* Astronomy

Members Login
Post Info TOPIC: 47 Tucanae


L

Posts: 130093
Date:
RE: 47 Tucanae
Permalink  
 


Title: An intermediate-mass black hole in the centre of the globular cluster 47 Tucanae
Author: Bülent Kzltan, Holger Baumgardt, Abraham Loeb

Intermediate mass black holes play a critical role in understanding the evolutionary connection between stellar mass and super-massive black holes. However, to date the existence of these species of black holes remains ambiguous and their formation process is therefore unknown. It has been long suspected that black holes with masses 10^2 - 10^4 solar masses should form and reside in dense stellar systems. Therefore, dedicated observational campaigns have targeted globular cluster for many decades searching for signatures of these elusive objects. All candidates found in these targeted searches appear radio dim and do not have the X-ray to radio flux ratio predicted by the fundamental plane for accreting black holes. Based on the lack of an electromagnetic counterpart upper limits of 2060 solar masses and 470 solar masses have been placed on the mass of a putative black hole in 47 Tucanae (NGC 104) from radio and X-ray observations respectively. Here we show there is evidence for a central black hole in 47 Tuc with a mass of M_.~2200 solar masses _{-800}^{+1500} when the dynamical state of the globular cluster is probed with pulsars. The existence of an intermediate mass black hole in the centre of one of the densest clusters with no detectable electromagnetic counterpart suggests that the black hole is not accreting at a sufficient rate and therefore contrary to expectations is gas starved. This intermediate mass black hole might be a member of electromagnetically invisible population of black holes that are the elusive seeds leading to the formation of supermassive black holes in galaxies.

Read more (6413kb, PDF)



__________________


L

Posts: 130093
Date:
Permalink  
 

A Middleweight Black Hole is Hiding at the Center of a Giant Star Cluster

All known black holes fall into two categories: small, stellar-mass black holes weighing a few Suns, and supermassive black holes weighing millions or billions of Suns. Astronomers expect that intermediate-mass black holes weighing 100 - 10,000 Suns also exist, but so far no conclusive proof of such middleweights has been found. Today, astronomers are announcing new evidence that an intermediate-mass black hole (IMBH) weighing 2,200 Suns is hiding at the center of the globular star cluster 47 Tucanae.
Read more



__________________


L

Posts: 130093
Date:
Permalink  
 

Hubble Catches a Stellar Exodus in Action

Using NASA's Hubble Space Telescope, astronomers have captured for the first time snapshots of fledgling white dwarf stars beginning their slow-paced, 40-million-year migration from the crowded center of an ancient star cluster to the less populated suburbs.
Read more



__________________


L

Posts: 130093
Date:
Permalink  
 

Title: When do stars in 47 Tucanae lose their mass?
Author: Jeremy Heyl, Jason Kalirai, Harvey B. Richer, Paola Marigo, Elisa Antolini, Ryan Goldsbury, Javiera Parada

By examining the diffusion of young white dwarfs through the core of the globular cluster 47 Tucanae, we estimate the time when the progenitor star lost the bulk of its mass to become a white dwarf. We find this to be not earlier than 40 Myr before the star reaches the tip of the asymptotic giant branch. According to stellar evolution models of the white-dwarf progenitors in 47 Tucanae, we find this epoch to coincide approximately with the star ascending the asymptotic-giant branch and well after the helium flash. With the current data and analysis we cannot exclude some mass loss on the red-giant branch, but we argue that the bulk of the mass loss must occur very late in the star's history on the asymptotic-giant branch. We also confront the observed magnitudes of stars on the horizontal branch in 47 Tucanae and find that they are consistent with the latest theoretical models of the horizontal branch stars of 0.8 - 0.9 solar masses, further supporting the conclusion that the stars in 47 Tucanae and likewise in other clusters lose the bulk of their mass on the asymptotic-giant branch.

Read more (500kb, PDF)



__________________


L

Posts: 130093
Date:
Caldwell 106
Permalink  
 


Title: The white dwarf cooling sequence of 47 Tucanae
Author: Enrique García-Berro, Santiago Torres, Leandro G. Althaus, Marcelo M. Miller Bertolami

47 Tucanae is one of the most interesting and well observed and theoretically studied globular clusters. This allows us to study the reliability of our understanding of white dwarf cooling sequences, to confront different methods to determine its age, and to assess other important characteristics, like its star formation history. Here we present a population synthesis study of the cooling sequence of the globular cluster 47 Tucanae. In particular, we study the distribution of effective temperatures, the shape of the color-magnitude diagram, and the corresponding magnitude and colour distributions. We do so using an up-to-date population synthesis code based on Monte Carlo techniques, that incorporates the most recent and reliable cooling sequences and an accurate modelling of the observational biases. We find a good agreement between our theoretical models and the observed data. Thus, our study, rules out previous claims that there are still missing physics in the white dwarf cooling models at moderately high effective temperatures. We also derive the age of the cluster using the termination of the cooling sequence, obtaining a good agreement with the age determinations using the main-sequence turn-off. Finally, we find that the star formation history of the cluster is compatible with that obtained using main sequence stars, which predict the existence of two distinct populations. We conclude that a correct modelling of the white dwarf population of globular clusters, used in combination with the number counts of main sequence stars provides an unique tool to model the properties of globular clusters.

