bumab Posted February 9, 2005 Report Share Posted February 9, 2005 So a star is leaving our galaxy, and not slowly, either... http://www.physorg.com/news2985.html The velocity came from gravity- as the star was accellerated past the central black hole, it sped up, and was slingshotted out of the galaxy. Can that acceleration be large enough to overcome the gravity of the black hole that did the accelerating in the first place? Seems like one of those funnel game things at Science Fairs. You drop a marble past the central hole on a big funnel, and it shoots up the other side due to the acceleration caused by falling towards the hole. But it never gets high enough to escape, due to friction. In this case, there's a whole galaxy of stars, each with some gravitational pull, pulling backwards on the star as it tries to leave. How can the origional sling shot be faster then that? Link to comment Share on other sites More sharing options...
alxian Posted February 10, 2005 Report Share Posted February 10, 2005 The velocity came from gravity- as the star was accellerated past the central black hole, it sped up, and was slingshotted out of the galaxy. Can that acceleration be large enough to overcome the gravity of the black hole that did the accelerating in the first place? yes but its not the gravitational force, that will be moot, the star had to be moving fast enough into the black holes gravity field in the first place to account for the energy required to escape on the other side.. and it most have been a glancing blow because as i understand it the distance from the event horizon of a black hole and its surface is more like a vacuum. the space after the point of no return is dubbed no return because it physically cannot be overcome... doesn't exist because the gravitational force is so strong. so while sci-fi will have you believe that such slingshots are possible the ship itself will have to be near relativistic speed to begin with, second a star?? hahaha a gas ball?? you must be kidding.. its documented that a star will stretch (because it has no structural integrity to speak of.. and then theirs its inertia and the aforementioned point of no return) not enter a blackhole whole. *impossible* nothing will ever have that kind of structural integrity. after the point of no return space is theoretical (not well understood). *reads artical* keeps laughing... like i said a glancing blow outside of the point of no return.. :) *phewf... funny this mirrors my yet unwritten story... fact preceeds fiction.. lol.. i wonder if it had any planets in orbit at the time? Link to comment Share on other sites More sharing options...
bumab Posted February 10, 2005 Author Report Share Posted February 10, 2005 but its not the gravitational force, that will be moot, the star had to be moving fast enough into the black holes gravity field in the first place to account for the energy required to escape on the other side.. yeah, i'm an idiot... so i wonder what the escape velocity for the galaxy is? it would be an x + y thing, where y is the sling shot acceleration, and x is the inital velocity... y would go away as the star slowed down, so x must be greater then the escape velocity for the galaxy... hmmm Link to comment Share on other sites More sharing options...
Tormod Posted February 10, 2005 Report Share Posted February 10, 2005 *reads artical* keeps laughing... I wonder what the hell you have been drinking to write a post like that. Consider yourself warned: if you want to make fun of other members while exposing your lack of knowledge, find yourself another forum. Link to comment Share on other sites More sharing options...
Tormod Posted February 10, 2005 Report Share Posted February 10, 2005 the star had to be moving fast enough into the black holes gravity field in the first place to account for the energy required to escape on the other side... Nowhere does the article state that the star has travelled *through* the black hole, nor that it has passed beyond the event horizon. And the speed is not high - 1.5 million miles per hour is not much compared to the 670 million miles per hour at which light travels in a vacuum. It's less than a quarter of a percent of the speed of light. I don't know what the escape velocity of the milky way is, but it is obviously less than the speed of this star. Link to comment Share on other sites More sharing options...
bumab Posted February 10, 2005 Author Report Share Posted February 10, 2005 Obviously... I would have assumed more. Would the rotation of the galaxy have some sort of effect on the gravity along the poles? Perhaps, similar to the way balck holes emit jets along their poles, the galaxy as a whole does that, and the star is along for the ride, as it were. Apparently, the escape velocity for the galaxy is about 700,000 km/sec, although it's not known for sure (That's from wikipedia) Link to comment Share on other sites More sharing options...
maddog Posted February 16, 2005 Report Share Posted February 16, 2005 Nowhere does the article state that the star has travelled *through* the black hole, nor that it has passed beyond the event horizon. And the speed is not high - 1.5 million miles per hour is not much compared to the 670 million miles per hour at which light travels in a vacuum. It's less than a quarter of a percent of the speed of light. I don't know what the escape velocity of the milky way is, but it is obviously less than the speed of this star.It could be computed using Newton's Laws of Gravitation F = G Mm / r^2 where M = Mass Galaxy, m = mass star, r = distance between two when foundFrom there is an escape velocity equation I will have to look for (I think derived from integrating F=ma). Maddog Link to comment Share on other sites More sharing options...
dagaz Posted February 16, 2005 Report Share Posted February 16, 2005 Acoording to this page at the Sydney Morning Herald Website the star is thought to have originally been part of a binary star system and was flung outwards when its companion star was captured by the black hole. The article also says:The outcast is going so fast - more than 2.4 million km/h ... That speed is about twice the velocity needed to escape the galaxy's grip ... said Warren Brown, an astronomer at the Harvard-Smithsonian Centre for Astrophysics. Which works out to be roughly 333 km/s escape velocity for the Milky Way. Link to comment Share on other sites More sharing options...
Tormod Posted February 16, 2005 Report Share Posted February 16, 2005 Which works out to be roughly 333 km/s escape velocity for the Milky Way. Interesting! The escape velocity for Earth is 11 km/s. So it's not THAT much higher, really. Link to comment Share on other sites More sharing options...
dagaz Posted February 16, 2005 Report Share Posted February 16, 2005 Interesting! The escape velocity for Earth is 11 km/s. So it's not THAT much higher, really. When I first came across that figure I was surprised it wasn't a lot higher, but when you think of the vast distances between objects in the galaxy it makes more sense. Link to comment Share on other sites More sharing options...
Tormod Posted February 16, 2005 Report Share Posted February 16, 2005 True. And we'd have to travel a looooong way before we could even think of getting out of the galaxy at all... ;) Link to comment Share on other sites More sharing options...
Fishteacher73 Posted February 16, 2005 Report Share Posted February 16, 2005 Velocity is also a relative measure...The milky way is also moving and has a velocity (I don''t know what it is), but if the vector of the star was in an opposite direction than the vector of the galaxy, you would subtract the velocity of the galaxy from the escape velocity (or at least a trig function of it depending on the angles between the two vectors). Correct? ;) Link to comment Share on other sites More sharing options...
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