HEA > ASCA > Objectives

ASCA (Advanced Satellite for Cosmology and Astrophysics, formerly ASTRO-D), an X-ray astronomy satellite of Japan, was launched on February 20, 1993, by the ISAS vehicle M-3S into an approximately circular orbit of 520-620 km altitude. The spacecraft weighs 417 kg and is three-axis stabilized.

After launch, ASCA was capable of space based X-ray spectrum observations at the highest energy resolution. It takes X-ray images at energies up to 10 keV. Utilizing these capabilities, the following scientific objectives were set.

(1) Explanation of Chemical Evolution

It has been believed that elements such as neon, magnesium, silicon, sulfur, and iron did not exist during the earliest stage of the "big bang", but rather that they were formed by nuclear fusion inside fixed stars. Therefore, because these elements have characteristic bright emission lines in the X-ray region, the objective is to explain the time and location of the formation of these heavy elements in the evolution of the universe, by detecting these emission lines with an energy resolution and sensitivity that has not been possible.

(2) Verification of Black Holes

The existence of black holes is an important key to confirming the validity of the general theory of relativity. It also holds great significance in the general knowledge of mankind. The sensing instruments on ASCA have excellent X-ray detection sensitivity up to the high-energy region to ~10 keV, and are optimally suited to research black holes. Therefore, the objective is to confirm the existence of black holes.

(3) Identify Particle-acceleration in Space

The particle acceleration phenomenon, in which some particles are accelerated to extremely high energies, is believed to occur at various places in space. Nevertheless, the locations of acceleration, as well as its mechanism are largely unknown. The objective is to make use of the imaging capabilities of ASCA to identify particle-acceleration sites.

(4) Determine Distribution of Dark Matter

Since the 1930s, it has been suggested that there exists in the universe, in addition to the matter whose electromagnetic radiation is observable, up to ten times as much "dark matter". The explanation of the true nature of dark matter is one of the top-level subjects of modern science. There is a strong tendency for high-temperature gases to collect and emit X-rays in places where there is a concentration of dark matter. Therefore, the objective is to determine, to a degree of accuracy not previously possible, in what kinds of environments and to what extent dark matter exists by observing the emission of X-rays from galaxies and galaxy clusters.

(5) Investigate Evolution of celestial X-ray sources

In spite of the progress in space observation, it has not been possible to verify when and how the first stars and galaxies were formed. Therefore, the objective is to make use of the excellent detection sensitivity of ASCA to understand the evolution of celestial bodies by measuring the distance functions of the centers of galaxy clusters and active galaxies.

(6) Explanation Cosmic X-ray Background (CXB)

X-ray background radiation is a strong and virtually constant in flux of X-ray radiation from all over the sky. The exact nature of this radiation has long remained an unsolved puzzle. Since the 1980s, the favored explanation is that background radiation is the superimposed X-ray radiation from distant active galaxies that were born in the initial stage of the universe. ASCA seeks to determine whether or not this explanation is correct.