European Space Agency has published a few days ago, on 16 Nov. 2015, an article under the title “Another Dimension: 3D visualisation redefines Milky Way’s local architecture“, (for German version see here).
In this article we can read about the first official results of ESA’s Hipparcos space astrometry mission. It was a pioneering European project which pinpointed the three-dimensional positions of 118218 stars with highest precision, and more than one million stars with lesser precision. Launched in August 1989, Hipparcos successfully worked for 3.5 years before operations ceased in March 1993. Astronomers (Herve Bouy from Center for Astrobiology CSIC-INTA in Spain, and João Alves from University of Vienna, Austria) have used modern techniques to visualize data from Hipparcos satellite in three dimensions. ESA comments:
“The treatment of the data has offered insights into the distribution of nearby stars and uncovered new groupings of stars in the solar neighbourhood, shedding light on the origins of the stars in Orion and calling into question the existence of the Gould Belt – an iconic ring-shaped structure of stars in the Milky Way. The results show the potential of 3D visualisation of the solar neighbourhood, an approach which is of particular relevance to ESA’s Gaia mission which will map the Milky Way and Local Group in 3D with unprecedented sensitivity and accuracy.”
The researchers have created a 3D map of massive O and B type stars, which live for a maximum of only a few tens of millions of years, and are important markers of recent star formation and much can be learned from studying their distribution in the solar neighborhood. Traditional studies have looked for groupings of these stellar giants by seeking out concentrations of them in 2D projections, looking at the position and velocity of the group of stars and picking out stars that are moving together, being thus most likely members of the same stellar group. In the new study, the astronomers used additionally the measured distances to O and B type stars to map the density and position of the stars in three dimensions.
The 3D data analysis found evidence for new, previously unknown structures in the distribution of nearby hot stars. The team found that the solar neighborhood is dominated by three huge stream-like structures made up of dense clusters and loose associations of young, blue, O and B type stars. Of course, the interpretation of those new structures is depending on the general paradigm used for the Solar System cosmic environment. What is most important, there are found the same dimensions and similar locations of the new structures as we have supposed in the Cosmic Hierarchy of the Solar System, as can be seen in the following figure. The figure suggests that the structures found in the new study based on ESA’s mission are first of all the energy bridges between the second and third and the first and second levels of the Cosmic Hierarchy, and the corresponding satellites of those centers of mass of the three lowest levels of the hierarchy.
In the ESA’s commentary we read:
“These results show just what 3D visualisation can deliver, and how much further it can take us,” explains Jos de Bruijne, ESA’s Gaia system scientist, also acting as ESA liaison scientist for the Hipparcos mission. “It provides an even stronger case for focussing on the local neighbourhood and, in particular, for doing so in three dimensions. This study really raises the expectations for what the Gaia mission will produce.”
Gaia is an ESA mission launched in 2013 (about which I have already reported in Chapter 6 of my recent online book “Our illusory physics“) to survey one billion stars in our Galaxy and local galactic neighborhood in order to build the most precise 3D map of the cosmic structure we traditionally considered to be the Milky Way galaxy and answer questions about its origin and evolution. Gaia’s routine science operations began in July 2014. The mission’s primary scientific product will be a catalogue with the positions, motions, brightnesses, and colors of the surveyed stars with unprecedented accuracy and sensitivity. An intermediate version of the catalogue should be released in 2016. It will include non-O and-B type stars and be able to identify clusters and groups not dense enough to register in the Hipparcos map.
Though the Hipparcos-mission comment suggests that the new data are “calling into question the existence of the Gould Belt”, the other teams are still studying the possibilities to explain its existence together with many other hitherto known structures in our cosmic neighborhood. One of the graphical presentations of the present state of knowledge can be seen in the diagram below.
(Diagram by Isabelle Grenier, reproduced with agreement of “NewScientist” redaction)
Our interpretation of the Cosmic Hierarchy of the Solar System contains not only the first three levels of this hierarchy, but the whole observable Universe. Nevertheless, it will be very important to have the observational confirmation of the nearest neighborhood. We can only hope, and wish the mission team that it will not take the next 25 years between the mission launch and the results publication.