Stars, lithium and exoplanets

[Arch2008]

“There are several ways in which a planet can disturb the internal motions of matter in its host star, thereby rearrange the distribution of the various chemical elements and possibly cause the destruction of lithium. It is now up to the theoreticians to figure out which one is the most likely to happen,”

 

http://www.eso.org/public/outreach/press-rel/pr-2009/pr-42-09.html

 

FYI, a lack of lithium in a star may indicate the presence of exoplanets. This could be a short cut for exoplanet hunters.

[Widdekind]

According to the Nov. 2009 AD Scientific American article The Long Lost Siblings of the Sun, stars that do not have planets lost their circumstellar disks to disruption, by nearby neighbors in their birth cluster "cradle" (as it were). Only stars that escaped such close encounters kept their proto-planetary systems.

 

Thus, this process of disruption, in the early parent "cradle" cluster, produces precisely the appropriate division of stars (no planets vs. planets) that correlates with the presence or lack of lithium (respectively).

 

So, it certainly doesn't seem likely, as it seems "backwards", but could this process of disruption in the cradle cluster account for the "lithium litmus test" ??

[Arch2008]

From what I’ve read, exoplanets would exert gravitational influence on their parent star. This causes internal changes in the star (perhaps with the convection currents) so that lithium is “destroyed”. The researchers seem pretty confident of this as they state: “Using our unique, large sample, we can also prove that the reason for this lithium reduction is not related to any other property of the star...“

Exactly how some stars may end up without exoplanets is still an unknown.

[Sisyphus]

Although the exoplanets we'd be most interested in(small, rocky planets in the habitable zone) would also have very little tidal influence on the star.

[Arch2008]

Precisely!

I’m not privy to the models being used, but why should a star have no exoplanets at all? I get the part where originally there was only hydrogen, helium and a dash of lithium in the early universe, so no possibility of planet formation. However, in a typical globular cluster huge stars form first and then go supernova in just a few million years. Each such SN spews out many solar masses of heavier elements, i.e., tens of thousands of Earth masses that then fill the surrounding space. So the stars like our Sun form thereafter with at least the opportunity for the elements common to planets. IMHO, I think that it is more likely that lithium is more prevalent in stars that have only a few small exoplanets or a certain low percentage of exoplanetary mass to star mass.

[Widdekind]

According to Astrophysics is Easy! by Mike Inglis, as a rough rule of thumb, "everything is faster for bigger brighter stars". Thus, in their birth clusters, bigger brighter stars are seen to have formed first -- and, even, finish their life-cyles -- before smaller dimmer stars even finish forming (from protostars, ~10-100 Myr).

 

Thus, the bigger brighter stars start shining, and stripping away the dusty mantles shrouding the smaller stars, before they finish forming. In some such cases, that dusty mantle shrouding said smaller star can be completely stripped away (even as whole collapsing and condensing clouds can be blown apart) before it can start to settle into a circum-stellar, pre-proto-planetary, disk (as argued by Prof. Portegeis Zwart, in said cited Sci.Am. article, as per the PP).

 

Evidently, on average, only about half of all low-mass stars' shrouds survive such stripping processes.

[Arch2008]

Yes, but what happens then? In a globular cluster that most likely consists largely of hydrogen to begin with, the bigger, brighter stars strip away smaller stars’ dusty disks that should initially be low in metallicity. These bigger stars then go SN and pepper the surrounding stars with many solar masses of material consisting of all the elements. A low mass star that originally attracted a dusty disk by its gravity will continue to attract material for the life of the star for the same reason. Right?

Stars like our Sun will also expand to Red Giant size and lose mass, to the point where their outer planets will simply no longer orbit their parent star. Where might these rogue planets end up?

A globular cluster is not only a stellar nursery it is a planetary nursery as well. IMHO, I don’t see how over a period of billions of years somehow random events could conspire to such a degree that the perfectly attractive mass of a star would never…ever…attract a planet.

(Merry Christmas to all!)

[Widdekind]

Are Exoplanets unique to the Milky Way ??

 

(1) Interstellar Dust contains much of the mass of 'metals' manufactured since the start of spacetime (~14 Gya), which metals make planets much more probable

 

Cosmic dust is of fundamental importance to astrophysics. Though dust is only a tiny fraction of the baryons in the Universe, it influences the formation of planets and stars in a fundamental way and contains half of all the metals synthesized over cosmic time.

 

https://indico.nbi.ku.dk/conferenceDisplay.py?confId=78

 

 

 

(2) Milky Way's Dust seems special, in shape & size, and perhaps other properties

 

The 2175 Å absorption bump, a feature often ascribed to graphite grains and ubiquitous in the spectra of sight lines through the Galactic diffuse interstellar medium, is generally weak or nonexistent for objects outside our Galaxy. Many active galaxies seem to have Small Magellanic Cloud-type dust extinction, suggesting that the presence of the bump in our Galaxy may be exceptional. Recently, it was suggested that the spectrum of the high-ionization broad absorption line QSO UM 425 shows a 2175 Å feature. This apparent feature seen in UM 425 and the rest frame spectra of other QSOs is intrinsic to the QSO spectrum. It is the result of a relative absence of emission near 2200 Å. Thus far, no significant detection of the 2175 Å bump in a QSO has been reported.

