Looking in all the wrong places

I see what you mean, again I partially agree. I still think that there
will be a combination of radio/laser/etc signals. and interstellar
probes.

Here's the perfect analogy of what I'm suggesting;

When trying to find other people who like to read books that interest
you, if you go to a library or even on-line, the chances are extremely
higher to finding that person than, let's say, going door to door.

You mentioned on one of my other post's how gamma radiation wouldn't
be used as a communication method, which I agree on. What I was
implying was that gamma radiation could be sign of either antimatter or
fusion type drive, the only two types of energy sources that are
powerful enough for interstellar travel. Again all of this is based on
what we know today, an advanced civilisation probably would have come
up with several new tricks that we aren't aware of, but those I can
only guess at and aren't good to base a hypothesis on.
If we can detect gamma radiation in the terrawatt level circling
several AU's from a black hole this could be a sign of something. (of
course detecting something like that so close to an object that emits
exawatts of energy would be a technical challenge, but thats another
story)
Also if a probe is in orbit, maybe a polar orbit around a black hole,
the blind spot you mentioned wouldn't be a problem.

Thanks guys you've made this discussion very interesting and helped
clairify alot.

I see what you mean, again I partially agree. I still think that there
will be a combination of radio/laser/etc signals. and interstellar
probes.

Here's the perfect analogy of what I'm suggesting;

When trying to find other people who like to read books that interest
you, if you go to a library or even on-line, the chances are extremely
higher to finding that person than, let's say, going door to door.

You mentioned on one of my other post's how gamma radiation wouldn't
be used as a communication method, which I agree on. What I was
implying was that gamma radiation could be sign of either antimatter or
fusion type drive, the only two types of energy sources that are
powerful enough for interstellar travel. Again all of this is based on
what we know today, an advanced civilisation probably would have come
up with several new tricks that we aren't aware of, but those I can
only guess at and aren't good to base a hypothesis on.
If we can detect gamma radiation in the terrawatt level circling
several AU's from a black hole this could be a sign of something. (of
course detecting something like that so close to an object that emits
exawatts of energy would be a technical challenge, but thats another
story)
Also if a probe is in orbit, maybe a polar orbit around a black hole,
the blind spot you mentioned wouldn't be a problem.

Thanks guys you've made this discussion very interesting and helped
clairify alot.

In message , Rob
Dekker writes

Sorry to repeat myself, but surely you don't need a beacon by a pulsar,
because the pulsar is the best beacon you could have. All you have to do
is modulate it.

Sorry for not catching that.
So, how do you modulate the signal of a pulsar at-will ?
Don't tell me you want to put a shutter in front of it, please.

Why not? You fire objects into the beam. If you had a sufficiently high
technology (or a big enough object) you could try blocking the beam, but
it might be more efficient if the object was destroyed - you'd get a lot
more energy and much of it would be outside the beam.


And a black hole gives you unlimited power.

How do you transform the black-hole's power into something useful, like
electricity ?

Drop objects into it, again. Something like one third the mass comes out
as energy. The only other process that comes close is positron/electron
annihilation. Gets rid of your garbage, too - nuclear waste, condemned
criminals, anything.

"Jonathan Silverlight" wrote
in message ...
In message , Rob
Dekker writes

[...]

And a black hole gives you unlimited power.

How do you transform the black-hole's power into something useful, like
electricity ?

Drop objects into it, again. Something like one third the mass comes out
as energy. The only other process that comes close is positron/electron
annihilation. Gets rid of your garbage, too - nuclear waste, condemned
criminals, anything.

OK. But this energy comes out as comic rays. Not as useful electricity, or
something else that is easy to control.

If you want to use this energy directly as a beacon, then I'm actually not
convinced that it would be so efficient.

First of all, near a black hole or pulsar lots of debrit will fall in and
radiates cosmic rays out. So you would need to drop considerably
more mass in to 'stand out' from the rest of the radiation.

