# The Naked Scientists Forum

### Author Topic: what warning would we get from nearby blackholes  (Read 1666 times)

#### syhprum

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##### what warning would we get from nearby blackholes
« on: 14/10/2010 16:51:41 »
As blackholes approach the end of their life presumably the radiation they give off increases at an exponential rate, if a BH was located 1 parasec from the solar system and was rapidly approaching the end of its life what sort of time would elapse between it becoming detectable and its life end burst of radiation that might endanger us

#### lightarrow

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##### what warning would we get from nearby blackholes
« Reply #1 on: 14/10/2010 19:24:25 »
It strongly depends on its mass:
http://xaonon.dyndns.org/hawking/

select the dimensions of the quantity you want to fix, then write the value of the quantity, then press "enter".

1 kg --> 8.4*10-17 s
228,270.5 kg --> 1 s
72,135.34 metric tons --> 1 year
1 Earth masses --> 5.668638*10+50 years
« Last Edit: 14/10/2010 19:26:40 by lightarrow »

#### syhprum

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##### what warning would we get from nearby blackholes
« Reply #2 on: 14/10/2010 19:37:21 »
I have been running thru the calculator and find that a BH with a one year life would have a temperature in the region of 10^15 °K hence its radiation would be in the Gamma ray region.
I see no hope of detecting such a small object at 1 parasec but I would welcome other opinions.

#### lightarrow

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##### what warning would we get from nearby blackholes
« Reply #3 on: 15/10/2010 11:53:03 »
I have been running thru the calculator and find that a BH with a one year life would have a temperature in the region of 10^15 °K hence its radiation would be in the Gamma ray region.
I see no hope of detecting such a small object at 1 parsec but I would welcome other opinions.
But at 1 parsec of distance it would be 206,400 times farther than the Sun so the power here would be 42.6 billions times lower (206,4002) at the same Sun's luminosity. But actually in the calculator you see that its luminosity would be: 1.76*10-10 times the solar luminosity so the power arriving here would be
1.76*10-10/42.6*109 = 4.1*10-21 times the solar power arriving here.
I think we shouldn't have to worry, in that case.

Obviously, at lower distances it would be another story...
« Last Edit: 15/10/2010 18:36:08 by lightarrow »

#### syhprum

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##### what warning would we get from nearby blackholes
« Reply #4 on: 15/10/2010 12:12:11 »
I don't think we have much to worry about from the Hawking radiation of BH,s but the gravitational effects of one wandering thru the solar system might be another matter!

#### imatfaal

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##### what warning would we get from nearby blackholes
« Reply #5 on: 15/10/2010 12:53:34 »
The gravitational effects would identical to those of a normal body wandering through our solar system.   A black hole the mass of the earth (which would not lose mass in our universe at present - ie it's colder than cosmic background) would cause the same disruption as a planet the mass of the earth.  The difference is we probably wouldnt see the BH coming - whereas I guess we would notice the reflected light off an incoming planet. What good that would do us heaven only knows.

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##### what warning would we get from nearby blackholes
« Reply #5 on: 15/10/2010 12:53:34 »