Slowing down stars

Jun 21, 2011 By Jon Voisey, Universe Today
Forming Star's Magnetic Field Interacting With Disc Credit: NASA/JPL-Caltech/R. Hurt (SSC).

One of the long standing challenges in stellar astronomy, is explaining why stars rotate so slowly. Given their large masses, as they collapsed to form, they should spin up to the point of flying apart, preventing them from ever reaching the point that they could ignite fusion. To explain this rotational braking, astronomers have invoked an interaction between the forming star’s magnetic field, and forming accretion disc. This interaction would slow the star allowing for further collapse to take place. This explanation is now over 40 years old, but how has it held up as it has aged?

One of the greatest challenges to testing this theory is for it to make predictions that are directly testable. Until very recently, were unable to directly observe circumstellar discs around newly formed stars. In order to get around this, astronomers have used statistical surveys, looking for the presence of these discs indirectly. Since dust discs will be warmed by the forming star, systems with these discs will have extra emission in the infrared portion of the spectra. According to the magnetic braking theory, young stars with discs should rotate more slowly than those without. This prediction was confirmed in 1993 by a team of astronomers led by Suzan Edwards at the University of Massachusetts, Amherst. Numerous other studies confirmed these general findings but added a further layer to the picture; stars are slowed by their discs to a period of ~8 days, but as the discs dissipate, the stars continue to collapse, spinning up to a period of 1-2 days.

Another interesting finding from these studies is that the effects seem to be most pronounced for stars of higher mass. When similar studies were conducted on young stars in the Orion and Eagle nebulae, researchers found that there was no sharp distinction between stars with or without disks for low mass stars. Findings such as these have caused astronomers to begin questioning how universal the magnetic disc braking is.

One of the other pieces of information with which astronomers could work was the realization around 1970 that there was a sharp divide in rotational speeds between high mass stars and lower mass ones at around the F spectral class. This phenomenon had been anticipated nearly a decade earlier when Evry Schatzman proposed that the stellar wind would interact with the star’s own magnetic field to create drag. Since these later spectral class stars tended to have more active magnetic fields, the braking effect would be more important for these stars.

Thus astronomers now had two effects which could serve to slow rotation rates of stars. Given the firm theoretical and observational evidence for each, they were both likely “right”, so the question became which was dominant in which circumstance. This question is one with which astronomers are still struggling.

To help answer the question, astronomers will need to gather a better understanding of how much each effect is at work in individual stars instead of simply large population surveys, but doing so is tricky. The main method employed to examine disc locking is to examine whether the inner edge of the disc is similar to the radius at which an object in a Keplarian orbit would have a similar angular velocity to the star. If so, it would imply that the star is fully locked with the disc’s inner edge. However, measuring these two values is easier said than done. To compare the values, astronomers must construct thousands of potential star/disc models against which to compare the observations.

In one recent paper astronomers used this technique on IC 348, a young open cluster. Their analysis showed that ~70% of stars were magnetically locked with the disc. However, the remaining 30% were suspected to have inner disc radii beyond the reach of the magnetic field and thus, unavailable for disc braking. However, these results are somewhat ambiguous. While the strong number of stars tied to their discs does support the disc braking as an important component of the rotational evolution of the stars, it does not distinguish whether it is presently a dominant feature. As previously stated, many of the stars could be in the process of evaporating the discs, allowing the star to again spin-up. It is also not clear if the 30% of stars without evidence of disc locking were locked in the past.

Research like this is only one piece to a larger puzzle. Although the details of it aren’t fully fleshed out, it is readily apparent that these magnetic braking effects, both with discs and stellar winds, play a significant effect on slowing the angular speed of . This runs completely contrary to the frequent Creationist claim that “[t]here is no know [sic] mechanical process which could accomplinsh [sic] this transfer of momentum”.

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omatumr
1.5 / 5 (15) Jun 21, 2011
The rapid rotation of the stellar core is not seen in the brightly glowing waste products that accumulate from the core.

See: "Neutron Repulsion", The
APEIRON Journal, in press, 19 pages (2011):

http://arxiv.org/...2.1499v1

With kind regards,
Oliver K. Manuel
TabulaMentis
1.4 / 5 (11) Jun 21, 2011
It sounds like there may be a form of intelligence happening on a basic level within stars after years of evolution. I can see a new movie in the works: "Invasion of the Killer Stars."
Tuxford
1.7 / 5 (12) Jun 21, 2011
Add another confirmation for LaViolette. If most new matter is generated from within the star as predicted by SubQuantum Kinectics, rather than from external accretion, then the star would be expected not to spin up much as it grows. No need to fabricate complex braking models to explain the effect.

Furthermore, in his model, more massive stars grow more rapidly. Thus, the effect would be more pronounced in higher mass stars, as observed in this study.
Nik_2213
4 / 5 (4) Jun 21, 2011
D'uh, those stars can't ALL form on your undetectable neutron star cores, surely ?
omatumr
1.4 / 5 (9) Jun 22, 2011
D'uh, those stars can't ALL form on your undetectable neutron star cores, surely ?


