to the many stars and diffuse nebulae lying near the plane of the Milky Way Galaxy
Milky Way Galaxy
a star containing heavy elements; typically young and found in the disk
population I star
a star with very low abundance of heavy elements; found throughout the Galaxy
population II star
a spiral-shaped region, characterized by relatively dense interstellar material and young stars, that is observed in the disks of spiral galaxies
spiral arm
the object in the center of most large galaxies that is so massive and compact that light cannot escape from it; the Milky Way’s one contains 4.6 millions of Suns’ worth of mass
supermassive black hole
period of the Sun’s revolution around the center of the Milky Way Galaxy (225 million years)
galactic year
any material from which we can detect electromagnetic radiation
luminous matter
