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ExpErdMann
2006-May-30, 11:53 PM
According to present theory, white dwarfs do not have an intrinsic heat source since the available fuels for fusion have been used up. I have a model which predicts that they should have such a heat source and that consequently a typical white dwarf will never have a luminosity lower than about 1/100 the solar luminosity. The model was developed more with geology in mind and the area of white dwarf luminosities is new to me. I was wondering if anyone can shed light on this. I did find this paper (http://arxiv.org/PS_cache/astro-ph/pdf/9704/9704125.pdf) which suggests there is indeed a lower cutoff in white dwarf luminosities. In standard cosmology, however, this cutoff could be explained by the white dwarf population all being younger than a certain age. Part of my problem is that the data on white dwarfs is all presented within certain model constructions. The raw data is harder to find. I am omitting the details of my model for now, since discussion of those would most likely dominate the thread to the exclusion of what I'm trying to find out.

tusenfem
2006-May-31, 12:49 PM
I thought white dwarfs get their luminosity mainly from shrinking and turning gravitational potential energy into heat.

ExpErdMann
2006-May-31, 01:59 PM
Yes, that's where there main heat comes from. But the white dwarfs cool over time and are thought to end as black dwarfs. What I'm supposing is that there is an additional energy source which will always give them a faint luminosity. Sorry if my post wasn't very clear.

tusenfem
2006-May-31, 02:03 PM
Well, you could at least have told us what this extra energy source is.

ExpErdMann
2006-May-31, 03:47 PM
Maybe since I'm basically asking a question here I should be posting in the Astronomy forum instead.

korjik
2006-May-31, 06:16 PM
I dont think we have determined where this thread should be yet. What is the source of the extra luminosity you are suggesting?

antoniseb
2006-May-31, 06:32 PM
The paper you pointed us to says that we've observed old white dwarfs at or below 1/20,000 the luminosity of the Sun. That was back in 1996. We may have seen dimmer ones by now.

ExpErdMann
2006-May-31, 06:47 PM
Where abouts in the paper did you see that?

antoniseb
2006-May-31, 09:09 PM
It was discussing the observed absolute visual magnitudes of the dimmest white dwarfs. It was using this figure to determine of the universe could be 18 billion years old or not (in the Early '90s a lot of us thought it was). They were coming up with 14 billion years based on the dimmest white dwarfs in the galactic halo were around Mv=16. If you go to a database of white dwarfs and sort by Absolute magnitude you'll find that that IS about the low end. The Sun has an Absolute Magnitude of about 5, and so the Sun is twenty thousand times brighter than the dimmest ones observed.

ExpErdMann
2006-Jun-01, 04:53 PM
Thanks, Antoniseb. That squares with some numbers I found in a paper by Geijo et al. (http://www.blackwell-synergy.com/doi/pdf/10.1111/j.1365-2966.2006.10354.x) In this paper they say that there is a lower luminosity cutoff described approximately as: -log (L/Ls) = 4.5 (see fig. 5), where L is the WD luminosity and Ls is the solar luminosity. This would match in proportional decrease the magnitude cutoff of 16 in the other paper.

I'm realizing that my initial post was not too good. The expression for internal energy release in a white dwarf, in my model, is

dE/dt = -UH,

where E is the energy generated, U is the internal gravitational potential energy of the star and H is Hubble's constant. We can write this as

dE/dt = (.4) G M^2 R^-1 H,

where M is the white dwarf mass and R its radius.


Basically, I'm saying that there is a turnover in a body's gravitational energy, such that internal photons are produced. Since I propose a universe at equilibrium, the gravitons are at the same time being regenerated from photons through the tired light effect. I've shown that the numbers work for the excess heating of planets. (I have a paper coming out soon in Annals of Geophysics on this.) Now what I forgot to mention is that only some of the photon energy produced will be released as heat. In a large body like a planet most of it will go into expansion. This forms the basis for earth expansion in my model. I found that only about 5 to 10 per cent of the generated photon energy goes into heat emission. So for white dwarfs my factor of 1/100 the solar luminosity was incorrect. It should have been about 10^-4 the solar luminosity. This gets us close to the observed cutoff. Another factor to consider is that some white dwarfs have only small masses (about .2 the solar mass) and so the emission from these WDs should be smaller as well from my equation.

antoniseb
2006-Jun-01, 05:08 PM
Glad to help, and also glad to see you found a slip that once corrected puts you into the 'can't tell' range instead the 'this is wrong' range.

