Sculptor Dwarf Galaxy (ground-based view)
Wide-field image of the sky around the Sculptor Dwarf Galaxy
Hubble observing the Sculptor Dwarf Galaxy
ESA’s Gaia satellite
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Zoom on a a part of the Sculptor Dwarf Galaxy
A team of astronomers used data from both
the NASA/ESA Hubble Space Telescope and ESA’s Gaia satellite to
directly measure the 3D motions of individual stars in a nearby galaxy.
The achieved accuracy is better than anything previously measured for a
galaxy beyond the Milky Way. The motions provide a field test of the
currently-accepted cosmological model and also measure the trajectory of
the galaxy through space. The results are published in Nature
Astronomy.
Astronomers from the Kapteyn Astronomical Institute and Leiden
Observatory, both in the Netherlands, used data from the NASA/ESA Hubble
Space Telescope and ESA’s Gaia space observatory to measure the motions of stars in the Sculptor Dwarf Galaxy. The Sculptor Dwarf is a satellite galaxy orbiting the Milky Way, 300 000 light-years away from Earth.
Only by combining the datasets from these two successful ESA missions
— produced more than 12 years apart — could the scientists directly
measure the exact 3D motions of stars within the Sculptor Dwarf Galaxy [1]. The is the first time this has been achieved with such accuracy for a galaxy other than the Milky Way [2].
Davide Massari, lead author of the study, describes the precision of the research: “With
the precision achieved we can measure the yearly motion of a star on
the sky which corresponds to less than the size of a pinhead on the Moon
as seen from Earth.” This kind of precision was only possible due
to the extraordinary resolution and accuracy of both instruments. Also
the study would not have been possible without the large interval of
time between the two datasets which makes it easier to determine the
movement of the stars.
The Sculptor Dwarf Galaxy is a dwarf spheroidal galaxy, which are among the most dark matter
dominated objects in the Universe. This makes them ideal targets for
investigating the properties of dark matter. In particular,
understanding how dark matter is distributed in these dwarf galaxies
allows astronomers to test the validity of the currently-accepted cosmological model. However, dark matter cannot be studied directly.
“One of the best ways to infer the presence of dark matter is to examine how objects move within it,” explains Amina Helmi, co-author of the paper. “In the case of dwarf spheroidals, these objects are stars.”
The information gathered about the 3D motion of stars in the Sculptor
Dwarf Galaxy can be translated directly into knowledge of how its total
mass — including dark matter — is distributed.
The new results show
that stars in the Sculptor Dwarf Galaxy move preferentially on elongated
radial orbits. This indicates that the density of dark matter increases
towards the centre instead of flattening out. These findings are in
agreement with the established cosmological model and our current
understanding of dark matter, taking into account the complexity of
Sculptor’s stellar populations.
As a side effect of the study, the team also presented a more
accurate trajectory of the Sculptor Dwarf Galaxy as a whole as it orbits
the Milky Way. Their results show that it is moving around the Milky
Way in a high-inclination elongated orbit that takes it much further
away than previously thought.
Currently, it is nearly at its closest
point to the Milky Way, but its orbit can take it as far as 725 000
light-years away.
“With these pioneering measurements, we enter an era where
measuring 3D motions of stars in other galaxies will become routine and
will be possible for larger star samples. This will mostly be thanks to
ESA’s Gaia mission,” concludes Massari.
Notes
[1] The team measured the proper motions of roughly a hundred stars
in the Sculptor Dwarf Galaxy.
For a smaller subset of ten stars, chosen among those with the smallest errors, the astronomers could also retrieve from the literature an estimate of the radial velocity, which quantifies the stellar motion along the line of sight. Using the proper motion and radial velocity measurements, they were able to reconstruct how these stars move in three dimensions.
[2] The data used contain images taken with Hubble’s Advanced Camera for Surveys in 2002. Newer positions of individual stars were taken from the Gaia, which was observed between 2014 and 2015.
More Informatiom
Image credit: ESA/Hubble & NASA, ESA/ATG medialab, Digitized Sky Survey 2
Links
Contacts
Davide Massari
Kapteyn Astronomical Institute
Groningen, The Netherlands
Tel: +31 50363 4094
Email: massari@astro.rug.nl
Amina Helmi
Kapteyn Astronomical Institute
Groningen, The Netherlands
Tel: +31 50363 4045
Email: ahelmi@astro.rug.nl
Mathias Jäger
ESA/Hubble, Public Information Officer
Garching bei München, Germany
Cell: +49 176 62397500
Email: mjaeger@partner.eso.org
For a smaller subset of ten stars, chosen among those with the smallest errors, the astronomers could also retrieve from the literature an estimate of the radial velocity, which quantifies the stellar motion along the line of sight. Using the proper motion and radial velocity measurements, they were able to reconstruct how these stars move in three dimensions.
[2] The data used contain images taken with Hubble’s Advanced Camera for Surveys in 2002. Newer positions of individual stars were taken from the Gaia, which was observed between 2014 and 2015.
More Informatiom
The Hubble Space Telescope is a project of international cooperation between ESA and NASA.
Gaia is an ESA mission to survey one billion stars in our Galaxy and
local galactic neighbourhood in order to build the most precise 3D map
of the Milky Way and answer questions about its structure, origin and
evolution. A large pan-European team of expert scientists and software
developers, the Data Processing and Analysis Consortium (DPAC), located
in and funded by many ESA member states, is responsible for the
processing and validation of Gaia's data, with the final objective of
producing the Gaia Catalogue.
The international team of astronomers in this study consists of D.
Massari (University of Groningen, The Netherlands), M. A. Breddels
(University of Groningen, The Netherlands), A. Helmi (University of
Groningen, The Netherlands), L. Posti (University of Groningen, The
Netherlands), A. G. A. Brown (Leiden University, The Netherlands) and E.
Tolstoy (University of Groningen, The Netherlands).
Image credit: ESA/Hubble & NASA, ESA/ATG medialab, Digitized Sky Survey 2
Links
Contacts
Davide Massari
Kapteyn Astronomical Institute
Groningen, The Netherlands
Tel: +31 50363 4094
Email: massari@astro.rug.nl
Amina Helmi
Kapteyn Astronomical Institute
Groningen, The Netherlands
Tel: +31 50363 4045
Email: ahelmi@astro.rug.nl
Mathias Jäger
ESA/Hubble, Public Information Officer
Garching bei München, Germany
Cell: +49 176 62397500
Email: mjaeger@partner.eso.org
Source: ESA/Hubble/News
