Compact Halo Objects Research Articles

Examining the brightness variability, accretion disk, and evolutionary stage of the binary OGLE-LMC-ECL-14413

Several intermediate-mass close binary systems exhibit photometric cycles longer than their orbital periods, potentially due to changes in their accretion disks. Past studies indicate that analyzing historical light curves can provide valuable insights into disk evolution and track variations in mass transfer rates within these systems. Our study aims to elucidate both short-term and long-term variations in the light curve of the eclipsing system with a particular focus on the unusual reversals in eclipse depth. We aim to clarify the role of the accretion disk in these fluctuations, especially in long-cycle changes spanning hundreds of days. Additionally, we seek to determine the evolutionary stage of the system and gain insights into the internal structure of its stellar components. We analyzed photometric time series from the Optical Gravitational Lensing Experiment (OGLE) project in the $I$ and $V$ bands, and from the MAssive Compact Halo Objects (MACHO) project in the $B_ M $ and $R_ M $ bands, covering a period of 30.85 years. Using light curve data from 27 epochs, we constructed models of the accretion disk. An optimized simplex algorithm was employed to solve the inverse problem, deriving the best-fit parameters for the stars, orbit, and disk. We also utilized the Modules for Experiments in Stellar Astrophysics ( MESA ) software to assess the evolutionary stage of the binary system, investigating the progenitors and potential future developments. We found an orbital period of 38.15917 pm 0.00054 days and a long-term cycle of approximately 780 days. Temperature, mass, radius, and surface gravity values were determined for both stars. The photometric orbital cycle and the long-term cycle are consistent with a disk containing variable physical properties, including two shock regions. The disk encircles the more massive star and the system brightness variations align with the long-term cycle at orbital phase 0.25. Our mass transfer rate calculations correspond to these brightness changes. MESA simulations indicate weak magnetic fields in the donor star's subsurface, which are insufficient to influence mass transfer rates significantly.

Dissipative dark cosmology: From early matter dominance to delayed compact objects

We demonstrate a novel mechanism for producing dark compact objects and black holes through a dark sector, where all the dark matter can be dissipative. Heavy dark sector particles with masses above 104 GeV can come to dominate the Universe and yield an early matter-dominated era before big bang nucleosynthesis (BBN). Density perturbations in this epoch can grow and collapse into tiny dark matter halos, which cool via self-interactions. The typical halo size is set by the Hubble length once perturbations begin growing, offering a straightforward prediction of the halo size and evolution depending on one’s choice of dark matter model. Once these primordial halos have formed, a thermal phase transition can then shift the Universe back into radiation domination and standard cosmology. These halos can continue to collapse after BBN, resulting in the late-time formation of fragmented dark compact objects and sub-solar-mass primordial black holes. We find that these compact objects can constitute a sizable fraction of all of dark matter. The resulting fragments can have masses between 1020 and 1032 g, with radii ranging from 10−2 to 105 m, while the black holes can have masses between 108 and 1034 g. Furthermore, a unique feature of this model is the late-time formation of black holes which can evaporate today. We compare where these objects lie with respect to current primordial black hole and massive (astrophysical) compact halo object constraints. Published by the American Physical Society 2024

Using Gravitational Waves to Determine if Primordial Black Holes are Sources of Dark Matter

Scientists do not have much information about or evidence of dark matter. Dark matter does not emit electromagnetic radiation and does not interact with normal matter, but some researchers have found evidence of its existence throughout the universe. Scientists have narrowed down to two possible sources of dark matter: Massive Compact Halo Objects (MACHOs) and Weakly Interacting Massive Particles (WIMPs). In our research, we analyzed MACHOs, which are primordial black holes, using gravitational wave data from the LIGO/Virgo collaboration. We hypothesized that MACHOs may be dark matter due to the higher black hole mass formed from binary mergers between primordial black holes, compared to the black hole mass between binary mergers from simulated stellar black holes. Using the data derived from primordial black hole pairs, we used Python to perform Bayesian inference parameter estimation to generate another set of simulated datasets (which are stellar black hole pairs) to compare the final masses of the black hole mergers in the simulated and original gravitational wave datasets. Our results showed that primordial black holes (MACHOs) may not be dark matter, but in the future, based on the research on dark matter, astrophysicists’ can further improve understanding of primordial black holes and their effect in the universe.

