what is the maximum density of light?

Question

OK, so maybe I didn't add enough detail... if a point source of light (lets say a galaxy far, far away..pun intended) contains X photons/sec that are directed toward our own planlet, based on the distance (beyond 13 billion light years just for fun, imagine a shpere 13billion light years in radius and our planet as a single point on the sphere) and potential interference of matter (possibility of hitting a dust paricle etc. 0.00001% no idea on if this is in the ball park) how many photons /sec must be generated by the point source in order for us to detect that source today (given a collection/viewing time of 10 min with a 10meter lens)? in other words what is the required "density" ( yes I know the term is not correct) of light in order for us to detect the source? and the big one... how far away can a point source be and still be detected by our telescopes?

Answer 1

i think it is 0/0, which is:

infinity OR 0

Answer 2

We can detect individual photons these days. With your huge lens and 10 minute exposure time you'd need onephoton every 10 minutes in your lens, area 78.5 sq.m., that's 2x10^-5 photons per sq.m. per sec.on the surface of your 13 billion ly radius sphere. so multiply 2x10^-5 by2x10^53 sq.m. and you get 4x10^48 photons per sec. need to be emitted by your distant source for it to be detectable by us. For visible light that's about 10^34 watts of luminous power, which is about 100 million Suns. So we'd just barely be able to detect a whole galaxy at this distance. That doesn't allow for absorption of light by the intergalactic medium or for energy loss due to redshifting.

Answer 3

It sounds like you want to know the luminosity of a star for us to be able to spot it. I have no idea what the actual equation would be to calculate it, or if you even could. It would take alot of equations to do if it were possible. You have alot of factors to look at, including distance away, what's in the line of sight, etc. But with a 10 m lens it would have to be pretty bright, regardless of luminosity. Andthe farther away you get, it would have to be comparably MUCH brighter to see it from so far away.

Answer 4

Perhaps you mean to say, "What is the maximum INTENSITY of light".

To my knowledge "light" is always near the same "density".

But you can measure the Intensity of light, say at the surface of the sun, (in Lumens) and you can measure the most intense laser beam mankind can make, but if light has Mass, (some say it doesn't ,I think it does, but so little we may never be able to measure it), then it's density would be determined by it's realized velocity in whatever Inertial Reference Frame it finds itself.