AAS News

Oh my! Run for your lives!

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Vanderbilt University press release: Galaxy may hold hundreds of rogue black holes (via Eurekalert)

Of course, the media is tying this to alarmist titles:

Expert warns of 'rogue' black holes
Rogue Black Holes Might Fill Our Galaxy

And the press release actually ends with calming reassurance:

Like fear itself?

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You have to admit it, the thought of being gobbled up by a black hole is far more "exciting" and scary, than an asteroid spoiling the party.

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If there are 200 intermediate black holes in our galaxy, that is one for every billion or so stars. We are (at least) a billion times more likely to have a close encounter with another star than one of these objects. They would probably be distributed like halo stars anyway, so would be even more widely spaced.

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I should think black hole mergers would occur millions of times less often than stars colliding, because of their smaller cross section and smaller total numbers. Near misses should occur about as often as stars have a near miss. Neil

Where are these black holes likely to be? My first guess is our Galaxy's core, since it is relatively dense in stars.

In that case, we do not have much to lose sleep over, since we will continue to orbit at a safe distance away from them.

What's to stop an intermediate black hole from getting a slingshot boost by good old Sgt A* into our neck of the woods?

Let's just say that if we do get gobbled up, we won't see what hit us.

I wonder if LIGO non-detections already rule out such copious black-hole merger rates...

It's too bad we can't generate a test gravitational wave to confirm the predicted sensitivity of the instrument. Or can we?

A black hole moving fast enough to "get us" would be plowing through stellar medium before it reached us. So there would be some detectable emissions. Unless it moved at lightspeed, we'd find it before it found us.

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"If this were play'd upon a stage now, I could condemn it as an improbable fiction."
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Illuminati's Razor-The most complicatedly evil answer is usually the most correct answer. - Fazor
"Every book is a children's book if the kid can read." - Mitch Hedberg
"Distance doesn’t matter much in space, where if you just start a thing off with the right kind of shove, sooner or later it will get where you want it to go." -Frederik Pohl, Mining the Oort

Assuming it hits something else before us, sure thing.

It would be "hitting" the solar wind of our Sun and the dust and debris of the Outer Solar system, long before it reached the Inner system. The denser the matter, the more emissions.

__________________
"If this were play'd upon a stage now, I could condemn it as an improbable fiction."
Shakespeare, Twelfth Night
Illuminati's Razor-The most complicatedly evil answer is usually the most correct answer. - Fazor
"Every book is a children's book if the kid can read." - Mitch Hedberg
"Distance doesn’t matter much in space, where if you just start a thing off with the right kind of shove, sooner or later it will get where you want it to go." -Frederik Pohl, Mining the Oort

If the mid size (less than 4000 solar mass) black hole has a cross sectional area of the event horizon of 1000 square kilometers and is cutting though the solar wind particles at 1000 kilometers per second (relative to the solar wind particles) it's radiation signature will will be different if the relative speed (or observation angle?) is different. We need to look from outside Earth's magnetoshere (or make lots of accomodations) for near by black holes passing though our Oort cloud. Are we planning a probe that is looking for such anomolies in the solar wind particles? My guess is the gravity pertubations of the 4 old probes leaving our solar system, are more detectable than the radiation, unless the black hole accreats an Oort cloud object, bigger than a tenis ball or already has a more significant accreation disk. Did I just solve the mystery of why the Oort cloud probes are mysteriously accellerating? They are each approching a black hole? Not likely that there are 4 black holes producing the same acceleration of each probe. Perhaps each of the probes are accelerating differently? Perhaps the volume just outside the event horizon does not produce a significant impact signature with the very thin Oort cloud solar wind particles? Can we detect the impact signature of Venus and Neptune which have much larger cross sectional area, but possibly slower than the black holes passing though our Oort cloud, if any? Why are we talking about thousand solar mass black holes instead of 20 solar mass black holes which might be typical of a single black hole merger? Neil