Could a super energetic light pulse create a black hole?

hmmm, this lay-person doesn't get how light could be a black hole. Wouldn't there have to be a nucleus of some sort?

Because that concentration of energy (10 ^ 50 Joules) in a light pulse 0.3 mm long would easily contain enough energy to close spacetime for a radius of about 30 kilometres (using German astrophysicist Kurt Schwarzschild famous equation, letting force = v^2/ r as v -> c = gravity GM/r^2 and solving for r as a function of M a stars Mass).

I have substituted E for M using e = mc^2, so just multiplied our suns mass 2 * 10^30 Kg by c^2 by a factor of 10 to make sure you get a black hole (any Sun 5 times bigger than ours forms a black hole eventually).

By keeping the light burst short the energy density falls within the critical Schwarzschild radius needed to ensure gravitational collapse.



But the challenge here (other than realising pure energy - not just pure mass - can cause gravitational collapse) is to query what happens if this energy is moving at lightspeed. Gravity propogates at lightspeed too, so the question is how do they synchronise and interact.

A Sun's collapse into a blackhole from start to end is modelled as takeing about 3 thousanths of a second. A light pulse can travel about a thousand kilometres in this timeframe so my question is can the gravitational collapse keep up with the moving front that is the trigger to the collapse.

* * *

Imagine our sun was 10 times bigger and at the end of its lifetime it almost completely imploded. But before it completely gravitationally collapses it channels all its energy almost instaneously into a beam of pure energy bisecting its poles of rotation - one beam travelling up and one travelling down emitted from its North and South poles.

In this hypothetical situtation if those light pulses contained all its energy and these were almost instaneous - say around a billionth of a second - you'd more or less have the thought experiment I described. You'd have your gravitation curvature of spacetime both concentrate and rip in half and seperate at lightspeed.

But a star is more than just light. Does light = energy = mass?

Those north and south jets don't form the resulting black hole, they escape it, no?

It does not seem to me a single beam of photons can produce a black hole except possibly by striking a neutron star or a quark star, if there are any quark stars.
A better strategy might be to scale up the thousand lasers used to try produce nuclear fission. The beams converge from all directions. I think some what more than one pico second is needed as the shock wave would propagate at slightly less than the speed of light and needs to be sustained until the shock wave converged at the center of the quark star = several nano seconds?
We don't know a mechanism for making Earth mass black holes, but we believe they would persist very long term if they could find mass to ingest at the same rate that they evaporate mass. Otherwise they would shrink in a few years until they exploded with a burst of gamma rays. Neil

Not anymore.

littlek

A star was an illustration of perhaps the engine that could produce such an energy blast, it was the fuel source no more or less in that example. In reality a star is unlikely to convert more than a small part of its mass to pure energy at any one time. The most it possibly converts / releases is during a super nova or implosion towards a black hole - what ever isn't sucked it gets ejected at fantastic energy levels.

My example assumed almost 100% conversion to energy and all in a micro or pico second - not a millisecond process. Two very unlikely but not impossible conditions.

But focusing trillions of powerful lasers could approximate the same scenario.

The escaping jets are like two lightspeed black holes racing apart. If in that scenario the two halves ejected as high speed suns split apart and moving in opposite directions - I am sure no one would deny they'd form black holes in their own right if both halves were massive enough.

Now simply speed them up towards lightspeed - still no problem. Now instead of having them as large chunks of matter consider them as super energetic beams of light; very short beams of light is all it takes to do the trick.

neil

If you combined enough laser pulses into one enormous pulse such that its energy level was far past that required to create fusion - trillions upon trillions upon trillions of times higher - and concentrated - than those factors together would give a greater energy concentration than any neutron star. Whilst such a beam hitting a neutron star would be catalysmic and could produce a black hole, we are talking about a beam of energy many times more powerful than a neutron star itself.

Yes it is fanciful in all but one or two situations - the birth of the Universe or the death of a protstar (those early stars believed to be 100s of times larger (and shorter lived) than stars today). Those conditions could have produced such a outburst. At temperatures above 10 ^ 25 Kelvin matter is likely to be transformed to pure energy anyway.

Tobruk

Energy and mass are equivalent, they are merely different states of a more fundamental thing (e.g. a 11 dimension string).

I thin I remember reading somewhere that when it comes to light energy and mass are not equiv.

From memory I know of no such constraint - impose enough energy and I guess you could alter just about any energy carrier photons, w, z or Higgs bosons into any other sub atomic particle.

But the energy levels I am pondering rarely if ever exist in this Universe. At those levels of energy density different laws of physics could hold sway even.

