Gravitational Microlensing

What is microlensing?

Gravitational microlensing refers to the apparent brightening of a background source caused by a lensing object located sufficiently close to the line of sight. This gravitational focusing effect does not require the intervening object to be luminous, and hence has been suggested as a way to detect dark matter. In the Galaxy, microlensing can be used to detect the so-called MAssive Compact Halo Objects (MACHOs) in the Galactic halo ranging from 10^-7 solar mass to 10^6 solar mass. A good introduction can be found at the PLANET collaboration web site.

Groups working on Microlensing

Microlensing Searches toward the Galactic Bulge, Magellanic Clouds and Spiral Arms:

DUO (Disk Unseen Objects)
EROS (Experience pour la Recherche d'Objets sombres)
MACHO (MAssive Compact Halo Object)
MOA (Microlensing Observations in Astrophysics)
OGLE (Optical Gravitational Lensing Experiment)
For Real-Time Ongoing Microlensing Events, check
MACHO Alert Events
OGLE Early-Warning System (EWS). This site contains photometric data on the ongoing events!!!
EROS Alert Events
Microlensing Searches toward M31:
AGAPE (Andromeda Galaxy and Amplified Pixels Experiment)
MEGA (Microlensing Experiment Towards the Galaxy in Andromeda)
Coll/VATT (Columbia/Vatican Telescope)
Munich (Munich University Observatory group)

Photometric Followup Teams of On-going Events:
PLANET (Probing Lensing Anomalies NETwork)
MPS (Microlensing Planet Search)
GMAN (Global Microlensing Alert Network)
Spectroscopic Followup Teams of On-going Events:
A Pilot Monitoring program in which I am involved

Software

The software for calculating the centroid motion in microlensing for an extended source (see Mao & Witt 1998, MNRAS, 300, 1041) can be downloaded .

Reviews on Microlensing

To learn more about microlensing, you can read the following reviews.

Paczynski (1996, ARAA, 34, 419), who started the field, wrote an excellent review on microlensing.
Roulet, E. and Mollerach, S. (1997), Phys. Reports, 279, 67,
Gould (1996) contains a very good review on the mass functions.
There are also two nice reviews on microlensing in the book Unsolved Problems In Astrophysics, eds. John Bahcall and Jerry Ostriker, by Gould (1997, p. 241), and by Alcock (1997, p. 253). The latter discusses why microlensing surveys are different from the traditional way of doing astrophysical research.
For a view on microlensing from Australia, see York's article
For the arguments in favor of self-lensing in LMC , see Zhao's article.
My own review (1999) contains an updated review on microlensing

If you have any questions or comments, please send an email to me (the address can be found in the Home Page section).