PDA

View Full Version : What's the closest black hole we know of?



IsaacKuo
2007-Sep-29, 01:29 PM
One pet theory I have for why aliens don't make Dyson swarms is that they've mastered extracting energy from sacrificially dumping matter into black holes. In comparison to the potential 50% mass-energy conversion of this, the entire stellar fusion process may be viewed as minor energy venting.

Regardless of whether this theory is plausible, black holes are certainly something interesting to us, and represent a resource we may wish to exploit someday. So here are my obvious questions...

How close is the nearest black hole we know of? How commonplace are black holes in our galaxy? Or do we have little idea how commonplace they might be?

Thanks!

01101001
2007-Sep-29, 02:01 PM
Cornell University Ask an Astronomer :: Where is the nearest black hole? (http://curious.astro.cornell.edu/question.php?number=473)


The closest known black holes are stellar mass black holes in our galaxy. These black holes have so far only been seen when they are in close contact with another star which is orbiting around them (well really they orbit each other). The black hole accretes material from the star and this produces a lot of energy. When jets are produced the systems are known as microquasars (by analogy with extragalactic quasars) and can be observed at many wavelengths, but usually are most distinctive in X-rays.

Here is a page with a summary of known microquasars (http://cats.sao.ru/~satr/XB/). Note: not all black hole systems that are known are microquasars.

All of these microquasars are within about 24 thousand light years of Earth. As of now the closest known one is thought to lie at about 1,600 light years from Earth. You can read about it in this [2000] space.com article (http://www.space.com/scienceastronomy/astronomy/v4641_microquasar_000114.html).

IsaacKuo
2007-Sep-29, 03:56 PM
Awesome, thanks! Hmm...plasma jet at 90%c...could be useful for propelling an interstellar colonization fleet?

KaiYeves
2007-Sep-29, 09:28 PM
Responding to title:
Why, do you need to dispose of an enemy?

eburacum45
2007-Sep-29, 10:08 PM
Awesome, thanks! Hmm...plasma jet at 90%c...could be useful for propelling an interstellar colonization fleet?

You have to get there first; and then you would only have jets pointing in one of two directions. Unless you can redirect the polar jets you will be a bit limited in the directions you can go.

Perhaps a drive could be made using an artificial microblack hole, utilising hawking radiation. But there are a list of problems with this concept too...

IsaacKuo
2007-Sep-29, 10:13 PM
Responding to title:
Why, do you need to dispose of an enemy?

No, but I wouldn't mind flushing some waste down a black hole if I could get half its mass in energy in return. ;)

IsaacKuo
2007-Sep-29, 10:21 PM
You have to get there first; and then you would only have jets pointing in one of two directions. Unless you can redirect the polar jets you will be a bit limited in the directions you can go.

I'd think that an interstellar civilization which has expanded a thousand light years to reach a black hole might have an idea or two for controlled dumping of (large amounts of ) matter into the black hole so as to aim the jet where they want.


Perhaps a drive could be made using an artificial microblack hole, utilising hawking radiation. But there are a list of problems with this concept too...

The ideas I've read about creating an artificial microblack hole make most mega-engineering projects like ringworlds or dyson spheres look like child's play. And even then, the object created is a research toy, not something that you could actually do something useful with.

Or so we think, today. It's not like we have actually observed any microblack holes to know for sure, and we're still looking around for primordial black holes which we sort of expect might be around for us to see.

Kaptain K
2007-Sep-29, 10:37 PM
I'd think that an interstellar civilization which has expanded a thousand light years to reach a black hole might have an idea or two for controlled dumping of (large amounts of ) matter into the black hole so as to aim the jet where they want.

No matter how you dump it, it is still going to squirt out the polar axis of the BH.

IsaacKuo
2007-Sep-29, 10:48 PM
No matter how you dump it, it is still going to squirt out the polar axis of the BH.

How does that work?

I thought the plasma jet would be lined up with the magnetic field, which is entirely dependent on the curving path of the infalling disc of material. So, for example, if the star losing matter to the black hole is in an orbit parallel to the galactic plane, then the gravitational acceleration of the plasma will be on a curve parallel to the galactic plane. Therefore, the acceleration of the charged particles is along the galactic plane. The velocity is along the galactic plane; the acceleration is also along the galactic plane. The two directions perpendicular to both will be the normal vectors of the galactic plane.

