Session D19: Undergrad Research V

Utilizing the Navier-Stokes Equations for Modelling Incompressible, Viscous, Non-Laminar Fluid Flow in Ultrasonic-Oscillatory Artificial Gravity

            One of the most significant challenges in developing technology for long-term space flight is addressing the physiological feasibility of microgravity and artificially-induced gravity conditions. As a part of Drake University's Magneto-Ionization Spacecraft Shield for Interplanetary Travel (MISSFIT) undergraduate research group, we investigate the impact of artificial gravity conditions on cardiovascular fluid flow to predict the changes prolonged exposure to ultrasonic-oscillatory-induced gravity may have on blood flow in the short-term by applying the varational form of the finite element method to solve the partially differential and notoriously unstable Navier-Stokes equations for incompressible and non-laminar flow of viscous fluid. By utilizing a modified form of Chorin’s method in the FEniCS platform, we predict the behavior of blood flow through a short, cylindrical vessel encased in a rectangular mesh. The results from this calculation are then analyzed using the CVSim model to determine the cardiovascular feasibility of oscillatory gravity conditions.   

Multipole expansion of the inverse-square law of gravity

We introduce the multipole expansion of the inverse-square law of gravity. The $1/R$ potential of gravity draws an immediate analogy with that of Coulomb's law and provides a powerful tool to address the effect of imperfections of instruments probing gravitational torques with high precision. We discuss our results in the context of a torsion balance experiment designed to search for non-Newtonian gravity at short-range distances.   

Novel Tests of Gravity Below Fifty Microns

Attempts to unify the Standard Model and General Relativity often include features that violate the Weak Equivalence Principle (WEP) and/or the gravitational Inverse-Square Law (ISL). A violation of these would question our fundamental understanding of gravity. To further understand nature, undergraduate researchers and faculty at Humboldt State University are using an experiment to measure gravitational interactions below 50 microns. The experiment uses a torsion pendulum with equal masses of two different materials arranged as a composition dipole. The twist of the torsion pendulum is measured as an attractor mass in a parallel-plate configuration is oscillated nearby. This creates a time dependent torque on the pendulum. The magnitude of this torque may lead to deviations in the WEP or ISL at this untested scale.   

Improved Measurement of the Newtonian Gravitational Constant G

The Newtonian gravitational constant, G, is one of the oldest known fundamental constants, but despite this, it is the least precisely known of all the fundamental constants to date. In the past 200 years, a wide variety of experimental methods have been used to measure G but consistently producing widely varying results even among recent measurements of high precision. Recently, two improved experiments have produced results that are consistent at the 12 ppm level. After examination of the methodology used in previous measurements, the research group at IUPUI, in collaboration with Cal Poly Humboldt, will use multiple approaches within a singular torsion pendulum apparatus to investigate sources of error between the incorporated techniques. Measurements of G will be made using both the angular acceleration feedback and time of swing methods in the apparatus. At Cal Poly Humboldt, further sources of error are being addressed through the development of an additional integrated optical system designed to detect residual simple pendulum motion aside from the angular rotational motion used to measure G. We expect to obtain a measurement at the 2 ppm level using these new methods. By continuing the use of a torsion pendulum apparatus, we also hope better to understand the current discrepancies among previous experimental results.    

A simple algorithm to predict the Stellar Masses of Nearby Satellites of Galaxies from DMO simulations

Due to the absence of various baryonic processes, Dark Matter Only (DMO) simulations have lower computational and time complexity compared to Hydrodynamical (HYDRO) simulations, although they cannot be used for comparison with observations for the same reason. A prediction tool to assign stellar masses to dark matter halos of DMO simulations would provide a more efficient testing of new dark matter models. The established relationship between halo mass and stellar mass connection lacks accuracy for nearby satellites due to the environmental influence of the host halo, such as gravitational tidal stripping and ram pressure stripping. This project intends to introduce a simple algorithm to assign stellar populations to nearby satellites in DMO simulations, based on relations reliant on more stable properties than Halo mass. To achieve this, we examine differences between DMO and HYDRO simulations, as well as the dependence of the probability distribution and stellar mass of luminous satellites at z = 0 on a more stable 'peak' parameter. We then obtain distinct relations constructing a straightforward map to obtain stellar mass functions and radial distribution of luminous satellites. This algorithm's simplicity initially led to an overestimation of bright halos in large simulations, prompting additional corrections for galaxies with host halo masses of ~ 10¹² M⊙ . The final results indicate that the stellar mass functions and radial distributions directly obtained from HYDRO simulations align well with those predicted solely from DMO simulations using our map, offering cost and complexity reduction, facilitating the goal for more efficient testing of dark matter models.    

