Astronomers using the VISTA telescope at
ESO’s Paranal Observatory have discovered a previously unknown component
of the Milky Way. By mapping out the locations of a class of stars that
vary in brightness called Cepheids, a disc of young stars buried behind
thick dust clouds in the central bulge has been found.
The Vista Variables in the Vía Láctea Survey (VVV) [1] ESO public survey is using the VISTA telescope
at the Paranal Observatory to take multiple images at different times
of the central parts of the galaxy at infrared wavelengths [2]. It is discovering huge numbers of new objects, including variable stars, clusters and exploding stars (eso1101, eso1128, eso1141).
A team of astronomers, led by Istvan Dékány of the
Pontificia Universidad Católica de Chile, has now used data from this
survey, taken between 2010 and 2014, to make a remarkable discovery — a
previously unknown component of our home galaxy, the Milky Way.
“The central bulge of the Milky Way is thought to consist of vast
numbers of old stars. But the VISTA data has revealed something new —
and very young by astronomical standards!” says Istvan Dékány, lead author of the new study.
Analysing data from the survey, the astronomers found 655 candidate variable stars of a type called Cepheids.
These stars expand and contract periodically, taking anything from a
few days to months to complete a cycle and changing significantly in
brightness as they do so.
The time taken for a Cepheid to brighten and fade again is longer for
those that are brighter and shorter for the dimmer ones. This
remarkably precise relationship, which was discovered in 1908 by
American astronomer Henrietta Swan Leavitt,
makes the study of Cepheids one of the most effective ways to measure
the distances to, and map the positions of, distant objects in the Milky
Way and beyond.
But there is a catch — Cepheids are not all the same — they come in
two main classes, one much younger than the other. Out of their sample
of 655 the team identified 35 stars as belonging to a sub-group called classical Cepheids — young bright stars, very different from the usual, much more elderly, residents of the central bulge of the Milky Way.
The team gathered information on the brightness, pulsation period,
and deduced the distances of these 35 classical Cepheids. Their
pulsation periods, which are closely linked to their age, revealed their
surprising youth.
“All of the 35 classical Cepheids discovered are less than 100
million years old. The youngest Cepheid may even be only around 25
million years old, although we cannot exclude the possible presence of
even younger and brighter Cepheids,” explains the study’s second author Dante Minniti, of the Universidad Andres Bello, Santiago, Chile.
The ages of these classical Cepheids provide solid evidence that
there has been a previously unconfirmed, continuous supply of newly
formed stars into the central region of the Milky Way over the last 100
million years. But, this wasn’t to be the only remarkable discovery from
the survey’s dataset.
Mapping the Cepheids that they discovered, the team traced an
entirely new feature in the Milky Way — a thin disc of young stars
across the galactic bulge. This new component to our home galaxy had
remained unknown and invisible to previous surveys as it was buried
behind thick clouds of dust. Its discovery demonstrates the unique power
of VISTA, which was designed to study the Milky Way’s deep structures
by wide-field, high-resolution imaging at infrared wavelengths.
“This study is a powerful demonstration of the unmatched
capabilities of the VISTA telescope for probing extremely obscured
galactic regions that cannot be reached by any other current or planned
surveys,” remarks Dékány.
“This part of the galaxy was completely unknown until our VVV survey found it!” adds Minniti.
Further investigations are now needed to assess whether these
Cepheids were born close to where they are now, or whether they
originate from further out. Understanding their fundamental properties,
interactions, and evolution is key in the quest to understand the
evolution of the Milky Way, and the process of galaxy evolution as a
whole.
Notes
[1] The VVV survey is observing the central parts of our galaxy in
five near-infrared bands. The total area of this survey is 520 square
degrees and contains at least 355 open and 33 globular clusters. The VVV
is multi-epoch in nature in order to detect a large number of variable
objects and will provide more than 100 carefully spaced observations at
different times for each part of the sky covered. A catalogue with about
a billion point sources including about a million variable objects is
expected. These will be used to create a three-dimensional map of the
bulge of the Milky Way galaxy.
[2] The dust clouds in interstellar space absorb and scatter visible light very effectively and make them opaque. But at longer wavelengths, such as those observed by VISTA, the clouds are much more transparent, allowing the regions beyond the dust to be probed.
