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antoniseb
2006-Apr-20, 10:55 AM
In the June 2006 Sky & Telescope, there is a brilliant and amusing article (by a man most of us are familiar with) about a scientist trying to sell movie scripts to a movie producer that have real scary science in them.

The final scenario discusses a ten solar mass black hole coming toward Earth at about 500 kilomters/second. In this article, the first awareness we have of it is that Uranus is out of place. I'm thinking that it would be impossible for such an object to make it through the Oort cloud without having a few xray flashes or worse.

Anyone else want to weigh in on this before I try doing some OOM work, and get beyond the gut feeling stuff?

korjik
2006-Apr-20, 05:16 PM
I wouldnt think it would get to within a couple ly before we noticed. Something that big could pull stars out of position

Bob
2006-Apr-20, 05:36 PM
This BH takes almost 400 years to travel a light year. When it was far enough out to move stars around, assuming it was passing a nearby star, observations were not highly accurate and/or are lost to history.

Somehow I don't think this movie has a happy ending.

antoniseb
2006-Apr-20, 05:54 PM
Somehow I don't think this movie has a happy ending.

I don't want to give you a spoiler in case you want to read Phil's article, but I agree with your notion that we would not observe it changing the positions of stars until it got pretty close to us (half a light year?), and then it would be changing our position, and perhaps doing some relatively easy to observe lensing.

Now that you mention it, the signals from the millisecond pulsars should make it detectable at about a light year (wild guess).

astromark
2006-Apr-21, 12:29 AM
Its the Debris orbiting it that would give its position away. I think we would see it at the Ort Cloud area. I will not read this book. I don't want to know. Bruce Willace cant save us from this.

astromark
2006-Apr-21, 07:13 AM
I've been thinking and its a new experience so be gentle. I don't think A direct hit would be worth writing about unless we are getting off this planet to avoid this thing.There would be little to say. Far more likely would be just the orbital mechanics of this solar system to be disrupted by the near enough approach of a ten solar mass black hole. As it swung past, the solar mass would be ripped away from its point at the center of this solar system and into what could be as bad as a direct impact. This system we call home would be torn to bits. As the distance we are orbiting is crucial to our survival the outlook would be bleak indeed. I might sagest that a safer distance might be out near the Orion nebular. where we might watch and not be dead.

Jeff Root
2006-Apr-21, 05:35 PM
I think it is unlikely that the incoming black hole would happen to
run into anything in the Oort cloud just as that part of the sky
was being looked at, creating radiation that would be detected
on Earth or by spacecraft such as Chandra or XMM-Newton.
Its gravity would strongly deflect passing starlight, but since
the black hole would have very little lateral motion relative to
Earth, there would be almost no change in that deflection, so
it wouldn't be noticed-- unless the BH and a distant star were
almost exactly in line. Even then, an instance of microlensing
would be unlikely to be caught by an observer.

-- Jeff, in Minneapolis

antoniseb
2006-Apr-21, 05:59 PM
I think it is unlikely that the incoming black hole would happen to run into anything in the Oort cloud just as that part of the sky was being looked at, creating radiation that would be detected on Earth or by spacecraft such as Chandra or XMM-Newton.

I have the impression that any object getting within its Roche limit would break up, and form an accretion disk. Could the black hole find a path through the Oort cloud where it never gets within 12 million miles of some object bigger than dust?

Jeff Root
2006-Apr-21, 10:44 PM
I have the impression that any object getting within its
Roche limit would break up, and form an accretion disk.
Probably. The vast majority of such objects would be flung
away from the black hole, even if they break up, but some of
the material could end up in orbit.

Lemme just remind everyone that the Roche limit applies to a
body held together only by gravity. Chemical forces also hold
comets and asteroids together, and they are far stronger than
gravity, and much more important than gravity in the case of
small bodies-- say, the size of Phobos. A solid rock the size
of Phobos would hold together way inside the Roche limit, but a
loose aggregate of rocks would come apart. On the other hand,
a solid rock the size of Earth's Moon would be torn apart just
barely inside the Roche limit.



Could the black hole find a path through the Oort cloud where it
never gets within 12 million miles of some object bigger than dust?
No. But... Where did you get the 12-million-mile figure? I'd
think the Roche limit would be less than one million miles, but
I'm just guessing. I'd expect that a solid comet-like body the
size of my living room could get within a few thousand miles of
a ten-solar-mass BH before breaking up. At that short distance,
it would be drawn into the BH relatively quickly. (I don't know
how quickly. A thousand years? A week? Somewhere in there. :-)
So I think that a BH which starts out without an accretion disk
in the first place is not going to collect enough material in
the Oort Cloud to make one: Most of the material is flung away,
and the little that is not flung away gets sucked in.

Suppose a mass of 1000 tons or more falling into the BH could
be detected from Earth with current instruments. And suppose
that happens about once every two years, on average, while the
BH is in the Oort Cloud. We might actually detect one in every
ten such events. One event detected in twenty years, on average.
But twenty years ago, the best existing instruments could only
have detected a body of 10,000,000 tons or more falling into the
then more distant black hole, and that might happen only once in
a thousand years.

-- Jeff, in Minneapolis