Therefore, the magnetic field will be lined up normal to the galactic plane, and any plasma jet will be directed normal to the galactic plane.

In other words, the jet can be aimed by adjusting the orbit of the sacrificial mass to be perpendicular to the desired target direction.

Kaptain K
2007-Sep-29, 10:59 PM
The polar axis is not necessarily perpendicular to the plane of the accretion disk.

IsaacKuo
2007-Sep-30, 12:53 AM
Well, obviously I don't understand how the mechanism works. I shall try to read up on it.

Kaptain K
2007-Sep-30, 01:52 AM
"The polar axis is not necessarily perpendicular to the plane of the accretion disk."

I should have added "but usually is."

This still doesn't change my objection to your assertion that "...the jet can be aimed by adjusting the orbit of the sacrificial mass to be perpendicular to the desired target direction."

The jet is going to be along the polar axis of the BH, regardless of the orbital parameters of the "sacrificial mass".

astromark
2007-Sep-30, 02:42 AM
Just a minute here... shifting the axis of a smbh might be just a little difficult, don't ya think...? Or any bh for that mater is by definition a great deal of matter as is detectable by the force of its gravity well. This is not the best method to propel in a controlled manner I am sure.
Back to the question re; Black holes proximity to us.. fortunately none have been detected in the local region of this Galaxy ( yet )

Neverfly
2007-Sep-30, 02:48 AM
Years ago, I heard rumors that there were three mini black holes inside of our sun...

novaderrik
2007-Sep-30, 03:23 AM
and don't forget about the black hole in the Bermuda triangle that is connected via wormhole to a white hole over by Japan.

Kaptain K
2007-Sep-30, 03:58 AM
The black hole of Calcutta! :)

astromark
2007-Sep-30, 10:18 AM
All :)jokes aside there is no black hole inside of sol. There can not be as it does not have sufficient mass to have created such. Let there be no doubt that inside of sol is a very hot and dense place but, not containing a black hole. Not one or three... To find a black hole you would need to look at star clusters and densely populated regions of the Galaxy. None of which are near here. Thankfully.

parejkoj
2007-Sep-30, 03:58 PM
You might be interested in reading the series about the Black Hole Project, which was published in Analog Magazine over the past year or so, by G. David Nordley and C. Sanford Lowe. It centers around future humanity attempting to create a black hole by colliding three ultra-relativistic large masses. And how one goes about doing that at great distance in a relativistic universe, where communication between stars takes years...

A (possibly incomplete) list of the stories in the series:

Kremer's Limit (July/August 2006)
Imperfect Gods (December 2006)
Small Pond (March 2007)
Loki's Realm (July/August 2007)
Vertex (September 2007)

Kaptain K
2007-Sep-30, 04:07 PM
astromark,
While I agree that there are probably no black holes in the sun, your certainty is based on certain assumptions that may be misguided. The conjecture is that the Sun may have captured one or more primordial black holes. The Schwartschild radius of such a BH would be so small (on the order of <1nm that it would take billions of years to absorb the Sun.

KaiYeves
2007-Sep-30, 05:23 PM
The black hole of Calcutta!
Black Hole High!
(Obscure)

eburacum45
2007-Oct-01, 01:36 AM
The Black Hole Project looks really good!
Here is a page about it I have found;
http://www.gdnordley.com/KL_Glossary.html


Black Hole Project (BHP)

The project started by physicist Zhau Tse-Wen to create a black hole with a mass on the order of a billion tons. Four billion-ton iron rods from four different stars would be accelerated to relativistic velocities and crashed together in a symmetric implosion. That would momentarily generate a pressure at their meeting point that far exceeds what even quantum mechanics can resist.

A billion tonne black hole, eh? That would be a useful souce of power and gravity. Sounds like a worthwhile project. That would be a so-called standard neuble as described in the book The Collapsium by Wil McCarthy


see also this page
http://xaonon.dyndns.org/hawking/
for details of the power that one could get from such a neuble.

