462 research outputs found
A re-analysis of the isolated black hole candidate OGLE-2011-BLG-0462/MOA-2011-BLG-191
There are expected to be isolated black holes (BHs) in the Milky
Way. OGLE-2011-BLG-0462/MOA-2011-BLG-191 (OB110462) is the only such BH with a
mass measurement to date. However, its mass is disputed: Lam et al. (2022a,b)
measured a lower mass of , while Sahu et al. (2022);
Mr\'{o}z et al. (2022) measured a higher mass of . We
re-analyze OB110462, including new data from the Hubble Space Telescope (HST)
and re-reduced Optical Gravitational Lensing Experiment (OGLE) photometry. We
also re-reduce and re-analyze the HST dataset with newly available software. We
find significantly different ( mas) HST astrometry than Lam et al.
(2022a,b) in the de-magnified epochs due to the amount of positional bias
induced by a bright star 0.4 arcsec from OB110462. After modeling the
updated photometric and astrometric datasets, we find the lens of OB110462 is a
BH. Future observations with the Nancy Grace Roman
Space Telescope, which will have an astrometric precision comparable or better
to HST but a field of view larger, will be able to measure hundreds
of isolated BH masses via microlensing. This will enable the measurement of the
BH mass distribution and improve understanding of massive stellar evolution and
BH formation channels.Comment: 23 pages, 18 figures, 8 tables. Accepted for publication in ApJ on 2
Aug 2023 [Same as v1, just fixed typo in email address
Natal Kicks from the Galactic Center and Implications on their Environment and the Roman Space Telescope
Most galaxies, including the Milky Way, harbor a central supermassive black
hole (SMBH) weighing millions to billions of solar masses. Surrounding these
SMBHs are dense regions of stars and stellar remnants, such as neutron stars
and black holes. Neutron stars and possibly black holes receive large natal
kicks at birth on the order of hundreds of km s. The natal kicks that
occur in the vicinity of an SMBH may redistribute the orbital configuration of
the compact objects and alter their underlying density distribution. We model
the effects of natal kicks on a Galactic Center (GC) population of massive
stars and stellar binaries with different initial density distributions. Using
observational constraints from stellar orbits near the GC, we place an upper
limit on the steepness of the initial stellar profile and find it to be
core-like. In addition, we predict that of compact objects become
unbound from the SMBH due to their kicks and will migrate throughout the
galaxy. Different black hole kick prescriptions lead to distinct spatial and
kinematic distributions. We suggest that the Roman Space Telescope may be able
to distinguish between these distributions and thus be able to differentiate
natal kick mechanisms.Comment: 18 pages, 11 Figure
Microlensing Events in Five Years of Photometry from the Zwicky Transient Facility
Microlensing has a unique advantage for detecting dark objects in the Milky
Way, such as free floating planets, neutron stars, and stellar-mass black
holes. Most microlensing surveys focus towards the Galactic bulge, where higher
stellar density leads to a higher event rate. However, microlensing events in
the Galactic plane are closer, and take place over longer timescales. This
enables a better measurement of the microlensing parallax, which serves as an
independent constraint on the mass of the dark lens. In this work, we
systematically searched for microlensing events in Zwicky Transient Facility
(ZTF) Data Release 17 from 2018--2023 in the Galactic plane region . We find 124 high-confidence microlensing events and 54 possible
events. In the event selection, we use the efficient \texttt{EventFinder}
algorithm to detect microlensing signals, which could be used for large
datasets such as future ZTF data releases or data from the Rubin Observatory
Legacy Survey of Space and Time (LSST). With detection efficiencies of ZTF
fields from catalog-level simulations, we calculate the mean Einstein timescale
to be days, smaller than previous
results of the Galactic plane to within 1.5-. We calculate optical
depths and event rates, which we interpret with caution due to the use of
visual inspection in creating our final sample. With two years of additional
ZTF data in DR17, we have more than doubled the amount of microlensing events
(60) found in the three-year DR5 search and found events with longer Einstein
timescales than before.Comment: 9 figures, 3 tables. Submitted to Ap
Gravitational Microlensing Event Statistics for the Zwicky Transient Facility
Microlensing surveys have discovered thousands of events with almost all
events discovered within the Galactic bulge or toward the Magellanic clouds.
The Zwicky Transient Facility (ZTF), while not designed to be a microlensing
campaign, is an optical time-domain survey that observes the entire northern
sky every few nights including the Galactic plane. ZTF observes
stars in g-band and r-band and can significantly contribute to the observed
microlensing population. We predict that ZTF will observe 1100
microlensing events in three years of observing within degrees
latitude of the Galactic plane, with 500 events in the outer Galaxy
(). This yield increases to 1400 (800) events
by combining every three ZTF exposures, 1800 (900) events if ZTF
observes for a total of five years, and 2400 (1300) events for a
five year survey with post-processing image stacking. Using the microlensing
modeling software PopSyCLE, we compare the microlensing populations in the
Galactic bulge and the outer Galaxy. We also present an analysis of the
microlensing event ZTF18abhxjmj to demonstrate how to leverage these population
statistics in event modeling. ZTF will constrain Galactic structure, stellar
populations, and primordial black holes through photometric microlensing.Comment: 19 pages, 13 figures, 5 tables, accepted to ApJ (6/4/2020),
microlensing simulation catalogs available at
https://portal.nersc.gov/project/uLens/Galactic_Microlensing_Distribution
The Impact of Initial-Final Mass Relations on Black Hole Microlensing
Uncertainty in the initial-final mass relation (IFMR) has long been a problem
in understanding the final stages of massive star evolution. One of the major
challenges of constraining the IFMR is the difficulty of measuring the mass of
non-luminous remnant objects (i.e. neutron stars and black holes).