Hi g_day,

You might want to check the following links to see if your thought experiment makes sense in light of the difference between reltivistic mass and invariant mass.

http://math.ucr.edu/home/baez/physics/Relativity/SR/mass.html

I realize the links talk about mass, and not light beams, but I think the energy equations still apply.



http://math.ucr.edu/home/baez/physics/Relativity/BlackHoles/black_fast.html

http://math.ucr.edu/home/baez/physics/ParticleAndNuclear/photon_mass.html

Best Regards,

To create gravity you need mass. I don't think light creates gravity because it only has energy and no rest mass and it is rest mass that creates gravity.

I'd like to clear up a mis-conception about only rest mass causing a gravitational field (thanks for all those links, they were all good but didn't express any comments about whether energy causes gravity.

To create gravity you need rest mass... wrong according to an advanced high energy physics forum

Einstein's theory of general relativity says that G_uv=-8(pi)T_uv. There is a way to formulate T_uv with respect to the electromagnetic field tensor F_uv=a_u,v-a_v,u where a is the electromagnetic potential. This would mean that energy actually creates a gravitational effect just like it's mass equivalent.

http://www.advancedphysics.org/viewthread.php?tid=519&page=1

and

Basically: Einstein's equivalance principle tells us that inertial mass is equivalent to gravitational mass. From special relativity we know that the inertial mass (in any given inertial frame) of a particle is basically it's energy, therefore light has 'gravity'.

So if energy creates gravity that would mean that if someone built a spaceship that could travel at close to light speed they would cause everything in the universe to collapse into black holes because they would see the mass/energy of everything in the universe to increase from their point of view.

I remember seeing that question stated somewhere and answered as being wrong because only rest mass creates gravity otherwise the universe would be doomed.

Now I am way beyond my education here, but wouldn't what you are suggesting create a black hole moving at near luminous speeds? And if so; wouldn't it bounce around the universe like a giant pinball, gobbling up smaller objects (like our sun) until it encountered a super massive black hole?

Tobruk

No strangely enough, well its more complex than that, the rest mass relitvistically increases - but if you went incredibly fast you still wouldn't have near infinite mass from your own perspective, you would only have massive weight to an external point of reference. A black hole must be a black hole in every frame of reference so you have to be careful with these arguments. I will look for more authorative links that deal with this better.

Hi occam bill: a Super massive black hole could have an event horizon as big as our sun. but a ten solar mass black hole has an event horizon of much less than one mile, so at .99 c it would gobble less than a cubic mile of matter from most things it would collide with. Many cubic miles if it passed though the center of a star. Even at that speed it would take more than 100,000 years to cross our galaxy's diameter. Likely it would miss all of the stars near Earth and hit only a few house size objects.
It would have an accretion disk that would give you a nasty dose of radiation poisoning if it missed you by a small distance.

Occam Bill, it would be something you wouldn't want to encounter, a fast moving blackhole.

But worse than that its high speed might theoretically even tear spacetime abit. A stationery singularity is bad enough, a high speed one is far more dangerous, a lightspeed one might just rip some of the fabric of our reality and I am not sure what would do the mending...

Such an object at such a speed would give us next to zero warning. When most folks can be struck by a car travelling at 80 kph and 'not know what hit them', it would be over so damn quick that even the 'Armagedonnists' wouldn't have time to say "told you so!!"

Neil, thanks, I obviously overstated the parameters of the danger zone. Again, I am way beyond my depth here but even with an event horizon of less than a mile, wouldn't it be gobbling a hell of a lot more than a mile's worth of matter? As I understand it; the gravitational pull outside of the event horizon, while not as intense as that within, is still enormous for quite a distance. Otherwise how could they not know for sure that a Quasar has to contain a Black Hole, as opposed to just a Neutron Star?

Also, I wouldn't think a 10 solar mass black hole would remain a 10 solar mass black hole forever. Depending on the trajectory, it could grow at an amazing rate and I can ill imagine how much mass it would have to devour to slow to a drift from .99 c. It would probably have to become a super massive black hole before it got anywhere near stopping.

Never having been one to let ignorance (my own) stand in my way, I have a pet theory that an event horizon is actually the distance that all matter is accelerated to the speed of light. If that theory were correct, a speeding black hole would literally tunnel through the larger objects it encountered, growing in mass the whole way through. If this last paragraph is to foolish, please comment on the other two instead.

We can only 'view' the Universe through a number of 'windows' that all travel at the speed of light. Anything can happen out there and until we get a visual (or its equivalent) we don't know about it.

For all we know the entire Universe went to Hades a billion years ago and we just haven't got the message yet. What would tell us that a significant amount of space had just disappeared?