 

http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2000PASP..112..537P

We report a superstrong 2175 Å absorption galaxy at a redshift of z_G = 0.8839 toward the background quasar SDSS J100713.68+285348.4 at z_Q = 1.047 identified from the Sloan Digital Sky Survey (SDSS) data. The bump is the strongest ever known, about 2.5 times the average in the Galactic interstellar extinction curves. About two dozens of narrow absorption lines are identified in this system in the SDSS and the follow-up Multiple Mirror Telescope (MMT) spectra, including Zn II, Cr II, Mn II, Si II, Fe II, Ti II, Ca II, Al III, Mg II, and Mg I. We have derived accurate measurements of the gas-phase column densities of most of these ions through their weak absorption lines. The combination of unprecedentedly strong 2175 Å absorption bump strength with the measured zinc column density suggests that carbon is likely to be the main carrier of the 2175 Å absorber assuming that the total abundance of the absorber relative to zinc is similar to the solar values and zinc is not heavily depleted onto dust grains. Under the same assumption, we found that dust depletion in this absorption galaxy is much less than that in the Milky Way, indicating possible different nucleosynthesis and/or chemical and interstellar medium evolution history.

 

http://www.iop.org/EJ/abstract/0004-637X/708/1/742

 

The 2175 Å extinction bump, first detected over 40 years ago (Stecher 1965), is an ubiquitous feature of the Milky Way ISM... the 2175 Å bump is relatively weaker in the LMC and absent in the SMC. This bump is largely absent in AGNs.

 

http://nedwww.ipac.caltech.edu/level5/Sept07/Li2/Li3.html

 

Note, tho, that "The broad absorption bump at 2175 Å due to dust, which is ubiquitous in the Galaxy, [is also] seen in the Magellanic clouds"*.

*

http://www.iop.org/EJ/article/1538-4357/488/2/L101/975424.text.html

 

 

 

(3) The Galactic Disk of the Milky Way contains a Jupiter-mass of metals for every Star (System?)

 

According to M.H.Jones & R.J.Lambourne's An Introduction to Galaxies & Cosmology (pp. 11-32), the Galactic Disk of the Milky Way contains ~10¹¹ [math]M_{\odot}[/math] in stars, and ~10⁸ [math]M_{\odot}[/math] of dust, indicating a Jupiter's mass of dust per star in said disk. Most of this dust dwells in the Dark Clouds in the inner disk dust lanes, from 4-7 Kpc (cf. [math]R_{\odot} = 8.5 kpc[/math].)

 

May I please point out, that Prof. Chandra Wickramasinghe seemingly says, that this 'dust' in the disk of the Milky Way may be microbial, bacterial, spores*. If so, given that the mass of Earth's Biosphere is about ~10¹⁶ kg (~10^-11 M_J)**, there might be many billions of times more microbes per star system, in our Galaxy's disk, than is known to exist, in our own Solar System. Such seems a somewhat staggering suggestion, but one which would be of potentially profound importance, if verifiable***^,#.

*

http://www.physicsforums.com/showpost.php?p=1998489&postcount=18

**

http://www.bigpicturesmallworld.com/funstuff/bignumbers.shtml

***

This author was told, by Prof. D.T. at USCD in ~2004 AD, that some astronomers say, that long-period comets actually come in on parabolic orbits, from beyond our Solar System, seemingly suggesting a very vast reservoir of inter-stellar comets. And, Prof. C.W. (

ibid

.) seemingly suggests, that the cores of comets could have been the birth-beginnings of the observed bacterial spores in space. You could conceive of a very vast reservoir of interstellar comets, careening around the

Galactic Disk

, like airplanes between airports upon this planet.

Biogenesis

began, in a single such comet,

after 10 Gya

(disk formation) but

before 5 Gya

(Solar System formation), like a terrorist infecting a single airplane w/

Ebola

. As the infected comet careened into some star system, it started to spew it spores across said star system, as it (and its bacteria) were warmed up by the starlight. The infected comet ("airplane") then careened back out of said star system ("airport"), and started a subsequent trek towards a subsequent star system, for the following

many millions of years

. But, meanwhile, more comets ("airplanes") could careen into the infected star system ("airport"), become coated w/ bacterial spores, which would then be carried across inter-stellar space towards myriad other star systems ("airports"). In this way, (primitive)

Life

could be carried across the

Galactic Disk

thru diffusion, like

SARS

spreading upon this planet from (air)port to (air)port, w/ a time scale of surely

some millions of years

, that being the travel time of interstellar comets on their interstellar trajectories. Given that the

Galactic Disk

would be, thusly, thousands of "diffusion time scales" old, such a "cometary dispersal diffusion mechanism" model might account for the copious quantities of this seemingly special 'dust' across the disk of this galaxy.

#

These potential bacterial space spores resemble spherical "nano-scale graphite onions with a central void", typically about 0.1-1.0 um across, and w/ a "ratio r/R of the inner and outer radii [of] r/R≃0.6", according to

Henrard, Lucas, & Lambin

. Prof. Wickramasinghe's suggestion should surely require this ratio to closely match microbes in their spore state (or viruses??).

---

Merged post follows:

Consecutive posts merged

Yes, but what happens then? In a globular cluster that most likely consists largely of hydrogen to begin with, the bigger, brighter stars strip away smaller stars’ dusty disks that should initially be low in metallicity. These bigger stars then go SN and pepper the surrounding stars with many solar masses of material consisting of all the elements. A low mass star that originally attracted a dusty disk by its gravity will continue to attract material for the life of the star for the same reason. Right?

Stars like our Sun will also expand to Red Giant size and lose mass, to the point where their outer planets will simply no longer orbit their parent star. Where might these rogue planets end up?

A globular cluster is not only a stellar nursery it is a planetary nursery as well. IMHO, I don’t see how over a period of billions of years somehow random events could conspire to such a degree that the perfectly attractive mass of a star would never…ever…attract a planet.

(Merry Christmas to all!)

 

Surely someone shall say something along the lines of capture requiring the conservation of momentum & energy to be broken, and something about 3 bodies being needed, but it seems pretty plausible to me.

(Happy Holidays !)

Edited December 27, 2009 by Widdekind
Consecutive posts merged.