Nav: Home

The Milky Way's ancient heart

October 12, 2016

A team led by Dante Minniti (Universidad Andrés Bello, Santiago, Chile) and Rodrigo Contreras Ramos (Instituto Milenio de Astrofísica, Santiago, Chile) used observations from the VISTA infrared survey telescope, as part of the Variables in the Via Lactea (VVV) ESO public survey, to carefully search the central part of the Milky Way. By observing infrared light, which is less affected by cosmic dust than visible light, and exploiting the excellent conditions at ESO's Paranal Observatory, the team was able to get a clearer view of this region than ever before. They found a dozen ancient RR Lyrae stars at the heart of the Milky Way that were previously unknown.

Our Milky Way has a densely populated centre -- a feature common to many galaxies, but unique in that it is close enough to study in depth. This discovery of RR Lyrae stars provides compelling evidence that helps astronomers decide between two main competing theories for how these bulges form.

RR Lyrae stars are typically found in dense globular clusters. They are variable stars, and the brightness of each RR Lyrae star fluctuates regularly. By observing the length of each cycle of brightening and dimming in an RR Lyrae, and also measuring the star's brightness, astronomers can calculate its distance [1].

Unfortunately, these excellent distance-indicator stars are frequently outshone by younger, brighter stars and in some regions they are hidden by dust. Therefore, locating RR Lyrae stars right in the extremely crowded heart of the Milky Way was not possible until the public VVV survey was carried out using infrared light. Even so, the team described the task of locating the RR Lyrae stars in amongst the crowded throng of brighter stars as "daunting".

Their hard work was rewarded, however, with the identification of a dozen RR Lyrae stars. Their discovery indicate that remnants of ancient globular clusters are scattered within the centre of the Milky Way's bulge.

Rodrigo Contreras Ramos elaborates: "This discovery of RR Lyrae Stars in the centre of the Milky Way has important implications for the formation of galactic nuclei. The evidence supports the scenario in which the bulge was originally made out of a few globular clusters that merged."

The theory that galactic bulges form through the merging of globular clusters is contested by the competing hypothesis that these bulges are actually due to the rapid accretion of gas. The unearthing of these RR Lyrae stars -- almost always found in globular clusters -- isvery strong evidence that the Milky Way bulge did in fact form through merging. By extension, all other similar galactic bulges may have formed the same way.

Not only are these stars powerful evidence for an important theory of galactic evolution, they are also likely to be over 10 billion years old -- the dim, but dogged survivors of perhaps the oldest and most massive star cluster within the Milky Way.
-end-
Notes

[1] RR Lyrae stars, like some other regular variables such as Cepheids, show a simple relationship between how quickly they change in brightness and how luminous they are. Longer periods mean brighter stars. This period-luminosity relationship can be used to deduce the distance of a star from its period of variation and its apparent brightness.

More information

This research was presented in a paper to appear in The Astrophysical Journal Letters.

The team is composed of D. Minniti (Instituto Milenio de Astrofísica, Santiago, Chile; Departamento de Física, Universidad Andrés Bello, Santiago, Chile; Vatican Observatory, Vatican City State, Italy; Centro de Astrofisica y Tecnologias Afines - CATA), R. Contreras Ramos (Instituto Milenio de Astrofísica, Santiago, Chile; Pontificia Universidad Católica de Chile, Instituto de Astrofísica, Santiago, Chile), M. Zoccali (Instituto Milenio de Astrofísica, Santiago, Chile; Pontificia Universidad Católica de Chile, Instituto de Astrofísica, Santiago, Chile), M. Rejkuba (European Southern Observatory, Garching bei München, Germany; Excellence Cluster Universe, Garching, Germany), O.A. Gonzalez (UK Astronomy Technology Centre, Royal Observatory, Edinburgh, UK), E. Valenti (European Southern Observatory, Garching bei München, Germany), F. Gran (Instituto Milenio de Astrofísica, Santiago, Chile; Pontificia Universidad Católica de Chile, Instituto 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

* Research paper - http://www.eso.org/public/archives/releases/sciencepapers/eso1636/eso1636a.pdf

* Variables in the Via Lactea (VVV) - https://vvvsurvey.org/ ESO public survey

Contacts

Dante Minniti
Universidad Andrés Bello
Santiago, Chile
Email: dante@astrofisica.cl

Rodrigo Contreras Ramos
Instituto Milenio de Astrofísica
Santiago, Chile
Email: rcontrer@astro.puc.cl

Mathias Jäger
Public Information Officer
Garching bei München, Germany
Cell: +49 176 62397500
Email: mjaeger@partner.eso.org

ESO

Related Globular Clusters Articles:

CU Boulder researchers explain mystery of 'banging' galaxy clusters
June 6, 2017 -Two galaxy clusters in the process of merging created a layer of surprisingly hot gas between them that University of Colorado Boulder astronomers believe is from turbulence caused by banging into each other at supersonic speeds.
Are dense star clusters the origin of the gravitational waves discovered by LIGO?
Much to their surprise, scientists are finding dozens of black holes deep within densely packed collections of stars called globular clusters.
Star clusters discovery could upset the astronomical applecart
The discovery of young stars in old star clusters could send scientists back to the drawing board for one of the Universe's most common objects.
Foot pain often occurs in clusters
A new study indicates that particular areas of foot pain are more likely to occur together, and these clusters have specific characteristics.
Closer ties for silver clusters
KAUST researchers develop silver nanoclusters with hydrogen-rich shells to offer new opportunities in catalysis and opto-electronics.
Frequency of tornado clusters in US is increasing
The frequency and magnitude of tornado outbreaks with many, or clusters, of tornadoes has increased in the United States over the past 50 years, a new study reports.
UCLA astronomers watch star clusters spewing out dust
A team led by UCLA astronomers has used new data to show that stars are responsible for producing dust on galactic scales.
Particle clusters named a culprit in premature birth
A new study of more than 100 pregnant women pinpoints the abnormal buildup of mineral-protein clusters in amniotic fluid (AF) as a potential culprit in premature birth.
Solved: One of the mysteries of globular clusters
A study shows that the most massive stars in the last stages of their lives are those which contaminate the interstellar medium with new chemical elements, giving rise to successive generations of stars in these 'astronomical fossils'.
Chemists create clusters of organelles by mimicking nature
Scientists from the University of Basel have succeeded in organizing spherical compartments into clusters mimicking the way natural organelles would create complex structures.

Related Globular Clusters Reading:

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Anthropomorphic
Do animals grieve? Do they have language or consciousness? For a long time, scientists resisted the urge to look for human qualities in animals. This hour, TED speakers explore how that is changing. Guests include biological anthropologist Barbara King, dolphin researcher Denise Herzing, primatologist Frans de Waal, and ecologist Carl Safina.
Now Playing: Science for the People

#SB2 2019 Science Birthday Minisode: Mary Golda Ross
Our second annual Science Birthday is here, and this year we celebrate the wonderful Mary Golda Ross, born 9 August 1908. She died in 2008 at age 99, but left a lasting mark on the science of rocketry and space exploration as an early woman in engineering, and one of the first Native Americans in engineering. Join Rachelle and Bethany for this very special birthday minisode celebrating Mary and her achievements. Thanks to our Patreons who make this show possible! Read more about Mary G. Ross: Interview with Mary Ross on Lash Publications International, by Laurel Sheppard Meet Mary Golda...