arXiv 1006.45772010-06-23astro-ph.GA

用球状星团在低加速度区检验牛顿引力：重新考察半人马座Ω的情况

Testing Newtonian gravity in the low acceleration regime with globular clusters: the case of omega Centauri revisited

Riccardo Scarpa, Renato Falomo

备注：: Accepted for Publication on A&A main journal
DOI：: 10.1051/0004-6361/201014443

摘要：

球状星团外部区域的恒星运动学可以用来研究牛顿定律在低加速度区域的有效性，而不需要考虑非重子暗物质。事实上，与研究星系时发生的情况相反，在球状星团中，速度色散剖面与预期的开普勒衰减的系统性偏差将提供牛顿动力学崩溃的迹象，而不是暗物质的存在。我们对半人马座球状星团的速度色散进行了详细的分析，以研究它是否像Sollima等人（2009）最近声称的那样随距离单调下降，或者它是否像Scarpa Marconi和Gilmozzi（2003 B）声称的那样朝着一个恒定值收敛。我们结合这两个作品的测量，几乎增加了一倍，在大半径的数据，以这种方式获得一个更好的确定在低加速度制度的速度色散曲线。我们发现半人马座欧米茄的内部区域显然是旋转的，而旋转速度趋于消失，并且与外部区域完全没有旋转一致。发现在离中心大半径处的团速度色散是相当恒定的。这项工作的主要结论是，球状星团和椭圆星系之间出现了很强的相似性，因为在这两类物体中，速度色散往往在大半径处保持恒定。在星系的情况下，这是由于存在大量的暗物质晕，这在球状星团的情况下是不可能的。这种相似性，如果得到证实，最好的解释是在临界加速度以下牛顿动力学的崩溃。

英文摘要：

Stellar kinematics in the external regions of globular clusters can be used to probe the validity of Newton's law in the low acceleration regimes without the complication of non-baryonic dark matter. Indeed, in contrast with what happens when studying galaxies, in globular clusters a systematic deviation of the velocity dispersion profile from the expected Keplerian falloff would provide indication of a breakdown of Newtonian dynamics rather than the existence of dark matter. We perform a detailed analysis of the velocity dispersion in the globular cluster omega Centauri in order to investigate whether it does decrease monotonically with distance as recently claimed by Sollima et al. (2009), or whether it converges toward a constant value as claimed by Scarpa Marconi and Gilmozzi (2003B). We combine measurements from these two works to almost double the data available at large radii, in this way obtaining an improved determination of the velocity dispersion profile in the low acceleration regime. We found the inner region of omega Centauri is clearly rotating, while the rotational velocity tend to vanish, and is consistent with no rotation at all, in the external regions. The cluster velocity dispersion at large radii from the center is found to be sensibly constant. The main conclusion of this work is that strong similarities are emerging between globular clusters and elliptical galaxies, for in both classes of objects the velocity dispersion tends to remain constant at large radii. In the case of galaxies, this is ascribed to the presence of a massive halo of dark matter, something physically unlikely in the case of globular clusters. Such similarity, if confirmed, is best explained by a breakdown of Newtonian dynamics below a critical acceleration.

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