Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Rotating globular clusters

09.05.2014

Recent observations of globular clusters with the VIRUS-W instrument at the McDonald observatory revealed a rotation signal at the centre of these huge agglomerations of stars.

This finding is very surprising, as the astronomers expected that any central rotation should have been erased by now due to the old age of these clusters.


The core of the globular cluster Messier 13 is just 25 000 light-years away and measures about 145 light-years in diameter. It lies in the constellation Hercules and sometimes can even be seen with small binoculars.

Credit: ESA / Hubble und NASA


The VIRUS-W instrument (inset) mounted on the 2.7m telescope of the McDonald Observatory (right). The special configuration of the instrument allows the astronomers to simultaneously measure position and velocity for all stars in their field of view. © MPE

In addition, the astronomers from the Max Planck Institute for Extraterrestrial Physics and the University of Texas found that the rotation axis agrees with the slight elongation found for some of the clusters, indicating that this flattening is caused by rotation.

Globular clusters are ancient formations orbiting most galaxies, including our own Milky Way: they consist of up to a million old, metal-poor stars, which are tightly bound by gravity. Due to their old age and fairly spherical shape, with a strong concentration of stars towards the centre, they have historically been viewed as simple systems. However, new observations keep revealing surprising results.

“For all globular clusters in our sample we find a rotation signal in the centre – an astonishing result,” says Maximilian Fabricius, lead scientists of this study at the Max Planck Institute for Extraterrestrial Physics (MPE). “We did not expect this; originally we observed these globular clusters to measure their central velocity dispersions.” The velocity dispersion is a measure of the amount of random stellar motion in a cluster. Rotation, on the other hand, means that the cluster has an actual rotation axis around which more stars revolve in one way than the other. 

“Theory and numerical simulations of globular clusters indicate that any central rotation should be erased on relatively short timescales,” says Eva Noyola, co-author of this study at the University of Texas in Austin. “Because these globular clusters were formed billions of years ago, we would expect that any rotation signature would have been eradicated by now. Even though previous measurements showed some rotation in a handful of systems, they only probed the motion of stars in the outer regions.”

The new measurements of a dozen globular cluster cores were only possible with the help of the VIRUS-W instrument developed at MPE. This “integral field spectrograph” (IFU) allows the scientists to simultaneously measure more than 260 spectra in their field of view, determining the motion of stars to an accuracy of a few kilometres per second. That means that for a given globular cluster, one night at the Harlan J. Smith 2.7m Telescope of the McDonald observatory in Texas with an observing time of a few hours is enough to determine the velocity field at the core of the cluster. Such a project was not possible before VIRUS-W.

Traditionally, astronomers determined the line-of-sight velocities of cluster member stars one-by-one using high resolution spectrographs that can measure the Doppler shift of the stars. This, however, is painstakingly slow and very hard to do in the core of globular clusters. Therefore, so far, there have been no systematic studies of the kinematics of globular cluster cores. Even though the VIRUS-W instrument was originally developed to study the kinematics of nearby galaxies, the astronomers realized that the combination of a large field of view and a relatively high spectral resolution make this instrument a very efficient tool to also study stellar motions in globular clusters. 

There are about 150 globular clusters in the Milky Way and the astronomers selected 27 of them, which are observable with the McDonald telescope (i.e. in the northern sky) during one night. Between August 2012 and August 2013 they observed the first 11 globular clusters and now present their surprising results: all clusters show signatures of rotation.

Furthermore, the new velocity measurements are actually in remarkably good agreement with the flattening measured for the globular clusters in this sample. This seems to indicate that the central rotation drives the flattening for these objects rather than the influence of the Milky Way tidal field.

These findings raise interesting questions about the formation history and evolution of globular clusters – none of the current theoretical models predict such a ubiquitous and strong rotation. However, it is worth noting that the present sub-sample does not include any “core-collapsed” globular clusters yet.

