UTexas: Globular Clusters Rotate at Heart

[bystander]

UTexas: Globular Clusters Rotate at Heart

Astronomers from The University of Texas at Austin and Germany’s Max Planck Institute for Extraterrestrial Physics (MPE) recently found a surprise when studying some of the oldest star clusters in our galaxy. The stars at the centers of these clusters are rotating around a common axis. It was previously thought any central rotation would have been long erased, leaving the central stars to random orbits.

MPE: Rotating Globular Clusters

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. 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.

Central Rotations of Milky Way Globular Clusters - Maximilian H. Fabricius et al

• Astrophysical Journal Letters 787(2) L26 (2014 Jun 01) DOI: 10.1088/2041-8205/787/2/L26
  arXiv.org > astro-ph > arXiv:1405.1722 > 07 May 2014

[Ann]

Click to view full size image

G1, the largest globular cluster of the Andromeda galaxy, is obviously flattened. It is clearly rotating, then.


Ann

[Nitpicker]

Omega Cen is also elongated (and a lot closer).

[geckzilla]

Both of those are suspected to not be true globular clusters, however. Flatness and rotation would also be something one might expect from the nuclear remnant of a dwarf galaxy.

[Nitpicker]

Perhaps flattened ones should be called "GCs with a mysterious past". Calling them "not true GCs" is never gonna stick.

In any event, it never occurred to me that the flattening might be caused by anything other than rotation about a statistically common axis. (I've not thought much [yet] about the orbits inside spherical GCs.)

[BDanielMayfield]

Both of those are suspected to not be true globular clusters, however. Flatness and rotation would also be something one might expect from the nuclear remnant of a dwarf galaxy.

Right. How can one distinquish between the largest globular clusters and the smallest dwarf elliptical galaxies? Might they be the same things, with the distinction just being location inside or outside of a far larger galaxy?

[geckzilla]

Spectroscopically, they look different.

[BDanielMayfield]

Spectroscopically, they look different.

Thanks. That implies differing formation histories, or at the least, ages, I would think.

[geckzilla]

Yes, just as a flattened, rotating structure would imply a different formation history. So you can see that they are not suspicious just because of one factor.