Peter Wilson
2006-Jun-01, 11:33 PM
What is the source of the extra luminosity you are suggesting?

I thought white dwarfs get their luminosity mainly from shrinking and turning gravitational potential energy into heat.

In my model, (energy release) is

dE/dt = -UH,

where E is the energy generated, U is the internal gravitational potential energy of the star and H is Hubble's constant.
I don't know about H, but you are agreeing with tusenfem that the "source of extra luminosity" is good-ol' gravity?

ExpErdMann
2006-Jun-02, 02:12 PM
Gravity is involved but it's not acting conventionally. During the collpase of a white dwarf gravitational potential energy is converted to heat. An enormous amount of heat is generated which makes the white dwarf bright. My model does not involve this. Instead, the gravitons which comprise the internal gravitational potential energy of the star are slowly being converted to photons at a rate proportional to H. Similarly, ordinary light is converted to gravitons while it passes through space (the "tired light" effect). For this reason the graviton content of the white dwarf is not affected by this process, except where expansion also occurs.

Nereid
2006-Jun-02, 08:20 PM
How does this EEM (ExpErdMann) mechanism differ in neutron stars? in black holes? (from how it works in white dwarfs)?

What is the (photon) spectrum of the newly generated photons ("gravitons [...] star are slowly being converted to photons")?
Similarly, ordinary light is converted to gravitons while it passes through space (the "tired light" effect)There seems to be an inconsistency here ... if you convert a photon into a graviton, it ceases to be a photon (and it most certainly doesn't turn into a photon with a longer wavelength).

ExpErdMann
2006-Jun-03, 01:54 AM
The EEM mechanism does not specify a specific wavelength range. It just gives a total energy output. There will be an equivalent energy release from neutron stars and black hole-type objects. From my limited reading the observed spectrum from neutron stars is towards the X-ray end. What I really need is some charts of total luminosities for these various objects which also supply the mass and radius. Bet my mechanism will check out.

Nereid
2006-Jun-03, 02:09 PM
[snip]

Instead, the gravitons which comprise the internal gravitational potential energy of the star are slowly being converted to photons at a rate proportional to H.

[snip]
It just gives a total energy output.So the power (energy per unit of time) is proportional to (the local value of) H.

How does it vary, by the mass and (average) density of the object?

Do you have any OOM estimates of the constants (of proportionality)? To what extent have any of these varied, over the life of the universe?

ExpErdMann
2006-Jun-04, 04:16 AM
I think I mentioned that the whole thing is premised on the Static Universe model, which we've discussed previously. In SU the value of the Hubble constant does not change appreciably over time. H is a measure of the recycling time of the universe; its inverse gives the mean time for all quantities of matter and energy to be recycled, which is close to what is called the age of the universe in the Big Bang model. The relationship to mass and density is covered in my earlier post.

Nereid
2006-Jun-04, 12:45 PM
I think I mentioned that the whole thing is premised on the Static Universe model, which we've discussed previously. In SU the value of the Hubble constant does not change appreciably over time. H is a measure of the recycling time of the universe; its inverse gives the mean time for all quantities of matter and energy to be recycled, which is close to what is called the age of the universe in the Big Bang model.That clears things up (no, I don't see that you did mention this earlier).
The relationship to mass and density is covered in my earlier post.In post #10 (http://www.bautforum.com/showpost.php?p=753657&postcount=10)*?

If I just plug in numbers, I will get the answer, per the EEM idea?

For example, for the Sun, the EEM power is ~4 x 10^23 J/s, or ~0.1% of its observed power.

For a 1 sol WD, with a radius of ~7000 km, the EEM power is ~4 x 10^25 J/s, or ~10% of the Sun's observed power.

For a 1 sol neutron star, with a radius of ~10 km, the EEM power is ~2.5 x 10^28 J/s, or ~60 times the Sun's observed power.

For a 3 sol black hole, which has a radius of ~9 km, the EEM power is ~2.5 x 10^29 J/s, or ~600 times the Sun's observed power.

