Binary Microlensing Events from the MACHO Project

Alcock, C.; Allsman, R. A.; Alves, D. R.; Axelrod, T. S.; Baines, D.; Becker, A. C.; Bennett, D. P.; Bourke, Andrew F. G.; Brakel, A.; Cook, K. H.; Crook, B.; Crouch, A. D.; Dan, J.; Drake, A. J.; Fragile, P. Chris; Freeman, K. C.; Gal‐Yam, A.; Geha, Marla; Gray, J.; Griest, K.; Gurtierrez, A.; Heller, Ana; Howard, J.; Johnson, B. R.; Kaspi, S.; Keane, Michael; Kovo, O.; Leach, C. M.; Leach, T.; Leibowitz, E. M.; Lehner, M. J.; Lipkin, Y.; Maoz, Dan; Marshall, Stuart; McDowell, D.; McKeown, S.; Mendelson, Haim; Messenger, B.; Minniti, D.; Nelson, C A; Peterson, Bruce A.; Popowski, Piotr; Pozza, E.; Purcell, P.; Pratt, M. R.; Quinn, J.; Quinn, Peter J.; Rhie, Sun Hong; Rodgers, A. W.; Salmon, Andrew; Shemmer, Ohad; Stetson, P. B.; Stubbs, C. W.; Sutherland, William J.; Thomson, Stuart; Tomaney, A.; Vandehei, T.; Walker, A. R.; Ward, Katherine Esther; Wyper, Grant M A

doi:10.1086/309393

Cited by 108 publications

(128 citation statements)

References 81 publications

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“…In fact, MACHO-LMC-14 is known to be due to selflensing (Alcock et al 2001c) because it has a binary source and the form of the accompanying deformation of the lightcurve with respect to the simple microlensing lightcurve requires that the lens be in the LMC. A second event, MACHO-LMC-9, is due to a binary lens and the self-lensing interpretation can be avoided only by assuming that the source is also a binary system and that each of the two widely separated components happened to land on the caustic on the two successive observations made of the caustic entrance (Alcock et al 2000a).…”

Section: Discussion Of the Resultsmentioning

confidence: 99%

Limits on the Macho content of the Galactic Halo from the EROS-2 Survey of the Magellanic Clouds

Tisserand

Guillou

Afonso

et al. 2007

A&A

943

908

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Aims. The EROS-2 project was designed to test the hypothesis that massive compact halo objects (the so-called "machos") could be a major component of the dark matter halo of the Milky Way galaxy. To this end, EROS-2 monitored over 6.7 years 33 × 10 6 stars in the Magellanic clouds for microlensing events caused by such objects. Methods. In this work, we use only a subsample of 7 × 10 6 bright stars spread over 84 deg 2 of the LMC and 9 deg 2 of the SMC. The strategy of using only bright stars helps to discriminate against background events due to variable stars and allows a simple determination of the effects of source confusion (blending). The use of a large solid angle makes the survey relatively insensitive to effects that could make the optical depth strongly direction dependent. Results. Using this sample of bright stars, only one candidate event was found, whereas ∼39 events would have been expected if the Halo were entirely populated by objects of mass M ∼ 0.4 M . Combined with the results of EROS-1, this implies that the optical depth toward the Large Magellanic Cloud (LMC) due to such lenses is τ < 0.36 × 10 −7 (95% CL), corresponding to a fraction of the halo mass of less than 8%. This optical depth is considerably less than that measured by the MACHO collaboration in the central region of the LMC. More generally, machos in the mass range 0.6 × 10 −7 M < M < 15 M are ruled out as the primary occupants of the Milky Way Halo.

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Section: Discussion Of the Resultsmentioning

confidence: 99%

Limits on the Macho content of the Galactic Halo from the EROS-2 Survey of the Magellanic Clouds

Tisserand

Guillou

Afonso

et al. 2007

A&A

943

908

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“…Interestingly, this is exactly the mass range at which the MACHO project found microlensing effects towards the Large Megallenic Cloud (LMC). Indeed a reanalysis of the data including the estimated number of binary MACHO's (Alcock 2000b), suggests that the optical depth of these primordial black holes could be greater than first reported (Alcock 2000a). Thus it is possible that these primordial black holes, could account for a greater degree of the optical depth required to explain the galactic rotation curves.…”