Thanks for your question Nik. The Sun is a very ordinary star.

When ordinary stars explode, the core is exposed.

Sometimes a naked neutron star is observed for a while.

But most become hidden inside the brightly glowing ball of waste products that accumulate around the neutron star - like the Earth's photosphere:

91 % H - the product of neutron decay
09% He - the product of H-fusion

Shootist
1 / 5 (1) Jun 22, 2011
Look to the rings of Saturn for an explanation. Hint: spokes.
Shootist
3.7 / 5 (3) Jun 22, 2011
The Sun is a very ordinary star.

When ordinary stars explode,


Doc, according to theory, and what we observe, stars the mass of Sol, don't go boom. First, the hydrogen runs out, then He fusion causes them to puff up to >1AU in diameter, while throwing off gas and dust, which, often, forms a (misnamed) planetary nebula. After the He core runs out, carbon ash, unfusable at these temps and pressure, sinks to the core causing fusion there to cease. H and He fusion continue in the outer shell for a time, then the dying star begins shrinking to a white dwarf (which doesn't look, act, taste, smell or sound, like a neutron star), and spends the rest of the lifetime of the Universe cooling off, a great big Diamond in the Sky.
Decimatus
5 / 5 (1) Jun 22, 2011
White dwarfs could still have a neutron star in them. Just not enough waste mass on the outside to explode after red giant stage.

I see a problem with a very rapidly spinning neutron star inside of a normal star though.

I would think that the resulting magnetic field of the combination would dward what we currently observe from our sun. I could be wrong though.
omatumr
1.4 / 5 (7) Jun 22, 2011
The Sun is a very ordinary star.

When ordinary stars explode,


Doc, according to theory, and what we observe, stars the mass of Sol, don't go boom. First, the hydrogen runs out, then He fusion causes them to puff up to >1AU in diameter, while throwing off gas and dust, which, often, forms a (misnamed) planetary nebula. After the He core runs out, carbon ash, unfusable at these temps and pressure, sinks to the core causing fusion there to cease. H and He fusion continue in the outer shell for a time, . . .


We are probably all familiar with the story.

Here are a few of the multitude of observations that contradict the story ["Neutron Repulsion", The APEIRON Journal, in press, 19 pages (2011)]

http://arxiv.org/...2.1499v1

With kind regards,
Oliver K. Manuel
Shootist
4 / 5 (4) Jun 22, 2011
Uh, yeah, I know, we know the narrative.

Please to point to a 1 Solar Mass star going pop?

Anyway.

Your paper referenced above is out of date, 2nd paragraph.

"The solar neutrino problem was a major discrepancy between measurements of the numbers of neutrinos flowing through the Earth and theoretical models of the solar interior, lasting from the mid-1960s to about 2002. The discrepancy has since been resolved by new understanding of neutrino physics, requiring a modification of the Standard Model of particle physics specifically, neutrino oscillation." wiki-yada.

You're asking us to believe thunderstorms are caused by errant UFOs decelerating too fast in the atmosphere.

Like the aethers and electric universe folks, it seems you seek credulity in your audience.

You ask too much to believe.
omatumr
1.8 / 5 (5) Jun 22, 2011
No.

Neutrinos don't oscillate.

That was another attempt to salvage the standard solar model.

- om

barakn
4 / 5 (4) Jun 22, 2011
Neutrinos don't oscillate.

- om

How long are you going to defend that position? Scientists are now making artificial neutrino beams of known pure composition and then detecting them after passing through a large amount of material, and some of these have changed "flavour."
Shootist
1 / 5 (1) Jun 22, 2011
http://www.iupac....0429.pdf

EXTREME REGIMES OF TEMPERATURE AND
PRESSURE IN ASTROPHYSICS
MALVIN A. RUDERMAN*
Department of Physics, Columbia University, New York, N. Y.

For the love of God, man; where is this wrong?

Ruderman even writes about nucleon repulsion, and gives its limits.
ubavontuba
1 / 5 (2) Jun 26, 2011
...as they collapsed to form, they should spin up to the point of flying apart, preventing them from ever reaching the point that they could ignite fusion.
How about coming at it from another angle? Could it be that some star forming nebulae have insignificant angular momentums, and this is why the stars rotate slowly? And then, couldn't the collapsing/forming stars stir and organize their accretion discs? I mean, isn't it equally as valid to state the star delivers angular momentum to the accretion disc, as it is to state the accretion disc takes angular momentum away from the star?

It seems to me this could equally explain why stars rotate so slowly relative to the apparent angular momentums of their accretion discs, and explain how/allow the star kernel (so to speak) to initialize the coalescing of, and subsequent collapse of the gas into a star to begin with.

Otherwise, it seems to me, high angular momentums in the nebulae would inhibit gravitational collapse.