| Project/Area Number |
02452012
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| Research Category |
Grant-in-Aid for General Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Research Field |
Astronomy
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| Research Institution | University of Tokyo |
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Principal Investigator |
SUGIMOTO Daiichiro University of Tokyo, College of Arts & Sciences, Professor, 教養学部, 教授 (10022592)
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| Co-Investigator(Kenkyū-buntansha) |
OKAMURA Sachiko (K. Sachi) University of Tokyo, College of Arts & Sciences, Research Associate, 教養学部, 助手 (20224842)
MAKINO Junichiro University of Tokyo, College of Arts & Sciences, Research Associate, 教養学部, 助手 (50229340)
EBISUZAKI Toshikazu University of Tokyo, College of Arts & Sciences, Associate Professor, 教養学部, 助教授 (10183021)
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| Project Period (FY) |
1990 – 1991
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| Project Status |
Completed (Fiscal Year 1991)
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| Budget Amount *help |
¥8,000,000 (Direct Cost: ¥8,000,000)
Fiscal Year 1991: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 1990: ¥7,500,000 (Direct Cost: ¥7,500,000)
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| Keywords | Special-purpose computer / Parallel computer / Gravitational Many-body problem / Galaxy / Stellar system |
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| Research Abstract |
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
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