page_title: Extreme mass ratio inspiral
section_title: Modelling
hierarchical_section_title: Extreme mass ratio inspiral / Modelling
caption_attribution_description: English: Diagram show the relationship between various approaches to modelling black hole binaries.
context_page_description: In astrophysics, an extreme mass ratio inspiral is the orbit of a relatively light object around a much heavier object, that gradually decays due the emission of gravitational waves. Such systems are likely to be found in the centers of galaxies, where stellar mass compact objects, such as stellar black holes and neutron stars, may be found orbiting a supermassive black hole. In the case of a black hole in orbit around another black hole this is an extreme mass ratio binary black hole. The term EMRI is sometimes used as a shorthand to denote the emitted gravitational waveform as well as the orbit itself.
  The main reason for scientific interest in EMRIs is that they are one of the most promising sources for gravitational wave astronomy using future space-based detectors such as the Laser Interferometer Space Antenna. If such signals are successfully detected, they will allow accurate measurements of the mass and angular momentum of the central object, which in turn gives crucial input for models for the formation and evolution of supermassive black holes.
context_section_description: Although the strongest gravitational wave from EMRIs may easily be distinguished from the instrumental noise of the gravitational wave detector, most signals will be deeply buried in the instrumental noise. However, since an EMRI will go through many cycles of gravitational waves (~10⁵) before making the plunge into the central supermassive black hole, it should still be possible to extract the signal using matched filtering. In this process, the observed signal is compared with a template of the expected signal, amplifying components that are similar to the theoretical template. To be effective this requires accurate theoretical predictions for the wave forms of the gravitational waves produced by an extreme mass ratio inspiral. This, in turn, requires accurate modelling of the trajectory of the EMRI.
  The equations of motion in general relativity are notoriously hard to solve analytically. Consequently, one needs to use some sort of approximation scheme. Extreme mass ratio inspirals are well suited for this, as the mass of the compact object is much smaller than that of the central supermassive black hole. This allows it to be ignored or treated perturbatively.
caption: Diagram showing the relationship between various approaches to modelling extreme mass ratio inspirals.
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