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Troon
2008-Oct-01, 07:22 AM
OK, so we know about lots of NEOs and their future risk to Earth, nicely tabulated to reassure us that we're not about to die in a blazing fireball.

There have also been discussions about Spaceguard-like projects that survey for incoming objects.

But what's to stop something extrasolar coming in from left field at Ludicrous Speed? If something came in at say 0.1c, it'd get from Neptune's orbit to here in less than two days. Clearly, there's little we can actually do about that, but have we ever observed any bodies zipping around "fast"?

Hornblower
2008-Oct-01, 09:18 AM
Clearly, there's little we can actually do about that, but have we ever observed any bodies zipping around "fast"?
To the best of my knowledge, no.

grant hutchison
2008-Oct-01, 09:30 AM
The fastest objects observed have been slightly hyperbolic comets. Last time I looked (admittedly several years ago) these all stopped being hyperbolic when their orbits were calculated relative to the solar system barycentre, rather than the sun. So all of them appear to have local, rather than extrasolar, origins.

Grant Hutchison

NEOWatcher
2008-Oct-01, 12:35 PM
But what's to stop something extrasolar coming in from left field at Ludicrous Speed?
Probability?
What I mean by that is even extrasolar objects will most likely be in the same orbit around the galaxy as we are and probably wouldn't be too much faster than solar escape velocity.

I would imagine the probability to be similar to the ratio of solar system masses to interstellar masses. And the extreme ones to be the ratio of galactic mass to intergalactic mass.
Am I close? :think:

antoniseb
2008-Oct-01, 01:01 PM
...But what's to stop something extrasolar coming in from left field at Ludicrous Speed?...

Nothing but probability. The Milky Way has absorbed some dwarf galaxies, and IIRC the star Arcturus might be from a stream of a shredded galaxy. So, one imagines that as we may sometimes pass through the Oort clouds of stars from merging galaxies that objects with an excess 100 miles-per-second velocity could zip through our solar system.

The good news is that you'd see the star associated with this Oort cloud tens or hundreds of thousands of years before the path intersection, and even of the paths were to cross, the odds of a direct hit on Earth would be low.

Don Alexander
2008-Oct-01, 02:31 PM
Have a look at this (http://arxiv.org/abs/0712.1571).

Only a few cm in size, but packing quite a speed.

Concerning larger, potentially dangerous obects, well, it's really hard to accelerate something to such a speed without turning it into plasma shrapnel...

You might get stuff accelerated via black holes, say, if you send a binary object close to the event horizon, one part of the binary would be accreted while the other would be flung out of the galaxy at hyperbolic velocity (see runaway stars). But even there, you will probably not exceed 0.01 c.

trinitree88
2008-Oct-01, 03:53 PM
The highest velocity pulsar I've seen is close to 2500 km/sec. This is an object about the size of Rhode Island, with ~ a million Earth Masses, moving fast enough to create little time to escape an impact. Strangely, an old article in the Los Alamos Journal of Science said Earth would survive it's passage...kind of like a 22 bullet hitting a jellyfish...but we as humans wouldn't.

I'll hunt the fast one, similar is...see:http://arxiv.org/abs/astro-ph/0702735



pete:shifty:

timb
2008-Oct-02, 12:34 AM
The fastest objects observed have been slightly hyperbolic comets. Last time I looked (admittedly several years ago) these all stopped being hyperbolic when their orbits were calculated relative to the solar system barycentre, rather than the sun.

A&A 376, 316-324 (2001)
DOI: 10.1051/0004-6361:20010945
A study of the original orbits of "hyperbolic" comets
M. Królikowska

After calculating elements relative to the barycenter and allowing for pertubations due to asymmetrical out-gassing, concludes that a list of "known" hyperbolic comets were most likely all originally elliptic.

jlhredshift
2008-Oct-02, 12:44 AM
What about supernova shell fragments, what kind of velocity would they have?

timb
2008-Oct-02, 01:51 AM
What about supernova shell fragments, what kind of velocity would they have?

Thousands of clicks per sec, but wouldn't that be nothing more substantial than gas and dust? As previously mentioned, hypervelocity stars travelling at over 1000km.s-1 exist in the galaxy. Recoil after the merger of two black holes can leave the product travelling at hundreds of km per sec. This process can even result in the ejection of the central SMBH from a galaxy. If a SMBH is detected in the orbit of Neptune approaching Earth at over 1000km.s-1, I think the best approach would be to not renew your subscriptions.

novaderrik
2008-Oct-04, 01:15 AM
But what's to stop something extrasolar coming in from left field at Ludicrous Speed?

as long as they are only going ludicrous speeds- and not all out plaid- then i think we'll be alright.

Noclevername
2008-Oct-07, 01:41 PM
Concerning larger, potentially dangerous obects, well, it's really hard to accelerate something to such a speed without turning it into plasma shrapnel...

I think the OP is talking about thigs that are already going at such speeds relative to us. Not about getting them to go that fast.

Don Alexander
2008-Oct-07, 03:38 PM
I think the OP is talking about thigs that are already going at such speeds relative to us. Not about getting them to go that fast.

Well, since the solar system is travelling at only a few hundred clicks vs. the CMB, almost all relative speed has to be instilled into the impactor. And it had to be accelerated sometime in the past. Nothing is "already going at such speeds relative to us" since forever.

zenbudda
2008-Oct-07, 03:59 PM
as long as they are only going ludicrous speeds- and not all out plaid- then i think we'll be alright.


hah! that being said, i've been looking for pics/vids of the sudan meteor and "i ain't found <expletive deleted>!"

Ara Pacis
2008-Oct-07, 10:49 PM
Well, there was the "Oh-my-G*d!" particle, that was travelling at just less than a gnats whisker slower than a photon, but that might be too small to count as an "object".