Note that a neuble is very, very small; about one femtometer.

astromark
2007-Oct-01, 05:18 AM
Kaptain K; No, my assumptions are based on science fact. I have little issue with your point of view. but that is all it is. The facts are clear. We know the mass of sol. We can study orbital velocities and masses about the sun... like planet Earth. Because of the facts we know we can be absolute about the mass and density of the sun. This is a much studied star and we know a great deal about the workings of it. Sol does not have a black hole inside it. Not even three of them...
I will be so presumptuous as to ask EDG to come to my rescue at this point please... I am aware of the amount of knowledge he can install to this conversation... He has a knowledge of stars workings that is tested as true.

Neverfly
2007-Oct-01, 06:57 AM
Primordial Black Holes!!
Thank you Kaptain K, that is the word I was looking for...

Kaptain K
2007-Oct-02, 02:07 AM
Because of the facts we know we can be absolute about the mass and density of the sun... Sol does not have a black hole inside it. Not even three of them...
Primordial black holes (if they exist) can have planetary mass or smaller. While we know the mass of the Sun very well, We do not know it well enough to positively say that it could not contain one, three or even three hundred Earth mass black holes.

Don't get me wrong, I don't think there are any Primordial black hole in the Sun. I'm just saying that we cannot rule them out by the criteria you gave.

George
2007-Oct-02, 02:50 AM
Primordial black holes (if they exist) can have planetary mass or smaller. While we know the mass of the Sun very well, We do not know it well enough to positively say that it could not contain one, three or even three hundred Earth mass black holes. But at the pressure and density in the Sun's core that is pretty well established, wouldn't any priomordial bh get slammed often enough to grow much quicker than you think? [Of course, I have been wondering where all the raisins went when the loaf expanded to today's size. ;)]

Kaptain K
2007-Oct-02, 03:17 AM
Even at the center of the Sun, matter is still mostly empty space!

George
2007-Oct-02, 03:44 AM
Yes, and some golfers say that trees are 90% air. :)

There are billions of tons per second that don't miss each other, at least in the core. Photons can hardly "walk" due to all the congestion. The MFP is probably close to only a few mm (it's a cm in the radiative zone, supposedly).

Ronald Brak
2007-Oct-02, 04:45 AM
and don't forget about the black hole in the Bermuda triangle that is connected via wormhole to a white hole over by Japan.

So that's what the Kobe shipyard and scrap metal emporium is.

mugaliens
2007-Oct-02, 12:28 PM
Just a minute here... shifting the axis of a smbh might be just a little difficult, don't ya think...? Or any bh for that mater is by definition a great deal of matter as is detectable by the force of its gravity well. This is not the best method to propel in a controlled manner I am sure.
Back to the question re; Black holes proximity to us.. fortunately none have been detected in the local region of this Galaxy ( yet )

Furthermore, how would one even support it here on Earth? Something the size of a period would weigh as much as a full-laden oil tanker. I would think that it would sink into whatever matter it's sitting on rather quickly, probably absorbing more matter as it rapidly sunch to the center of the Earth.

I hope no one goes around trying to create one, at least not here on this planet...

Sock puppet
2007-Oct-02, 01:59 PM
Yes, and some golfers say that trees are 90% air. :)

There are billions of tons per second that don't miss each other, at least in the core. Photons can hardly "walk" due to all the congestion. The MFP is probably close to only a few mm (it's a cm in the radiative zone, supposedly).

The mean free path you are referring to is for photons: They don't tend to get all that far in the centre of the sun because everything is ionised. The capture cross section for a primordial black hole may be tiny (I don't know), leading to a substantial time between interactions.

John Mendenhall
2007-Oct-02, 05:39 PM
Re BH's and the Sun:

1. While theoretically possible, no candidate primordial black holes have been observed. Very small black holes may be made in high energy cosmic ray collisions in the upper atmosphere, but the jury's still out.

2. The Sun is still here, and doesn't seem to have had any digestive upsets over the last 4.5 billion years plus. I think even a primordial BH, at the temperatures and pressures of the Sun's center, would grow.