For a 1 million sol (supermassive) black hole, which has a radius of ~3 million km, the EEM power is ~ ~8 x 10^34 J/s, or ~200 million times the Sun's observed power.

Could you please confirm that these calculations are (more or less) correct, and in accord with the EEM power idea?

*"dE/dt = (.4) G M^2 R^-1 H,

where M is the white dwarf mass and R its radius."

ExpErdMann
2006-Jun-05, 08:16 PM
You've basically got the calculations right, except you haven't included the factor I mentioned to Antoniseb. The equation gives only a total production of energy and some of this energy can go into expansion of the objects. From the planetary data I have inferred that the luminosity is only about 5-10 per cent of the total energy generated. The rest goes into expansion. So if you were to multiply your numbers by .05-.10 I would agree.

I didn't check your numbers for the black hole objects. I'm sure they are right, but for this scale of object a different factor appears in my model which affects the results. Recalling that photons are converted to gravitons and vice versa, what happens is that photons emitted from a black hole (assuming they could escape) would be subject to such a heavy intrinsic redshift that the luminosity could be reduced by many OOMs. I haven't worked it all through myself, partly because I have some uncertainty about what black holes really are. I'm happy at this point to be testing the model using white dwarfs and neutron stars. You've noted that for ordinary stars the effect is too small to be distinguished from their fusion output.

Sorry for not mentioning the business about H being constant.

Nereid
2006-Jun-05, 08:58 PM
You've basically got the calculations right, except you haven't included the factor I mentioned to Antoniseb. The equation gives only a total production of energy and some of this energy can go into expansion of the objects. From the planetary data I have inferred that the luminosity is only about 5-10 per cent of the total energy generated. The rest goes into expansion. So if you were to multiply your numbers by .05-.10 I would agree.Ah yes, I'd forgotten that component.

Is this factor well-constrained, in your idea? I mean, does the theory limit it, or is it tied down only empirically ("from planetary data")?
I didn't check your numbers for the black hole objects. I'm sure they are right, but for this scale of object a different factor appears in my model which affects the results. Recalling that photons are converted to gravitons and vice versa, what happens is that photons emitted from a black hole (assuming they could escape) would be subject to such a heavy intrinsic redshift that the luminosity could be reduced by many OOMs. I haven't worked it all through myself, partly because I have some uncertainty about what black holes really are.Well, from the OOMs I did, using your equation, it would seem they would be a very good test of your idea!

Not only is the energy so huge, not only should it allow testable predictions (gravitational radiation that LIGO could detect, for example), but the regimes probed by BH are so much more extreme than planetary and stellar ones.
I'm happy at this point to be testing the model using white dwarfs and neutron stars.Well, if the Jodrell Bank Observatory Pulsar team can detect 0.1 mm on a pulsar (http://www.jb.man.ac.uk/news/neutronstar/), I'd be surprised if they couldn't detect any expansion that the EEM effect predicted!

More generally, pulsars, especially binary pulsars, permit some mind-blowingly accurate tests to be done, even if they are kiloparsecs away.

And since some binary pulsars are pulsar + WD, you get to test both your prime target objects, in one go!
You've noted that for ordinary stars the effect is too small to be distinguished from their fusion output.It might be worth re-visiting this ... 0.1% for the Sun is certainly within our power to detect, whether as 'more photons' or 'expansion'. Of course, I'm sure considerable care would be needed to specify just what could be observed (what the signal for the EEM effect would actually be), but at least the sensitivity is (likely) there.

antoniseb
2006-Jun-05, 09:20 PM
For a 1 sol neutron star, with a radius of ~10 km, the EEM power is ~2.5 x 10^28 J/s, or ~60 times the Sun's observed power

Hmm. We've observed isolated neutron stars with total energy outputs significantly less than the Solar output.

ExpErdMann
2006-Jun-05, 09:41 PM
Hmm. We've observed isolated neutron stars with total energy outputs significantly less than the Solar output.

Don't forget the correction factor! Multiplying by .05 (the lower value) we would then have 1.2 x 10^27 J/s. How does that square?

ExpErdMann
2006-Jun-05, 10:17 PM
Is this factor well-constrained, in your idea? I mean, does the theory limit it, or is it tied down only empirically ("from planetary data")?

