galaxy theory Comparison Table

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galaxy theory comparison table

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Bahcall-Soneira Model or reasearch group A model for the Galaxy first published by John Bahcall and Raymond Soneira in 1980. In its original form, it sought to reproduce star counts in different parts of the sky by employing only a (thin) disk and a halo; it had no thick disk.

biased galaxy formation or reasearch group The theory that bright galaxies form preferentially from anomalously overdense perturbations in the early universe.

bottom-up scenario or reasearch group The idea that small structures, perhaps galaxies or even smaller substructures, form first in the universe, followed later by larger structures.

density wave theory Lindblad (1925) the density waves rotate more slowly than the galaxy's stars and gas Spiral structure is modelled as a small-amplitude wave propagating with fixed angular velocity, as the compression wave goes through, it triggers star formation on the leading edge of the spiral arms.

explosive galaxy formation or reasearch group A theory of galaxy formation wherein the explosion of a large number of stars creates a giant shock wave that travels outward and compresses the surrounding gas. Galaxies form in the regions of high-density gas.

local hypothesis of quasars or reasearch group The hypothesis that quasars are not at the distances inferred from their redshifts.

spiral density wave or reasearch group A wave, due to a local increase in the gravitational field, that produces a series of alternate compressions and rarefactions as it propagates with fixed angular velocity in a rotating galaxy. The compression also acts on interstellar gas in the galaxy, which is triggered to form stars on the leading edges of the spiral arms. The large-scale structure of spiral galaxies can be understood in this way.

top-down scenario or reasearch group A scenario of galaxy formation in which large structures form first and then fragment to become galaxies.

Tully-Fisher relation or reasearch group An observed relation between the intrinsic luminosity of a spiral galaxy and the rotational speed of its stars. More luminous galaxies have stars that are moving faster.

twin-exhaust model or reasearch group A theoretical model for radio galaxies in which a compact source in the galactic nucleus is assumed to emit twin beams of rapidly moving plasma that traverse hundreds of thousands of light-years, eventually splattering to a halt in the ambient intergalactic gas, where the resulting dissipation energizes the radio lobes.

Subject	has author	has implication	has definition
Bahcall-Soneira Model	or reasearch group		A model for the Galaxy first published by John Bahcall and Raymond Soneira in 1980. In its original form, it sought to reproduce star counts in different parts of the sky by employing only a (thin) disk and a halo; it had no thick disk.
biased galaxy formation	or reasearch group		The theory that bright galaxies form preferentially from anomalously overdense perturbations in the early universe.
bottom-up scenario	or reasearch group		The idea that small structures, perhaps galaxies or even smaller substructures, form first in the universe, followed later by larger structures.
density wave theory	Lindblad (1925)	the density waves rotate more slowly than the galaxy's stars and gas	Spiral structure is modelled as a small-amplitude wave propagating with fixed angular velocity, as the compression wave goes through, it triggers star formation on the leading edge of the spiral arms.
explosive galaxy formation	or reasearch group		A theory of galaxy formation wherein the explosion of a large number of stars creates a giant shock wave that travels outward and compresses the surrounding gas. Galaxies form in the regions of high-density gas.
local hypothesis of quasars	or reasearch group		The hypothesis that quasars are not at the distances inferred from their redshifts.
spiral density wave	or reasearch group		A wave, due to a local increase in the gravitational field, that produces a series of alternate compressions and rarefactions as it propagates with fixed angular velocity in a rotating galaxy. The compression also acts on interstellar gas in the galaxy, which is triggered to form stars on the leading edges of the spiral arms. The large-scale structure of spiral galaxies can be understood in this way.
top-down scenario	or reasearch group		A scenario of galaxy formation in which large structures form first and then fragment to become galaxies.
Tully-Fisher relation	or reasearch group		An observed relation between the intrinsic luminosity of a spiral galaxy and the rotational speed of its stars. More luminous galaxies have stars that are moving faster.
twin-exhaust model	or reasearch group		A theoretical model for radio galaxies in which a compact source in the galactic nucleus is assumed to emit twin beams of rapidly moving plasma that traverse hundreds of thousands of light-years, eventually splattering to a halt in the ambient intergalactic gas, where the resulting dissipation energizes the radio lobes.

Next astronomy theory: planetary theory Up: astronomy theory Previous astronomy theory: cosmology theory