Star Flung From Milky Way at High Speed

fenimor writes "Using the MMT Observatory in Tucson, astronomers have discovered a star three times bigger than the sun, leaving our galaxy at a speed of over 1.5 million miles per hour (670 kilometers per second). The first-of-its-kind finding not only confirms an earlier theory about the existence of such speeding stars, but also reinforces the notion that the Milky Way spins around a black hole."

1.5 Million MPH...

[sidepocket]

relative to what?

It still amazes me how they can measure that kind of stuff.

Speed is relative

[Hoi Polloi]

What are they measuring the star's speed against? The center of our galaxy? The earth?

Re:1.5 million miles per hour!!

[witte]

It's relative speed to us (eg. the sun, or any other mass).
In the void of space this has no consequences for the mass that is speeding. (Until it collides with something that has a different speed.)

Abruptly increasing acceleration could rip it apart though, but that's another story.

Re:1.5 million miles per hour!!

[juangonzo]

They aren't torn apart for multiple reasons. One of them is that there is nothing for them to hit that will tear them apart. Going millions of mph is different in a vacuum than it is in the earth's atmosphere. To get more complex, to the star it's not moving, the rest of the galaxy is. To understand more of what I'm talking about read about the reference frame in any basics physics book.

Re:Speed is relative

[grahamsz]

Presumably if it's leaving our galaxy then that'd be the normal way to look at it.

Alternatively maybe it's staying still and we are being flung away from it at 1.5M mph.

Re:1.5 million miles per hour!!

[merlin_jim]

I just wonder why the star and the planets are not torn apart by such huge speeds?

a) we're not sure it has planets.

b) it's not velocity that kills, it's acceleration.

c) this acceleration can only be explained by current theory if it was a gravitational acceleration.

d) gravitational acceleration acts on all elements of an object equally, meaning that there was no force from the acceleration itself acting to tear the object apart. Just like when you're in freefall, you don't feel gravity acting on you.

Now TIDAL gravity can tear objects apart, but since the gravitationally assisted acceleration likely happened in the galactic core, the tides were probably pretty gentle... the tidal force at a black hole's horizon can be expressed as a function of mass over surface area; the bigger the hole, the less the tides.

Re:Speed is relative

[FirienFirien]

It'll be measured relative to the galactic hub - measuring the speed relative to the earth is irrelevant, since you don't look out of your car and think that cars coming the other way are going at twice the speed limit, instead it's relative to the frame of reference of the ground {hub}.

Then again, with a speed that high, the speed of the earth/sun becomes insignificant anyway (8.5 miles/s and 155 miles/s respectively)

Re:1.5 million miles per hour!!

[essreenim]

Exactly, although conceivably, the star has had a great deal of its mass stripped away by the event in question. The only predictable change would be due to gravitation from the black hole and the resultant cling-shot of acceleration afterwards. An interesting point though. That star is / was ( we are observing history - the star would have been very far away and is by now much much further away) in a different time frame. From the point of view of an observer at the outcast star, they are actually moving away from the galaxy at a much slower rate. Consequently, if any sentient observer were at that star, they are much further away from the galaxy than they might intuitively think they are..Ahhh relativity..

Inertia & Momentum

[mreed911]

While this seems astounding, leaving some to wonder "how's a star stay together at 1.5MM mph?", it's important to remember that, for all intents and purposes, it's travelling through NOTHING, through a vacuum. As long as its velocity is stable (not running into things to slow it down), there's no inertia to change it's shape, etc.

Is there *really* a difference, physically, on an object moving at 1.5MM mph and one standing completely still, if they're not interacting with anything else? No. Their inertias are the same, so their physical properties and interactions are the same.

Momentum, however, could be a bitch. Imagine this star slamming into another star (or, a la the Death Star, a small planet in the Aldeberan system). Ka-pow, with the graphic like on the old Batman series! Would make Levy-Shoemaker look like a BB gun (you're gonna put your eye out!)...

Re:Speed is relative

[jridley]

It's moving like hell compared to any large body in the galaxy, or the average.

I remember this story:
Professor: The temperature in this kind of reaction is about 3 million degrees.
Student: Is that Celcius or Kelvin?
Professor: It doesn't matter!

IOW, the difference between C and K at ~3m* is insignificant. In the same way, the speed of this star is practically the same from any point of reference near any star in the galaxy.

Re:milky way munching stars and galaxies

[corngrower]

there probably would be no kinetic interaction between the two if they were to "collide".

I would bet that there would be a number of stars in the galaxies that would have their motions markedly changed. You'ld probably have a number of stars being scattered around and exiting the galaxies at high velocities relative to other stars . There may even be an actual collision or two.