Section: The Equation For the Solar Mass Horizon (M H ) Is Given By Tmentioning

confidence: 94%

Advances in Black Hole Physics and Dark Matter Modelling of the Galactic Halo

Worsley¹

2012

APR

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One of the most important unresolved issues of modern physics is the presence of cold dark matter (CDM). Such dark matter appears to be essential in explaining the observed galactic rotation curves and the missing Cosmological dark matter. Recent attention has focused on galactic halos as an explanation of the galactic rotation curves, and on the possibility that galactic halos may consist of massive compact halo objects (MACHOs). Indeed results of experiment by the MACHO collaboration group have confirmed the presence of MACHOs in the galactic halo at statistically significant levels. What remains unclear is, what percentage of the galactic halo can be explained by such MACHOs, and what these MACHOs are likely to be composed of. Recent research shows the "most plausible" candidates for such MACHOs are being identified as primordial black holes. Such primordial black holes can also explain quasar brightness, spectral variations, and multiply lensed quasar systems. The presence of these primordial black holes in the galactic halo can be further modelled using advances in black hole gravitational physics. Indeed it has previously been shown that advances in black hole physics can be used to accurately model both CDM associated with the supermassive black hole at the centre of the galaxy, and Cosmological cold dark matter. To establish whether the same mechanism applies to primordial black holes in galactic halos, the original data from the MACHO project are reanalyzed using these advances in black hole physics. It is concluded that the majority of the CDM mass of the galactic halo can be accounted for by MACHOs by using a reanalysis of the data, and by applying advances in black hole gravitational physics. Importantly these advances in black hole physics offer further readily testable gravitational predictions.Keywords: Primordial black hole, Gravitation, Black hole physics, Galactic halo, Cold dark matter, Cosmology IntroductionThe presence of CDM remains to date one of the most important unsolved mysteries of modern Cosmology. It is particularly important not only to the understanding of the large scale structure of the Universe, but also in explaining the formation of galaxies. To date the search has concentrated on two main forms of CDM; weakly interactive massive particles (WIMPs), and massive compact halo objects (MACHOs) (Cline 2003). While the presence of WIMPs or some other form of exotic particle is still the favoured model, there has been a recent increase in the interest in MACHOs. Indeed research indicates that the statistical likely hood of MACHOs being present in the galactic halo is high (Alcock et al. 2000a).The question however, remains as to how prevalent these MACHOs are in the galactic halo, and what form do these MACHOs take? Interestingly, a recent comprehensive review suggests that the most "plausible" form these MACHO's take is that of primordial black holes (Hawkins 2011). In that review, a wide range of experimental evidence from quasar brightness, spectral variations, and multip...

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“…Of 21 light curves consistent with binary lenses analyzed by MACHO, two produced acceptable fits with companion masses as small 0.05M 0 (Alcock et al 2000). The first suggestion of possible planetary-mass lenses (Bennett et al 1997) came from MACHO survey data for MACHO 1994-BLG-4, which could be modelled as an M-dwarf/5M J pair, and MACHO 1995-BLG-3, a very short duration event modelled as an isolated 2MJ lens.…”

Section: Have Exoplanets Been Discovered With Microlensing?mentioning

confidence: 96%

Results from Microlensing Searches for Extrasolar Planets

Sackett¹

2004

Symp. - Int. Astron. Union

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Abstract.Specially-designed microlensing searches, some of which have been underway for several years, are sensitive to extrasolar planets orbiting the most common stars in our Galaxy. Microlensing is particularly well-suited to the detection of Jupiter-mass planets orbiting their parent stars at several AU. Since Jovian analogs are thought to influence the subsequent evolution of most planetary systems, they are particularly important to study. The orbital radii and distances to the planetary systems probed by microlensing are larger than those currently studied by radial velocity techniques; the two methods are thus complementary. Recent results from microlensing searches are discussed, including constraints on Jovian analogs orbiting typical Galactic stars. Benefits and drawbacks of the technique for the characterization of planetary systems, and future prospects are briefly reviewed.

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Binary Microlensing Events from the MACHO Project

Cited by 108 publications

References 81 publications

Limits on the Macho content of the Galactic Halo from the EROS-2 Survey of the Magellanic Clouds

Limits on the Macho content of the Galactic Halo from the EROS-2 Survey of the Magellanic Clouds

Advances in Black Hole Physics and Dark Matter Modelling of the Galactic Halo

Results from Microlensing Searches for Extrasolar Planets

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