Gemini Observatory GeMS image of NGC 6624 revealing individual stars to
the cluster’s core. The Cluster’s age as determined with this study is
between 11.5-12.5 billion years old, which confirms that it formed when
the Universe was only a fraction of its current age of about 13.8
billion years. Composite color image by Travis Rector, University of
Alaska Anchorage. Image Credit: Gemini Observatory/AURA.
Full resolution JPEG | TIFF
The color-magnitude diagrams of NGC6624 obtained from the Gemini
observations. All the main evolutionary sequences of the cluster are
easily visible. These NIR diagrams turn out to be comparable to the HST
optical ones, both in depth and in photometric accuracy. The photometric
errors for each bin of Ks and J magnitudes are shown on the right side of the panels.
An international team of astronomers, using the Gemini Multi-conjugate
adaptive optics System (GeMS) and the high resolution camera GSAOI,
brought the ancient globular cluster NGC 6624 into razor-sharp focus and
determined its age with very high accuracy － a challenging observation
even from space. In addition to producing a beautiful image, this work
ultimately helps astronomers to better understand the formation and
evolution of our Galaxy during its earliest development when the
Universe was less than two billion years old.
Researchers using advanced adaptive optics technology at the Gemini
South telescope in Chile probed the depths of the highly compact
globular cluster NGC 6624, revealing pinpoint images of thousands of
stars. The sharpness of the near-infrared images is competitive with
that obtained from space with the Hubble Space Telescope in optical
light. “With images this sharp, astronomers can do things that we never
dreamed were possible from the ground,” says team member Douglas Geisler
of the University of Concepción in Chile.
The team obtained the imaging data using two filters that are sensitive
to specific wavelength bands of near-infrared light, then plotted them
on a color-magnitude diagram – a technique that reveals details about
the evolutionary history of the cluster’s stars. According to first
author Sara Saracino from the University of Bologna, this is the most
accurate, and deepest, near-infrared color-magnitude diagram ever
produced of this cluster and indeed perhaps the best-ever made for any
bulge cluster. The results of this research will be published in The Astrophysical Journal. A preprint of the paper can be found here.
The observations provide a clear detection of the so-called
“main-sequence knee,” a distinctive bend in the evolutionary track of
low mass main-sequence stars (those that burn hydrogen into helium at
their cores). This feature is extremely faint and therefore difficult to
detect, requiring very precise photometry (measuring the brightness of
individual stars). Photometry is generally a problem with most adaptive
optics data.
This is the first time the main-sequence knee has been identified in
this globular cluster. “Analysis of these razor-sharp images, and the
very deep color-magnitude diagram, allows us to determine the age of the
cluster to extremely high precision,” says Saracino. In turn, this
helps to better understand the formation and evolution of our Milky Way
bulge, which may well be the oldest component of the Galaxy. The new
Gemini data reveal that the age of NGC 6624 is between 11.5-12.5 billion
years old, almost as old as the Universe itself － estimated to be about
13.8 billion years old.
NGC 6624 is also interesting because it has been classified as what
astronomers call a post-core collapse cluster, meaning that this is a
highly evolved system. The high quality of the data also allowed the
researchers to perform a detailed study of the distribution of
main-sequence stars of different masses outward from the center. As
expected for such a highly evolved system, the team found evidence of a
significant increase in low-mass stars at increasing distances from the
cluster center.
This study is part of a much larger research program aimed at shedding
new light on the still debated processes that formed the Milky Way’s
bulge using its globular cluster population. Due to the large amount of
absorption by material between the stars in the Milky Way Galaxy,
detailed studies of bulge globular clusters have been severely hampered
until now. Geisler notes that the advent of the GeMS instrument now
allows astronomers to penetrate the dust and study these clusters in the
great detail they deserve. “It will certainly continue to provide us
with very important clues about how our Galaxy formed and evolved,” he
says.
The Gemini Multi-conjugate adaptive optics System (GeMS), combined with
the Gemini South Adaptive Optics Imager (GSAOI), delivers near
diffraction-limited images of near-infrared light
(0.9-2.5 microns), over a field nearly as large as the Hubble Space
Telescope’s Wide Field Camera 3 (WFC3). Using five artificial laser
guide stars, and up to three natural guide stars, GeMS/GSAOI can correct
for atmospheric turbulence at an unprecedented level, making it the
most powerful wide-field adaptive optics system currently available to
astronomers.
Science Contacts:
Sara Saracino
Department of Physics and Astronomy
University of Bologna, Italy
Email: sara.saracino@unibo.it
Office: +39 051 2095788
Cell: +39 3201607913
Douglas Geisler
Departamento de Astronomia
Universidad de Concepción, Chile
Email: dgeisler@astroudec.cl
Office: 56-41-2203092
Cell: 56-9-93078848
Media Contacts:
Peter Michaud
Gemini Observatory
Hilo, Hawai‘i
Email: pmichaud@gemini.edu
Cell: (808) 936-6643
Manuel Paredes
Gemini Observatory<
br /> La Serena, Chile
Email: mparedes@gemini.edu
Phone: +56 (51) 2205671
Source: Gemini Observatory
