17 October: Globular Cluster Dynamics and Gravitational Wave Observations of Structure
If globular clusters are icebergs, electromagnetic observations of globular clusters reveal only the tip. Massive stars have evolved, and low-mass stars are dim: in the end, most of the mass range is visible electromagnetically only when active mass transfer is occurring. Gravitational wave observations, on the other hand, are sensitive to all compact binaries in a rather wide frequency range.
- How would observations of the overall population of binaries inform and clarify the modeling of globular cluster dynamics?
- How does the dynamical evolution and underlying structure of globular clusters influence the distribution of binaries in (and outside of) the clusters?
- What gravitational wave observations of these binaries are possible and what information about the binaries or their population statistics can be gleaned from these observations?
18 October: White Dwarf binaries in Globular Clusters
The theoretical maximum mass of a white dwarf is the Chandrasekhar mass. Since white dwarf masses are measured accurately only for a small number of pairs the maximum mass, or the mass spectrum, that occurs in nature is not known. The LISA detector will observe a confusion limited background of white dwarf binaries from the disk, as well as resolving some individual white dwarf binaries, which will include some globular cluster binaries. The resolved cluster binaries may provide more mass measurements, which will complement disk dwarf mass measurements by including different metallicity ranges. What do we currently know about white dwarf binaries in globular clusters and what may we learn about them from gravitational wave observations: e.g.,
- How close to the Chandrasekhar mass can and do real white dwarf stars get?
- What is the distribution of masses for white dwarf stars in compact binaries?
- How well can gravitational wave observations resolve individual white dwarf binaries? * What is the shortest orbital period for a white dwarf binary?
- Are white dwarf oscillation modes excited in white dwarf binaries and, if so, how well can they be observed and what information about white dwarf stars can their observation provide?
19 October: Neutron star binaries in globular clusters
Neutron stars should not exist in globular clusters since the escape velocity from clusters is low (< 50 km/s) compared to the expected kick velocity received at birth. Nonetheless, there are numerous observations of neutron stars in globular clusters: millisecond pulsars and low-mass X-ray binaries (LMXBs) are two examples of neutron star populations that are overabundant in globular clusters compared to galactic systems. Both of these populations are understood to have an origin in the special dynamics of globular cluster binary systems
- What is the nature of LMXB and millisecond pulsar populations in globular clusters and what role does dynamics play in shaping these populations?
- What unique gravitational wave signatures can be observed from LMXBs and millisecond pulsars, and what can these observations reveal about the neutron star component of these systems.
- How can this information be used to inform us about the relationship between these populations and the dynamics that are responsible for them.
20 October: Black hole binaries in globular clusters
As the end product of the most massive stars in globular clusters, black holes will play a significant role in cluster dynamics. Observational evidence for black holes in globular clusters today is very limited. Theoretical model predictions range from a single, large black hole at the center, to a population of stellar mass black holes in binaries throughout; but, observations have yet to speak on the question.
- What is the evidence for black holes in globular clusters?
- How do theoretical models of dynamics describe the black hole population?
- The gravitational wave signature of globular cluster black holes will depend on the characteristics of the population: how can gravitational wave observations tell us about the population and, correspondingly, help us choose among the theoretical models?
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