PDA

View Full Version : First stellar outcast discovered by astronomers



Kullat Nunu
2005-Feb-08, 06:55 PM
CfA press release: First Stellar Outcast Discovered by Astronomers (http://www.cfa.harvard.edu/press/pr0505.html)


Using the MMT Observatory in Tucson, AZ, astronomers at the Harvard-Smithsonian Center for Astrophysics (CfA) are the first to report the discovery of a star leaving our galaxy, speeding along at over 1.5 million miles per hour. This incredible speed likely resulted from a close encounter with the Milky Way's central black hole, which flung the star outward like a stone from a slingshot. So strong was the event that the speedy star eventually will be lost altogether, traveling alone in the blackness of intergalactic space.

Crazieman
2005-Feb-08, 07:11 PM
Wonder what it would be like to live on a planet orbiting a rogue star

Argos
2005-Feb-08, 07:12 PM
Why is this event so rare (one case in several tens of billions) in a star-soaked galactic core?

Padawan
2005-Feb-08, 07:29 PM
Why is this event so rare (one case in several tens of billions) in a star-soaked galactic core?


I would imagine that it is rare that a star gets close to such a massive black hole that it will be flung away with enough speed to leave the milky way (and the massive black hole too!)

John Kierein
2005-Feb-08, 07:36 PM
How do they know it is moving away from the galaxy? Do they see a proper motion? If it is known to be travelling away because of its red shift, maybe it has an intrinsic red shift. Is it bright in the radio?

Crazieman
2005-Feb-08, 07:49 PM
Probably shift, point in sky, and parallax data all calculated over time.

tlbs101
2005-Feb-08, 08:20 PM
1.5 million mph is 0.22% of the speed of light!

Relativistic effects start to become significant.

frogesque
2005-Feb-08, 08:41 PM
Where would the energy come from to accelerate it to Galaxy escape velocity? (? hyperbolic trajectory?) Why wouldn't it just remain within the Galaxy in an exagerated eliptical orbit. Could this star actually be galaxy collision debris?

(thinking along the lines of solar and extra solar comets here - maybe this doesn't apply)

Padawan
2005-Feb-08, 09:09 PM
Where would the energy come from to accelerate it to Galaxy escape velocity? (? hyperbolic trajectory?)


Apparently, the authors of the article believe it could only have come from a close passage to the giant black hole in the centre of the milky way

Kaptain K
2005-Feb-08, 10:41 PM
IIRC - It takes a three-body interaction to throw an object completely out of a system!

Kullat Nunu
2005-Feb-08, 10:42 PM
IIRC - It takes a three-body interaction to throw an object completely out of a system!

That's why they think the star had a companion which the black hole captured.

frogesque
2005-Feb-08, 10:49 PM
IIRC - It takes a three-body interaction to throw an object completely out of a system!

That's why they think the star had a companion which the black hole captured.

Yep. I sort of figured that when I re-read the link. It would explain the change of momentum. Must have been some event to rip a binary apart, swallow one and fling the other totally out of the Galaxy at ~.22c :o

Philippe
2005-Feb-09, 05:06 PM
Wonder what it would be like to live on a planet orbiting a rogue star

Well, if we overlooked the fact that any planetary system around that star most likely wouldn't have survived the "sudden" acceleration, I guess it wouldn't change much.

Once in inter-galactic space, the sky would be quite bare at night, I guess.

Argos
2005-Feb-09, 05:22 PM
1.5 million mph is 0.22% of the speed of light!

Relativistic effects start to become significant.

Nit picking (and probly OT), relativistic effects donīt become noticeable until you get very close to c (up to 80%, or .80)

Doodler
2005-Feb-09, 05:30 PM
Wonder what it would be like to live on a planet orbiting a rogue star

Well, if we overlooked the fact that any planetary system around that star most likely wouldn't have survived the "sudden" acceleration, I guess it wouldn't change much.

Once in inter-galactic space, the sky would be quite bare at night, I guess.

Having played around with that Rogue star simulator, the odds of any planets it might have had still being around the star are so slim that they can be considered zero. Even a simulated star only 100 times the size of the sun would hurl them into space on the furthest possible flyby trajectory it allowed.

TheGalaxyTrio
2005-Feb-09, 05:51 PM
This raises the important question: what the heck did someone do to get their whole solar system bounced out of the galaxy? #-o

And where's the bouncer? :o

Doodler
2005-Feb-09, 06:01 PM
This raises the important question: what the heck did someone do to get their whole solar system bounced out of the galaxy? #-o

And where's the bouncer? :o

Wrong place, wrong time, and the bouncer is the big three million solar mass bruiser in the middle of it all.

Captain Kidd
2005-Feb-09, 07:07 PM
This raises the important question: what the heck did someone do to get their whole solar system bounced out of the galaxy? #-o

And where's the bouncer? :oIt was probably a contestant on Survivor: Galactic Core and got voted off.

EckJerome
2005-Feb-10, 12:50 AM
I would imagine that it is rare that a star gets close to such a massive black hole that it will be flung away with enough speed to leave the milky way (and the massive black hole too!)

Unless the star was already in orbit of the black hole, it would have escaped from it anyway. A pet peeve of mine is the layperson view of black holes as "cosmic vacuum cleaners." Black holes, in and of themselves, cannot capture objects passing near to them. (Not without interaction of a third body.) Objects will take a (hyperbolic?) course around the black hole just as some comets do around our sun. They're like any other mass out there, just a lot bigger. Orbital mechanics do not change simply because it is a black hole.

