What is a Gravitational Microlensing Method?

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The hunt for extra-solar planets certain has exhilarated adult in a past decade. Thanks to improvements done in record and methodology, a series of exoplanets that have been celebrated (as of Dec 1st, 2017) has reached 3,710 planets in 2,780 star systems, with 621 complement braggadocio mixed planets. Unfortunately, due to several boundary astronomers are forced to contend with, a immeasurable infancy have been rescued regulating surreptitious methods.

One of a some-more commonly-used methods for indirectly detecting exoplanets is famous as Gravitational Microlensing. Essentially, this process relies on a gravitational force of apart objects to hook and concentration light entrance from a star. As a world passes in front of a star relations to a spectator (i.e. creates a transit), a light dips measurably, that can afterwards be used to establish a participation of a planet.

In this respect, Gravitational Microlensing is a scaled-down chronicle of Gravitational Lensing, where an inserted intent (like a universe cluster) is used to concentration light entrance from a universe or other intent located over it. It also incorporates a pivotal component of a highly-effective Transit Method, where stars are monitored for dips in liughtness to prove a participation of an exoplanet.


In suitability with Einstein’s Theory of General Relativity, sobriety causes a fabric of spacetime to bend. This outcome can means light influenced by an object’s sobriety to turn twisted or bent. It can also act as a lens, causing light to turn some-more focused and creation apart objects (like stars) seem brighter to an observer. This outcome occurs usually when a dual stars are roughly accurately aligned relations to a spectator (i.e. one positioned in front of a other).

These “lensing events” are brief, though plentiful, as Earth and stars in a universe are always relocating relations to any other. In a past decade, over one thousand such events have been observed, and typically lasted for a few days or weeks during a time. In fact, this outcome was used by Sir Arthur Eddington in 1919 to furnish a initial experimental justification for General Relativity.

This took place during a solar obscure of May 29th, 1919, where Eddington and a systematic speed trafficked to a island of Principe off a seashore of West Africa to take cinema of a stars that were now manifest in a segment around a Sun. The cinema reliable Einstein’s prophecy by display how light from these stars was shifted somewhat in response to a Sun’s gravitational field.

The technique was creatively due by astronomers Shude Mao and Bohdan Paczynski in 1991 as a means of looking for binary companions to stars. Their offer was polished by Andy Gould and Abraham Loeb in 1992 as a process of detecting exoplanets. This process is many effective when looking for planets towards a core of a galaxy, as a galactic gush provides a vast series of credentials stars.


Microlensing is a usually famous process means of anticipating planets during truly good distances from a Earth and is means of anticipating a smallest of exoplanets. Whereas a Radial Velocity Method is effective when looking for planets adult to 100 light years from Earth and Transit Photometry can detect planets hundreds of light-years away, microlensing can find planets that are thousands of light-years away.

While many other methods have a showing disposition towards smaller planets, a microlensing process is a many supportive means of detecting planets that are around 1-10 astronomical units (AU) divided from Sun-like stars. This creates it generally effective when interconnected with a Radial Velocity and Transit Methods, that can endorse a existence of exoplanets as good as furnish accurate estimates of a planet’s radius and mass.

Taken together, these advantages make microlensing a many effective process for anticipating Earth-like planets around Sun-like stars (alone or in multiple with other methods). In addition, microlensing surveys can be effectively mounted regulating ground-based facilities. Like Transit Photometry, a Microlensing Method advantages from a fact that it can be used to consult tens of thousands of stars simultaneously.


Because microlensing events are singular and not theme to repeat, any planets rescued regulating this process will not be understandable again. In addition, those planets that are rescued tend to be really distant way, that creates follow-up investigations probably impossible. This creates microlensing a good means for detecting exoplanet candidates, though a really bad means for confirming candidates.

Another problem with microlensing is that it is theme to a substantial domain of blunder when fixation constraints on a planet’s characteristics. For example, microlensing surveys can usually furnish severe estimations of a planet’s distance, withdrawal vast margins for error. This means that planets that are tens of thousands of light-years from Earth would furnish stretch estimates with a domain of several thousand light-years.

Microlensing is also incompetent to furnish accurate estimates of a planet’s size, and mass estimates are theme to lax constraints. Orbital properties are also formidable to determine, given a usually orbital evil that can be directly dynamic with this process is a planet’s stream semi-major axis. As such, planet’s with an individualist circuit will usually be detectable for a little apportionment of a circuit (when it is distant divided from a star).

The gravitational microlensing outcome increases as a outcome of a planet-to-star mass ratio, that means that it is easiest to detect planets around low-mass stars. This creates microlensing effective in a hunt for hilly planets around low mass, M-type (red dwarf) stars, though boundary a efficacy with some-more large stars. Finally, microlensing is contingent on singular and pointless events – a thoroughfare of one star precisely in front of another, as seen from Earth – that creates detections both singular and unpredictable.

Examples of Gravitational Microlensing Surveys:

Surveys that rest on a Microlensing Method embody a Optical Gravitational Lensing Experiment (OGLE) during a University of Warsaw. Led by Andrzej Udalski, a executive of a University’s Astronomical Observatory, this international plan uses a 1.3 scale “Warsaw” telescope during Las Campanas, Chile, to hunt for microlensing events in a domain of 100 stars around a galactic bulge.

The Astronomical Observatory during a University of Warsaw, used to control a OGLE project. Credit: ogle.astrouw.edu.pl

There is also a Microlensing Observations in Astrophysics (MOA) group, a collaborative bid between researchers in New Zealand and Japan. Led by Professor Yasushi Muraki of Nagoya University, this organisation uses a Microlensing Method to control surveys for dim matter, extra-solar planets, and stellar atmospheres from a southern hemisphere.

And afterwards there’s a Probing Lensing Anomalies NETwork (PLANET), that consists of 5 1-meter telescopes distributed around a southern hemisphere. In partnership with RoboNet, this plan is means to furnish near-continuous observations for microlensing events caused by planets with masses as low as Earth’s.

We have created many engaging articles on exoplanet showing here during Universe Today. Here is What are Extra Solar Planets?, What is a Transit Method?, What is a Radial Velocity Method?, What is Gravitational Microlensing? and Kepler’s Universe: More Planets in a Galaxy than Stars

For some-more information, be certain to check out NASA’s page on Exoplanet Exploration, a Planetary Society’s page on Extrasolar Planets, and a NASA/Caltech Exoplanet Archive.

Astronomy Cast also has applicable episodes on a subject. Here’s Episode 208: The Spitzer Space Telescope, Episode 337: Photometry, Episode 364: The CoRoT Mission, and Episode 367: Spitzer Does Exoplanets.

Further readings:

  • NASA – 5 Ways to Find a Planet
  • Planetary Society – Microlensing
  • Wikipedia – Methods of Detecting Exoplanets

Source: Universe Today, created by Matt Williams.

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