Five Massive Contact Binaries with Twin Components in LMC

Massive contact binaries refer to the close binary systems in which the components have filled their respective Roche lobes and share a common envelope with early-type spectra. Twin binaries are a special type of binary system characterized by two components with nearly equal masses. The Magellanic Cloud, comprising the Large Magellanic Cloud (LMC) and the Small Magellanic Cloud, is a fascinating galaxy that is distinct from the Milky Way. With its low metallicity, it serves as an ideal test bed for studying the formation and evolution of massive binaries and testing theoretical models. In this work, based on long-term observations with Optical Gravitational Lensing Experiment and MAssive Compact Halo Object in the LMC, we identified and performed comprehensive analyses of five massive twin contact binaries via the method of the light travel time effect and Wilson–Devinney code. The results show that all of these twin binaries are accompanied by low-mass third bodies. The third bodies have minimum masses ranging from 0.33 to 1.46 M ⊙. Their orbital periods range from 4.34 to 12.03 yr. The maximum distances between the third bodies and the central binary systems range from 6.7 to 11.4 au. Remarkably, four out of the five massive twins have evolved into deep-contact binaries, which indicates that all of them may have originated from Case A mass transfer. These results strongly suggest the significant influence of the third body in the formation and evolution of massive contact binaries and may hold the key to unraveling the origins of massive binaries.

Axion stars in MGD background

The minimal geometric deformation (MGD) paradigm is here employed to survey axion stars on fluid branes. The finite value of the brane tension provides beyond-general relativity corrections to the density, compactness, radius, and asymptotic limit of the gravitational mass function of axion stars, in a MGD background. The brane tension also enhances the effective range and magnitude of the axion field coupled to gravity. MGD axion stars are compatible to mini-massive compact halo objects for almost all the observational range of brane tension, however, a narrow range allows MGD axion star densities large enough to produce stimulated decays of the axion to photons, with no analogy in the general-relativistic (GR) limit. Besides, the gravitational mass and the density of MGD axion stars are shown to be up to four orders of magnitude larger than the GR axion stars, being also less sensitive to tidal disruption events under collision with neutron stars, for lower values of the fluid brane tension.

Observational Evidence for Cosmological Coupling of Black Holes and its Implications for an Astrophysical Source of Dark Energy

Observations have found black holes spanning 10 orders of magnitude in mass across most of cosmic history. The Kerr black hole solution is, however, provisional as its behavior at infinity is incompatible with an expanding universe. Black hole models with realistic behavior at infinity predict that the gravitating mass of a black hole can increase with the expansion of the universe independently of accretion or mergers, in a manner that depends on the black hole’s interior solution. We test this prediction by considering the growth of supermassive black holes in elliptical galaxies over 0 < z ≲ 2.5. We find evidence for cosmologically coupled mass growth among these black holes, with zero cosmological coupling excluded at 99.98% confidence. The redshift dependence of the mass growth implies that, at z ≲ 7, black holes contribute an effectively constant cosmological energy density to Friedmann’s equations. The continuity equation then requires that black holes contribute cosmologically as vacuum energy. We further show that black hole production from the cosmic star formation history gives the value of ΩΛ measured by Planck while being consistent with constraints from massive compact halo objects. We thus propose that stellar remnant black holes are the astrophysical origin of dark energy, explaining the onset of accelerating expansion at z ∼ 0.7.

