Microlensing might detect planets as well as MACHOs

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In summary, massive compact halo objects (MACHOs) have been detected through microlensing, where an invisible object passing in front of a distant source causes a temporary spike in the light curve. This was studied in the late 1990s to determine the upper bound of MACHO's contribution to dark matter. However, it was later discovered that a "double spike" microlensing effect could potentially be used to detect even Earth-sized planets. This method would require the lensing object's path to be closely aligned with the orbital plane of the planet, making the detection rate low. There was some excitement over a potential planet detection through this method, but it remains uncertain. A webpage called "Microlensing Planet Search" discusses
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marcus
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massive compact halo objects have been detected by microlensing

an invisible compact object passing in front of a distant source causes a temporary spike in the light curve by gravitational lensing---the brightening might last a couple of days

this was written about in the late 1990s when they wanted an upper bound on the contribution of MACHO to dark matter and a bunch of invisible massive objects were observed

but wait! the story isn't over apparently. I recently came across a page of some people who think they can detect earth-size and larger-size planets by a "double spike" microlensing effect.

the star causes a large broad blip in the lightcurve and the planet causes a smaller sharp blip superimposed on it.

I cannot vouch for this. It may not be a reliable webpage. It has a lot of links to established microlensing searches and established planet searches, so it might be a useful page as well as being a curiosity. The page is called "Microlensing Planet Search". Tell me if you think it has any interest or is just weird

http://bustard.phys.nd.edu/MPS/
 
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It's not wierd, but the detection rate would be pretty low, even if there were lots and lots of planets. Planets orbit in a plane, so the path of lensing object (as seen by us) would need to be in (or sufficiently close to) the orbital plane.

IIRC, there was quite a lot of excitement over the light curve of a caustic crossing lens event, some saw it as evidence of a planet.
 

1. How does microlensing detect planets?

Microlensing detects planets by using the gravitational lensing effect of the planet's mass on the light of a distant star. When the planet passes in front of the star, the gravitational pull of the planet causes the light from the star to bend, creating a temporary increase in brightness that can be detected by telescopes.

2. What are MACHOs and how are they related to microlensing?

MACHOs (Massive Astrophysical Compact Halo Objects) are objects, such as black holes or brown dwarfs, that do not emit light but can still be detected through their gravitational effects. Microlensing can detect MACHOs by observing the gravitational lensing effect they have on light from distant stars.

3. Can microlensing detect all types of planets?

Microlensing can detect planets that are relatively close to their host star, typically within a few astronomical units (AU). This method is not as effective for detecting planets that are farther away from their star, such as gas giants in the outer regions of a solar system.

4. What advantages does microlensing have over other planet detection methods?

Microlensing is able to detect planets that are relatively far from Earth, making it a useful method for discovering planets in distant solar systems. It is also sensitive to smaller planets, including Earth-sized planets, which can be difficult to detect with other methods.

5. Are there any limitations to using microlensing for planet detection?

One limitation of microlensing is that it is only effective for detecting planets that are aligned with the observer's line of sight. This means that only a small fraction of planets in the galaxy can be detected through this method. Additionally, microlensing events are rare, so it may take a long time to observe a planet using this method.

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