# Luminosity

#### Michael Varn

Is there a limit to luminosity?

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 galaxies.

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

##### "Science begets knowledge, opinion ignorance.
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.

#### Catastrophe

##### "Science begets knowledge, opinion ignorance.
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

vincenzosassone

#### 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. ]

Catastrophe

#### Pogo

It seems that many things invented after the separation of the British and American cultures have different terms for each. Flashlight v torch; truck v lorry; hood v bonnet; trunk v boot, to name a few. It’s what they were named by each culture.

vincenzosassone

#### Pogo

I’ve heard that since I was a kid. Lorry tends to refer the more commercial size trucks, but I found an article at bbc UK that refers to them as pickups. Not even sure where the term ‘pickup’ came from. Check out the Truck article at Wikipedia. Perhaps @Catastrophe or someone can enlighten us about the term ‘lorry’.

#### vincenzosassone

It seems that many things invented after the separation of the British and American cultures have different terms for each. Flashlight v torch; truck v lorry; hood v bonnet; trunk v boot, to name a few. It’s what they were named by each culture.
Being not native, this scare me. I really can't believe that sometimes you don't understand each other, that's strange.
Anyway, talking about limits, we found a lot of limits in our Universe (even though I don't think they are limits of our Universe, but our limits in the understanding of it instead!). I've heard about limits in time (the smallest unit of time possible) as well as in distance (always the same stuff). We have a limit in speed, but this is something we all know, and a limit in temperature as well. I have never thought about it before, but a limit in brightness is something I've never heard about. Well then, if I'm not mistaken though, some limits must even be present in brightness since nothing can be darker than a Black Hole and nothing can be brighter than a Quasar. Correct me if I'm wrong.

#### Pogo

A few terms are different in English in different countries or regions. I believe it may be the same in other languages, for example, Latin American Spanish is not the same as Spanish in Spain. Anyway, Planck units, speed of light and the constant of gravitation are fundamental units of nature, absolute zero temperature is calculated where all molecular motion stops, in theory. Maximum light or EM radiation is limited by the material emitting the light and its ability to propagate and emit the energy, not a fundamental unit. Very good discussion, though.

#### vincenzosassone

A few terms are different in English in different countries or regions. I believe it may be the same in other languages, for example, Latin American Spanish is not the same as Spanish in Spain.
You're right after all, I'm not so used to this speech since my language isn't so spoken throughout the world...
absolute zero temperature is calculated where all molecular motion stops
If I'm not mistaken, this is something that can be found in Black Holes too. I know that Black Holes are very cold in their central point, the singularity. We are talking about a fraction of a kelvin, and, since Black Holes are all roughly the same (their properties are the same), and besides that, the 0 kelvin cannot be reached, these objects are the coldest ones. Anyway, maybe, the same speech can be done for luminosity, that is very close to zero in their singularity.
Maximum light or EM radiation is limited by the material emitting the light and its ability to propagate and emit the energy, not a fundamental unit.
The Maximum point, in my opinion can't be calculated.

Catastrophe

#### IG2007

##### "Don't criticize what you can't understand..."
Is there a limit to luminosity?

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 galaxies.

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.

There is indeed a limit to luminosity. We know that,

Luminosity = Stefan-Boltzmann Constant x Surface Area x Temperature in Kelvin^4

Now, the Stefan-Boltzmann Constant is based on the fact that "the total intensity radiated over all wavelengths increases as the temperature increases." And, as we know, planck temperature is the maximum limit of heat/energy possible. Therefore (someone do the Maths for me ), there is indeed a limit to luminosity.

And, anyway, you can check this out: https://en.wikipedia.org/wiki/Eddington_luminosity

#### Catastrophe

##### "Science begets knowledge, opinion ignorance.
I’ve heard that since I was a kid. Lorry tends to refer the more commercial size trucks, but I found an article at bbc UK that refers to them as pickups. Not even sure where the term ‘pickup’ came from. Check out the Truck article at Wikipedia. Perhaps @Catastrophe or someone can enlighten us about the term ‘lorry’.

Google gives you this short version:
"In the British transport industry, most drivers would categorise an HGV as a lorry, a truck, or an artic (an articulated vehicle.) ... The truth is, a lorry in American English is a truck. The British lorry is almost the same as the American truck, and the two words have morphed into synonyms of each other."

Helio

#### Helio

It looks like that a lorry is a commercial truck, typically larger than a pickup, used for hauling materials. We have, for instance, "dump trucks"," tankers", "haul trucks" -- the heavy haulers have "tractors" (more often still called trucks) pulling trailers.

A personal vehicle seems to be called a truck, perhaps even a "pickup truck". Is this an accurate statement?

BTW, though Spanish for truck is camion (a road is called "camino"), in Texas it is often called a "trucka" (Tex-Mex).

Last edited:

#### IG2007

##### "Don't criticize what you can't understand..."
Oh, come on. Lorry = Truck, over.

P.S.: We call it lorry in India too, but we also call it truck.

Catastrophe

#### Catastrophe

##### "Science begets knowledge, opinion ignorance.
BTW, we often personalize our vehicles by giving them female names. So I assume there is a song in the UK called Lorrie Lorry?
Never heard that one! Cat

#### Helio

Never heard that one! Cat
Yep. My wife, before we were married, had names for all her previously owned vehicles. All were quite used and problematic, providing some character context, perhaps.

"Murphy" was her Biscayne (Chevy)
"Stanley" was her Olds
"Nelle Bell" was her Impala (Chevy)

Note that women give male names to cars, men use female names. Naming cars isn't that common, but it is true in our family. Of course, all horses have names, so maybe it is more common than I suggest.

Her "Nelle Bell" is a female name only because it's the original name given it by the former male owner.

I have a mustang named Frankie (female for Frank, for Frank Bullit, for the movie "Bullit").

Catastrophe

#### Catastrophe

##### "Science begets knowledge, opinion ignorance.
BTW, you can Google emphasis italics underline quotes.

There is a lot there, but I'm not sure I would go by all or it. Possibly, there was some influence when people used typewriters instead of computers. There were quotation marks, bit no underlining or italics. Hence, the use of quote marks took over the emphasis mantle.

Cat

#### Catastrophe

##### "Science begets knowledge, opinion ignorance.
Helio, it was Lorrie Lorry I had not heard of. Yes, vehicles are/were given names, but, I think, especially old vehicles. What was that film?

Cat

#### IG2007

##### "Don't criticize what you can't understand..."
I love the fact that we are discussing lorries in a luminosity thread!

Catastrophe

#### Helio

What was that film?
Video of Bullitt's world famous chase scene.

This is arguably the first great car chase scene in movies. There was an earlier movie made in England, IIRC, that had a chase scene and Hollywood liked what they saw, hired him, and made this big production.

Steve McQueen was not only a great actor but was also a race car driver, always requiring that he drive the vehicles in lieu of stunt men. The Mustang was souped-up for the movie.

Last edited:

Replies
107
Views
9K
Replies
10
Views
2K
Replies
0
Views
637
Replies
5
Views
1K
Replies
17
Views
2K