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The Forefront of Space Science

Next Space VLBI Mission "VSOP-2" by HALCA
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The VSOP-2 project, space VLBI science mission, was selected as ISAS’s 25th scientific satellite project. It is the first ISAS mission selected after JAXA’s reorganization and the satellite was named ASTRO-G. The project’s budgetary request was submitted based on the schedule to start the EM (Engineering-Model) in FY2007 and launch in FY2011. Here I will outline the VSOP-2 project including its scientific targets, project management and implementation, and current status.

From HALCA to VSOP-2

The radio astronomy satellite HALCA was launched in 1997, marking the first VLBI (Very Long Baseline Interferometry) astronomy mission in history.

In HALCA, various technological experiments were conduced successfully including the deployment of its large, 10m-across antenna in orbit. High-resolution observation of 0.4mm arc sec. was also accomplished. The observation plan of VSOP (VLBI Space Observatory Programme) using HALCA was realized by close international collaboration with research organizations around the world. The VSOP project successfully provided various scientific results. For example, its high spatial resolution and high imaging performance revealed the structure and movement of jets in active galactic nuclei (AGNs) and the plasma’s disk structure surrounding black holes of galactic nucleus. In addition, the project was the first to detect the existence of very high-brightness celestial sources.

The HALCA project started in 1989. The satellite was first named MUSES-B, and its objectives as a technological experiment satellite were to demonstrate technologies necessary for space VLBI and to conduct international space VLBI observation. MUSES-B extended its wings in space after launch and was renamed HALCA. HALCA far surpassed its anticipated roles as a technological experiment satellite and accomplished many astronomical results.

The next space VLBI working group was organized by VSOP group inside and outside Japan, while inviting the broader scientific community to join, in May 1997, soon after the interferometry experiment between space and the ground was successfully conducted with HALCA. The group’s purpose was to pioneer uncharted areas in astronomy based on the experiences obtained by HALCA. The working group has striven to create a better project plan over the past 10 years while operating HALCA.

What is VSOP-2 ?

In the VSOP-2 project, observation bands will be shifted to shorter frequencies compared to the VSOP. The project features direct imaging observation of astronomical phenomena with a level of high-spatial resolution (40 micro arc sec. at its best) never before achieved. This capability allows us to study the environments of huge black holes and accretion disks, generation and acceleration of jets, etc., which are important clues to understand the AGN, etc. Further, observation targets will be extended to research areas such as the magnetosphere’s structure of protostars. The main themes to be explored by the VSOP-2 are as follows (Fig. 1):
  • Study of the region where jets are generated and accelerated

  • Structure of accretion disks around AGN’s black holes

  • Study of movement of star formation region within our galaxy , etc., by H2O maser

  • Observation of H2O maser in outer galaxies

  • Observation of magnetosphere of protostars

Among the projects within JAXA’s Space Science Long-term Plan, the VSOP-2 will look closely into the physics of extreme astrophysical region. Many researchers are attracted to study those active phenomena in the center of many galaxies, and those phenomena are related to huge mass black holes.

Figure 1
Figure 1. Radio image of M87 taken by VSOP. Its sharp jet extends to 8,000 light years, and the VSOP observed the root of the jet extending to 10 light years. . The VSOP-2 can take image with resolution several times of the size of the black hole present in the center of M87.

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