* Astronomy

Blobrana · L

RE: Globular ClusterS

Blobrana · L

Globular star clusters, dense bunches of hundreds of thousands of stars, have some of the oldest surviving stars in the universe. A new study of globular clusters outside our Milky Way Galaxy has found evidence that these hardy pioneers are more likely to form in dense areas, where star birth occurs at a rapid rate, instead of uniformly from galaxy to galaxy. Astronomers used NASA's Hubble Space Telescope to identify over 11,000 globular clusters in the Virgo cluster of galaxies. Most are older than 5 billion years. The sharp vision of Hubble's Advanced Camera for Surveys resolved the star clusters in 100 galaxies of various sizes, shapes, and brightnesses, even in faint, dwarf galaxies. The images in this photo show four members of the Virgo cluster of galaxies. Comprised of over 2,000 galaxies, the Virgo cluster is the nearest large galaxy cluster to Earth, located about 54 million light-years away.

Read more

Blobrana · L

NGC 2808

Blobrana · L

RE: Globular ClusterS

Blobrana · L

Title: XMM-Newton observations of the Galactic globular clusters NGC 2808 and NGC 4372
Authors: M. Servillat, N. A. Webb, D. Barret

Galactic globular clusters harbour binary systems that are detected as faint X-ray sources. These close binaries are thought to play an important role in the stability of the clusters by liberating energy and delaying the inevitable core collapse of globular clusters. The inventory of close binaries and their identification is therefore essential. We present XMM-Newton observations of two Galactic globular clusters: NGC 2808 and NGC 4372. We use X-ray spectral and variability analysis combined with ultra-violet observations made with the XMM-Newton optical monitor and published data from the Hubble Space Telescope to identify sources associated with the clusters. We compare the results of our observations with estimates from population synthesis models. Five sources out of 96 are likely to be related to NGC 2808. Nine sources are found in the field of view of NGC 4372, none being located inside its half-mass radius. We find one quiescent neutron star low mass X-ray binary candidate in the core of NGC 2808, and propose that the majority of the central sources in NGC 2808 are cataclysmic variables. An estimation leads to ~20+/-10 cataclysmic variables with luminosity above 4.25 x 10^31 erg s^-1. Millisecond pulsars could also be present in the core of NGC 2808, and some sources outside of the half-mass radius could possibly be linked to the cluster.

Read more (1093kb, PDF)

Blobrana · L

Title: Six New Galactic Orbits of Globular Clusters in a Milky-Way-Like Galaxy
Authors: Christine Allen (1), Edmundo Moreno (1), Barbara Pichardo (1,2) ((1) Instituto de Astronomia, Universidad Nacional Autonoma de Mexico, México, (2) Institute for Theoretical Physics, University of Zurich, Switzerland.)

Absolute proper motions for six new globular clusters have recently been determined. This motivated us to obtain the Galactic orbits of these six clusters both in an axisymmetric Galactic potential and in a barred potential, such as the one of our Galaxy. Orbits are also obtained for a Galactic potential that includes spiral arms. The orbital characteristics are compared and discussed for these three cases. Tidal radii and destruction rates are also computed and discussed.

Read more (314kb, PDF)

Blobrana · L

After ten years of research, Korean astronomers have discovered scores of new densely packed collections of stars, called globular clusters, in the Andromeda galaxy, which is referred to as a sibling of our own galaxy.
These so-called astronomical fossils were made in the early stages of the galaxy's formation, so astronomers expect the discovery will be a milestone in the study of the formation and evolution of the universe.
The research team, led by Kim Sang-chul of the Korea Astronomy and Space Science Institute and Lee Myung-gyoon with the Department of Physics and Astronomy of Seoul National University, said it discovered 113 new GCs in Andromeda.

Read more

Blobrana · L

Title: Evidence for Three Subpopulations of Globular Clusters in the Early-Type Post-Starburst Shell Galaxy AM 0139-655
Authors: A. Maybhate (STScI), P. Goudfrooij (STScI), F. Schweizer (OCIW), T. Puzia (HIA), D. Carter (LJMU)

We present deep HST ACS images of the post-starburt shell galaxy AM 0139-655. We find evidence for the presence of three distinct globular cluster subpopulations associated with this galaxy: a centrally concentrated young population (~ 0.4 Gyr), an intermediate age population (~ 1 Gyr) and an old, metal-poor population similar to that seen around normal galaxies. The g-I colour distribution of the clusters is bimodal with peaks at 0.85 and 1.35. The redder peak at g-I=1.35 is consistent with the predicted colour for an old metal-poor population. The clusters associated with the peak at g-I=0.85 are centrally concentrated and interpreted as a younger and more metal-rich population. We suggest that these clusters have an age of ~ 0.4 Gyr and solar metallicity based on a comparison with population synthesis models. The luminosity function of these "blue" clusters is well represented by a power law. Interestingly, the brightest shell associated with the galaxy harbours some of the youngest clusters observed. This seems to indicate that the same merger event was responsible for the formation of both the shells and the young clusters. The red part of the colour distribution contains several very bright clusters, which are not expected for an old, metal-poor population. Furthermore, the luminosity function of the "red" GCs cannot be fit well by either a single gaussian or a single power law. A composite (gaussian + power law) fit to the LF of the red clusters yields both a low rms and very plausible properties for an old population plus an intermediate-age population of GCs. Hence, we suggest that the red clusters in AM 0139-655 consist of two distinct GC subpopulations, one being an old, metal-poor population as seen in normal galaxies and one having formed during a recent dissipative galaxy merger.

Read more (583kb, PDF)

Blobrana · L

If we could view our Milky Way galaxy from afar, wed see a giant disk of stars. A big bar of stars would light up the centre, with lacy spiral arms wrapped around it. And scattered above, below, and through the disk, wed see cottonball-shaped puffs of stars.
Read more

Blobrana · L

Koposov 1 and 2