Limits on stellar-mass compact objects as dark matter from gravitational lensing of type Ia supernovae

Abstract: The nature of dark matter (DM) remains unknown despite very precise knowledge of its abundance in the universe. An alternative to new elementary particles postulates DM as made of macroscopic compact halo objects (MACHO) such as black holes formed in the very early universe. Stellar-mass primordial black holes (PBHs) are subject to less robust constraints than other mass ranges and might be connected to gravitational-wave signals detected by the Laser Interferometer Gravitational-Wave Observatory (LIGO). New methods are therefore necessary to constrain the viability of compact objects as a DM candidate. Here we report bounds on the abundance of compact objects from gravitational lensing of type Ia supernovae (SNe). Current SNe datasets constrain compact objects to represent less than 35.2% (Joint Lightcurve Analisis) and 37.2% (Union 2.1) of the total matter content in the universe, at 95% confidence-level. The results are valid for masses larger than $\sim 0.01M_\odot$ (solar-masses), limited by the size SNe relative to the lens Einstein radius. We demonstrate the mass range of the constraints by computing magnification probabilities for realistic SNe sizes and different values of the PBH mass. Our bounds are sensitive to the total abundance of compact objects with $M \lesssim 0.01M_\odot$ and complementary to other observational tests. These results are robust against cosmological parameters, outlier rejection, correlated noise and selection bias. PBHs and other MACHOs are therefore ruled out as the dominant form of DM for objects associated to LIGO gravitational wave detections. These bounds constrain early-universe models that predict stellar-mass PBH production and strengthen the case for lighter forms of DM, including new elementary particles.

• The paper constrains stellar-mass primordial black holes as dark matter by analyzing gravitational lensing of Type Ia supernovae and limiting their contribution to under 37% of total matter.
• It utilizes realistic magnification probability models with JLA and Union 2.1 datasets to assess the impact of varied lens masses and supernova sizes.
• The study challenges LIGO-scale PBHs as dominant dark matter candidates, reinforcing the need to explore lighter dark matter particles.

Limits on Stellar-Mass Compact Objects as Dark Matter from Gravitational Lensing of Type Ia Supernovae

The paper investigates constraints on the role of stellar-mass compact objects, specifically primordial black holes (PBHs), as candidates for dark matter (DM) by examining their gravitational lensing effects on Type Ia supernovae (SNe). This research is set against the backdrop of cosmological puzzles regarding the true nature of DM, which is yet unidentified despite its critical role in cosmic structure formation.

Primordial Black Holes are macro-scale, non-relativistic entities formed in the early universe. Unlike elementary particles, PBHs do not exhibit interactions detectable by typical high-energy physics experiments. Importantly, the PBH mass range from 10 to 100 solar masses ($M_\odot$) corresponds intriguingly to the masses of black holes detected by LIGO, prompting reevaluation of PBHs as potential dark matter constituents.

Through analyzing current SNe datasets, notably the Joint Lightcurve Analyses (JLA) and Union 2.1 samples, the paper constrains the possibility of compact objects like PBHs forming a significant portion of the universe's matter. Specifically, the study finds that such objects can constitute no more than 35.2% and 37.2% of total matter as per JLA and Union 2.1, respectively, at a 95% confidence level. These results apply to masses exceeding approximately 0.01 $M_\odot$, considering the relative scale of supernovae compared to the lens Einstein radius.

The methodology involves computing magnification probabilities using realistic models of supernova sizes and varied PBH masses. The analysis indicates that the results obtained are robust against a multitude of factors including cosmological parameter variations, rejection of data outliers, as well as correlated observational noise and biases in data selection.

Notably, PBHs within the stellar mass range commonly associated with LIGO detections, and other machos are effectively ruled out as predominant dark matter candidates. This conclusion also places constraints on theoretical early-universe models predicting the production of such stellar-mass PBHs, thereby reinforcing models that suggest lighter dark matter candidates like new elementary particles.

The paper contributes to the growing body of work refuting PBHs as a singular solution to the dark matter problem, corroborating constraints from other methodologies such as microlensing surveys and cosmic microwave background studies. The lensing of type Ia supernovae presents a significant observational test, synergizing with advancements in other analytic methods to refine the constraints on dark matter's nature and distribution.

In conclusion, this research fortifies the theoretical landscape by narrowing down viable candidates for dark matter, simultaneously spotlighting the efficacy of leveraging cosmological phenomena like gravitational lensing in distinguishing between competing theories. Future investigations might further focus on integrating broader swathes of observational data to tighten constraints or explore novel mass ranges and distributions for primordial black holes as part of the diverse dark matter puzzle.