Experimental Limits on Primordial Black Hole Dark Matter from the First Two Years of Kepler Data

TL;DR

The paper tests whether primordial black holes can constitute all dark matter in the mass window $2\times 10^{-9}M_\odot$ to $10^{-7}M_\odot$ by analyzing two years of Kepler photometry for microlensing signatures. It develops a rigorous background handling framework to distinguish true microlensing from variable stars, flares, and moving objects, and uses a detailed Monte Carlo efficiency calculation under a halo model to convert non-detections into limits. No PBH microlensing events are found, yielding 95% CL limits that rule out PBHs in the target mass range as the dominant DM component and close a full order of magnitude of previously allowed mass space. The results demonstrate Kepler's unique sensitivity to ultra-low-mass compact objects and set the stage for future surveys and analyses to comprehensively probe the PBH dark matter hypothesis.

Abstract

We present the analysis on our new limits of the dark matter (DM) halo consisting of primordial black holes (PBHs) or massive compact halo objects (MACHOs). We present a search of the first two years of publicly available Kepler mission data for potential signatures of gravitational microlensing caused by these objects, as well as an extensive analysis of the astrophysical sources of background error. These include variable stars, flare events, and comets or asteroids which are moving through the Kepler field. We discuss the potential of detecting comets using the Kepler lightcurves, presenting measurements of two known comets and one unidentified object, most likely an asteroid or comet. After removing the background events with statistical cuts, we find no microlensing candidates. We therefore present our Monte Carlo efficiency calculation in order to constrain the PBH DM with masses in the range of 2 x 10^-9 solar masses to 10^-7 solar masses. We find that PBHs in this mass range cannot make up the entirety of the DM, thus closing a full order of magnitude in the allowed mass range for PBH DM.

Figures (6)

• Figure 1: Examples of bumps in Kepler lightcurves caused by stellar flares. The Kepler source star IDs are shown in the upper left corners, the solid blue line is the rather poor fit to the microlensing shape, and the solid green line is a (better) fit to flare event. The top panel shows a medium amplitude flare event, the middle panel shows a high amplitude event, and the bottom panel shows a very low amplitude flare.
• Figure 2: Examples of bumps in Kepler lightcurves. The top two panels show very short duration events that can be well fit with either microlelensing or flare shapes. The bottom panel is an event of unknown origin that is a poor fit to the microlensing shape. The Kepler source star IDs are shown as are fits to microlensing (solid blue line) and flare (solid green line) shapes.
• Figure 3: Examples of bumps in Kepler lightcurves caused by comet C/2006 Q1 (McNaught) during quarter 5. The Kepler source star IDs are shown and the solid blue line is a fit microlensing model.
• Figure 4: Examples of bumps in Kepler lightcurves caused by comets during quarter 9. The upper panel is from C/2007 Q3 (see Table \ref{['tab:comets']}) and the lower panel from an unidentified comet or asteroid. The Kepler source star IDs are shown as are fits to a microlensing shape.
• Figure 5: Part (a) shows right ascension (RA) and declination (dec) of bumps caused by comet C/2006 Q1 as it passed through the Kepler field during quarter 5. Part (b) shows the angular distance moved by the comet vs. Kepler time. Part (c) shows RA and dec of two separate objects moving through the field during quarter 9, and part (d) shows the distance moved by these two objects. The constant slopes in parts (b) and (d) imply a constant angular speed. The point circled is a bump that did not pass all the cuts but is shown here so there are more than two points on the line.