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Astro-E Scientific Objectives

The science to be explored with Astro-E includes:

1. Hot plasmas in cluster galaxies

Tremendous energy emerges in X-rays from the most active and hot regions of the Universe. In a cluster of galaxies, thousands of galaxies are embedded in hot plasmas from 10 to 100 million degrees. The mass of hot gas in the X-ray band is more than three times larger than the mass of visible component of the galaxies. X-ray observations are critical to examine the physics of cluster of galaxies.

Five times more mass than "visible" mass (sum of galaxies and the hot gas) is required to bind such hot gas. This is called "invisible mass" or "dark matter."

2. Evolution of the universe

The high resolution spectrometer will reveal the atomic abundance and physical status of the hot gas with one order better accuracy than previous experiments. Based on the observations of the gas dynamics it is expected to study the formation of galaxies and the cluster galaxies. This will provide us with clues to the evolution of the Universe.

Each element has its own characteristic energy of emission line. Observed line energy and the intensity indicate the atomic abundance, ionization states and the ionization temperature.

The motion of a gas is derived from the Doppler shift of the observed line emission.

3. Accretion onto black holes

It has been well know that the gravitational energy of accretion matter onto compact objects, such as neutron stars and black holes, is released by the strong radiation in X-rays. The high resolution spectrometer and the CCD cameras on the focal plane of Astro-E X-ray telescopes are capable of detecting the velocity of accretion matter. This tells us about the mass of black holes and the geometry around them

ASCA found many active galactic nuclei harbor such black holes. With better sensitivity, Astro-E will discover and examine those objects farther away, or hidden in thick clouds.

Apparent wave length becomes longer than the intrinsic, when the X-ray is emitted from the region of strong gravitational field around black holes.

4. Acceleration of high energy particles

On the ground, extremely high energy cosmic ray particles have been detected. The highest energy discovered so far is 16 joule per particle. 1 Joule corresponds to the heat needed to warm up 1 gram of water, by 4 degrees C .

In the Universe, there should be huge accelerators to produce such high energy particles. We want to find the origin, mechanism, and site of such high energy particle acceleration from the broad band X-ray and gamma-ray spectra observed with the combination of HXD and focal plane detectors of Astro-E mission.

ISAS/JAXA Department of High Energy Astrophysics