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."

Comments

To put that in perspective...

[GillBates0]

That's 0.002 times the speed of light or only about 1/500th the speed of light.

Plugging 670*10^3m/s into Lorent'z equation:

t = t'/(sqrt(1-(v^2/c2))
where v=6.7*10^5m/s
and c = 2.99*10^8,

I got a time dilation of factor of 1.00000249. That is, time in the moving system (the star) will be observed by a stationary observer to be running slower by a factor of 1.00000249.

Not as impressive as I hoped it would be when I started the calculations.

Supermassive black holes

[Spy der Mann]

Recently I saw on Discovery that many galaxies (if not all) were orbiting around supermassive black holes. And that the orbiting speed of the stars is proportional to the black holes' mass. This is known as the "M-sigma" relation.

This meant that the supermassive black holes actually contributed to the process of galaxy formation.

The theory is more or less the following:

In the center of a galaxy-sized gas cloud, a star collapsed, forming a black hole. The black hole began eating the gas around it, forming a quasar (quasars are the matter just about to be swallowed by a black hole, disintegrating and generating enormous amounts of energy).

The quasar, due to its high temperature and rotational speed, heated the surrounding gas cloud, activating a chain reaction that gave birth to all the stars in the new-forming galaxy.

Eventually, the quasar pushed away the stars, so the black hole could only be fed by the quasar itself. After that, the black hole enters a dormant phase (it has nothing else to eat), and the galaxy is already formed (of course, I'm talking about a process that takes billions of years).

Re:Supermassive black holes

[bigmaddog]

Call me a bitch about details, but... (I know, someone else will be a detail bitch about my details.)

Quasars radiate tremendous amounts of energy not because matter "disintergrates" as it falls inwards but merely because it falls inwards.

It's as if a bucket of bricks fell on your head from ten stories up (well, almost) - while up there, the bricks & bucket have potential gravitational energy. As the whole thing falls, gravitational potential energy is converted to kinetic energy, some of which is lost to friction with the surrounding air. It may generate sound, like a low whistle or thunderous roar, depending on the aerodynamic properties of the bucket. When the bucket hits, all the remaining kinetic energy is dissipated by your skull and brain, and "radiates away" as sounds and splattering gore. (This last part about the brain and plattering is not necessary for the analogy but I just like talking about gore.)

So, same thing with quasars, more or less. Stuff far away from the quasar has a lot of gravitational potential energy because quasars are so damn massive, which leads to powerful gravity. As it falls inwards, it trades this energy for kinetic enrgy, moving faster, and, as it grinds against other stuff in the accretion disk around the quasar, some of which is moving slower, some of this energy is lost to friction, except instead of sound (whistling) with the bucket & bricks, you get EM radiation. (If the bucket fell from really high up, it might heat up from friction and start emmiting some radiation of its own, in infra red and then in visible light.)

Sice the black holes at the centre of galaxies are so damn huge, and because falling into a black hole release several orders of magnitude more of the massenergy of a piece of matter than fission or fusion ever could (astronomy textbook not at hand, so can't quote the numbers), we get a whole lot of radiation this way, and so quasars are really really bright.

Re:1.5 million miles per hour!!

[merlin_jim]

That's not entirely true. The force excerted by gravity goes as 1/r^2, where r is the distance between both masses.

If you have for example two large m1 and m2 each attached one end of a very long pole in a gravitational field caused by another mass M, the mass nearest to the M would experience a slightly stronger force than the other one. So that could, in theory, break the pole.

What you're talking about is tidal gravity. And tidal gravity is exactly what caused one star of a companion to be accelerated away while the other one was captured into an orbit.

On the scale of the objects themselves, though, the tides were probably extremely gentle. AFAIK companion stars are generally light-months apart. Even if this star was a planetary system, it's nearest planets are probably only a few light-minutes away...

Re:Does anyone know...

