吸积盘的角动量损失

1。 恒星形成的角动量损失
from： http://iask.games.sina.com.cn/b/5723040.html

“角动量损失和磁场分离则仍然是两个无法解决的问题；我们只能指出一、二种解决这些难题的可能途径。

。。。

一个可能的途径就是仅仅收集对银心有相同角动量的那些物质。比方说，如果假定全部气体粒子都绕着银心作圆周运动，那么我们就只能收集到距银心为某个确定半径Rc的一个环上的物质。
”

以上从一个侧面反应出太阳系的角动量比原始星云由于交差转动形成的角动量小，意味着在从星云形成恒星的过程中有角动量损失到太阳系之外。

2。有文章专门介绍角动量的转移

astro-ph/9902335

Evolution of Disk Accretion

Authors: Nuria Calvet, Lee Hartmann, Stephen E. Strom
Comments: 21 pages, 7 Postscript figures. To appear in Protostars and Planets IV, University of Arizona Press

We review the present knowledge of disk accretion in young low mass stars, and in particular, the mass accretion rate and its evolution with time. The methods used to obtain mass accretion rates from ultraviolet excesses and emission lines are described, and the current best estimates of mass accretion rate for Classical T Tauri stars and for objects still surrounded by infalling envelopes are given. We argue that the low mass accretion rates of the latter objects require episodes of high mass accretion rate to build the bulk of the star. Similarity solutions for viscous disk evolution suggest that the inner disk mass accretion rates can be self-consistently understood in terms of the disk mass and size if the viscosity parameter alpha is approximately 1e-2. Close companion stars may accelerate the disk accretion process, resulting in accretion onto the central star in less or equal than 1Myr; this may help explain the number of very young stars which are not currently surrounded by accretion disks (the weak emission T Tauri stars).

Full-text: PostScript, PDF, or Other formats

其中有说“his may help explain the number of very young stars which are not currently surrounded by accretion disks”。也就是存在一些没有盘的年轻恒星，那它们的角动量跑哪儿去了呢？

在文章15页中说盘可以一致膨胀，使得角动量保持不变。14页反对Pudritz and
Norman 1983, Konigl 1989认为角动量可以通过外盘区的盘风损失。说是在他的Hartmann
1995中讲了。那下面就看看这篇文章怎么说的。

ft，是一篇会议文章，通过观测的，因为题目是：“Observational Constraints on Disk Winds”

不过下面有一篇他在ApJ上的文章，内容应该相同：

3。 通过盘风损失角动量的不支持观测证据

Title:		Observational constraints on FU ORI winds
Authors:		Hartmann, Lee; Calvet, Nuria
Publication:		Astronomical Journal (ISSN 0004-6256), vol. 109, no. 4, p. 1846-1855 (AJ Homepage)
Publication Date:		04/1995

Abstract

We have searched for velocity shifts in the photospheric lines of four FU Orionis objects that could show that their winds originate from the surfaces of pre-main sequence accretion disks. We confirm the pattern of photospheric line shifts in FU Ori first observed by Petrov and Herbig, in which increasingly strong photospheric lines are increasingly blueshifted as the two absorption components move closer together in wavelength. We show that this pattern is precisely that predicted by a disk wind model: the profiles of the weaker lines exhibit mostly Keplerian rotation, and thus should show nearly symmetric double-peaked absorption, while the stronger lines, formed farther out in the expanding wind, are more blueshifted and less doublepeaked. These observations provide at present the only direct evidence for a continuously accelerating wind originating from the surface of a pre-main-sequence disk. Similar velocity shifts are not observed in the photosheric lines of V1057 Cyg, V1515 Cyg, and Z CMa, even though all exhibit strong blueshifted absorption in the Na I and H-beta line profiles. We suggest that the Na I and H-beta lines are generally saturated and thus not sensitve measures of mass loss rates, and that V1057 Cyg and V1515 Cyg have smaller mass loss rates than FU Ori. Z CMa may have a mass loss rate similar to that of FU Ori, but photospheric velocity shifts may be less apparent because Z CMa has a higher projected rotational velocity. Our estimates of mass loss rates do not support the extreme wind model, in which all of the angular momentum needed for accretion is removed by the wind.

注意最后一句话：“Our estimates of mass loss rates do not support the extreme wind model, in which all of the angular momentum needed for accretion is removed by the wind.”

4。 借助磁场

astro-ph/9903168

Disk Winds and the Accretion--Outflow Connection

Authors: Arieh Konigl (University of Chicago), Ralph E. Pudritz (McMaster University)
Comments: 32 pages, 3 figures, TeX, to appear in Protostars and Planets IV, ed. V. Mannings, A. Boss, and S. Russell (Arizona: University of Arizona Press)

We review recent observational and theoretical results on the relationship between circumstellar accretion disks and jets in young stellar objects. We then present a theoretical framework that interprets jets as accretion-powered, centrifugally driven winds from magnetized accretion disks. Recent progress in the numerical simulation of such outflows is described. We also discuss the structure of the underlying magnetized protostellar disks, emphasizing the role that large-scale, open magnetic fields can play in angular momentum transport.

Full-text: PostScript, PDF, or Other formats

上面abstract说大尺度开放的磁场可以用以转移角动量出去。

这里：http://farside.ph.utexas.edu/teaching/plasma/lectures/node68.html
也提供了类似的说法，说磁场可以帮助带走角动量，不过对象是太阳的星风。

5. 如果是星系的话，还会牵涉到暗物质。

这里有一篇最近2006年的MN上的文章，专门介绍星系角动量的损失。
Mon. Not. R. Astron. Soc. 372, 1525–1530 (2006)
How galaxies lose their angular momentum
ABSTRACT
The processes are investigated by which gas loses its angular momentum during the protogalactic collapse phase, leading to disc galaxies that are too compact with respect to the observations. High-resolution N-body/SPH simulations in a cosmological context are presented including cold gas and dark matter (DM). A halo with quiet merging activity since redshift z ∼ 3.8 and with a high-spin parameter is analysed that should be an ideal candidate for the formation of an extended galactic disc. We show that the gas and the DM have similar specific angular momenta until a merger event occurs at z ∼ 2 with a mass ratio of 5:1. All the gas involved in the merger loses a substantial fraction of its specific angular momentum due to tidal torques and dynamical friction processes falls quickly into the centre. In contrast, gas infall through small subclumps or accretion does not lead to catastrophic angular momentum loss . In fact, a new extended disc begins to form from gas that was not involved in the 5:1 merger event and that falls in subsequently. We argue that the angular momentum problem of disc galaxy formation is a merger problem: in cold dark matter cosmology substantial mergers with mass ratios of 1:1 to 6:1 are expected to occur in almost all galaxies. We suggest that energetic feedback processes could in principle solve this problem, however only if the heating occurs at the time or shortly before the last substantial merger event. Good candidates for such a coordinated feedback would be a merger-triggered starburst or central black hole heating. If a large fraction of the low angular momentum gas would be ejected, late-type galaxies could form with a dominant extended disc component, resulting from late infall, a small bulge-to-disc ratio and a low baryon fraction, in agreement with observations.


一个可行的方案，参见“小问题集”137页。