Discrepancy between Values of the Hubble Constant Obtained by Different Methods

AbstractIn the early 2030s, after the end of operations for the epochal Hubble Space Telescope and the long-anticipated James Webb Space Telescope, astrophysics will lose access to a general purpose high-spatial resolution space observatory to cover the UV–optical–NIR wavelength range with a variety of imaging bandpasses and high-multiplexing mid-resolution spectroscopy. This will greatly impact astrophysical “discovery space” at visible wavelengths, in stark contrast to progress at most other wavelengths enabled by groundbreaking new facilities between 2010 and 2030. This capability gap will foreseeably limit progress in a number of fundamental research directions anticipated to be pressing in the 2030’s and beyond such as: What are the histories of star formation and cosmic element production in nearby galaxies? What can we learn about the nature of dark matter from dwarf galaxies? What is the local value of the Hubble Constant? A multi-purpose optical–NIR imaging and multiplexed spectroscopy Workhorse Camera (HWC) onboard NASA’s 4m-class Habitable Exoplanet Observatory (HabEx) space mission would provide access to these required data. HabEx is currently under study by NASA for the US Decadal Survey on Astronomy and Astrophysics 2020, and if selected would launch around 2035. Aside from its direct imaging of Earth-like exoplanets, it will have a general-observatory complement of instrumentation. The versatile Workhorse Camera will provide imaging and R$\sim $ ∼ 1000 spectroscopy from 370nm to 1800nm, diffraction-limited over the whole wavelength range, with simultaneous observations of the visible and NIR. Spectroscopic multiplexing will be achieved through microshutter arrays. All necessary HWC technology is already at Technology Readiness Level 5, hence technological risks are low. HWC has a rough-order-of-magnitude (ROM) cost of 300 M€, and could be European-funded within the cost envelope of an ESA S-class mission in the Voyage 2050 program, with matching funds by national funding agencies to construct HWC by a European instrument consortium. This White Paper is intended to put a European HabEx Workhorse Camera into ESA’s considerations. If ESA shares the wide interest and if HabEx were to be selected by NASA, there would be ample time to identify interested institutes for a European instrument consortium, including MPIA, to design, finance, and build the HabEx Workhorse Camera.

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China’s first step towards probing the expanding universe and the nature of gravity using a space borne gravitational wave antenna

Communications Physics ◽

10.1038/s42005-021-00529-z ◽

2021 ◽

Vol 4 (1) ◽

Author(s):

Keyword(s):

Gravitational Wave ◽

Hubble Constant ◽

Gravitational Wave Detector ◽

Expanding Universe ◽

Satellite Mission ◽

Gravitational Wave Detection ◽

Wave Detection ◽

Wave Detector ◽

Wave Antenna ◽

Gravitational Wave Antenna

AbstractIn this perspective, we outline that a space borne gravitational wave detector network combining LISA and Taiji can be used to measure the Hubble constant with an uncertainty less than 0.5% in ten years, compared with the network of the ground based gravitational wave detectors which can measure the Hubble constant within a 2% uncertainty in the next five years by the standard siren method. Taiji is a Chinese space borne gravitational wave detection mission planned for launch in the early 2030 s. The pilot satellite mission Taiji-1 has been launched in August 2019 to verify the feasibility of Taiji. The results of a few technologies tested on Taiji-1 are presented in this paper.

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Does the Cosmological Expansion Change Local Dynamics?

Symmetry ◽

10.3390/sym13081417 ◽

2021 ◽

Vol 13 (8) ◽

pp. 1417

Author(s):

Marcelo Schiffer

Keyword(s):

Dark Matter ◽

Modified Gravity ◽

Hubble Constant ◽

Matter Content ◽

Matter Distribution ◽

Present Value ◽

Field Equations ◽

Local Dynamics ◽

Cosmological Expansion ◽

Modified Gravity Theories

It is a well-known fact that the Newtonian description of dynamics within Galaxies for its known matter content is in disagreement with the observations as the acceleration approaches a0≈1.2×10−10 m/s2 (slighter larger for clusters). Both the Dark Matter scenario and Modified Gravity Theories (MGT) fail to explain the existence of such an acceleration scale. Motivated by the closeness of the acceleration scale and the Hubble constant cH0≈10−9 h m/s2, we are led to analyze whether this coincidence might have a Cosmological origin for scalar-tensor and spinor-tensor theories by performing detailed calculations for perturbations that represent the local matter distribution on the top of the cosmological background. Then, we solve the field equations for these perturbations in a power series in the present value of the Hubble constant. As we shall see, for both theories, the power expansion contains only even powers in the Hubble constant, a fact that renders the cosmological expansion irrelevant for the local dynamics.