[Overzeetop]

Well, if we can simplify the motion to (1) the galactic core and (2) the star, Kepler's equations require that it be decelerating. Based on the fact that it has 2x the escape velocity of the galaxy, that would put it on a hyperbolic path with the galactic core at its focus (the real one). After an (infinite) period of time, it will slow to a spped which is 1.7x escape velocity (v-inf^2=v^2 - v-esc^2) based on the 2x number being the maximum velocity obtained. This is more commonly known as the "hyperbolic excess speed".

This post brought to you in part by Bates, Mueller, and White...the best textbook value in the world ($6 for an astrodynamics text...and a pretty good on at that).

Explanation

[af_robot]

For those, who didnit get it.
Puppeteers are alien race from novel "Ringworld" by Larry Nivel. They were moving their home star system to a new galaxy to escape from the Core explosion.

Re:Hindmost

[chiph]

FYI: the 5-planet Klemperer Rosette used as a plot device by Larry Niven for the Puppeteer's home worlds has been shown to be unstable:
http://burtleburtle.net/bob/physics/kempler.html

(warning, contains java applets which will probably freeze up Firefox)

Chip H.

Re:Relative speeds

[Spackler]

You seem to be using "through space" as a non-relative term. If the sun is moving "through space" at 155 miles a second, how can earth be moving "through space" at only 18 miles a second. It that was the case we would be 16,000 miles farther from the sun since I started writing this email. 3 million miles more than when I woke up this morning and 180,795,888,000 miles since I was born.

Re:1.5 million miles per hour!!

[LurkerXXX]

Right on the tidel forces.

As for his body being accelerated and his blood isn't... That's only the case in as much as right now your body is trying to accelerate at 9.8 m/s/s toward the center of the earth. Your bone structure and muscles lets you resist it. Your blood is also trying to accelerate towards the center of the earth at the same rate. Your arteries and veins and your heart let you resist that as well.

Your body and blood aren't accelerating at different rates. They both deal with the same acceleration in the same way, with it acting as 'weight'. The problem with weight/acceleration is that your body was designed to handle only so much of it.

Now let's kick it up a notch. blood pooling...

Imagine a test pilot in a centrafuge machine. It takes him up to 6 G's and holds him there for an hour. Just like he was on a planet with 6x earth's gravity.

His body is accelerating at 6 G's.
His blood is also accelerating at 6 G's (otherwise it would all leak out the back of his chair and that would be a 'bad thing' ;)

His blood resists accelerating as you say, but so does his body (Bodies at rest tend to stay at rest tend to stay at rest, bodies in motion tend to stay in motion and all that). Nevertheless, the back of his chair is causing the lot of them to accellerate at 6 G's.

His heart, however is now trying to pump blood that 'weighs' 6x as much. The heart can't pump the heavier blood as easily or 'high' (relatively) as it could normally. His veins can't constrict as much as they normally would to force blood back into the right areas of the body, because the blood is pushing against them with much greater force. The veins also have valves to prevent blood from flowing back the wrong way, but these may give way under the additional pressure.

The blood is not accelerating at a different rate from the body, it's still in his veins and artieris, and so still in his body. His body is being accellerating at 6 G's and the blood, being trapped inside, is going along for the ride. But it acts as a much heavier fluid. So it starts to pool in the lower extremeties since it can't be pumped efficiently. Depending on how strong his heart is (and resilient his veins are), he might be able to handle 6 G's for a good long while. But if they aren't in quite as good of shape he might not be able to pump the blood well enough and might black out after a few seconds or minutes.

Once again the blood isn't accelerating at a different rate than the body (both are resisting being accelerated), anymore than your blood and body accelerate at different speeds on earth, it just has a higher 'weight' then the body was structurally designed to pump.

The next stage is to crank up the centrifuge chair/other-planet to 1000g's density. 1000 G's. Now the test pilot's ribs are trying to hold up themselves and the muscles etc attached to them. But they weight 1000x as much. The bones werent' constructed to hold such a high weight, so they snap. The 'body' isn't accelerating at a different rate than the... 'body', but it breaks down because it wasn't designed for such mechanical forces. Everything is being accelerated (and trying to resist it). Everything is accelerating at the same rate. It just can't handle the rate.