Scientific Targets

The Evolution of Galaxies

Exploring Protogalaxies

When and how were galaxies born and how did they evolve to the present epoch? Light from stars which were born in earlier phases of the Universe are observed at infrared wavelength due to a cosmological Doppler effect. Moreover, newborn galaxies may be most luminous at infrared wavelengths because they are thought to be undergoing large scale star formation enshrouded in dust clouds. ASTRO-F will search for newborn galaxies (protogalaxies) with high infrared sensitivity. ASTRO-F is expected to detect more than ten million galaxies from all over the sky.

Origin and Evolution of Galaxies

(Photo by STScI/NASA)

IRAS, the first infrared astronomical satellite in the world, discovered infrared luminous galaxies. It turned out that they were active star forming galaxies. Some of them are colliding with each other in which a large number of stars are arising. It is also thought that a massive black-hole is at the center of such galaxies and enormous energy is radiating from it. This sort of interaction is believed to be frequent a phenomenon in the early Universe. ASTRO-F will make a systematic survey going back to the initial stages of the Universe, and investigate the origin and evolution of galaxies.

The Universe is believed to be born 10-20 billion years ago in the big bang.

IRAS : The infrared space telescope launched in 1983. It had a 57 cm mirror and was developed by the US, UK, and the Netherlands. IRAS observed 96 % of the sky for about ten months.

The Life Cycle of Stars

The Birth of a Star

Stars form in a cloud of gas and dust in a galaxy. A new star is hidden behind thick dust clouds, so we can not see it with visible light but this dust is bright at infrared wavelengths. ASTRO-F will approach the mechanism of the star formation by infrared observations of various star-forming regions.

Death of a Star

When a star finishes its life, it supplies materials to make the next generation stars by a supernova explosion or by blowing its outer layer off. In the gas emitted from stars, dust is formed. The process of a star formation and the amounts and ingredients of gas and dust are unsolved questions. ASTRO-F will observe this process and study it.

The Search for Brown Dwarves

(Photo by STScI/NASA)

There is invisible matter which has not been discovered but is believed to exist in the Universe. It is called the dark matter. It is known that the quantity of the dark matter is more than that of matter observed by visible light. However it is still unidentified.

Brown dwarves have been thought to be a candidate for some of the dark matter. A lightweight star the mass of which is less than 8 % of the Sun can not give off light at high temperature, but it still radiates at infrared wavelengths. Such a small and low-temperature star which can not be seen by visible light is referred to as Brown Dwarf. ASTRO-F can look into it by using the high sensitivity of its infrared cameras. It is expected that the mass and number of brown dwarves in our Galaxy will be estimated accurately and the mystery of the baryonic dark matter will be resolved by ASTRO-F infrared wide area observations.

To Seek out Planetary Systems Outside Our Own Solar System

(Photo by STScI/NASA)

One of our great concerns is whether there are planetary systems except for our own Solar System and whether life exists there. A planet forms inside a disk (protoplanetary disk) composed of gas and dust around a star. ASTRO-F can look for the radiation from a protoplanetary disk within 1000 light-years. It will reveal the forming process of planetary systems through infrared observations. It is also expected to detect the dust disks which are a trace of planetary systems in formation around nearby stars.

Discover New Comets

ASTRO-F has the potential to detect a lot of unknown comets. A comet's light we usually see is the sunlight scattered by the comet. ASTRO-F can detect the intrinsic infrared light radiated by a comet itself which is warmed by the Sun. ASTRO-F is expected to detect more than 50 new comets.

Whether a star dies with an explosion or throws out its mass slowly depends on the mass of the star.

Dark matter : Material that gravitates but we have not been able to see it