Second, again, cosmic ray's are very expensive : one cosmic ray photon
carries around 10^10 eV. That's more than 10 proton's if I'm not mistaken.
And a factor of 10^11 more than a Infrared photon.
So even if you drop your garbage in, you still don't get that many photons
back.

Third, since we are just dumping matter in, the direction in which the
cosmic rays will be hard to control. I'm not so sure if you can even
control at all in which direction(s) your beacon transmits. Worst case
it is omnidirectional (or half-omni-directional, since the other half gets
lots into the black hole). In that case, your photon density per arc sec
will be lousy. I did not do the math (even though this should not be too
difficult), but you might need to through-in a planet to transmit one
bit of information detectable at 10,000LYs...

Mmm. using a pulsar or black-hole as a beacon might not be so easy
after all huh ?

"Jonathan Silverlight" wrote
in message ...
In message , Rob
Dekker writes

Sorry to repeat myself, but surely you don't need a beacon by a pulsar,
because the pulsar is the best beacon you could have. All you have to
do
is modulate it.

Sorry for not catching that.
So, how do you modulate the signal of a pulsar at-will ?
Don't tell me you want to put a shutter in front of it, please.

Why not? You fire objects into the beam. If you had a sufficiently high
technology (or a big enough object) you could try blocking the beam,

That is still the 'shutter' idea. Point is that you don't need a pulsar
if you have a solar-size shutter. Any star will do. See previous postings on
this.

And a pulsar does NOT radiate omnidirectionally (as a star does).
Only in a narrow disk. Not very effective as a beacon.

Actually, one advantage of a pulsar over an ordinary star is that it is
small.
I give you that ) I think 10km or so.
So your shutter (for one particular direction) will not have to be large.

However, since its gravity is so immense, you could not possibly park
your shutter close to it. So the small shutter is both a curse and a
blessing.
One shutter will only 'aim' a very narrow part of the sky.
To create a omnidirectional beacon with a pulsar, you need a Dyson
sphere (or Dyson ring) with shutters. And we know these are horribly
instable, and
if that problem is solved they are exceptionally expensive.
Especially around a neutron star.

No. I think a optical beacon with ns laser pulses is still a LOT easier
and a LOT cheaper than any attempt to use the pulsar or black hole
itself as a beacon.

wrote in message
oups.com...

Rob Dekker wrote:

Sorry to repeat myself, but surely you don't need a beacon by a
pulsar,
because the pulsar is the best beacon you could have. All you have
to do
is modulate it.

Sorry for not catching that.
So, how do you modulate the signal of a pulsar at-will ?
Don't tell me you want to put a shutter in front of it, please.

And a black hole gives you unlimited power.

How do you transform the black-hole's power into something useful,
like
electricity ?

Maybe just drop matter in at regular intervals and you get a burst of
Hawkins Radiation?


And how do you turn the Hawkins Radiation into something useful,
like electricity ?

wrote in message
oups.com...
I see what you mean, again I partially agree. I still think that there
will be a combination of radio/laser/etc signals. and interstellar
probes.

Here's the perfect analogy of what I'm suggesting;

When trying to find other people who like to read books that interest
you, if you go to a library or even on-line, the chances are extremely
higher to finding that person than, let's say, going door to door.

You mentioned on one of my other post's how gamma radiation wouldn't
be used as a communication method, which I agree on. What I was
implying was that gamma radiation could be sign of either antimatter or
fusion type drive, the only two types of energy sources that are
powerful enough for interstellar travel.

That's indeed not a bad idea. I did not think of that.
So you mean that some gamma-ray's might actually be the 'exhaust'
of some alien space ship. Interesting.

Do you dare to speculate on the 'signature' of such an exhaust ?
I mean, how could we differentiate it from any natural gamma-ray's ?


