Type Ia supernovae, standardizable candles, and gravity

Abstract

Type Ia supernovae (SNe Ia) are generally accepted to act as standardisable candles, and their use in cosmology led to the first confirmation of the as yet unexplained accelerated cosmic expansion. Many of the theoretical models to explain the cosmic acceleration assume modifications to Einsteinian General Relativity which accelerate the expansion, but the question of whether such modifications also affect the ability of SNe Ia to be standardisable candles has rarely been addressed. This paper is an attempt to answer this question. For this we adopt a semi-analytical model to calculate SNe Ia light curves in non-standard gravity. We use this model to show that the average rescaled intrinsic peak luminosity -a quantity that is assumed to be constant with redshift in standard analyses of Type Ia supernova (SN Ia) cosmology data -depends on the strength of gravity in the supernova's local environment because the latter determines the Chandrasekhar mass -the mass of the SN Ia's white dwarf progenitor right before the explosion. This means that SNe Ia are no longer standardisable candles in scenarios where the strength of gravity evolves over time, and therefore the cosmology implied by the existing SN Ia data will be different when analysed in the context of such models. As an example, we show that the observational SN Ia cosmology data can be fitted with both a model where (ΩM, ΩΛ) = (0.62, 0.38) and Newton's constant G varies as G(z) = G0(1 + z) −1/4 and the standard model where (ΩM, ΩΛ) = (0.3, 0.7) and G is constant, when the Universe is assumed to be flat. I. INTRODUCTIONCosmology observations from Type Ia supernovae (SNe Ia) gave the first evidence for a late-time acceleration in the expansion of the Universe [1,2]. A Type Ia supernova (SN Ia) is the cataclysmic explosion of a white dwarf star that occurs when the white dwarf accretes enough mass from a binary partner for the material in its core to undergo runaway thermonuclear fusion. SNe Ia are thought to act as standardisable candles because of an observed relationship between a SN Ia's peak brightness and how rapidly this peak brightness is achieved and subsequently left behind [3] (the so-called width-luminosity relation, or WLR). After standardisation procedures, which are often at least partially based on the WLR, are applied, any remaining difference in the peak brightnesses of the two SNe Ia should be due to a difference in distance to the observer. Thus the relative distances between SNe Ia can be measured, and along with measurements of their redshifts can be used to infer the details of the expansion of the Universe through the construction of the distance-redshift relation.After the late-time acceleration of the expansion of the Universe was discovered, Einstein's idea of a small, positive cosmological constant Λ was revived and established as the leading candidate for the acceleration's origin. However, the idea of Λ as the cause of cosmic acceleration is not without theoretical difficulties, such as the cosmological constant fine-tuning and coin...

Local resolution of the Hubble tension: The impact of screened fifth forces on the cosmic distance ladder

“…for G SN the effective Newton's constant of the SN in question. We set C = 1.46 from a linear fit to [151] fig. 7 (left).…”

Limitations on Standard Sirens tests of gravity from screening

“…G s is the local gravitational constant at the source, m N is the nucleon mass and all quantities are defined in the Appendix of Ref. [54]. Here, we simply note that…”

Constraints on Newton’s constant from cosmological observations

“…Newton's constant influences the light curve of SNIa via the Chandrasekhar mass M Ch ∝ G −3/2 mainly. If the Newton's constant G increases, the peak luminosity of light curve L raises and its width drops [11]. In this section, we introduce a new parameter λ 1 = L/L 0 to quantify the deviation of L from L 0 resulting from the deviation of G from G N .…”

“…In the laboratory, cold atom interferometry is also used to detect Newton's constant [1]. In cosmology, the cosmic microwave background (CMB) [2][3][4][5][6][7], big bang nucleosynthesis (BBN) [8][9][10], type Ia supernovae (SNIa) [11][12][13][14][15] and gravitational waves [14,16] can provide different measurements of Newton's constant at corresponding epochs of our universe. Obviously, there is a problem whether Newton's constant is always a constant really or not.…”