3. Even our inference of supernova remnant and galactic center black holes is that, an inference. At present it's the best explanation we have, and it's probably correct. But, ol' Albert didn't like the idea, and he's got quite a track record so far. We can't conveniently make them to study them, except maybe CERN can do it on the next upgrade.

John Mendenhall
2007-Oct-02, 05:44 PM
On making a BH other than in a particle accelerator, implosion technology is well understood (see Fat Man atomic bomb, Hiroshima, AIR). I have read, and I don't remember where, could even have been Analog, that a cluster of nuc's around a suitable mass, set off simultaneously, can probably compress the mass into a black hole.

antoniseb
2007-Oct-02, 06:00 PM
On making a BH other than in a particle accelerator, implosion technology is well understood (see Fat Man atomic bomb, Hiroshima, AIR). A cluster of nuc's around a suiable mass, set of simultanously, can probably shove the mass into a black hole.

Looking at the numbers, I don't think that's right. You are talking about a *lot* of compression required. Do you know how big a mass is required to make a black hole larger than an atom? Do you know how hard it would be to aim the compression forces on such a mass to get it into a target smaller than an atom? I think your above statement was a wild incorrect guess.

parejkoj
2007-Oct-02, 09:01 PM
3. Even our inference of supernova remnant and galactic center black holes is that, an inference. At present it's the best explanation we have, and it's probably correct. But, ol' Albert didn't like the idea, and he's got quite a track record so far. We can't conveniently make them to study them, except maybe CERN can do it on the next upgrade.

More than an inference: the only remaining explanation. There are currently (as opposed to ~7-10 years ago) zero viable alternatives to explain the observations of our galaxy's center, and stellar mass black holes (of which I know less) are also the only remaining explanation for the highest energy accreting binary systems.

Ol' Albert also didn't like Quantum Mechanics, but it turns out he was quite wrong on that count.

George
2007-Oct-03, 01:14 PM
The mean free path you are referring to is for photons: They don't tend to get all that far in the centre of the sun because everything is ionised. Good point. I realized too late that this was a limited comparison.


The capture cross section for a primordial black hole may be tiny (I don't know), leading to a substantial time between interactions. Using a guess of 0.1nm for the Schwartzchild diameter, this cross section is about 10 billion times greater than that of a proton (using 10-15m]. Yet, protons, even with their repulsive charge, do slam and combine. Admittedly, it takes billions of years for a reasonable portion of protons to do so. Is this a reasonable assertion?

IsaacKuo
2007-Oct-03, 01:35 PM
I'm rather glad that those protons take their good sweet time to run into each other. It'd suck for the Sun to burn out quickly...

Sock puppet
2007-Oct-03, 03:02 PM
Good point. I realized too late that this was a limited comparison.

Using a guess of 0.1nm for the Schwartzchild diameter, this cross section is about 10 billion times greater than that of a proton (using 10-15m]. Yet, protons, even with their repulsive charge, do slam and combine. Admittedly, it takes billions of years for a reasonable portion of protons to do so. Is this a reasonable assertion?

According to this (http://physics.about.com/gi/dynamic/offsite.htm?zi=1/XJ&sdn=physics&cdn=education&tm=308&f=00&tt=12&bt=0&bts=0&zu=http%3A//xaonon.dyndns.org/hawking/) calculator, a black hole of mass 109 tons would have a Schwartzchild diameter of ~3femtometer (fm=10-15) and a lifetime of ~3 trillion years. That might be realistic, but as others have pointed out, we have no reason to believe there is such an object in the sun.

George
2007-Oct-03, 09:11 PM
According to this (http://physics.about.com/gi/dynamic/offsite.htm?zi=1/XJ&sdn=physics&cdn=education&tm=308&f=00&tt=12&bt=0&bts=0&zu=http%3A//xaonon.dyndns.org/hawking/) calculator, a black hole of mass 109 tons would have a Schwartzchild diameter of ~3femtometer (fm=10-15) and a lifetime of ~3 trillion years. That might be realistic, but as others have pointed out, we have no reason to believe there is such an object in the sun.
Cool calculator. :) According to what looks like a controversial cosmologist blog site (http://riofriospacetime.blogspot.com/), she states on 9/16/07 ...