All I have is that the total energy production can go into luminosity or expansion (at least for planets). Looking at the heat emission from the larger planets and Earth, it seems about 5 - 10 per cent of the available energy is radiated out. The rest can go into expansion and the amount matches what Earth needed to expand from about 60 per cent of its original radius.


Well, from the OOMs I did, using your equation, it would seem they would be a very good test of your idea!

Not only is the energy so huge, not only should it allow testable predictions (gravitational radiation that LIGO could detect, for example), but the regimes probed by BH are so much more extreme than planetary and stellar ones.

It would be too hard to make predictions in my model to cover this situation at present, but it is an interesting place to look.


Well, if the Jodrell Bank Observatory Pulsar team can detect 0.1 mm on a pulsar (http://www.jb.man.ac.uk/news/neutronstar/), I'd be surprised if they couldn't detect any expansion that the EEM effect predicted!

More generally, pulsars, especially binary pulsars, permit some mind-blowingly accurate tests to be done, even if they are kiloparsecs away.

That's a very good suggestion! My quick Google on this seems to suggest that other factors can affect the spindown rate more than the EEM factor would, but I'll keep checking.


It might be worth re-visiting this ... 0.1% for the Sun is certainly within our power to detect, whether as 'more photons' or 'expansion'. Of course, I'm sure considerable care would be needed to specify just what could be observed (what the signal for the EEM effect would actually be), but at least the sensitivity is (likely) there.

The sensitivity is there if we could isolate the fusion luminosity somehow from the EEM luminosity, but we can't know the relative proportions here. The .1 % factor would just seem like a necessary correction to make to conventional theory.

I've just found a paper by Thompson and Duncan (ApJ 473, 322, 1996) which says that (X-ray) luminosities of magnetars are in the range of 10^27-10^29 J/s, which falls right in with the our estimates for a neutron star. I don't have a link to the article.

antoniseb
2006-Jun-06, 01:07 AM
Don't forget the correction factor! Multiplying by .05 (the lower value) we would then have 1.2 x 10^27 J/s. How does that square?

Still about a factor of 100 more energetic than the coolest known Neutron Stars.
Similarly Sgr A* by Nereid's computations should be giving off vastly more energy than it currently emits.

ExpErdMann
2006-Jun-06, 02:38 AM
That may not be so bad. It depends on the mass and radius of these coolest stars, especially the mass. Also, the less massive stars tend to have larger radii. Do you happen to have a table of values?

Nereid
2006-Jun-06, 04:18 PM
All I have is that the total energy production can go into luminosity or expansion (at least for planets). Looking at the heat emission from the larger planets and Earth, it seems about 5 - 10 per cent of the available energy is radiated out. The rest can go into expansion and the amount matches what Earth needed to expand from about 60 per cent of its original radius.So, essentially an empirically-based fit, with no necessary reason to think the fraction going to radiation (cf expansion) is 5-10%?
It would be too hard to make predictions in my model to cover this situation at present, but it is an interesting place to look.

That's a very good suggestion! My quick Google on this seems to suggest that other factors can affect the spindown rate more than the EEM factor would, but I'll keep checking.One good thing about binary pulsars is that there are so many parameters that can be used, as tests - not only the spindown rate, but also the radius (especially if it's an eclipsing binary!) - as well as highly precise orbital elements.

To test the EEM effect, I expect that you may have to either analyse the pulse arrival data, or (perhaps easier) estimate the (OOM) size of the effect on pulse arrival times (over a decade or more's baseline).
The sensitivity is there if we could isolate the fusion luminosity somehow from the EEM luminosity, but we can't know the relative proportions here. The .1 % factor would just seem like a necessary correction to make to conventional theory.Indeed.

However, you also have the expansion ... there are several (observational) constraints on the extent to which the Sun has expanded (or not); combine these with observations on the power output, and you may have accurate enough data to test the EEM effect idea.

ExpErdMann
2006-Jun-07, 02:19 PM
Still about a factor of 100 more energetic than the coolest known Neutron Stars.
Similarly Sgr A* by Nereid's computations should be giving off vastly more energy than it currently emits.