The example I usually use is to imagine replacing our sun with a black hole of one solar mass (for the sake of argument). Other than it being rather much darker, the planets will continue to orbit that black hole just as they orbit the sun, since the mass has not changed. Too many people, I find, seem to think that suddenly the entire solar system will get sucked in...and that's just not the case. Black holes do not suck. :wink:

Evan
2005-Feb-10, 12:59 AM
Orbital mechanics do not change simply because it is a black hole.

Not so fast. We aren't talking about Newtonian orbital mechanics any more. Relativistic orbital mechanics is a different ball game. We aren't even able to accurately simulate it near the event horizon because the equations blow up. Current numerical approaches don't have fine enough time resolution.

I suspect a black hole could capture a planet and then eat it through frame dragging if the planet was in a retrograde orbit to the rotation of the black hole.

ToSeek
2005-Feb-10, 01:26 AM
And if an object comes close enough to pass the event horizon, it's not coming out again.

Argos
2005-Feb-10, 12:40 PM
And a very big BH has a large Schwarzschild radius. You could come within without even noticing. Furthermore, most of the galaxy is eligible for being attracted by a BH ina newtonian fashion, since most of the stars have companions.

Edited

Captain Kidd
2005-Feb-10, 01:14 PM
Interestingly, Space.com has an article about how black hole growth rates are self-limiting (http://www.space.com/scienceastronomy/050902_black_hole.html).

EckJerome
2005-Feb-10, 04:49 PM
Orbital mechanics do not change simply because it is a black hole.

Not so fast. We aren't talking about Newtonian orbital mechanics any more. Relativistic orbital mechanics is a different ball game. We aren't even able to accurately simulate it near the event horizon because the equations blow up.

Allow me to clarify...a star is going to have to get VERY close to the black hole for that to become a consideration. As I said in my example, if you replace our sun with a one-solar-mass black hole (for the sake of arguement), the orbits of the planets will not change, not even Mercury. Does anyone dispute this?

A sun-grazing comet in a retrograde orbit might be a different story.

Invariably, when I give my example, most laypeople assume the black hole will suck in the entire solar system. That's just not true. At moderate distances, BHs are just like any other mass out there. Even in multi-body interactions, the black hole will not create different orbital dynamics than an actual star of the same mass. That's my point: most people have a very poor understanding of what black holes are...even without getting into the Hollywoodesque rubbish of wormholes and doorways to alternate universes.

I think I have a fairly solid idea of what black holes are, but I'm no Einstein. Exactly how close must one get to a black hole for relativistic orbital mechanics to be a consideration? I don't know...but my guess it's much closer than the radius of a star of the same mass.

EckJerome
2005-Feb-10, 05:02 PM
And a very big BH has a large Schwarzschild radius. You could come within without even noticing. Furthermore, most of the galaxy is eligible for being attracted by a BH ina newtonian fashion, since most of the stars have companions.

Just as most of the galaxy is eligible for being "attracted" by a star of the same mass as our hypothetical black hole. Again, that's my point. Whether our massive object is a star or a black hole, at moderate distances their gravity wells have the same characteristics.

Evan
2005-Feb-10, 05:28 PM
Exactly how close must one get to a black hole for relativistic orbital mechanics to be a consideration?

I'm not sure how to calculate that. Since at the event horizon the escape velocity is the speed of light do you take the inverse square of the speed of light from distance to the center of the black hole? If so then anywhere out from the black hole where the escape velocity is an appreciable percentage of the speed of light then relativistic effects come into play. They needn't be very large. I dispute your assertion that Mercury wouldn't be affected. It is affected relativistically already by the sun. Also, we can't have a solar mass black hole, it would have to be somewhat more massive.

Kaptain K
2005-Feb-10, 05:41 PM
Also, we can't have a solar mass black hole, it would have to be somewhat more massive.

We can have a solar mass black hole, we just can't create one.

EckJerome
2005-Feb-10, 05:58 PM
Also, we can't have a solar mass black hole, it would have to be somewhat more massive.

Which part of "for the sake of arguement" didn't you understand?

And are you saying that a hypothetical one solar mass BH would have greater relativistic effects on Mercury than the sun does?

TravisM
2005-Feb-10, 06:12 PM
If the sun turned into a black hole right now, it would just be dark. Nothing much else... unless it began to feed... :o

Doodler
2005-Feb-10, 07:03 PM
If the sun turned into a black hole right now, it would just be dark. Nothing much else... unless it began to feed... :o

That's the thing, it wouldn't feed, except the occassional comet. Its pull on anything else currently in a stable orbit wouldn't change on iota. Its only when you approached the horizon, which would be well inside where the fireball is now, that things would get hinky.

TravisM
2005-Feb-10, 08:26 PM
Yup, they aren't vacuum cleaners :D I was talking about feeding because that would probably involve radiations of some kind. Also, in acuality, the sun turning into a black hole is pretty much impossible (mass) but if you suddenly found a way to shrink the sun, it would be a catostrophic event... Barring all that, yeah, nothing would happen... :-?

John Dlugosz
2005-Feb-10, 08:29 PM
Must have been some event to rip a binary apart, swallow one and fling the other totally out of the Galaxy at ~.22c :o

That's 0.0022c. Over an hour to cross the distance from here to the moon, not a few seconds.

frogesque
2005-Feb-10, 08:46 PM
Must have been some event to rip a binary apart, swallow one and fling the other totally out of the Galaxy at ~.22c :o

That's 0.0022c. Over an hour to cross the distance from here to the moon, not a few seconds.

My BAD :oops: missed the % sign when I read the post by tlbs101