[....]
If we can detect gamma radiation in the terrawatt level circling
several AU's from a black hole this could be a sign of something. (of
course detecting something like that so close to an object that emits
exawatts of energy would be a technical challenge, but thats another
story)

At gamma-ray fequencies, you need a lot more than terra-watts or
even exowatts. You need something in the range of 10^23 watts,
to compensate for the 10^11 energy difference between IR and
gamma photons.


Thanks guys you've made this discussion very interesting and helped
clairify alot.


Yeah. It's fun, isn't it ? I love these thought experiments to test wild
ideas.

"Rob Dekker" wrote in message
. com...


At gamma-ray fequencies, you need a lot more than terra-watts or
even exowatts. You need something in the range of 10^23 watts,
to compensate for the 10^11 energy difference between IR and
gamma photons.


Oops. Made a mistake here. Energy difference between gamma
and IR photons is about 10^7. So you 'only' need 10^19 Watt.
The 10^11 factor versus IR is cosmic rays. These are the ones
with energy of 10 protons.

In message , Rob Dekker
writes

wrote in message
roups.com...

Rob Dekker wrote:

Sorry to repeat myself, but surely you don't need a beacon by a
pulsar,
because the pulsar is the best beacon you could have. All you have
to do
is modulate it.

Sorry for not catching that.
So, how do you modulate the signal of a pulsar at-will ?
Don't tell me you want to put a shutter in front of it, please.

And a black hole gives you unlimited power.

How do you transform the black-hole's power into something useful,
like
electricity ?

Maybe just drop matter in at regular intervals and you get a burst of
Hawkins Radiation?


And how do you turn the Hawkins Radiation into something useful,
like electricity ?

Slight confusion here - that's Hawking, not Hawkins, radiation, and for
a black hole of any reasonable size it's negligible. It's not produced
by matter falling into the BH but from pair production close to the
event horizon.

In message , Rob
Dekker writes

"Jonathan Silverlight" wrote
in message ...
In message , Rob
Dekker writes

[...]

And a black hole gives you unlimited power.

How do you transform the black-hole's power into something useful, like
electricity ?

Drop objects into it, again. Something like one third the mass comes out
as energy. The only other process that comes close is positron/electron
annihilation. Gets rid of your garbage, too - nuclear waste, condemned
criminals, anything.

OK. But this energy comes out as comic rays. Not as useful electricity, or
something else that is easy to control.

If you want to use this energy directly as a beacon, then I'm actually not
convinced that it would be so efficient.

First of all, near a black hole or pulsar lots of debrit will fall in and
radiates cosmic rays out. So you would need to drop considerably
more mass in to 'stand out' from the rest of the radiation.

Second, again, cosmic ray's are very expensive : one cosmic ray photon
carries around 10^10 eV. That's more than 10 proton's if I'm not mistaken.
And a factor of 10^11 more than a Infrared photon.
So even if you drop your garbage in, you still don't get that many photons
back.

Third, since we are just dumping matter in, the direction in which the
cosmic rays will be hard to control. I'm not so sure if you can even
control at all in which direction(s) your beacon transmits. Worst case
it is omnidirectional (or half-omni-directional, since the other half gets
lots into the black hole). In that case, your photon density per arc sec
will be lousy. I did not do the math (even though this should not be too
difficult), but you might need to through-in a planet to transmit one
bit of information detectable at 10,000LYs...

Sorry, but everything you've said convinces me I'm right :-)
The energy from a black hole peaks in the keV X-ray region - at least
that's what I gather from reading about Cygnus X-1, the best candidate.
Coincidentally, that's about 10,000 ly away (2500 parsecs). X-ray pulses
would be obvious to another technological civilisation, but you could
probably convert them to radio.
The accretion rate is about 10^18 g/s according to
http://www.journals.uchicago.edu/ApJ...87n1/35947/sc5
..html - you're right, we need a fair size asteroid to make a
difference. Think big.
The omnidirectional effect is actually an advantage for a beacon, but
I'm not convinced you'll get it. You'd probably get a jet and the
resultant beaming.