I checked some numbers on Sagittarius A*. From this paper (http://www.journals.uchicago.edu/ApJ/journal/issues/ApJ/v509n2/38297/38297.html) the radius of Sagittarius A* is less than .015 pc or about 5 x 10^11 km. If it were this radius, that would be significantly greater than Nereid's radius for a supermassive black hole of about 3 million km. From a study of motions of stars around Sgr A* the mass is estimated at 2.6 million solar masses. Plugging these numbers in the ouput is only about 3 X 10^24 J/s. This is much lower than the total luminosity inferred from the heating of the dust around the object (eg., this paper (http://adsabs.harvard.edu/abs/1982ApJ...258..135B) ), which is around 10 million solar luminosities. So assuming that much of Sagittarius A* is composed of ordinary stars, and with this radius of .015 pc, the EEM power would be too feeble to be detected against the ordinary stellar power. Even if we reduce the radius by several OOMs this would still hold.

Nereid
2006-Jun-07, 03:16 PM
I checked some numbers on Sagittarius A*. From this paper (http://www.journals.uchicago.edu/ApJ/journal/issues/ApJ/v509n2/38297/38297.html) the radius of Sagittarius A* is less than .015 pc or about 5 x 10^11 km. If it were this radius, that would be significantly greater than Nereid's radius for a supermassive black hole of about 3 million km. From a study of motions of stars around Sgr A* the mass is estimated at 2.6 million solar masses. Plugging these numbers in the ouput is only about 3 X 10^24 J/s. This is much lower than the total luminosity inferred from the heating of the dust around the object (eg., this paper (http://adsabs.harvard.edu/abs/1982ApJ...258..135B) ), which is around 10 million solar luminosities. So assuming that much of Sagittarius A* is composed of ordinary stars, and with this radius of .015 pc, the EEM power would be too feeble to be detected against the ordinary stellar power. Even if we reduce the radius by several OOMs this would still hold.More recent research has provided much tighter constraints.

For example, Schödel et al (http://lanl.arxiv.org/abs/astro-ph/0210426) reported an analysis of the orbit of star S2, around SgrA*, and found that its pericentre distance was a mere 17 light-hours.

Assuming that S2 grazed the very edge of SgrA*, and that SgrA* has a mass of 3.7 million sols, the EEM power would be ~2 x 10^32 J/s, or ~half a million times the Sun's power.

SgrA* most certainly doesn't emit this much EM power, nor even 5-10% of it.

Further, S2 clearly survived its pericentre passage, so SgrA* must be considerably smaller than 17 light-hours in radius (if nothing else, a close passage to SgrA*'s surface would have produced tides in S2 that would have been easily observed). This means that the EEM power must be considerably higher.

Note that none of this assumes that SgrA* is an SMBH; merely that it has a mass consistent with the orbits determined from the VLT observations (http://www.eso.org/outreach/press-rel/pr-2002/pr-17-02.html) (oh, and that either Newton or Einstein got it right, wrt gravity, on these scales).

[Edit: -centre, not -helion (:doh: )]

ExpErdMann
2006-Jun-07, 07:00 PM
My calculation checks out with yours using the numbers from Schodel et al. However, from my previous post we have the total estiamted luminosity of Sgr A* as 10^7 solar luminosities. So the new value corresponds to about 5 per cent of what we actually measure. Once again, the effect would be masked by the ordinary starlight emitted from Sgr A*, if we were to assume it is composed of ordinary stars.

Nereid
2006-Jun-07, 07:47 PM
My calculation checks out with yours using the numbers from Schodel et al. However, from my previous post we have the total estiamted luminosity of Sgr A* as 10^7 solar luminosities.Er, you might want to read that paper again (my bold).
Far-infrared observations of the central 4 arcmin of the Galaxy with 30-arcsec resolution [...]The total luminosity of the sources heating the dust which radiates the far-infrared emission from the central few parsecs ...Compare this with Figures a, b, and c in the VLT work (http://www.eso.org/outreach/press-rel/pr-2002/pr-17-02.html), where the scale bars are light-days.

Also, note that SgrA* itself is not imaged, while S2 is, so at least in the IR its luminosity can't be more than a few sols (it'd take some detective work to put tighter constraints on it. Of course, it's bright in the radio, and occassionally burps in the X-ray, but its a pretty wimpy source).
So the new value corresponds to about 5 per cent of what we actually measure. Once again, the effect would be masked by the ordinary starlight emitted from Sgr A*, if we were to assume it is composed of ordinary stars.Er, SgrA* cannot possibly be "composed of ordinary stars" (my bold)! No way you can get a few million sols of mass into an object less than 17 light-hours across, and call it "an ordinary star" (or even a very tight 'cluster', of, say, 3 or 4 stars).

