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 NASA's SDO sees partial eclipse in space
29.05.2017 | NASA/Goddard Space Flight Center

nachricht Strathclyde-led research develops world's highest gain high-power laser amplifier
29.05.2017 | University of Strathclyde

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: Strathclyde-led research develops world's highest gain high-power laser amplifier

The world's highest gain high power laser amplifier - by many orders of magnitude - has been developed in research led at the University of Strathclyde.

The researchers demonstrated the feasibility of using plasma to amplify short laser pulses of picojoule-level energy up to 100 millijoules, which is a 'gain'...

Im Focus: Can the immune system be boosted against Staphylococcus aureus by delivery of messenger RNA?

Staphylococcus aureus is a feared pathogen (MRSA, multi-resistant S. aureus) due to frequent resistances against many antibiotics, especially in hospital infections. Researchers at the Paul-Ehrlich-Institut have identified immunological processes that prevent a successful immune response directed against the pathogenic agent. The delivery of bacterial proteins with RNA adjuvant or messenger RNA (mRNA) into immune cells allows the re-direction of the immune response towards an active defense against S. aureus. This could be of significant importance for the development of an effective vaccine. PLOS Pathogens has published these research results online on 25 May 2017.

Staphylococcus aureus (S. aureus) is a bacterium that colonizes by far more than half of the skin and the mucosa of adults, usually without causing infections....

Im Focus: A quantum walk of photons

Physicists from the University of Würzburg are capable of generating identical looking single light particles at the push of a button. Two new studies now demonstrate the potential this method holds.

The quantum computer has fuelled the imagination of scientists for decades: It is based on fundamentally different phenomena than a conventional computer....

Im Focus: Turmoil in sluggish electrons’ existence

An international team of physicists has monitored the scattering behaviour of electrons in a non-conducting material in real-time. Their insights could be beneficial for radiotherapy.

We can refer to electrons in non-conducting materials as ‘sluggish’. Typically, they remain fixed in a location, deep inside an atomic composite. It is hence...

Im Focus: Wafer-thin Magnetic Materials Developed for Future Quantum Technologies

Two-dimensional magnetic structures are regarded as a promising material for new types of data storage, since the magnetic properties of individual molecular building blocks can be investigated and modified. For the first time, researchers have now produced a wafer-thin ferrimagnet, in which molecules with different magnetic centers arrange themselves on a gold surface to form a checkerboard pattern. Scientists at the Swiss Nanoscience Institute at the University of Basel and the Paul Scherrer Institute published their findings in the journal Nature Communications.

Ferrimagnets are composed of two centers which are magnetized at different strengths and point in opposing directions. Two-dimensional, quasi-flat ferrimagnets...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Marine Conservation: IASS Contributes to UN Ocean Conference in New York on 5-9 June

24.05.2017 | Event News

AWK Aachen Machine Tool Colloquium 2017: Internet of Production for Agile Enterprises

23.05.2017 | Event News

Dortmund MST Conference presents Individualized Healthcare Solutions with micro and nanotechnology

22.05.2017 | Event News

 
Latest News

New insights into the ancestors of all complex life

29.05.2017 | Earth Sciences

New photocatalyst speeds up the conversion of carbon dioxide into chemical resources

29.05.2017 | Life Sciences

NASA's SDO sees partial eclipse in space

29.05.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>