Day 1619

Tuesday.

1908.08951

Probing the theory of gravity with gravitational lensing of gravitational waves and galaxy surveys

Mukherjee, Wandelt, Silk

The cross-correlation of gravitational wave events with upcoming galaxy surveys probe theories of gravity in a fundamentally new way, with the potential to reveal clues as to the nature of dark energy and dark matter. We find that within 10 years, the combination of the Advanced-LIGO and VIRGO detector network with planned galaxy surveys can detect weak gravitational lensing of gravitational waves in the low redshift Universe ($z<0.5$). With the next generation gravitational wave experiments such as Voyager, LISA, Cosmic-Explorer and Einstein Telescope, we can extend the range of this probe up to a redshift of $z\sim 20$. This new probe will test the theory of gravity using both gravitational wave propagation through spacetime and also the effect of cosmic structures on gravitational waves, opening up a new observational window for cosmology and fundamental physics.

1908.09084

A future percent-level measurement of the Hubble expansion at redshift 0.8 with advanced LIGO

Farr, et al

Simultaneous measurements of distance and redshift can be used to constrain the expansion history of the universe and associated cosmological parameters. Merging binary black hole (BBH) systems are standard sirens---their gravitational waveform provides direct information about the luminosity distance to the source. Because gravity is scale-free, there is a perfect degeneracy between the source masses and redshift; some non-gravitational information is necessary to break the degeneracy and determine the redshift of the source. Here we suggest that the pair instability supernova (PISN) process, thought to be the source of the observed upper-limit on the black hole (BH) mass in merging BBH systems at $\sim 45 \, M_\odot$, imprints a mass scale in the population of BBH mergers and permits a measurement of the redshift-luminosity-distance relation with these sources. We simulate five years of BBH detections in the Advanced LIGO and Virgo detectors with realistic assumptions about the BBH merger rate, a mass distribution incorporating a smooth PISN cutoff, and measurement uncertainty. We show that after one year of operation at design sensitivity (circa 2021) the BBH population can constrain $H(z)$ to $6.1\%$ at a pivot redshift $z \simeq 0.8$. After five years (circa 2025) the constraint improves to $2.9\%$. This measurement relies only on general relativity and the presence of a cutoff mass scale that is approximately fixed or calibrated across cosmic time; it is independent of any distance ladder or cosmological model. Observations by future ``third-generation'' gravitational wave detectors, which can see BBH mergers throughout the universe, would permit sub-percent cosmographical measurements to $z \gtrsim 4$ within one month of observation.

1908.09339

The Spaceline:  practical space elevator alternative achievable with current technology

Penoyre, Sandford

Perhaps the biggest hurdle to mankind's expansion throughout the Solar System is the prohibitive cost of escaping Earth's gravitational pull. In its many forms, the space-elevator provides a way to circumvent this cost, allowing payloads to traverse along a cable extending from Earth to orbit. However, modern materials are not strong enough to build a cable capable of supporting its own weight. In this work we present an alternative to the classic space elevator, within reach of modern technology: The Spaceline. By extending a line, anchored on the moon, to deep within Earth's gravity well, we can construct a stable, traversable cable allowing free movement from the vicinity of Earth to the Moon's surface. With current materials, it is feasible to build a cable extending to close to the height of geostationary orbit, allowing easy traversal and construction between the Earth and the Moon.

1908.09613

Comparison of the deep atmospheric dynamics of Jupiter and Saturn in light of the Juno and Cassini gravity measurements

Kaspi, et al

The nature and structure of the observed east-west flows on Jupiter and Saturn has been one of the longest-lasting mysteries in planetary science. This mystery has been recently unraveled due to the accurate gravity measurements provided by the Juno mission to Jupiter and the Grand Finale of the Cassini mission to Saturn. These two experiments, which coincidentally happened around the same time, allowed determination of the vertical and meridional profiles of the zonal flows on both planets. This paper reviews the topic of zonal jets on the gas giants in light of the new data from these two experiments. The gravity measurements not only allow the depth of the jets to be constrained, yielding the inference that the jets extend roughly 3000 and 9000 km below the observed clouds on Jupiter and Saturn, respectively, but also provide insights into the mechanisms controlling these zonal flows. Specifically, for both planets this depth corresponds to the depth where electrical conductivity is within an order of magnitude of 1 S/m, implying that the magnetic field likely plays a key role in damping the zonal flows.

1908.09639

Systematics in the ALMA proposal review rankings

Carpenter

The results from the ALMA proposal peer review process in Cycles 0-6 are analyzed to identify any systematics in the scientific rankings that may signify bias. Proposal rankings are analyzed with respect to the experience level of a Principal Investigator (PI) in submitting ALMA proposals, regional affiliation (Chile, East Asia, Europe, North America, or Other), and gender. The analysis was conducted for both the Stage 1 rankings, which are based on the preliminary scores from the reviewers, and the Stage 2 rankings, which are based on the final scores from the reviewers after participating in a face-to-face panel discussion. Analysis of the Stage 1 results shows that PIs who submit an ALMA proposal in multiple cycles have systematically better proposal ranks than PIs who have submitted proposals for the first time. In terms of regional affiliation, PIs from Europe and North America have better Stage 1 rankings than PIs from Chile and East Asia. Consistent with Lonsdale et al. (2016), proposals led by men have better Stage 1 rankings than women when averaged over all cycles. This trend was most noticeably present in Cycle 3, but no discernible differences in the Stage 1 rankings are present in recent cycles. Nonetheless, in each cycle to date, women have had a lower proposal acceptance rate than men even after differences in demographics are considered. Comparison of the Stage 1 and Stage 2 rankings reveal no significant changes in the distribution of proposal ranks by experience level, regional affiliation, or gender as a result of the panel discussions, although the proposal ranks for East Asian PIs show a marginally significant improvement from Stage 1 to Stage 2 when averaged over all cycles. Thus any systematics in the proposal rankings are introduced primarily in the Stage 1 process and not from the face-to-face discussions.