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baric
2011-Mar-07, 06:56 PM
All, I am continuing to work on my astronomy program on the side and need to come up with a straightforward classification of astronomical bodies. This is a compositional classification, not orbital, and is intended to ensure that various dynamics of the bodies are modeled properly. For example, knowing whether a 1-solar-mass body is a dwarf star or a white dwarf has implications on how properties such as size and luminosity are determined.

From small to large, the list below provides an idea of my current thoughts on this subject. If you can spot any classification problems or bodies types that I’ve left out, please let me know.

Rocky Body – low-mass bodies, not spherical. Phobos and Deimos would be good examples. Airless.

Terrestrial – rocky bodies large enough to become spherical at zero rotation, but not large enough to retain their Type I atmosphere of H and He. Larger terrestrials may have differentiated interiors (iron core, silicate mantle) and retain a Type II atmosphere. Large moons, KBOs and the 4 inner planets are all examples of this type.

Gas Giant – these bodies with iron cores retain their Type I atmosphere. Larger versions, such as Jupiter, may contain layers of metallic hydrogen while the smaller versions do not.

Brown Dwarfs – massive gas giants whose internal pressures have produced an electron degenerate core, but not high enough to fuse hydrogen. Because of the internal heat generation, the outer layers are much more convective than gas giants.

T-Tauri stars – protostars generating heat through gravitational collapse, but not yet fusing.

Dwarf Stars – stars fusing hydrogen on the main sequence. Will vary from long-lived red dwarfs to short lived blue giants

Subgiant Stars – a stellar stage immediately preceding the giant phase where hydrogen fusion in the core has stopped but moves to outer layers. Wolf-Rayet stars may be massive examples of this class.

Giant Stars – stars fusing metals in their core. They have an expansive atmosphere of hydrogen that has been pushed out from the core.

White Dwarfs – a stellar core maintained by electron degeneracy.

Neutron Stars – a stellar core maintained by neutron degeneracy

Black Hole – a stellar core with surface gravity > c (edit: "escape velocity > c")

chornedsnorkack
2011-Mar-07, 07:54 PM
Is the distinction between comets and asteroids relevant?

baric
2011-Mar-07, 07:59 PM
Is the distinction between comets and asteroids relevant?

I would generally classify them as rocky bodies. A "Rubble" classification might be appropriate for even smaller bodies that are only loosely bound.

Amber Robot
2011-Mar-07, 11:42 PM
Black Hole – a stellar core with surface gravity > c

I think you need more constants here. c is a speed, and surface gravity is an acceleration.

baric
2011-Mar-08, 12:48 AM
I think you need more constants here. c is a speed, and surface gravity is an acceleration.

You are absolutely correct. I mean to type "escape velocity > c"

Good catch!

Glom
2011-Mar-08, 06:27 PM
Nothing > c. That's the whole point of c.

baric
2011-Mar-08, 06:32 PM
Nothing > c. That's the whole point of c.

The escape velocity of a black hole is > c. That's why it's black.

neilzero
2011-Mar-10, 12:54 AM
It is perhaps misleading to suggest that the event horizon of a super massive black hole is a surface. I don't think a space craft near the event horizon could determine where the event horizon is, except by trying to leave. Neil

neilzero
2011-Mar-10, 01:10 AM
Gas giant planets are thought to have a T-tauri period= extremely high temperature at the core. Are we sure the iron nuclei stay in the core under these extreme temperature pressure conditions? Perhaps Jupiter produces excess heat, partly because the iron atoms, and nickle atoms, are very slowly settling toward the core, but most of them are still widely distributed, after 4.6 billion years? Single molecule dust particles take decades to settle out of Earth's thin atmosphere = slower settling out in a much thicker atmosphere? Neil

neilzero
2011-Mar-10, 02:00 AM
In gas giant and brown dwarf, you inferred that a brown dwarf produces lots more internal heat, by saying brown dwarfs are much more convective. Proportional to the mass, perhaps, but why lots more convection and/or lots more internal heat? Neil

baric
2011-Mar-10, 05:18 AM
Gas giant planets are thought to have a T-tauri period= extremely high temperature at the core. Are we sure the iron nuclei stay in the core under these extreme temperature pressure conditions?

Iron settles to the core because of its greater atomic weight. This should not change under high-pressure, high-temperature conditions. After all, stars retain iron in their core.


In gas giant and brown dwarf, you inferred that a brown dwarf produces lots more internal heat, by saying brown dwarfs are much more convective. Proportional to the mass, perhaps, but why lots more convection and/or lots more internal heat? Neil

More gravitational contraction = more heat.

Ultimately, I think the most striking structural difference may be an electron degenerate core in the brown dwarf.