Weighing the Darkness. III. How Gaia Could, but Probably Will Not, Astrometrically Detect Free-floating Black Holes

The gravitational pull of an unseen companion to a luminous star is well known to cause deviations to the parallax and proper motion of a star. In a previous paper in this series, we argue that the astrometric mission Gaia can identify long-period binaries by precisely measuring these arcs. An arc in a star’s path can also be caused by a flyby: a hyperbolic encounter with another massive object. We quantify the apparent acceleration over time induced by a companion star as a function of the impact parameter, velocity of interaction, and companion mass. In principle, Gaia could be used to astrometrically identify the contribution of massive compact halo objects to the local dark matter potential of the Milky Way. However, after quantifying their rate and Gaia’s sensitivity, we find that flybys are so rare that Gaia will probably never observe one. Therefore, every star in the Gaia database exhibiting astrometric acceleration is likely in a long-period binary with another object. Nevertheless, we show how intermediate-mass black holes, if they exist in the local stellar neighborhood, can induce anomalously large accelerations on stars.

New limits from microlensing on Galactic black holes in the mass range 10 M⊙ &lt; M &lt; 1000 M⊙

We searched for long-duration microlensing events originating from intermediate-mass black holes (BH) in the halo of the Milky Way, using archival data from the EROS-2 and MACHO photometric surveys towards the Large Magellanic Cloud (LMC). We combined data from these two surveys to create a common database of light curves for 14.1 million objects in the LMC, covering a total duration of 10.6 years, with flux series measured in four wide passbands. We carried out a microlensing search on these light curves, complemented by the light curves of 22.7 million objects, observed only by EROS-2 or only by MACHO, over about 7 years, with flux series measured in only two passbands. A likelihood analysis, taking into account the LMC self-lensing and Milky Way disk contributions, allows us to conclude that compact objects with masses in the range 10 − 100 M⊙ cannot make up more than ∼15% of a standard halo total mass (at a 95% confidence level). Our analysis sensitivity weakens for heavier objects, although we still rule out the possibility of ∼50% of the halo being made of ∼1000 M⊙ BHs. Combined with previous EROS results, an upper limit of ∼15% of the total halo mass can be obtained for the contribution of compact halo objects in the mass range 10−6 − 102 M⊙.

NGC 2004 #115: a black hole imposter containing three luminous stars

ABSTRACT NGC 2004 #115 is a recently identified black hole (BH) candidate in the Large Magellanic Cloud (LMC) containing a B star orbiting an unseen companion in a 2.9 d orbit and a Be star tertiary. We show that the unseen companion is not a 25 M⊙ BH, but a $(2\!-\!3)\, {\rm M}_{\odot }$ luminous star. Analysing the Optical Gravitational Lensing Experiment (OGLE) and MAssive Compact Halo Object (MACHO) light curves of the system, we detect ellipsoidal variability with amplitude 10 times larger than would be expected if the companion were a 25 M⊙ BH, ruling out the low inclination required for a massive companion. The light curve also shows a clear reflection effect that is well modelled with a $2.5\, {\rm M}_{\odot }$ main-sequence secondary, ruling out a lower mass BH or neutron star companion. We consider and reject models in which the system is a binary containing a stripped star orbiting the Be star: only a triple model with an outer Be star can explain both the observed light curve and radial velocities. Our results imply that the B star, whose slow projected rotation velocity and presumed tidal synchronization were interpreted as evidence for a low inclination (and thus a high companion mass), is far from being tidally synchronized: despite being in a 2.9 d orbit that is fully or nearly circularized (e &amp;lt; 0.04), its surface rotation period appears to be at least 20 d. We offer cautionary notes on the interpretation of dormant BH candidates in binaries.