Core-collapse is a process that might eradicate rotation. Future observations of the remaining clusters in the full sample will shed light on additional questions such as a possible correlation between rotation and the position of a globular cluster inside our galaxy.

Contact 

Dr. Hannelore Hämmerle

MPE Pressesprecherin

Phone:+49 (0)89 30000 3980Fax:+49 (0)89 30000 3569
Email:pr@...

Max-Planck-Institut für extraterrestrische Physik, Garching 

 

Maximilian Fabricius

Optische und interpretative Astronomie

Phone:+49 89 3000 3779Fax:+49 89 30000 3569
Email:mxhf@...

Max-Planck-Institut für extraterrestrische Physik, Garching

  

Original publication

 
1
M. H. Fabricius, E. Noyola, S. Rukdee et al.
accepted by ApJ Letters

Dr. Hannelore Hämmerle | Max-Planck-Institute
Further information:
http://www.mpe.mpg.de/5872915/News_20140507

More articles from Physics and Astronomy:

nachricht Basque researchers turn light upside down
23.02.2018 | Elhuyar Fundazioa

nachricht Attoseconds break into atomic interior
23.02.2018 | Max-Planck-Institut für Quantenoptik

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Attoseconds break into atomic interior

A newly developed laser technology has enabled physicists in the Laboratory for Attosecond Physics (jointly run by LMU Munich and the Max Planck Institute of Quantum Optics) to generate attosecond bursts of high-energy photons of unprecedented intensity. This has made it possible to observe the interaction of multiple photons in a single such pulse with electrons in the inner orbital shell of an atom.

In order to observe the ultrafast electron motion in the inner shells of atoms with short light pulses, the pulses must not only be ultrashort, but very...

Im Focus: Good vibrations feel the force

A group of researchers led by Andrea Cavalleri at the Max Planck Institute for Structure and Dynamics of Matter (MPSD) in Hamburg has demonstrated a new method enabling precise measurements of the interatomic forces that hold crystalline solids together. The paper Probing the Interatomic Potential of Solids by Strong-Field Nonlinear Phononics, published online in Nature, explains how a terahertz-frequency laser pulse can drive very large deformations of the crystal.

By measuring the highly unusual atomic trajectories under extreme electromagnetic transients, the MPSD group could reconstruct how rigid the atomic bonds are...

Im Focus: Developing reliable quantum computers

International research team makes important step on the path to solving certification problems

Quantum computers may one day solve algorithmic problems which even the biggest supercomputers today can’t manage. But how do you test a quantum computer to...

Im Focus: In best circles: First integrated circuit from self-assembled polymer

For the first time, a team of researchers at the Max-Planck Institute (MPI) for Polymer Research in Mainz, Germany, has succeeded in making an integrated circuit (IC) from just a monolayer of a semiconducting polymer via a bottom-up, self-assembly approach.

In the self-assembly process, the semiconducting polymer arranges itself into an ordered monolayer in a transistor. The transistors are binary switches used...

Im Focus: Demonstration of a single molecule piezoelectric effect

Breakthrough provides a new concept of the design of molecular motors, sensors and electricity generators at nanoscale

Researchers from the Institute of Organic Chemistry and Biochemistry of the CAS (IOCB Prague), Institute of Physics of the CAS (IP CAS) and Palacký University...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

2nd International Conference on High Temperature Shape Memory Alloys (HTSMAs)

15.02.2018 | Event News

Aachen DC Grid Summit 2018

13.02.2018 | Event News

How Global Climate Policy Can Learn from the Energy Transition

12.02.2018 | Event News

 
Latest News

Basque researchers turn light upside down

23.02.2018 | Physics and Astronomy

Finnish research group discovers a new immune system regulator

23.02.2018 | Health and Medicine

Attoseconds break into atomic interior

23.02.2018 | Physics and Astronomy

VideoLinks
Science & Research
Overview of more VideoLinks >>>