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Stellar Seed Theory

Page history last edited by PBworks 12 years, 6 months ago

Stellar Seed Theory

 

Truth is ever to be found in the simplicity, and not in the multiplicity and confusion of things.

-Isaac Newton

 

Problems to solve

  • HD 149026 b - Unusually dense core, difficult to explain by accretion model.
  • HD 188753 Ab - Gas giant in a closely bound triple star system.
  • Hot Jupiter - Migration?
  • missing mass in Kuiper Belt
  • capture process for Triton
  • sideways rotation of Uranus
  • Twin planemo system
  • Hypergiant accretion discs

 

Evidence

 

Preamble

Recent discoveries or extrasolar planetary systems, including so-called 'hot jupiters' and planets in tightly bound triple star systems. These discoveries call into question the current theories on stellar and planetary formation. As such, Stellar Seed Theory is an attempt to qualitatively explain the formation of all varieties of planets, stars and sub-stellar objects (collectively referred to hereafter as 'Celestials') as possible probabilistic outcomes of a single accretion model. This theory differs from current leading theories by proposing that all celestials initially form in the same way through a nucleation process - from points of heterogeneous density in interstellar molecular clouds (hereafter termed 'Stellar Seeds'). Thus, celestials are initially the same, and it is the effects of a variety of factors (including gravitation, density, stellar seed density and localised elemental abundance) that cause the nucleation and growth of planets and stars. In this model, all celestials grow simultaneously. Hopefully, this model can help to explain many of the observed phenomena that currently contradict the accepted models of stellar and planetary formation.

 

Fundamental Concepts

  • A giant molecular cloud is a supercooled region of gaseous hydrogen. Below the critical temperature, TC, condensation into a liquid/solid state will be energetically favourable.
  • Gravitational attraction around heavier particles (eg: metal atoms) will seed the cloud, providing nucleation sites. These sites will preferentially attract heavier atoms and molecules. The implication is that all planets and stars have at their centre a metal/silicate core akin to those found in terrestrial planets.

 

  • Each of these 'Stellar seeds' has the potential to become any kind of 'celestial', dependant upon it's mass and therefore gravitational potential at any given time.
  • Continued stellar nucleation causes planets and stars to be indistinguishable until such a time as a significant mass difference is observable. This mass difference then becomes one of the main factors in the continued evolution of the celestial.

 

  • Protostars and planetessimals therefore form at the same time, possibly explaining the unusual locations of planets in observed extrasolar systems.

 

Metallicity

Metallicity of a proplyd is tantamount in explaining the number of stellar seeds formed and thus, planet formation. The model assumes that more metals correspond to more seeds and thus a greater likelihood of planets. As a result, the more seeds, the smaller the resulting star, due to planetary accretion.

Thus,

Metallicity is directly proportional to number of celestials formed.

Metallicity is inversely proportional to star size.

Having fewer seeds, a metal-poor GMC will condense primarily on one seed and form a supergiant. Red dwarfs form from metal rich clouds, and thus are frequently observed in multiple planet systems (and probably frequently ejected from them).

 

Observed Multiple planet systems

F - 2

G - 13

K - 2

M - 1

Most observed are spectral class G, but current techniques lean towards giant planets. M class stars would be more likely to form terrestrial planets.

 

Observed Planet-Bearing Stars

0 - 0

B - 0

A - 0

F - 21

G - 104

K - 43

M - 7

Most observed are still around class G stars. Two possible reasons for this are that astronomers have given particular attention to G class stars and that G-class stars may be particularly suited to forming gas giants.

 

Snippets

  • No low mass stars of zero metallicity have been observed.

 

Population III Stars - Seedless?

Population III stars are a hypothetical population of extremely massive stars that are believed to have been formed in the early universe. They have not been observed directly, but are thought to be components of faint blue galaxies. Their existence is necessary to account for the fact that heavy elements, which could not have been created in the Big Bang, are observed in quasar emission spectra as well as the existence of faint blue galaxies. It is believed that these stars triggered a period of reionization.

 

If these stars were able to form properly, their lifespan would be extremely short, certainly less than one million years. As they can no longer form today, viewing one would require us to look to the very edges of the observable universe.

