Visualising the local solar neighbourhood in 3D. Credit: ESA. Acknowledgement: H. Bouy (CSIC-INTA) & J. Alves (U. Vienna
Astronomers have used modern techniques to visualise data from ESA’s Hipparcos space astrometry mission in 3D. This 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.
3D map of massive O and B type stars (sometimes referred to as OB stars) has been mapped. These stars, which live for a maximum of only a few tens of millions of years, are important markers of recent star formation.
Previous studies have looked for groupings of these stellar giants by seeking out concentrations of them in 2D projections look at the position and velocity of the stars in a given region They picked out stars that are moving together, and are thus most likely members of the same stellar group.
Among other drawbacks, all 2D projection methods, including those not described here, can be affected by the presence of binary stars which can interfere with measurements of the motion of the stars in a group causing smaller or less tightly bound groups to be missed when searching for them solely on the basis of their common motion. In this study the astronomers used the measured distances to O and B type stars to map the density and position of the stars in 3 dimensions. The 3D data analysis and interactive visualisation techniques and lack of reliance on velocities led to several discoveries that had been missed in 25 years of 2D analysis of the data.
The team found the solar neighbourhood is dominated by 3 huge stream-like galactic structures made up of dense clusters and loose associations of young, blue, O and B type stars. These contain several tens of O and B type stars, most of the local well-known clusters, and some previously unreported stellar groups. The first structure runs from the constellation Scorpius to the constellation Canis Majoris covering more than 1100 light years and at least 65 million years of star formation history. The second, located in the constellation Vela, covers at least 500 light years and 30 million years of history. Although all 3 of the newly discovered streams have a story to tell, it is the third structure, located in the constellation Orion, that is perhaps the most significant due to its mystery-solving qualities.
The origin of the blue supergiants that define the body and belt of the Orion constellation has long been a mystery. The 5 giant O and B type stars are between 250 and 800 light years from Earth and as a result it was assumed that their origin was not, despite their name, in the prolific Orion Nebula star-forming region, which lies around 1300 light years from Earth. However, the discovery of the Orion stream offers a simple solution. It implies that these relatively distant populations are in fact linked as part of a large galactic structure, which spans more than 1000 light years and at least 25 million years of star formation history.
“One exciting find from this study relates to Betelgeuse, the red giant in the arm of Orion,” remarks Bouy. “The origin of this star has always been shrouded in mystery but through this study we have uncovered a new loosely organised group – or OB association – named Taurion which we believe to be Betelgeuse’s birthplace and to contain its sibling stars.”
“The Gould Belt is the perfect example of how 2D projections can deceive astronomers,” argues Alves. “Our results imply that it is just a projection effect produced by the Sun’s position between two of the streams of stars, rather than representing the architecture of the solar neighbourhood itself.”
“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 was launched in 2013 with the aim of unveiling the origin and evolution of our Galaxy. It will provide measurements of the positions and velocities with respect to Earth of up to one billion stars in our Galaxy and Local Group with unprecedented accuracy and sensitivity. The three-dimensional map produced by Gaia will far outdo any current or foreseen maps of the stars in the Milky Way. 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.
An interactive tool showing the Hipparcos data represented in three dimensions is available online. http://sci.esa.int/hipparcos/ob-stars-interactive/
http://sci.esa.int/hipparcos/56834-another-dimension-3d-visualisation-redefines-milky-ways-local-architecture/
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