Research on Evolution of Stellar Systems with Highly Parallelized Special-purpose Computer for Gravitational Many-body Problems

1990年，我们在绕线板上构建了GRAPE-1A。这是一个用于引力多体问题的专用计算机的原型。与富士施乐电子成像和设备研究实验室密切合作，然后，我们在一个定制的LSI上设计了一个处理器芯片，它容纳了GRAPE-1A的所有逻辑。该LSI的尺寸为8x8毫米，包含113，000个晶体管。1991年，我们用这种处理器芯片构造了一台并行机GRAPE-3：在一块VME板上布线24个处理器芯片，并通过适当设计的接口将两块板与主机工作站连接起来。这台机器在1991年进行了调整，达到了14 Gflops的峰值性能，并在解决200，000个引力物体的问题时达到了10 Gflops的持续速度。就持续速度而言，它比1991年任何商用超级计算机都快。我们利用GRAPE-3对恒星系统的演化进行了各种模拟，发现 ...更多信息 星系的碰撞和合并在星系和星系团的演化中起着重要的作用。1）当两个中心有大质量黑洞的星系相互碰撞时，黑洞会受到轨道远心附近场星的动力学摩擦。它们失去的与其说是能量，不如说是角动量。轨道的离心率接近于1，黑洞可能很快合并。与此同时，场星获得能量并变热。这一图像很好地解释了核半径与残骸总质量之间的关系。2）星系碰撞过程中引力场发生剧烈变化。结果，恒星在相空间中完全混合。另一方面，在能量空间中，混合只在碰撞的初始阶段进行得很快，之后就慢得多。因此，将这一过程称为“剧烈”弛豫是不恰当的。3）在这一过程之后，碰撞前各星系核（或晕）中的恒星倾向于留在合并的核（或晕）中。因此，在巨椭圆星系中观察到的颜色梯度不能证明其起源的合并假说。4）星系的合并是通过与晕中的恒星一起排出角动量来进行的。因此，星系的合并可以被认为是一种常见的现象，并可能在星系和宇宙的演化和历史中发挥主导作用。少

In 1990 we constructed GRAPE-1A on a wire-wrapped board. It is a prototype of a special-purpose computer for gravitational many-body problems. In close collaboration with Electronic Imaging and Device Research Laboratory of Fuji XEROX Co., Ltd. we then designed a processor chip on one customized LSI which accommodated all the logics of GRAPE-1A. This LSI is 8x8 mm in size and contains 113, 000 transistors. Using this processor chip we constructed a parallelized machine GRAPE-3 in 1991 : We wired 24 processor chips on a VME board, and connected two boards with the host workstation via appropriately designed interface. The machine was tuned in 1991 to reach the peak performance of 14 Gflops, and the sustained speed of 10 Gflops in solving a gravitational 200, 000body problem. It is faster than the any commercially available supercomputer in 1991 so far as the sustained speed is concerned. Using GRAPE-3 we have done a variety of simulations on evolution of stellar systems, and have found … More that collision and resultant merging of galaxies play important roles in evolution of galaxies and their clusters. In what follows we summarize the new findings.1) When two galaxies with central massive black holes collide each other, the black holes suffer from dynamical friction due to the field stars near the apocenter of the orbit. They loose rather their angular momentum than their energy. The eccentricity of the orbit approaches to unity and the black holes may merge quickly. At the same time the field stars aquire energy and become hot. Such picture nicely interprets the relation between the core radius and the total mass of the remnants.2) During the collision of galaxies the gravitational field changes violently. As a result the stars become throughly mixed in the phase space. On the other hand, in the energy space the mixing proceeds quickly only in the initial phases of their collision and much more slowly afterward. Therefore, it is not appropriate to call such process as the "violent" relaxation.3) After such process, the stars in the core (or halo) of each galaxy before the collision tend to stay in the core (or halo) of the merger. Therefore, the color gradient observed in giant elliptical galaxies can not testify against the merger hypothesis of their origin.4) Merging of galaxies proceeds effectively by expelling the angular momentum together with the stars in the halo. Thus, the merging of galaxies may be regarded to be frequent phenomena and may play one of the leading roles in the evolution and history of galaxies and the universe. Less