Constraints on Earth-mass primordial black holes from OGLE 5-year microlensing events

By Hiroko Niikura, M. Takada, Shuichiro Yokoyama, T. Sumi, Shogo Masaki. Physical Review D, 2019

295 citations recorded by the source corpus.

We constrain the abundance of primordial black holes (PBH) using 2622 microlensing events obtained from 5-years observations of stars in the Galactic bulge by the Optical Gravitational Lensing Experiment (OGLE). The majority of microlensing events display a single or at least continuous population that has a peak around the light curve timescale $t_{\rm E}\simeq 20~{\rm days}$ and a wide distribution over the range $t_{\rm E}\simeq [1, 300]~{\rm days}$, while the data also indicates a second population of 6 ultrashort-timescale events in $t_{\rm E}\simeq [0.1,0.3]~{\rm days}$, which are advocated to be due to free-floating planets. We confirm that the main population of OGLE events can be well modeled by microlensing due to brown dwarfs, main sequence stars and stellar remnants (white dwarfs and neutron stars) in the standard Galactic bulge and disk models for their spatial and velocity distributions. Using the dark matter (DM) model for the Milky Way (MW) halo relative to the Galactic bulge/disk models, we obtain the tightest upper bound on the PBH abundance in the mass range $M_{\rm PBH}\simeq[10^{-6},10^{-3}]M_\odot$ (Earth-Jupiter mass range), if we employ null hypothesis that the OGLE data does not contain any PBH microlensing event. More interestingly, we also show that Earth-mass PBHs can well reproduce the 6 ultrashort-timescale events, without the need of free-floating planets, if the mass fraction of PBH to DM is at a per cent level, which is consistent with other constraints such as the microlensing search for Andromeda galaxy (M31) and the longer timescale OGLE events. Our result gives a hint of PBH existence, and can be confirmed or falsified by microlensing search for stars in M31, because M31 is towards the MW halo direction and should therefore contain a much less number of free-floating planets, even if exist, than the direction to the MW center.

Subfields: Astronomy and Astrophysics, Atomic and Molecular Physics, and Optics

View Paper: https://www.semanticscholar.org/paper/ac73790992bb05739ab6d2301711fc93b96f3660

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Citations in the corpus

Primordial black holes and gravitational waves from parametric amplification of curvature perturbations (2019, background): “the extragalactic gamma ray background (EG [12]), galactic 511 keV line (e+ [87{89]), white dwarf explosions (WD [90], see [91] for criticism), gravitational lensing events (HSC [92], EROS [93], OGLE [94]), dynamical eects (SEGUE [95]), and cosmic microwave background (CMB [96]). where is the Newton”
Primordial black holes confront LIGO/Virgo data: current situation (2020, methodology): “The lensing bounds include those from supernovae [91], the MACHO and EROS experiments [92, 93], ICARUS [94] and radio observations, such as [95] and [96] (Ogle).”
Two populations of LIGO-Virgo black holes (2020, methodology): “Other shaded regions in figure 5 show the constraints from microlensing results from EROS [79], OGLE [80], and MACHO [81], lensing of type Ia supernovae (SNe) [82], survival of a stars in dwarf galaxies (Seg I and Eri II) [83, 84], distribution of wide binaries (WB) [85], Lyman-α forest data [86, 87”
Challenges and opportunities of gravitational-wave searches at MHz to GHz frequencies (2020, background): “In particular, the planetary-mass range, in which recent detections of star and quasar microlensing events (Niikura et al. 2019; Hawkins 2020; Bhatiani et al. 2019) suggest a dark matter fraction made of primordial BHs of fPBH 0:01, could be probed in a novel way.”
Revisiting constraints on asteroid-mass primordial black holes as dark matter candidates (2019, background): “Here the main challenge is the “background” of real microlensing events from astrophysical compact objects [94]; for example, the WFIRST Galactic Bulge survey is expected to yield ∼ 5 × 104 astrophysical microlensing events [95].”
Gravitational wave constraints on the primordial black hole dominated early universe (2020, background): “This kind of long-lived PBHs are attracting a lot of attention as potential candidates for explaining dark matter [7, 8], the binary black holes responsible for the LIGO/VIRGO gravitational waves (GW) detection [9–11], the seeds of supermassive black holes [12, 13], the microlensing events by planet”
Primordial black holes as dark matter candidates (2021, methodology): “also claim that data from the five-year OGLE survey of ML events in the Galactic bulge [124]”
Primordial Black Holes as Dark Matter: Recent Developments (2020, methodology): “also claim that data from the five-year OGLE survey of 2622 microlensing events in the Galactic bulge [166] have revealed six ultra-short ones attributable to planetary-mass objects between 10−6 and 10−4M .”