Centrifugal vs Gravity

[Joel Wright]

Updated: 05:39 PM EST
Star Escaping the Milky Way Galaxy
By Deborah Zabarenko, Reuters



AFP/Getty Images
In this artist's rendition, an outcast star is zooming out of the Milky Way, ejected from the galactic center after a close encounter with a black hole.

WASHINGTON (Feb. 9) - An outcast star is zooming out of the Milky Way, the first ever seen escaping the galaxy, astronomers reported on Tuesday.

The star is heading for the emptiness of intergalactic space after being ejected from the heart of the Milky Way following a close encounter with a black hole, said Warren Brown, an astronomer at the Harvard-Smithsonian Center for Astrophysics.

The outcast is going so fast -- over 1.5 million mph -- that astronomers believe it was lobbed out of the galaxy by the tremendous force of a black hole thought to sit at the Milky Way's center. That speed is about twice the velocity needed to escape the galaxy's grip, Brown said by telephone.

"We have never before seen a star moving fast enough to completely escape the confines of our galaxy," he said. "We're tempted to call it the outcast star because it was forcefully tossed from its home."

The star used to be part of a binary pair, waltzing with its companion star close to the rim of the black hole. In this case, "close" is a relative term; the actual distance was probably about 50 times the 93 million-mile distance between Earth and the sun.


Talk About It


· Post Messages

As the two stars twirled around each other, they were pulled faster and faster toward the edge of the black hole, one of those monster drains in space whose gravity is so strong that nothing, not even light, can escape once it is consumed.

While the companion star was captured by the black hole, the outcast continued on its whirling path around its edge.

Objects go faster the closer they get to black holes and this star was probably moving at extraordinary speed, perhaps as high as 20 million mph. That very speed, coupled with the speed of its twirling, sent the outcast zooming toward the edge of the Milky Way and beyond.

At this point, the outcast is about 180,000 light-years from Earth, in an outer region of the galaxy known as the halo. A light-year is about 6 trillion miles, the distance light travels in a year.


02/08/05 16:52 ET

Copyright 2005 Reuters Limited. All rights reserved. Republication or redistribution of Reuters content, including by framing or similar means, is expressly prohibited without the prior written consent of Reuters. Reuters shall not be liable for any errors or delays in content, or for any actions taken in reliance thereon. All active hyperlinks have been inserted by AOL.

[Vic Hays]

This just shows that gravity can do work even though it is considered a conservative force.

Hmm, two weights or masses working as a pair.

[ovyyus]

Gravity is not supplying the work. The increased momentum of the star comes at the expense of momentum of the black hole.

[Vic Hays]

Gravity is not supplying the work. The increased momentum of the star comes at the expense of momentum of the black hole.

How exactly did the black hole lose momentum? Was it rotational or velocity through space?

[ovyyus]

'Gravity assist' (should be called 'planet assist') is the same principle at a smaller scale to the star/blackhole proposal:

http://www.windows.ucar.edu/tour/link=/ ... l&edu=high

[Vic Hays]

I think this depends on your point of view. How do we know that the black hole had "momentum? In relationship to what? Perhaps it was stationary and the star actually started it moving. In this case gravity was the contributing energy.

[rlortie]

I think this depends on your point of view. How do we know that the black hole had "momentum? In relationship to what? Perhaps it was stationary and the star actually started it moving. In this case gravity was the contributing energy.

Point of view. The universe is said to be everything, yet it is expanding. What is it expanding into if it's already everything

[Jonathan]

Actually in this case I think it was that the star had been spiraling toward the black hole, losing potential and gaining kinetic energy, for who knows how long. At some point it got awefully close to both the black hole and another star which was moving quickly too, and they interacted via gravity assit and launched one star. The other probably got lauched toward the black hole and has been consumed.
To answer your question Vic, which one is "really" moving in this case is not relevant, because the math predicts the same outcome for all equivalent reference frames. So the black hole could be stationary and the star is moving at speed 2 in a direction, or the star could be stationary and the black hole is moving at speed 2 in the opposite direction. (And the black hole's momentum is probably substantially rotational relative to the galaxy, hence my first point, since it doesn't have linear or instantaneously-revolutionary momentum to give away).

[ovyyus]

Gravity contributes no additional energy in the planetary slingshot maneuver just like David's slingshot contributed no additional energy to the stone that killed Goliath.

[Jonathan]

If that reply is to me, I have no reason to disagree.

[winkle]

ovyyus As the two stars twirled around each other, they were pulled faster and faster toward the edge of the black hole, one of those monster drains in space whose gravity is so strong that nothing, not even light, can escape once it is consumed _____________________________________________________________ is gravity doing no work when it holds light back?

[Jonathan]

Oh, I completely forgot that the article actually said there were two stars! I guess that would explain how I came up with it...
About the light, in theory no, because the as the light moves out it gains potential energy.

[winkle]

Oh, I completely forgot that the article actually said there were two stars! I guess that would explain how I came up with it...
About the light, in theory no, because the as the light moves out it gains potential energy _____________________________________________________________in a black it does not move out

[Jonathan]

I thought you were refering to the red-shift related loss of energy as light moves away from a black hole. No, gravity does no work on light in a black hole because the light continues on down into the singularity, gaining energy, but looseing potential all the way. At the event horizontal, some light hovers motionless.

[winkle]

that's neat i would like to see that