FRBs Lensed by Point Masses. II. The Multipeaked FRBs from the Point View of Microlensing

Abstract The microlensing effect has developed into a powerful technique for a diverse range of applications including exoplanet discoveries, structure of the Milky Way, constraints on MAssive Compact Halo Objects, and measurements of the size and profile of quasar accretion disks. In this paper, we consider a special type of microlensing events where the sources are fast radio bursts (FRBs) with ∼milliseconds (ms) durations for which the relative motion between the lens and source is negligible. In this scenario, it is possible to temporally resolve the individual microimages. As a result, a method beyond the inverse ray shooting method, which only evaluates the total magnification of all microimages, is needed. We therefore implement an algorithm for identifying individual microimages and computing their magnifications and relative time delays. We validate our algorithm by comparing to analytical predictions for a single microlens case and find excellent agreement. We show that the superposition of pulses from individual microimages produces a light curve that appears as multipeaked FRBs. The relative time delays between pulses can reach 0.1–1 ms for stellar-mass lenses and hence can already be resolved temporally by current facilities. Although not yet discovered, microlensing of FRBs will become regular events and surpass the number of quasar microlensing events in the near future when 104−5 FRBs are expected to be discovered on a daily basis. Our algorithm provides a way of generating the microlensing light curve that can be used for constraining stellar-mass distribution in distant galaxies.

Period-change rates in Large Magellanic Cloud Cepheids revisited

ABSTRACT The period-change rate (PCR) of pulsating variable stars is a useful probe of changes in their interior structure, and thus of their evolutionary stages. So far, the PCRs of classical Cepheids in the Large Magellanic Cloud (LMC) have been explored in a limited sample of the total population of these variables. Here, we use a template-based method to build observed-minus-computed (O − C) period diagrams, from which we can derive PCRs for these stars by taking advantage of the long time baseline afforded by the Digital Access to a Sky Century @ Harvard light curves, combined with additional data from the Optical Gravitational Lensing Experiment, the MAssive Compact Halo Object project, Gaia’s Data Release 2, and in some cases the All-Sky Automated Survey. From an initial sample of 2315 sources, our method provides an unprecedented sample of 1303 LMC classical Cepheids with accurate PCRs, the largest for any single galaxy, including the Milky Way. The derived PCRs are largely compatible with theoretically expected values, as computed by our team using the Modules for Experiments in Stellar Astrophysics code, as well as with similar previous computations available in the literature. Additionally, five long-period ($P\,\gt\, 50\, \rm {d}$) sources display a cyclic behaviour in their O − C diagrams, which is clearly incompatible with evolutionary changes. Finally, on the basis of their large positive PCR values, two first-crossing Cepheid candidates are identified.

Crater morphology of primordial black hole impacts

ABSTRACT In this work, we propose a novel campaign for constraining relativistically compact massive compact halo object (MACHO) dark matter, such as primordial black holes (PBHs), using the Moon as a detector. PBHs of about 1019 to 1022 g may be sufficiently abundant to have collided with the Moon in the history of the Solar system. We show that the crater profiles of a PBH collision differ from traditional impactors and may be detectable in high-resolution lunar surface scans now available. Any candidates may serve as sites for in situ measurements to identify high-pressure phases of matter which may have formed near the PBH during the encounter. While we primarily consider PBH dark matter, the discussion generalizes to the entire family of MACHO candidates with relativistic compactness. Moreover, we focus on the Moon since it has been studied well, but the same principles can be applied to other rocky bodies in our Solar system without an atmosphere.

Gamma-rays from ultracompact minihaloes: effects on the Earth’s atmosphere and links to mass extinction events

ABSTRACT Recent studies of the effects on the Earth’s atmosphere by astrophysical sources, such as nearby gamma-ray bursts or supernovae, have shown that these events could lead to severe changes in atmospheric composition. Depletion of ozone, the most notable of these changes, is extremely dangerous to living organisms as any decrease in ozone levels leads to an increase in the irradiance of harmful solar radiation at the Earth’s surface. In this work, we consider dark matter as an astrophysical source of gamma-rays, by the annihilation and decay of weakly interacting massive particles found within dark compact halo objects known as ultracompact minihaloes (UCMHs). We calculate the fluence of gamma-rays produced in this way and simulate the resulting changes to terrestrial ozone levels using the Goddard Space Flight Center 2D Atmospheric Model. We then calculate the rate at which such events would occur, using estimates for the mass distribution of these haloes within the Milky Way. We find that the ozone depletion from UCMHs can be significant, and even of similar magnitude to the levels which have been linked to the cause of the Late-Ordovician mass extinction event. However, we also find that the rate of such extinction-level events due to UCMHs is markedly lower than for other astrophysical phenomena. This suggests that, while dark compact objects such as UCMHs could have had an impact on the Earth’s biosphere, events such as gamma-ray bursts or supernovae seem a more likely source of these effects.