"We can consider the possibility of primordial black holes. The typical mass of such objects is about 10^12 kg".

This gives a radius of 10-12m. [That is an easy one to remember: a trillion kg to reach a trillionith of a meter. :)]

[Edit: Oops, a trillion kg yields a 10^-15 m radius. A tillion tons yields a trillionith of a meter in radius. So, the following is true for a trillion tons, not kg.]

This puts it > million times the cross section of a photon. I would think a PMBH that size would overcome a star the age of the Sun. Hmmm.... however, I could be wrong and that might explain why the Sun has been looking kinda pale lately, it isn't near the color it used to be.

Sock puppet
2007-Oct-04, 08:05 AM
According to this calculator, a black hole of mass 109 tons would have a Schwartzchild diameter of ~3femtometer (fm=10-15) and a lifetime of ~3 trillion years. That might be realistic, but as others have pointed out, we have no reason to believe there is such an object in the sun.
Cool calculator. :) According to what looks like a controversial cosmologist blog site (http://riofriospacetime.blogspot.com/), she states on 9/16/07 ...

"We can consider the possibility of primordial black holes. The typical mass of such objects is about 10^12 kg".

This gives a radius of 10-12m. [That is an easy one to remember: a trillion kg to reach a trillionith of a meter. :)]

This puts it > million times the cross section of a photon. I would think a PMBH that size would overcome a star the age of the Sun. Hmmm.... however, I could be wrong and that might explain why the Sun has been looking kinda pale lately, it isn't near the color it used to be.

109tons=1012kg
That's why I chose that mass. I think the capture cross section will be considerably larger than the Schwartzchild radius, though. Also IIRC, the proton-proton capture cross section is much smaller than their actual radii- on the order of a few barns or so.... So I think a primordial black hole could be ruled out.

George
2007-Oct-04, 12:46 PM
109tons=1012kg
That's why I chose that mass. I think the capture cross section will be considerably larger than the Schwartzchild radius, though. Thanks for catching my units error.


Also IIRC, the proton-proton capture cross section is much smaller than their actual radii- on the order of a few barns or so.... So I think a primordial black hole could be ruled out. A few barns, wow. Some barns are harder to hit than others. ;)

IsaacKuo
2007-Oct-04, 01:31 PM
Either way...how long would it take to gobble up the Sun? Or to make it easier to calculate...roughly how long would it take to gobble up 10% its own mass? (I'm just chosing 10%, or 10^11kg, so you can simplify and assume the thing doesn't get any bigger during this time. That's a lot of protons, isn't it?)

EvilEye
2007-Oct-04, 03:25 PM
I supposed in the near future, the answer will be "the ones in Geneva Switzerland. "

KaiYeves
2007-Oct-06, 05:46 PM
Geneva coma, Switzerland.

Kaptain K
2007-Oct-06, 08:37 PM
KaiYeves,
FWIW, minor corrections of spelling or grammar are generally frowned on on this board, since English is not the first language of many of the poster. If it can be read and understood, let it slide!

Neverfly
2007-Oct-06, 09:41 PM
KaiYeves,
FWIW, minor corrections of spelling or grammar are generally frowned on on this board, since English is not the first language of many of the poster. If it can be read and understood, let it slide!

You mean, "many of the poster(s)."

:p

Kaptain K
2007-Oct-06, 10:25 PM
:naughty: :lol: :clap: :rolleyes:

KaiYeves
2007-Oct-07, 02:59 AM
Aye, aye Kaptain!

George
2007-Oct-08, 01:50 AM
You mean, "many of the poster(s)."

:p
:) Incorrigibleness.

EvilEye
2007-Oct-08, 02:40 AM
KaiYeves,
FWIW, minor corrections of spelling or grammar are generally frowned on on this board, since English is not the first language of many of the poster. If it can be read and understood, let it slide!

English is my first language. Punctuation is not,. ;)

novaderrik
2007-Oct-08, 03:55 AM
Geneva coma, Switzerland.
comma
unless, of course, you meant that going to Switzerland puts one into a vegetative state.