European astronomers provide new insight into evolution of the Milky Way

Brussels, 06 Apr 2004

A team of European astronomers has published the results of 15 years worth of observations of the Milky Way, significantly improving understanding of our own Galaxy's evolution, and consequently that of all galaxies in the Universe.

Human insight into our nearest stellar neighbours has long been incomplete, and even undermined by the idea that observations should focus on 'interesting' stars. In order to gain an accurate picture of the evolution of our Galaxy, however, it is necessary to focus observations towards the most typical stars.

Therefore, a team of Danish, Swiss and Swedish researchers, led by Dr Birgitta Nordström, set out to study the numerous Sun-like stars (so called F- and G-type stars) that make up the Milky Way, some of which have existed since its formation.

'It is fundamental to have unbiased samples,' Dr Nordström told CORDIS News. 'Now we have a sample that is as unbiased as possible.'

Having spent over 1,000 nights during the last 15 years observing 14,000 or so F- and G-type stars using telescopes in France and Chile, the team has now determined the motions of almost all such stars within around 500 light-years from Earth. They published their results in the Astronomy and Astrophysics Journal on 6 April.

Most of the stars studied by the team had already been plotted by the European Space Agency's Hipparcos satellite, but this data only gave their position in two dimensions. In order to understand their motion, however, it was necessary to plot the stars in three dimensions, which was achieved by making an average of four observations of each star over the 15 years. The team was also able to identify the many binary stars (two stars orbiting each other) in the sample, and eliminate or correct the misleading data that is generated when these are assumed to be single Sun-like stars.

'In effect, this gave us an accurate four-dimensional view of the Galaxy, as we were also able to plot the stars' positions over time,' explained Dr Nordström. Using this data, the team then computed the changing positions of these stars within the Milky Way during the last 225 million light-years.

The results were more startling than Dr Nordström could have imagined. They revealed that objects in the galactic disk, such as molecular clouds, spiral arms, and black holes, have had a dramatic effect on stellar velocities throughout the history of the Milky Way. This pointed to a far more chaotic process of galactic evolution than was previously thought.

'It was assumed that the Galaxy had epochs of violence,' said Dr Nordström, 'but we can now see that objects such as black holes and spiral arms have been disturbing the Galaxy throughout time.'

Not only have these results already provided a new insight into the history of our Galaxy, and the billions of others like it throughout the Universe, they will also act as an invaluable resource for other astronomers. The evolution of galaxies is an important topic in modern astrophysics, and the data generated by Dr Nordström and her team is the most significant in terms of advancing our understanding of the Milky Way since the first results from Hipparcos appeared seven years ago.

Further information

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