Institute of Astronomy

Gaia and microlensing - an opportunity for Black Holes search

SpeakerTalk DateTalk Series
Kris Rybicki (Warsaw)28 March 2018Institute of Astronomy Seminars


It is expected that there are about 500 milions stellar black holes floating in our Galaxy. Not
more than 30 are known, and only in binary systems. Even though there are some
candidates for single ones, none of them was confirmed yet. Partially it comes from the fact
that they are very hard to detect, but detecting multiple such objects would vastly increase
our understanding of the latest stages of stellar evolution and the Galaxy structure. The
perfect tool for measuring the mass of unseen objects is microlensing, yet the very special
circumstances are needed to measure the mass of the lens, which is the one and only
parameter which allow us to judge weather the object is a single black hole or not.

Gaia satellite will give an opportunity to look at microlensing events from the different
angle. With its exquisite astrometry, it may be possible to measure not only the
magnification of the source, but also its apparent displacement during the event, which
provides additional information about the lens properties.

We consider a possibility of simultaneous observation of the microlensing event by the Gaia
mission from space and the OGLE project from the ground. Basing on the example of
OGLE-ULENS-PAR-02, which is likely a black hole, we predict that for bright events with
clear parallax signal and Gaia astrometry available for them, it will be possible to determine
the mass of the 10 M⊙ lens with accuracy between few to 15%. We estimate that the rate of
astrometric microlensing events caused by the stellar-origin black holes is ≈ 4 × 10−7 yr−1,
which implies, that after 5 years of Gaia operation and ≈ 5 × 10^6 bright sources in Gaia, it
will be possible to identify few such events in its final catalogues. The talk is based on our
recent paper: Rybicki et al. 2018 (2018MNRAS.476.2013R).


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