 

One theory, which seems to be borne out by computer models of star formation, is that with no heavy elements from the Big Bang, it was easy to form stars much more massive than the ones visible today. Typical masses for population III stars would be expected to be about several hundred solar masses, which is much larger than current stars. Analysis of data on low-metallicity Population II stars, which are thought to contain the metals produced by Population III stars, suggests that these metal-free stars had masses of 10 to 100 solar masses instead.

 

Either way, Population III stars were extremely massive, supporting the stellar seed model, in that the lack of nucleation points would cause an entire stellar nebula to condense into a single massive star.

 

The Population III Puzzle

The highest-mass star which may form today is about 110 solar masses. Any attempt to form a star greater than this results in the protostar blowing itself apart during the initial ignition of nuclear reactions. Without enough carbon, oxygen and nitrogen in the core, however, the CNO cycle could not begin and the star would not go nuclear with such enthusiasm. Direct fusion through the proton-proton chain does not proceed quickly enough to produce the copious amounts of energy such a star would need to support its immense bulk. The end result would be the star collapsing into a black hole without ever actually shining properly. This is why astronomers consider population III to be somewhat of a mystery--by all rights they should not exist, yet they're needed to explain the quasar observations.

 

Red Dwarfs

One mystery which has not been solved as of 2006 is the lack of red dwarf stars with no metals (in astronomy a metal is any element other than hydrogen and helium). The Big Bang model predicts the first generation of stars should have only hydrogen, helium, and lithium. If such stars included red dwarfs, they should still be observable today, but as yet none have been identified. One explanation is that without heavy elements, low mass stars cannot form. Alternatively as they are dim and could be few in number, we simply may not have observed them yet.

 

Subdwarf

Subdwarfs are seemingly a thorn in the side of Stellar Seed Theory. Subdwarfs are smaller then other main sequence stars, and have a low metallicity. This flies in the face of the concept that high metallicity forms smaller stars. The only immediate solution is that Subdwarfs are actually a low metallicity analog of planets. Having less metal, they would accrete more mass and thus acquire enough to initiate fusion.

 

Some known subdwarfs have very high transverse velocities. If this is due to their being ejected from their parent systems, this could support this concept.

 

Supergiants

Because of their extreme masses they have short lifespans of only 10 to 50 million years and are only observed in young cosmic structures such as open clusters, the arms of spiral galaxies, and in irregular galaxies. They are less abundant in spiral galaxy bulges, and are not observed in elliptical galaxies, or globular clusters, all of which are believed to be composed of old stars.

 

Presumably, regions containing large quantities of mass (such as globular clusters) will attract metals, and thus generate more stellar seeds. These would not be conductive to the formation of massive stars, so smaller stars would form.

 

Hypergiants

A hypergiant (luminosity class 0) is a massive star whose spectrum indicates the presence of an extended atmosphere. Hypergiants are at least as large as supergiants, having masses up to 100 times that of the Sun. This approaches the theoretical upper limit of star mass (about 120 solar masses), the point at which a star generates so much radiation that it throws off its outer layers. Some hypergiants appear to be more than 100 solar masses and may have initially been 200 to 250 solar masses, challenging current theories of star formation and evolution. Hypergiants are the most luminous stars, thousands to millions of times the solar luminosity; however, their temperatures vary widely between 3,500 K and 35,000 K. They have extremely short lives, lasting approximately 1 to 3 million years, before turning into supernovae or possibly hypernovae. It is theorised that a hypergiant gone supernova or hypernova will leave a remnant black hole.

 

There are only a handful of known hypergiants in the Milky Way. More are known to exist in the Magellanic clouds.

 

The Pistol Star

10 million times as bright as the Sun, about 100-150 times as massive and with a stellar wind 10 billion times stronger, the Pistol Star is probably the most luminous object in the Milky Way. It's extreme mass calls into question, current theories of star formation, as it may exceed the current theoretical upper size limit. Located near the centre of the galaxy may be a factor.

 

It's plausible that the high concentration of mass at the galactic centre may attract any and all surrounding mass towards it, leaving a region of low mass gas clouds. These clouds, composed primarily of material not attracted by the galactic hub and material ejected from the hub through stellar mass loss mechanisms, would likely be metal poor. Thus, massive stars could form relatively easily, due to the relatively small number of stellar seeds available.

 

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