What was the very beginning of the universe?

I'd like to describe two topics that were clarified based on data obtained with high dispersion spectroscopy. The first one is relating to the production of the elements and the chemical evolution in the universe. Immediately after the Big Bang at the beginning of the universe, almost no element existed except hydrogen and helium. On the other hand, we know that today over 100 different elements exist on earth. However, the abundance of heavy elements with large atomic numbers is low for stars that were formed long, long ago. This shows that heavy elements were produced with the evolution of the universe. Our current understanding is that the majority of elements heavier than helium were produced in the core of stars over their lifetimes (stellar evolution) and released into space when stars ended their lives with Super-Nova (SN) explosions. New-generation stars are born by collecting elements ejected from SN. Thus, newly-born stars contain much more heavy elements than old stars. Stellar evolution contributes to the increase in the abundance of heavy elements.

First-generation stars contain only hydrogen and a tiny amount of helium. If stellar mass is great enough, the temperature of the core becomes sufficiently high through gravitational energy, initiating a nuclear fusion reaction. In other words, hydrogen burns to convert it into helium. In massive stars, this helium burns to produce other heavy elements. The stellar light is the release of this nuclear fusion energy. The reaction converts elements into those with an atomic number of up to 26 (iron). Massive stars containing iron finish their lives as supernova explosions, resulting in the release of various elements less heavy than iron into space. These elements again aggregate due to the gravitational force to form next-generation stars, which then distribute the produced elements into space repeatedly in a cycle of birth and death of individual stars that also results in an increase in the abundance of heavy elements.

HDS installed on the optical Nasmyth platform

The origin of the universe clarified by observing old stars with HDS

High dispersion spectral observations of stars reveal the abundance of elements when individual stars are born. By observing a great number of stars which were born at various times, we can understand how elements increased in amount (chemical evolution). HDS, which was developed in cooperation with Nikon, is a powerful instrument for this study.

As an example, here is one recent result which was reported in April 2005. We discovered a star with the least amount of iron ever observed. Iron abundance represents the amount of elements heavier than helium. The star's iron content is only one 250,000^th that of the sun. This data will be very valuable in helping us understand elemental abundance at the earliest stages of the universe.