Gravitational Lensing-III
“Now, here, you see, it takes all the running you can do, to keep in the same place. If you want to get somewhere else, you must run twice as fast as that.”-Lewis Carol (The Red Queen in Lewis Carroll’s Through the Looking Glass)
We know the weak equivalence principle, where the trajectory of a freely falling test body depends only on its initial position and velocity and is independent of its composition, and the inertial mass and the gravitational mass are equal.
We now consider a weak gravitational field where the traversing gravitational potential \phi is much less than the velocity of light.
Hence as \phi tends to 0, r tends to infinity.
where k is the Unperturbed photon.
from an axially symmetric lens, the deflection is the direction pointing from the lens center to the object given by
We know for massive galaxies like our Milky Way Galaxy or elliptic galaxies, the value for \sigma is approximately equal to 200km/s
Hence, we get the value of \beta from equation 8. Here, we limited our discussion to single-plane lensing; in the next blog, we will discuss multiplane lensing.
Till the Byee❤
Keynotes:
- An unperturbed photon is a photon that is not interacting with any other particles or fields. This means it travels in a straight line at the speed of light, and its energy and momentum are conserved. Unperturbed photons are rare in the universe. Most photons interact with other particles or fields, such as electromagnetic or gravitational fields. However, unperturbed photons can be found in special cases, such as cosmic microwave background radiation. Unperturbed photons are essential for understanding the universe. They can be used to study the early universe, dark matter, and dark energy. For example, the cosmic microwave background radiation is a remnant of the Big Bang, providing information about the universe's conditions shortly after the Big Bang.
- lensed quasars are nothing but quasars that are gravitationally lensed by an object.
To understand gravitational lensing, I’ve gone through books like
- Introduction to Cosmology by Barbara Ryden
- Dynamics and Astrophysics of Galaxies by Joe Bovy
- lecture notes on GR and SR by the Hong Kong University of Science and Technology
- Gravitational Lensing: Strong, Weak andMicro Saas-Fee Advanced Course 33, Swiss Society for Astrophysics and Astronomy (Edited by G. Meylan, P. Jetzer and P. North)
