Lecture

Introduction to Astrophysics: Gravitational Lensing

Graph Chat

Chat with Graph Search

Ask any question about EPFL courses, lectures, exercises, research, news, etc. or try the example questions below.

DISCLAIMER: The Graph Chatbot is not programmed to provide explicit or categorical answers to your questions. Rather, it transforms your questions into API requests that are distributed across the various IT services officially administered by EPFL. Its purpose is solely to collect and recommend relevant references to content that you can explore to help you answer your questions.

In course

PHYS-209: Astrophysics I: introduction to astrophysics

Ce cours décrit de façon simple les processus physiques qui expliquent l'univers dans lequel nous vivons. En couvrant une large gamme de sujets, le but du cours est aussi de donner un aperçu général des objets astrophysiques qui nous entourent. ...

Description

This lecture introduces the concept of gravitational lensing in astrophysics, focusing on the deflection angle and the Einstein radius. It explains the solution for a point-like lens and its application to galaxies and the whole universe, illustrated with images of Einstein rings and gravitational arcs.

In MOOC

Introduction to Astrophysics

How can we study the Universe we live in using the only available information it provides us with: light ? This course provides an overview of the physical phenomena at play in the astronomical objects surrounding us, from planets and stars to the cosmic filaments, from galaxies such as our own Milky Way to large galaxy clusters. The course emphasizes the links between theoretical predictions and observations. In this course, you will learn the basics of astrophysics using simplified mathematical developm

Official source

Ontological neighbourhood

Astronomy

Astrophysics: Physical cosmology, Stellar astronomy

Related concepts (32)

Gravitational lens

A gravitational lens is a distribution of matter (such as a cluster of galaxies) or a point particle between a distant light source and an observer that is capable of bending the light from the source as the light travels toward the observer. This effect is known as gravitational lensing, and the amount of bending is one of the predictions of Albert Einstein's general theory of relativity. Treating light as corpuscles travelling at the speed of light, Newtonian physics also predicts the bending of light, but only half of that predicted by general relativity.

Einstein ring

An Einstein ring, also known as an Einstein–Chwolson ring or Chwolson ring (named for Orest Chwolson), is created when light from a galaxy or star passes by a massive object en route to the Earth. Due to gravitational lensing, the light is diverted, making it seem to come from different places. If source, lens, and observer are all in perfect alignment (syzygy), the light appears as a ring. Gravitational lensing is predicted by Albert Einstein's theory of general relativity.

Strong gravitational lensing

Strong gravitational lensing is a gravitational lensing effect that is strong enough to produce , arcs, or even Einstein rings. Generally, for strong lensing to occur, the projected lens mass density must be greater than the critical density, that is . For point-like background sources, there will be multiple images; for extended background emissions, there can be arcs or rings. Topologically, multiple image production is governed by the odd number theorem.

Weak gravitational lensing

While the presence of any mass bends the path of light passing near it, this effect rarely produces the giant arcs and multiple images associated with strong gravitational lensing. Most lines of sight in the universe are thoroughly in the weak lensing regime, in which the deflection is impossible to detect in a single background source. However, even in these cases, the presence of the foreground mass can be detected, by way of a systematic alignment of background sources around the lensing mass.

General relativity

General relativity, also known as the general theory of relativity and Einstein's theory of gravity, is the geometric theory of gravitation published by Albert Einstein in 1915 and is the current description of gravitation in modern physics. General relativity generalizes special relativity and refines Newton's law of universal gravitation, providing a unified description of gravity as a geometric property of space and time or four-dimensional spacetime.

Related lectures (64)

Gravitational Lenses MOOC: Introduction to Astrophysics

Covers gravitational lenses, deflection angle, lens equation, and their application to galaxies and the universe.

Thermal history of the Universe

Explores the evolution of the Universe, from its early stages to the present, covering topics such as astroparticle physics and the thermal history.

Hubble's Universe: Redshift and Distance MOOC: Introduction to Astrophysics

Delves into the universe's evolution using Hubble's observations and concepts like redshift, distance measurement, Cepheid stars, and supernovae.

Cosmological Constraints on Neutrino Masses

Explores Boltzmann H-theorem, entropy conservation, neutrino freezing, nucleosynthesis, and cosmological constraints.

Cosmic Magnetic Fields: Generation and Backreaction