Green Bank Observatory | National Radio Astronomy Observatory | 2017 Sep 12
Astronomers have spent nearly two decades meticulously tracing the motions of 36 rapidly rotating pulsars, so-called millisecond pulsars, inside Terzan 5 -- a massive, ancient star cluster near the center of the Milky Way. The pulsars are gradually “falling” throughout the cluster, tugged by gravity toward regions with greater mass. This new research, published in the Astrophysical Journal, is giving astronomers a clearer picture of the cluster’s interior and likely birthplace.The Milky Way is chock-full of star clusters. Some contain just a few tens-to-hundreds of young stars. Others, known as globular clusters, are among the oldest objects in the universe and contain up to a million ancient stars.
- Graphic showing locations of millisecond pulsars inside the globular cluster Terzan 5 in an optical image taken by the Hubble space telescope. Pulsars represented in blue are accelerating toward observers on Earth; those in red are accelerating away.
Credit: B. Saxton (NRAO/AUI/NSF); GBO/AUI/NSF; NASA/ESA/Hubble, F. Ferraro
Some globular clusters are thought to be fragments of our galaxy, chiseled off when the Milky Way was in its infancy. Others may have started life as standalone dwarf galaxies before being captured by the Milky Way during its formative years.
Regardless of their origins, many globular clusters reside either in or behind the dusty regions of our galaxy. For ground- and space-based optical telescopes, however, this poses a challenge. Though it is possible to observe the cluster as a whole, the dust hinders astronomers’ efforts to study the motions of individual stars. If astronomers could track the motions of individual stars, they could see how “lumpy” the globular cluster is or if it contains something really dense, like a giant black hole at its center.
Fortunately, radio waves -- like those emitted by pulsars -- are unhindered by galactic dust. So rather than tracing the motions of the stars, astronomers should be able to map the motions of pulsars instead. But, of course, things are never that simple. Though globular clusters are brimming with stars, they contain far fewer pulsars. ...
Using Long-term Millisecond Pulsar Timing to Obtain Physical
Characteristics of the Bulge Globular Cluster Terzan 5 - Brian J. Prager et al
- Astrophysical Journal 845(2):148 (20 Aug 2017) DOI: 10.3847/1538-4357/aa7ed7
arXiv.org > astro-ph > arXiv:1612.04395 > 13 Dec 2016 (v1), 12 Jul 2017 (v3)