On Neural Architectures for Astronomical Time-series Classification with Application to Variable Stars

Abstract Despite the utility of neural networks (NNs) for astronomical time-series classification, the proliferation of learning architectures applied to diverse data sets has thus far hampered a direct intercomparison of different approaches. Here we perform the first comprehensive study of variants of NN-based learning and inference for astronomical time series, aiming to provide the community with an overview on relative performance and, hopefully, a set of best-in-class choices for practical implementations. In both supervised and self-supervised contexts, we study the effects of different time-series-compatible layer choices, namely the dilated temporal convolutional neural network (dTCNs), long-short term memory NNs, gated recurrent units and temporal convolutional NNs (tCNNs). We also study the efficacy and performance of encoder-decoder (i.e., autoencoder) networks compared to direct classification networks, different pathways to include auxiliary (non-time-series) metadata, and different approaches to incorporate multi-passband data (i.e., multiple time series per source). Performance—applied to a sample of 17,604 variable stars (VSs) from the MAssive Compact Halo Objects (MACHO) survey across 10 imbalanced classes—is measured in training convergence time, classification accuracy, reconstruction error, and generated latent variables. We find that networks with recurrent NNs generally outperform dTCNs and, in many scenarios, yield to similar accuracy as tCNNs. In learning time and memory requirements, convolution-based layers perform better. We conclude by discussing the advantages and limitations of deep architectures for VS classification, with a particular eye toward next-generation surveys such as the Legacy Survey of Space and Time, the Roman Space Telescope, and Zwicky Transient Facility.

Tests of Dark MACHOs: lensing, accretion, and glow

Dark matter could take the form of dark massive compact halo objects (dMACHOs); i.e., composite objects that are made up of dark-sector elementary particles, that could have a macroscopic mass from the Planck scale to above the solar mass scale, and that also admit a wide range of energy densities and sizes. Concentrating on the gravitational interaction of dMACHOs with visible matter, we map out the mass-radius parameter space that is consistent with gravitational lensing experiments, as well as anisotropies of the cosmic microwave background (CMB) based on the spherical accretion of matter onto a dMACHO in the hydrostatic approximation. For dMACHOs with a uniform-density mass profile and total mass in the range of ∼ 10−12–10 M⊙, we find that a dMACHO could explain 100% of the dark matter if its radius is above ≈ 3 times the Einstein radius of the lensing system. For a larger mass above 10 M⊙, a dMACHO with radius above ∼ 1 × 108 cm ×(M/100 M⊙)9/2 is consistent with CMB observables. For a lighter dMACHO with mass below ∼ 10−12 M⊙, there still is not a good experimental probe. Finally, we point out that heavier dMACHOs with masses ∼ 0.1 M⊙ may be observed by X-ray and optical telescopes if they reside at rest in a large molecular cloud, nearby to our solar system, and accrete ordinary matter to emit photons.