Read more (349kb, PDF)



__________________


L

Posts: 130093
Date:
NGC 104
Permalink  
 


NGC 104 (also 47 Tucanae, Melotte 1, Caldwell 106, ESO 50-SC9 and GCL 1) is a magnitude +4.91 globular star cluster located 16,700 ±850 light-years away in the constellation Tucana.

The cluster was discovered by French astronomer Nicolas Louis de Lacaille using a 1.27 cm (0.5 inch), 8x magnification, refractor at the Cape of Good Hope on the 14th September 1751. 

Right Ascension 00h 24m 05.67s, Declination -72° 04' 52.6"

It is the second brightest globular cluster in the sky (after Omega Centauri), and is noted for having a very bright and dense core. It is also one of the most massive globular clusters in the Galaxy, containing millions of stars.
Read more

NGC 104



__________________


L

Posts: 130093
Date:
RE: 47 Tucanae
Permalink  
 


Title: Chandra detection of a new diffuse X-ray component from the globular cluster 47 Tucanae
Author: E. M. H. Wu (1), C. Y. Hui (2), A. K. H. Kong (3), P. H. T. Tam (3), K. S. Cheng (1), V. A. Dogiel (4) ((1) The University of Hong Kong, (2) Chungnam National University, (3) National Tsing Hua University, (4) P.N. Lebedev Institute of Physics)

In re-analyzing the archival Chandra data of the globular cluster 47 Tucanae, we have detected a new diffuse X-ray emission feature within the half-mass radius of the cluster. The spectrum of the diffuse emission can be described by a power-law model plus a plasma component with photon index Gamma~1.0 and plasma temperature kT~0.2 keV. While the thermal component is apparently uniform, the non-thermal contribution falls off exponentially from the core. The observed properties could possibly be explained in the context of multiple shocks resulted from the collisions among the stellar wind in the cluster and the inverse Compton scattering between the pulsar wind and the relic photons.

Read more (833kb, PDF)



__________________


L

Posts: 130093
Date:
Permalink  
 

47 Tucanae: Probing Extreme Matter Through Observations of Neutron Stars

47tuc_525.jpg

Three telescopes - Chandra, ESA's XMM-Newton, and NASA's Rossi X-ray Timing Explorer (RXTE) - were used to observe 8 neutron stars, including one in 47 Tucanae, a globular cluster located about 15,000 light years away in the outskirts of the Milky Way. The image shown here was constructed from a long Chandra observation of 47 Tucanae. Lower-energy X-rays are red, X-rays with intermediate energies are green, and the highest-energy X-rays are shown in blue.
Read more



__________________


L

Posts: 130093
Date:
Permalink  
 

Title: Fundamental parameters of red giants in 47 Tucanae
Authors: A. O. Thygesen, L. Sbordone

In these proceedings we present initial results of a spectroscopic analysis of a small sample of evolved K-giants in the globular cluster 47 Tucanae. We derive the effective temperature, surface gravity and microturbulence of all targets using standard methods. Further we derive LTE abundances of [Fe/H] and [O/Fe] as well as the abundance of sodium, using NLTE corrections. We find a mean metallicity for the cluster of [Fe/H]=-0.75±0.10, in excellent agreement with several other studies. Also, we confirm the sodium-oxygen anticorrelation previously reported by a number of other authors. Finally, we see indications of the sodium enriched stars also being enriched in heavy magnesium isotopes.

Read more (761kb, PDF)



__________________


L

Posts: 130093
Date:
Permalink  
 

New VISTA snap of star cluster 47 Tucanae

eso1302a.jpg

This new infrared image from ESO's VISTA telescope shows the globular cluster 47 Tucanae in striking detail. This cluster contains millions of stars, and there are many nestled at its core that are exotic and display unusual properties. Studying objects within clusters like 47 Tucanae may help us to understand how these oddballs form and interact. This image is very sharp and deep due to the size, sensitivity, and location of VISTA, which is sited at ESO's Paranal Observatory in Chile.
Read more



__________________
1 2 3  >  Last»  | Page of 3  sorted by
Quick Reply

Please log in to post quick replies.



Create your own FREE Forum
Report Abuse
Powered by ActiveBoard