ExpErdMann
2006-Jun-08, 06:01 PM
Thanks for those clarifications. Taking Sgr A* to be a black hole-type object, and that the 10^7 solar luminosity figure I gave is in error, then my position reverts to saying that the EEM calculation is outside its comfort zone here. There is even the additional possibility, given Arp's matter creation/quasar ejection hypothesis, that energy is going into new mass. It would be better for now to limit the discussion to white dwarfs and neutron stars.

Nereid
2006-Jun-08, 11:45 PM
OK, so what (in the EEM effect idea) is the rate of expansion of the Sun? Of a 1 sol neutron star?

Given the EEM effect, how will the evolution tracks of normal stars, through the HR diagram, be different (than those in standard astrophysics)?

In the case of contact binaries, what differences would there be in the evolutionary history of each star?

In the case of Type 1a supernovae, what tweaks would need to be made, to the expected light curves?

In the case of core collapse supernovae, what differences should we observe, compared with what we expect using standard astrophysics? In particular, to what extent are the rebound and neutrinosphere phases different? Also, how would the EEM effect change the expected neutrino flux?

For inspiral events, how does the expected incidence (rate) of LIGO-observables change, when the EEM effect is factored in?

ExpErdMann
2006-Jun-09, 06:59 PM
OK, so what (in the EEM effect idea) is the rate of expansion of the Sun? Of a 1 sol neutron star?

Given the EEM effect, how will the evolution tracks of normal stars, through the HR diagram, be different (than those in standard astrophysics)?

I'm not sure expansion is an expected result for ordinary stars. The EEM power is just a small fraction (less than 1 per cent) of the ordinary fusion output. A main-sequence star does not expand because it has already expanded, to the point where gravity balances the thermal expansion. In the case of a neutron star or a white dwarf, however, the EEM power appears as a new, significant source arising from the gravitational collapse. The gravitational potential energy is now so negative that a huge EEM power is generated. The way I think of it is the reverse of the old saying "what goes up must come down". We have "what falls down, must bounce up (but slowly!)".


In the case of contact binaries, what differences would there be in the evolutionary history of each star?

In the case of Type 1a supernovae, what tweaks would need to be made, to the expected light curves?

In the case of core collapse supernovae, what differences should we observe, compared with what we expect using standard astrophysics? In particular, to what extent are the rebound and neutrinosphere phases different? Also, how would the EEM effect change the expected neutrino flux?

For inspiral events, how does the expected incidence (rate) of LIGO-observables change, when the EEM effect is factored in?

I don't think the lightcurve of supernovae will be affected that much, since the main energy released at that point is from the gravitational infall and that energy is much more than the EEM power emitted from the collapsed object during the time interval of the infall and rebound phases. I'm not up on the neutrinosphere, so I can't comment here.

Nereid
2006-Jun-12, 10:05 PM
OK, so it seems that there is a wide variety of reasonably well-known (and well-observed) astronomical/astrophysical phenomena that could, potentially, provide tests of the EEM effect.

However, at the moment, the author of this idea has not developed it to the point where the relevance of these phenomena, to testing the idea, can be quantified.

Fair summary?

ExpErdMann
2006-Jun-14, 03:40 PM
Well, that's not quite how I would summarize it. I started off just wanting to find out if my simple equation fitted luminosity observations from white dwarfs and neutron stars. From what I've seen, they seem to fall pretty close to my model predictions.

You earlier pointed out that slowing of pulsar rotations could be another test, for expansion in these objects. In this case, from what I've read, it seems that spindown energy of pulsars is thought to be the source of energy for pulsar luminosities. So here I'm not sure how you would separate a possible expansion effect from the other mainstream spindown mechanisms which have been postulated.

Finally, you've listed some other phenomena which you suppose could be used to test the idea. I either am not following your suggestions or am not in a good position to quantify with these and it would take a lot more time for me to sort it out.

All in all, I think this would be a not bad place to adjourn the discussion for now. I need to do some more digging. Thanks a lot for the very good feedback, especially in a thread which had few participants.