Astronomers observing the ancient star cluster NGC 288 have found streams of stars near it. They believe these are tidal tails formed by gravitational interaction with the Milky Way and the Large Magellanic Cloud.
What are tidal tails in star clusters?
By analyzing data from different astronomical observations, astronomers investigated an old globular cluster known as NGC 288. As a result, they identified several elongated tidal tails associated with this cluster. The discovery is described in a paper published on September 25 on the arXiv preprint server.
Tidal tails are thin, elongated regions of stars stretching out into space of interstellar gas. They are formed by gravitational interactions between galaxies and star clusters. Observations show that some interacting objects have two distinct tails, while other systems have only one tail.
Identifying and studying tidal tails provides clues about the tidal accumulations experienced and their internal dynamics. Such studies could also reveal important information about the evolution of the cluster and shed new light on the clumpy distribution of dark matter in the galaxy. However, as of today, only a few clusters with tidal tails have been discovered in the Milky Way galaxy.
Tidal streams in the cluster NGC 288
NGC 288 is a galactic globular cluster located about 29,200 light-years away. It is an old, metal-poor cluster with an estimated mass of about 96,000 solar masses and a half-radius of about 27.9 light-years.
Previous observations of NGC 288 have revealed its extended shell and found evidence of tidal streams emanating from the cluster. Now, a team of astronomers led by Carl J. Grillmair of the California Institute of Technology (Caltech) reports that these tidal streams are more complex than previously thought.
Observations by Grillmair’s team found an apparent excess of stars extending at least 40 degrees north of NGC 288, along the 300-degree meridian, and perhaps as far as about 80 degrees from the cluster, where it is overlapped by the Galactic disk. This feature, named the leading tail, consists of two or more spatially offset and kinematically distinct stellar streams, each less than about 650 light-years wide.
In addition, astronomers found a 35 to 70 degree-long trailing tail stretching toward the upper right corner of the cluster. This tail appeared significantly narrower in the sky than the front tail. The researchers added that the position of the tail fits well with the flow model, which includes the massive Large Magellanic Cloud (LMC), a satellite galaxy of the Milky Way.
Further studies of the cluster NGC 288
According to the paper, the affiliation of these stars in the tidal streams to NGC 288 still requires further confirmation, which should be done through subsequent radial velocity measurements.
“If even a few of the most outlying candidates can be confirmed as having once belonged to NGC 288, this stream will become another particularly sensitive probe of the shape of the inner halo potential and an important contributor to our understanding of the influence of the LMC and other components of the galaxy,” the scientists concluded.
According to phys.org
