The movement of the stars of the Milky Way
For more than a decade, RAVE, one of the first and largest systematic spectroscopic surveys of the sky, studied the movement of stars in the Milky Way. For more than half a million observations, the RAVE collaboration has now presented the results in its sixth and final data release.
RAVE observed almost half a million stars in our galaxy. The sun is at the center of the coordinate system. The colors represent radial speeds: moving stars are shown in red, approaching stars in blue.
image: AIP / K. Riebe, RAVE collaboration; Milky Way image (background): R. Hurt (SSC); NASA / JPL-Caltech [Groansicht]
The RAdial Velocity Experiment RAVE is a spectroscopic survey of the southern hemisphere. It was developed to get a complete picture of the movements of stars in the wider environment of the sun. With the help of spectroscopy, the light of a star is broken down into its rainbow colors. By analyzing the spectra, the radial speed of a star – its movement in the direction of observation – can be determined. In addition, star spectra also enable the determination of star parameters such as temperature, surface gravity and individual chemical composition.
In order to understand the structure and shape of our galaxy, RAVE successfully recorded 518,387 spectra for 451,783 Milky Way stars. In astronomy you are not only used to thinking in large time scales – the projects are often long-term endeavors as well. RAVE observed the sky on almost every clear night between 2003 and 2013 at the 1.2-meter Schmidt telescope on Anglo-Australian Observatory in Siding Spring in Australia. A special fiber-optic setup was used for the sky survey in order to simultaneously record spectra of up to 150 stars with a single observation. This enabled a large number of objects to be targeted – the largest spectroscopic survey before RAVE only included around 14,000 objects.
In this way, the sky survey resulted in an extensive sample of the stars around our sun, which are approximately in a volume with a diameter of 15,000 light years. Over the past 15 years, RAVE has released an increasing number of stars and improved data products. The final RAVE data release not only provides the spectra of all RAVE stars for the first time; the stars were also added to those from the satellite’s DR2 catalog Gaia adjusted.
Thanks to the of Gaia Measured distances and own movements could be derived from significantly improved star temperatures, surface gravity and the chemical composition of the star atmosphere. “The RAVE data releases provided new insights into the movement of the stars and the chemical composition of our Milky Way,” emphasizes Matthias Steinmetz, head of the RAVE collaboration and scientific director at the Leibniz Institute for Astrophysics Potsdam (AIP). “The final data release completes one of the first systematic spectroscopic studies of galactic archeology. It is really exciting that this 15-year project is now coming to an end. Thanks to RAVE, we have gained new insights into the structure and composition of our Milky Way.”
One of the most important results of RAVE is determining the minimum speed a star needs to escape the attraction of the Milky Way. The results confirmed that dark matter, an invisible component of the universe of unknown nature, dominates the mass of our galaxy.
With RAVE it could also be shown that the Milky Way disk is asymmetrical and flutters due to the interaction with spiral arms and the invasion of satellite galaxies. RAVE also made it possible to identify star currents in the solar environment. These star streams are the remains of older torn-apart dwarf galaxies that have merged with our Milky Way in the past.
The chemical element frequencies of the observed stars provide important information on the chemical composition and the metal enrichment of the interstellar medium by stars of different ages and metal contents. With RAVE, astronomers were also able to search efficiently for the very first and very low-metal stars, which provide information about the star formation and the chemical development of the Milky Way. The RAVE collaboration is coordinated by the AIP and consists of researchers from over 20 institutions worldwide.
Since the first data release, more than 100 peer-reviewed scientific articles have been published based on RAVE data.