Looking for MACHOs in the spectra of fast radio bursts

ABSTRACT We explore a novel search strategy for dark matter in the form of massive compact halo objects (MACHOs) such as primordial black holes or dense mini-haloes in the mass range from $10^{-4}\, \mathrm{M}_{\odot }$ to $0.1\, \mathrm{M}_{\odot }$. These objects can gravitationally lens the signal of fast radio bursts (FRBs), producing a characteristic interference pattern in the frequency spectrum, similar to the previously studied femtolensing signal in gamma-ray burst spectra. Unlike traditional searches using microlensing, FRB lensing will probe the abundance of MACHOs at cosmological distance scales (∼Gpc) rather than just their distribution in the neighbourhood of the Milky Way. The method is thus particularly relevant for dark mini-haloes, which may be inaccessible to microlensing due to their finite spatial extent or tidal disruption in galaxies. We find that the main complication in FRB lensing will be interstellar scintillation in the FRB’s host galaxy and in the Milky Way. Scintillation is difficult to quantify because it heavily depends on turbulence in the interstellar medium, which is poorly understood. We show that, nevertheless, for realistic scintillation parameters, FRB lensing can set competitive limits on compact dark matter object, and we back our findings with explicit simulations.

New era of dark matter particle detection

The astronomical evidence of the existence of dark matter is overwhelming. However, the physical nature of dark matter is still unknown. It is widely believed that dark matter is some kind of new particles beyond the standard model of particle physics. Alternative candidates include the massive compact halo objects such as primordial black holes. Among all these candidates, the class of so-called weakly interacting massive particles (WIMPs) is the most natural and well theoretically motivated one. The WIMP scenario can naturally explain the abundance of dark matter in the universe via a canonical thermal production mechanism. It also gives a practical way of detecting those particles via various kinds of particle physics experiments. The direct detection method measures the momentum exchange when a dark matter particle scatters off a nucleus. The sensitivities of direct detection increase remarkably during the past 30 years since it was first proposed in the 1980s. China has operated two direct detection experiments, the CDEX and PandaX experiments, in the Jinping underground laboratory. Through the efforts of all the direct detection experiments, including CDEX and PandaX, the current upper limit about the spin-independent scattering cross section between the dark matter particle and the nucleon reaches the level of 10⁻⁴⁷ cm² which is only about two orders of magnitude higher than the neutrino-induced background. Although no convincing signal has been detected yet, such null results can constrain severely many kinds of theoretical models of dark matter. Several experiments are upgrading now, with the goal of a fiducial detector mass of several tons, which are expected to further improve the direct detection sensitivities. The indirect detection method is to search for the annihilation or decay products of dark matter in cosmic rays and gamma-rays, which is complimentary to the direct detection. The main indirect detection experiments in operation include the alpha magnetic spectrometer and the calorimeter electron telescope on the International Space Station, the Fermi gamma-ray space telescope, and China’s dark matter particle explorer. Several anomalies have been reported by the indirect detection experiments, such as the positron excess, the excess of the total electron plus positron spectrum, the gamma-ray excess in the Galactic center region. Interpretations of these excesses are still in debate. Nevertheless, these anomalies offer us targets for further investigation with increased statistics and improved understanding of the astrophysical backgrounds. Both the direct detection and indirect detection experiments will have significantly upgrading in the coming years. Particularly, China’s PandaX experiment is currently building a 4-ton scale detector which is expected to start to operate in 2021. The long-term plan of the CDEX experiment is also a ton-scale detector for multi-purpose studies including the dark matter searches. For the indirect detection, the HERD payload onboard the Chinese Space Station is in the prototype phase, and the next generation very large area gamma-ray space telescope is under design. On the ground we are building the large high-altitude air shower observatory for high-sensitivity sky survey in the very high energy gamma-ray band. All these efforts will make China play a significant or even leading role in the campaign of dark matter detection. We are looking forward to the breakthroughs in the exploration of the nature of dark matter.