Gravitational wave detectors have opened the possibility of finding large
numbers of compact objects in other galaxies, but all in merging binary
systems. Gravitational lensing experiments using astrometry and photometry are
capable of finding compact objects, both isolated and in binaries, in the Milky
Way. In this work we improve the PopSyCLE microlensing simulation code in order
to explore the possibility of constraining the IFMR using the Milky Way
microlensing population. We predict that the Roman Space Telescope's
microlensing survey will likely be able to distinguish different IFMRs based on
the differences at the long end of the Einstein crossing time distribution and
the small end of the microlensing parallax distribution, assuming the small
() microlensing parallaxes characteristic of black hole
lenses are able to be measured accurately. We emphasize that future
microlensing surveys need to be capable of characterizing events with small
microlensing parallaxes in order to place the most meaningful constraints on
the IFMR.Comment: 24 pages, 17 figures Accepted to Ap
Disentangling the Black Hole Mass Spectrum with Photometric Microlensing Surveys
From the formation mechanisms of stars and compact objects to nuclear
physics, modern astronomy frequently leverages surveys to understand
populations of objects to answer fundamental questions. The population of dark
and isolated compact objects in the Galaxy contains critical information
related to many of these topics, but is only practically accessible via
gravitational microlensing. However, photometric microlensing observables are
degenerate for different types of lenses, and one can seldom classify an event
as involving either a compact object or stellar lens on its own. To address
this difficulty, we apply a Bayesian framework that treats lens type
probabilistically and jointly with a lens population model. This method allows
lens population characteristics to be inferred despite intrinsic uncertainty in
the lens-class of any single event. We investigate this method's effectiveness
on a simulated ground-based photometric survey in the context of characterizing
a hypothetical population of primordial black holes (PBHs) with an average mass
of . On simulated data, our method outperforms current black hole
(BH) lens identification pipelines and characterizes different subpopulations
of lenses while jointly constraining the PBH contribution to dark matter to
\%. Key to robust inference, our method can marginalize over
population model uncertainty. We find the lower mass cutoff for stellar origin
BHs, a key observable in understanding the BH mass gap, particularly difficult
to infer in our simulations. This work lays the foundation for cutting-edge PBH
abundance constraints to be extracted from current photometric microlensing
surveys.Comment: 31 pages, 18 figures, submitted to AA
A Reanalysis of Public Galactic Bulge Gravitational Microlensing Events from OGLE-III and IV
Modern surveys of gravitational microlensing events have progressed to
detecting thousands per year. Surveys are capable of probing Galactic
structure, stellar evolution, lens populations, black hole physics, and the
nature of dark matter. One of the key avenues for doing this is studying the
microlensing Einstein radius crossing time distribution (). However,
systematics in individual light curves as well as over-simplistic modeling can
lead to biased results. To address this, we developed a model to simultaneously
handle the microlensing parallax due to Earth's motion, systematic instrumental
effects, and unlensed stellar variability with a Gaussian Process model. We
used light curves for nearly 10,000 OGLE-III and IV Milky Way bulge
microlensing events and fit each with our model. We also developed a forward
model approach to infer the timescale distribution by forward modeling from the
data rather than using point estimates from individual events. We find that
modeling the variability in the baseline removes a source of significant bias
in individual events, and previous analyses over-estimated the number of long
timescale ( days) events due to their over simplistic models ignoring
parallax effects and stellar variability. We use our fits to identify hundreds
of events that are likely black holes.Comment: Submitted version, in review, 33 pages, 18 figures, MCMC posterior
samples available by publisher after acceptanc
Roman CCS White Paper: Characterizing the Galactic population of isolated black holes
Although there are estimated to be 100 million isolated black holes (BHs) in
the Milky Way, only one has been found so far, resulting in significant
uncertainty about their properties. The Galactic Bulge Time Domain Survey
provides the only opportunity in the coming decades to grow this catalog by
order(s) of magnitude. This can be achieved if 1) Roman's astrometric potential
is fully realized in the observation strategy and software pipelines, 2)
Roman's observational gaps of the Bulge are minimized, and 3) observations with
ground-based facilities are taken of the Bulge to fill in gaps during non-Bulge
seasons. A large sample of isolated BHs will enable a broad range of
astrophysical questions to be answered, such as massive stellar evolution,
origin of gravitational wave sources, supernova physics, and the growth of
supermassive BHs, maximizing Roman's scientific return.Comment: 20 pages. Submitted in response to Nancy Grace Roman Space Telescope
white paper call: https://roman.gsfc.nasa.gov/science/ccs_white_papers.htm
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