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The effects of peculiar velocities in SN Ia environments on the local H0 measurement

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3456 ◽

2020 ◽

Vol 500 (3) ◽

pp. 3728-3742

Author(s):

Thomas M Sedgwick ◽

Chris A Collins ◽

Ivan K Baldry ◽

Philip A James

Keyword(s):

Hubble Constant ◽

Density Parameter ◽

Host Galaxies ◽

Peculiar Velocities ◽

Standard Candle ◽

Modern Cosmology ◽

Type Ia ◽

The Difference ◽

Ia Supernovae ◽

Distance Indicators

ABSTRACT The discrepancy between estimates of the Hubble constant (H0) measured from local (z ≲ 0.1) scales and from scales of the sound horizon is a crucial problem in modern cosmology. Peculiar velocities (vpec) of standard candle distance indicators can systematically affect local H0 measurements. We here use 2MRS galaxies to measure the local galaxy density field, finding a notable z < 0.05 underdensity in the SGC-6dFGS region of 27 ± 2 per cent. However, no strong evidence for a ‘Local Void’ pertaining to the full 2MRS sky coverage is found. Galaxy densities are used to measure a density parameter, Δϕ+−, which we introduce as a proxy for vpec that quantifies density gradients along a supernova (SN) line of sight. Δϕ+− is found to correlate with local H0 estimates from 88 Pantheon Type Ia supernovae (SNe Ia; 0.02 < z < 0.05). Density structures on scales of ∼50 Mpc are found to correlate strongest with H0 estimates in both the observational data and in mock data from the MDPL2-Galacticus simulation. Using trends of H0 with Δϕ+−, we can correct for the effects of density structure on local H0 estimates, even in the presence of biased vpec. However, the difference in the inferred H0 estimate with and without the peculiar velocity correction is limited to < 0.1 per cent. We conclude that accounting for environmentally induced peculiar velocities of SN Ia host galaxies does not resolve the tension between local and CMB-derived H0 estimates.

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Varying Physical Constants, Astrometric Anomalies, Redshift and Hubble Units

Galaxies ◽

10.3390/galaxies7020055 ◽

2019 ◽

Vol 7 (2) ◽

pp. 55 ◽

Cited By ~ 3

Author(s):

Rajendra P. Gupta

Keyword(s):

Hubble Constant ◽

Astronomical Unit ◽

Lunar Laser Ranging ◽

Current Time ◽

Physical Constants ◽

Lunar Laser ◽

Walker Metric ◽

The One ◽

Two Parameters ◽

Secular Increase

We have developed a cosmological model by allowing the speed of light c, gravitational constant G and cosmological constant Λ in the Einstein filed equation to vary in time, and solved them for Robertson-Walker metric. Assuming the universe is flat and matter dominant at present, we obtain a simple model that can fit the supernovae 1a data with a single parameter almost as well as the standard ΛCDM model with two parameters, and which has the predictive capability superior to the latter. The model, together with the null results for the variation of G from the analysis of lunar laser ranging data determines that at the current time G and c both increase as dG/dt = 5.4GH0 and dc/dt = 1.8cH0 with H0 as the Hubble constant, and Λ decreases as dΛ/dt = −1.2ΛH0. This variation of G and c is all what is needed to account for the Pioneer anomaly, the anomalous secular increase of the moon eccentricity, and the anomalous secular increase of the astronomical unit. We also show that the Planck’s constant ħ increases as dħ/dt = 1.8ħH0 and the ratio D of any Hubble unit to the corresponding Planck unit increases as dD/dt = 1.5DH0. We have shown that it is essential to consider the variation of all the physical constants that may be involved directly or indirectly in a measurement rather than only the one whose variation is of interest.

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Ultralong-period Cepheids: a possible primary distance indicator?

Proceedings of the International Astronomical Union ◽

10.1017/s1743921312021552 ◽

2012 ◽

Vol 8 (S289) ◽

pp. 282-286 ◽

Cited By ~ 2

Author(s):

G. Fiorentino ◽

F. Annibali ◽

G. Clementini ◽

R. Contreras Ramos ◽

M. Marconi ◽

...

Keyword(s):

Spiral Galaxies ◽

Hubble Space Telescope ◽

Hubble Constant ◽

Variable Stars ◽

Evolutionary Status ◽

Stellar Systems ◽

Classical Cepheids ◽

Type Ia ◽

Distance Indicator ◽

Crucial Test

AbstractWe present a project that aims to provide a complete theoretical and observational framework for an as yet unexplored class of variable stars, the ultralong-period Cepheids (P longer than 80–100 days). Given their very high luminosities (MV up to −7 mag), with the Hubble Space Telescope we will be able to observe them easily in stellar systems located at large distances (~ 100 Mpc). This limit will be further increased, out to the Hubble flow (~ 350 Mpc), using future ground-based facilities such as the European Extremely Large Telescope. The nature of their pulsation is as yet unclear, as is their evolutionary status, which seems different from the central helium-burning phase generally associated with classical Cepheids. These objects have been found to cover a very large metallicity range, from [Fe/H] ~ −2 dex to solar values, and they are located in heterogeneous stellar systems, from dwarf to spiral galaxies. Once completely characterized, they could provide a crucial test, since they have been found in all Type Ia supernova host spiral galaxies that have been monitored for variability over long periods and that currently offer sound constraints on the estimated value of the Hubble constant.

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