The MUSE-Faint survey

Aims. It has been shown that the ultra-faint dwarf galaxy Eridanus 2 may host a stellar cluster in its centre. If this cluster is shown to exist, it can be used to set constraints on the mass and abundance of massive astrophysical compact halo objects (MACHOs) as a form of dark matter. Previous research has shown promising expectations in the mass range of 10−100 M⊙, but lacked spectroscopic measurements of the cluster. We aim to provide spectroscopic evidence regarding the nature of the putative star cluster in Eridanus 2 and to place constraints on MACHOs as a constituent of dark matter. Methods. We present spectroscopic observations of the central square arcminute of Eridanus 2 from MUSE-Faint, a survey of ultra-faint dwarf galaxies with the Multi Unit Spectroscopic Explorer on the Very Large Telescope. We derived line-of-sight velocities for possible member stars of the putative cluster and for stars in the centre of Eridanus 2. We discuss the existence of the cluster and determine new constraints for MACHOs using the Fokker–Planck diffusion approximation. Results. Out of 182 extracted spectra, we identify 26 member stars of Eridanus 2, seven of which are possible cluster members. We find intrinsic mean line-of-sight velocities of 79.7+3.1−3.8 km s−1 and 76.0+3.2−3.7 km s−1 for the cluster and the bulk of Eridanus 2, respectively, as well as intrinsic velocity dispersions of &lt; 7.6 km s−1 (68% upper limit) and 10.3+3.9−3.2 km s−1, respectively. This indicates that the cluster most likely exists as a distinct dynamical population hosted by Eridanus 2 and that it does not have a surplus of dark matter over the background distribution. Among the member stars in the bulk of Eridanus 2, we find possible carbon stars, alluding to the existence of an intermediate-age population. We derived constraints on the fraction of dark matter that can consist of MACHOs with a given mass between 1 and 105 M⊙. For dark matter consisting purely of MACHOs, the mass of the MACHOs must be less than ∼7.6 M⊙ and ∼44 M⊙ at a 68- and 95% confidence level, respectively.

Streaming classification of variable stars

ABSTRACTIn the last years, automatic classification of variable stars has received substantial attention. Using machine learning techniques for this task has proven to be quite useful. Typically, machine learning classifiers used for this task require to have a fixed training set, and the training process is performed offline. Upcoming surveys such as the Large Synoptic Survey Telescope will generate new observations daily, where an automatic classification system able to create alerts online will be mandatory. A system with those characteristics must be able to update itself incrementally. Unfortunately, after training, most machine learning classifiers do not support the inclusion of new observations in light curves, they need to re-train from scratch. Naively re-training from scratch is not an option in streaming settings, mainly because of the expensive pre-processing routines required to obtain a vector representation of light curves (features) each time we include new observations. In this work, we propose a streaming probabilistic classification model; it uses a set of newly designed features that work incrementally. With this model, we can have a machine learning classifier that updates itself in real time with new observations. To test our approach, we simulate a streaming scenario with light curves from Convention, Rotation and planetary Transits (CoRoT), Orbital Gravitational Lensing Experiment (OGLE), and Massive Compact Halo Object (MACHO) catalogues. Results show that our model achieves high classification performance, staying an order of magnitude faster than traditional classification approaches.

Probing dynamics of boson stars by fast radio bursts and gravitational wave detection

Boson stars may consist of a new type of light singlet scalar particles with nontrivial self-interactions, and may compose a fraction of the dark matter in the Universe. In this work, we study the dynamics of boson stars with Liouville and logarithmic scalar self-interaction potentials as benchmarks. We perform a numerical analysis as well as a semi-analytic study on how the compactness and the total mass will deviate from that of the usual boson stars formed with a quartic repulsive self-interaction. We apply the recently suggested Swampland conjecture to examine whether boson stars with such benchmark potentials belong to the Landscape of a quantum gravity. Using the mass constraint on the macroscopic compact halo object (MACHO) and the cold dark matter (CDM) isocurvature mode constraint from the cosmic microwave background (CMB), we derive the allowed mass range of scalar particles which compose the boson star. We further analyze applications of the lensing of fast radio bursts (FRBs) and the gravitational wave (GW) detection to probe the presence of such boson stars and constrain the parameter space of their corresponding models. We discuss how the two types of boson star potentials can be discriminated by the FRB and GW measurements.