[2] The dust clouds in interstellar space absorb and scatter visible light very effectively and make them opaque. But at longer wavelengths, such as those observed by VISTA, the clouds are much more transparent, allowing the regions beyond the dust to be probed.
More Information
This research was presented in a paper entitled “The VVV Survey
reveals classical Cepheids tracing a young and thin stellar disk across
the Galaxy’s bulge”, by I. Dékány et al., in the Astrophysical Journal Letters.
The team is composed of I. Dékány (Instituto Milenio de Astrofísica, Santiago, Chile; Pontificia Universidad Católica de Chile, Santiago, Chile), D. Minniti (Universidad Andres Bello, Santiago, Chile; Instituto Milenio de Astrofísica MAS and Basal CATA, Santiago, Chile; and Vatican Observatory, Vatican City State), D. Majaess (Saint Mary’s University, Halifax, Nova Scotia, Canada; Mount Saint Vincent University, Halifax, Nova Scotia, Canada) , M. Zoccali (Pontificia Universidad Católica de Chile, Santiago, Chile; Instituto Milenio de Astrofísica, Santiago, Chile), G. Hajdu (Pontificia Universidad Católica de Chile, Santiago, Chile; Instituto Milenio de Astrofísica, Santiago, Chile), J. Alonso-García (Universidad de Antofagasta, Antofagasta, Chile; Instituto Milenio de Astrofísica, Santiago, Chile), M. Catelan (Pontificia Universidad Católica de Chile, Santiago, Chile; Instituto Milenio de Astrofísica, Santiago, Chile), W. Gieren (Universidad de Concepción, Concepción, Chile; Instituto Milenio de Astrofísica, Santiago, Chile) and J. Borissova (Universidad de Valparaíso, Valparaíso, Chile; Instituto Milenio de Astrofísica, Santiago, Chile).
ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It is supported by 16 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom, along with the host state of Chile. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world’s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is a major partner in ALMA, the largest astronomical project in existence. And on Cerro Armazones, close to Paranal, ESO is building the 39-metre European Extremely Large Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.
The team is composed of I. Dékány (Instituto Milenio de Astrofísica, Santiago, Chile; Pontificia Universidad Católica de Chile, Santiago, Chile), D. Minniti (Universidad Andres Bello, Santiago, Chile; Instituto Milenio de Astrofísica MAS and Basal CATA, Santiago, Chile; and Vatican Observatory, Vatican City State), D. Majaess (Saint Mary’s University, Halifax, Nova Scotia, Canada; Mount Saint Vincent University, Halifax, Nova Scotia, Canada) , M. Zoccali (Pontificia Universidad Católica de Chile, Santiago, Chile; Instituto Milenio de Astrofísica, Santiago, Chile), G. Hajdu (Pontificia Universidad Católica de Chile, Santiago, Chile; Instituto Milenio de Astrofísica, Santiago, Chile), J. Alonso-García (Universidad de Antofagasta, Antofagasta, Chile; Instituto Milenio de Astrofísica, Santiago, Chile), M. Catelan (Pontificia Universidad Católica de Chile, Santiago, Chile; Instituto Milenio de Astrofísica, Santiago, Chile), W. Gieren (Universidad de Concepción, Concepción, Chile; Instituto Milenio de Astrofísica, Santiago, Chile) and J. Borissova (Universidad de Valparaíso, Valparaíso, Chile; Instituto Milenio de Astrofísica, Santiago, Chile).
ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It is supported by 16 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom, along with the host state of Chile. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world’s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is a major partner in ALMA, the largest astronomical project in existence. And on Cerro Armazones, close to Paranal, ESO is building the 39-metre European Extremely Large Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.
Links
Contacts
Instituto Milenio de Astrofísica, Pontificia Universidad Católica de Chile
Santiago, Chile
Email: idekany@astro.puc.cl
Dante Minniti
Universidad Andres Bello
Santiago, Chile
Tel: +56 2 2661 8732
Email: dante@astrofisica.cl
Daniel Majaess
Saint Mary’s University, Mount Saint Vincent University
Halifax, Canada
Email: dmajaess@ap.smu.ca
Richard Hook
ESO Public Information Officer
Garching bei München, Germany
Tel: +49 89 3200 6655
Cell: +49 151 1537 3591
Email: rhook@eso.org
Source: ESO
