ترغب بنشر مسار تعليمي؟ اضغط هنا

Regarding the Potential Impact of Double Star Observations on Conceptions of the Universe of Stars in the Early 17th Century

113   0   0.0 ( 0 )
 نشر من قبل Christopher Graney
 تاريخ النشر 2009
  مجال البحث فيزياء
والبحث باللغة English




اسأل ChatGPT حول البحث

Galileo Galilei believed that stars were distant suns whose sizes, measured via his telescope, were a direct indication of distance -- fainter stars (appearing smaller in the telescope) were farther away than brighter ones. Galileo argued in his Dialogue that telescopic observation of a chance alignment of a faint (distant) and bright (closer) star would reveal annual parallax, if such double stars could be found. This would provide support both for Galileos ideas concerning the nature of stars and for the motion of the Earth. However, Galileo actually made observations of such double stars, well before publication of the Dialogue. We show that the results of these observations, and the likely results of observations of any double star that was a viable subject for Galileos telescope, would undermine Galileos ideas, not support them. We argue that such observations would lead either to the more correct conclusion that stars were sun-like bodies of varying sizes which could be physically grouped, or to the less correct conclusion that stars are not sun-like bodies, and even to the idea that the Earth did not move. Lastly, we contrast these conclusions to those reached through applying Galileos ideas to observations of visible stars as a whole.



قيم البحث

اقرأ أيضاً

We study the effects of the ionizing and dissociating photons produced by Pop III objects on the surrounding intergalactic medium. We find that the typical size of a H_2 photodissociated region is smaller than the mean distance between sources at z=2 0-30, but larger than the ionized region. This implies that clearing of the intergalactic H_2 occurs before reionization of the universe is complete. In the same redshift range, the soft-UV background in the Lyman- Werner bands, when the intergalactic H and H_2 opacity is included, is found to be J_LW = 10^-28 - 10^-26 erg cm^-2 s^-1 Hz^-1. This value is well below the treshold required for the negative feedback of Pop III objects on the subsequent galaxy formation to be effective. We have combined these semi-analytical results with high-resolution N-body simulations, to study the topological structure of photoionization and photodissociation and the evolution of the H^+ and H_2 filling factor.
99 - Brenda L. Frye 2008
We present a high signal-to-noise spectrum of a bright galaxy at z = 4.9 in 14 h of integration on VLT FORS2. This galaxy is extremely bright, i_850 = 23.10 +/- 0.01, and is strongly-lensed by the foreground massive galaxy cluster Abell 1689 (z=0.18) . Stellar continuum is seen longward of the Ly-alpha emission line at ~7100 AA, while intergalactic H I produces strong absorption shortward of Ly-alpha. Two transmission spikes at ~6800 Angstroms (A) and ~7040 A are also visible, along with other structures at shorter wavelengths. Although fainter than a QSO, the absence of a strong central ultraviolet flux source in this star forming galaxy enables a measurement of the H I flux transmission in the intergalactic medium (IGM) in the vicinity of a high redshift object. We find that the effective H I optical depth of the IGM is remarkably high within a large 14 Mpc (physical) region surrounding the galaxy compared to that seen towards QSOs at similar redshifts. Evidently, this high-redshift galaxy is located in a region of space where the amount of H I is much larger than that seen at similar epochs in the diffuse IGM. We argue that observations of high-redshift galaxies like this one provide unique insights on the nascent stages of baryonic large-scale structures that evolve into the filamentary cosmic web of galaxies and clusters of galaxies observed in the present universe.
The ``Century Survey (CS hereafter) is a complete redshift survey of a 1$^circ$-wide strip. It covers 0.03 steradians to a limiting m$_R$ = 16.13. The survey is 98.4% complete and contains 1762 galaxies. Large-scale features in the survey are qualita tively similar to those in other surveys: there are large voids surrounded or nearly surrounded by thin dense regions which are sections of structures like (and including) the Great Wall. The survey crosses the classical Corona Borealis supercluster. The galaxy density enhancement associated with this system extends for $simgreat 100 h^{-1}$ Mpc (the Hubble constant is H$_0 = 100h$ km s$^{-1}$Mpc$^{-1}$). The Schechter (1976) luminosity function parameters for the CS are: $M^*_{CS} = -20.73 ^{+0.17}_{-0.18}$, $alpha_{CS} = -1.17 ^{+0.19}_{-0.19}$, and $phi^*_{CS} = 0.0250pm0.0061$ Mpc$^{-3}$mag$^{-1}$. In concert with the ESO Key Program (cite{vet97}; cite{zuc97}) and the AUTOFIB (cite{ell96}) surveys, the CS indicates that the absolute normalization of the luminosity function exceeds estimates based on shallower and/or sparser surveys.
التعليقات
جاري جلب التعليقات جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
mircosoft-partner

هل ترغب بارسال اشعارات عن اخر التحديثات في شمرا-اكاديميا