AGNs and Cross Matching Algorithms

17/4/2019 Cross Matching in a nutshell.

We begin our story with Active Galactic Nuclei colloquially known as AGN. In a nutshell they are Supermassive Black Holes surrounded by accretion disks of matter that shoot out jets of radiation in the form of radio lobes that are pretty exotic things to see in the radio spectrum.

Here is an artists rendition:

This is what they look like in the Radio

They are primordial objects found in the early universe. To borrow a quote from Armand Delsemme "When the Quazars shone their dazzling brilliance"... that "dazzling brilliance" refers to the fact that AGNs can shine at much higher than normal luminosity in all over the EM spectrum.

And in fact they do.

The radiation from the accretion disk is brightest in Optical and Ultraviolet

The Gas and Dust that surrounds the Black Hole is visible in the Infrared

Hot gas surrounding the black hole gets heated up and emits X Rays

The jets emitted by the black hole are visible for many lightyears in radio frequencies

So we point many different telescopes in the same direction in order to see them. There's a diverse ecosystem of telescopes and eyes on the sky that humanity has at its disposal. All of which can be used to study Active Galactic Nuclei

But there is a problem. y and X-ray telescopes are located in space and orbit the Earth with different periodicity. Optical Telescopes are placed on mountain tops all over the world, and radio telescopes are situated in barren deserts tucked far away from any radio frequency interference. 

How do we study the same brilliant dazzling objects with such different equipment?

Coordinating these instruments to look at the same object in the sky require a herculean task of cooperation and cross border collaboration that demonstrate capacity for humans to let go of their differences and unite in the effort of studying the Cosmos, ancient and vast from which we spring.

The solution to this problem is: Cross Matching Algorithms 

Here is a diagram of what cross matching implies:

Cross Matching Astronomical Objects from different Catalogs. VLA, SDDS, Hubble

This is what a naive cross matcher (pseudocode) would look like:

for l in range (0, len(cat A)):
    for m in range (0, len(cat B)):
        calculate offset = angulardistance (A, B)
        if offset < radius
            if offset = smallest value so far
            return best_match = (A, B, offset)

Where A, B are RA, Dec values for a catalog.

These have a connection to big data, and to the whole Billions and Billions thing in the Universe. I will talk about in following entries.