# Lumenosity

#### Michael Varn

Is there a limit to lumenosity?

Put simply, is there a limit to how bright light sources can get, like stars, or anything else in the universe?

I believe that the brightest light source in the universe are gamma ray bursts from distant galaxys.

I know that some light sources are larger than others, but I am thinking about limits in terms of comparisons to absolute zero, and Einstien's speed limit as it pertains to things in the universe that can only travel as fast as the speed of light, and no faster.

#### Helio

Nice question(s).

Luminosity refers more to flux, which is the number of photons per second for a star. It can be expressed in watts (energy per second). Think of the question of how big or small a drop of water can be ,then compare that to the question of how big a river can be. Those are two different questions.

A star is limited on its luminosity since if it were too luminous its radiation would blow itself apart. When stars form they get hotter and hotter and, if they are massive, the radiation they generate will push-away the disk that had been forming them. This limits how massive stars can be when they first form.

There may be some upper limit for how much energy can be in a single photon or other particle. The problem is to find a process that would channel incredible energy into such a particle. There are some events that do incredible things. For instance, a cosmic ray (proton) was found to have had the energy of a Nolan Ryan fast ball, and more powerful events have been observed since then.

Catastrophe

#### Catastrophe

Helio is, of course, correct.

Look at it this way - any luminosity, or, more generally, electromagnetic radiation, needs energy to generate it. Try shining your torch without any batteries in it.

So, simply, the output (electromagnetic radiation), needs input - so the limit is the amount of energy you can input.

Helio

#### Helio

Try shining your torch without any batteries in it.
I vaguely recall that your torch is our flashlight. I wonder what the history is behind that change?

Catastrophe

#### Catastrophe

Correct. We use flashlight to describe a larger version probably about 4-6 inches across. A torch (for us) is a smaller thing probably using AAA batteries (do you have AA AAA etc?).

Strange for us, because we also use the word torch to describe a larger flaming source of light. Hence the expression (do you have same?) "carry a torch for someone"? - probably meaning carry this to light their path, try to get "in" with them i.e., become friendly.

Has anyone produced a US/UK English dictionary

#### Helio

Correct. We use flashlight to describe a larger version probably about 4-6 inches across.
That's interesting. Any handheld, directional light is typically a flashlight for us. A lantern can be electric or otherwise, but that is for general area lighting and not directional.

A torch (for us) is a smaller thing probably using AAA batteries (do you have AA AAA etc?).
Yes, but usually for our little "torches".

Strange for us, because we also use the word torch to describe a larger flaming source of light.
So a torch is either a small flashlight or a large flaming source?

A literal torch for us is about any flame used for lighting. Most are hand-held. [We once (more than once, actually) ran a 160km relay carrying a hand torch that was used to light a college bonfire.]

Hence the expression (do you have same?) "carry a torch for someone"? - probably meaning carry this to light their path, try to get "in" with them i.e., become friendly.
Yep, we have that as well; no reason to miss-out on charming metaphors.

Has anyone produced a US/UK English dictionary
After presenting a new pair of cowboy boots to a German factory owner, I later that day gave him a cd of how to talk Texan. I told him that if he was gonna "walk the walk" he should "talk the talk". [A year or so later he told me he did wear those boots every time he rode his Harley. He still sounded German, however. ]