Measuring Stellar Angular Diameter Through Optical Asteroid Occultation

The resolution of a point source can be limited in the deep sky. Asteroid occultation provided another approach for measuring stellar angular diameter. An asteroid occultation is when an asteroid passes in front of a star. This work is a continuation of W. Benbow et al. (Nature, 2019), which demonstrates the accessibility of angular diameter measurements to imaging atmospheric Cherenkov telescopes (IACTs) through asteroid occultations events. The data used for this project was observed with the IACT array VERITAS (Very Energetic Radiation Imaging Telescope Array System) located near Tucson, Arizona. VERITAS is designed to observe gamma-ray, specialized with a large collecting mirror (>100 m²) and a fast-timing system (500 MHz bandwidth). VERITAS, with different specifications compared to other optical telescopes and optical observation updates, allows us to observe asteroid occultations. Each occultation observed and detected by VERITAS will be fitted to a diffraction pattern to determine the size of the occulted star. Asymmetries between the diffraction patterns of the stellar ingress and egress across the occulting asteroid may provide additional information on the shape of the asteroid. Simulated asteroid occultation data have also been analyzed to test the reliability of the method. The primary star and asteroid presented here are TYC 2924-02100-1 and Egeria respectively. The resulting angular diameter will contribute to the angular diameter catalog from VERITAS to support future studies.   

Neutron Star Glitch - Revisiting Starquake Model

Neutron stars are observed to have sudden jumps in angular velocity, known as glitches, where they are supposed to only simply spin down over time. The starquake model [1] is one of the proposals attempting to explain this glitch by connecting it with the breaking of the neutron star's crust. This project revisits the starquake model by considering neutron stars with more updated microphysics, from which we search for connections with neutron star observables. Expanding on previous studies, in this talk we present new starquake models by considering realistic nuclear EOS [2], detailed neutron star profiles, and updated shear modulus of nuclear crust. With data from 75 observed glitch events, we were able to identify events that can be associated with the starquake model.  We further examine the dependence of the startquake model on some model parameters. This project suggests an alternative way to derive neutron star observables through neutron star glitch events.

[1] G. Baym and D. Pines, Annals of Physics 66, 816 (1971).

[2] A. F. Fantina, N. Chamel, J. M. Pearson, and S. Goriely, 559, A128 (2013).   

Quantum Effects in the Interior of a Black Hole

The interiors of black holes provide a convenient space for exploring quantum effects because the curvature of spacetime becomes infinite at the central singularity.  We consider a massless, minimally coupled, scalar quantum field φ, which can be thought of as a simple model for the electromagnetic field. We work with eternal black holes in two dimensions and consider two important states: the Boulware, or vacuum state, and the Unruh state, which describes black hole evaporation. To analyze the quantum effects, we calculate the expectation value of the square of the field <φ²>,  and the stress-energy tensor of the field.  We analyze the behavior of these quantities in the region between the event horizon and the singularity. We also calculate these quantities for a black hole that forms from the collapse of a massless shell of radiation.   

CWISE J105512.11+544328.3: A Nearby Y Dwarf Spectroscopically Confirmed with Keck/NIRES

Y dwarfs, the coolest known spectral class of brown dwarfs, overlap in mass and temperature with giant exoplanets, providing unique laboratories for studying low-temperature atmospheres. However, only a fraction of Y dwarf candidates have been spectroscopically confirmed. We present Keck/NIRES near-infrared spectroscopy of the nearby (d ~ 6-8 pc) brown dwarf CWISE J105512.11+544328.3.  Although its near-infrared spectrum aligns best with the Y0 standard in the J-band, no standard matches well across the full YJHK wavelength range. The CWISE J105512.11+544328.3 NH₃-H = 0.427 ± 0.0012 and CH₄-J = 0.0385 ± 0.0007 absorption indices and absolute Spitzer [4.5] magnitude of 15.18 ± 0.22 are also indicative of an early Y dwarf rather than a late T dwarf. CWISE J105512.11+544328.3 additionally exhibits the bluest Spitzer [3.6]–[4.5] color among all spectroscopically confirmed Y dwarfs. Despite this anomalously blue Spitzer color given its low luminosity, CWISE J105512.11+544328.3 does not show other clear kinematic or spectral indications of low metallicity. Atmospheric model comparisons yield a log(g) ≤ 4.5 and T_eff ≈ 500 ± 150 K for this source. We classify CWISE J105512.11+544328.3 as a Y0 (pec) dwarf, adding to the remarkable diversity of the Y-type population. JWST spectroscopy would be crucial to understanding the origin of this Y dwarf's unusual preference for low-gravity models and blue 3-5 μm color.