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."

To put that in perspective...

[GillBates0]

That's 0.002 [google.com] 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.

Still...

[SharpFang]

...only 0.2% c

Re:Any astronomers out there?

[FirienFirien]

The ergosphere around a black hole is full of matter that's orbiting the black hole at a speed that's not enough to get back out again - as a fast body comes through, it slingshots through the buzz of energy provided and comes out faster than it went in. This is above the point of no return, but there's still a lot of energy flying around there.

Supermassive black holes

[Spy der Mann]

Recently I saw on Discovery that many galaxies (if not all) were orbiting around supermassive black holes [berkeley.edu]. And that the orbiting speed of the stars is proportional [arxiv.org] 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:1.5 Million MPH...

[maird]

I don't actually know how they measured it (and I'm not an astrophysicist and don't offer this as opinion, let alone fact) but 1.5 million miles per hour probably creates a significant doppler shift. The spectra of stars shows distinct bands that correspond with the absorption of photons at specific wavelengths. The reason the absorption is at specific, discrete wavelengths is that electrons in specific elements (e.g. Hydrogen, Helium, etc) absorb at specific wavelengths. The distance between absorption lines for different elements is fixed. For example, say Helium absorbs at some wavelength x and Hydrogen at some wavelength y. The difference between x and y is a constant (even under a doppler shift). So, if you see two absorption lines and they are x - y apart then one is the Hydrogen and one the Helium. This is overly simplified but the principle is the same (it just involves more than two lines). You can then tell how much doppler shift because you know what wavelength they should appear at and see what wavelength they actually appear at. Doppler shift is directly proportional to speed (I hope that's accurate). So, knowing the doppler shift you know the speed relative to the point of observation. Presumably you can work out the speed of the earth relative to some object by measuring the relationship between doppler shift from that body and the doppler shift from various other celestial bodies. Or, maybe they had a very long tape measure, a very powerful radar, or a very powerful laser or just guessed ;-)

Re:This must mean

[thpr]

This must mean that the galaxy is actually speeding up?

No

Or does it just mean the stars mass is greater than it was before..?

Yes, but only very slightly... since it's traveling at about 1/500th the speed of light, it did gain some mass, but very, very little relative to its original mass

If its neither of these, why has the star suddenly broken away from the galaxy

It all has to do with the angle and distance at which the star approached the black hole.

If it passes by a long distance away or at a slow speed (I don't know the equation to show you the threshold of speed/distance/mass), the chance is that it will enter some form of orbit, if irregular.

If it is nearly tangent to the object (but doesn't strike it), and it is already moving at a high enough velocity, then it will use the black hole as a slingshot and will gain velocity. You can check out the Cassini satellite's mission trajectory [nasa.gov] to see how it used Venus and Earth to gain velocity (relative to the sun)

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:Any astronomers out there?

[The_countess]

the black hole presumed to be at the center of our galaxy has probably swallowed a huge amount of stars by now, so its gravity pull will be MUCH larger then even the largest know starts. as for the slingshot effect. as something small(er) gets pulled toward something heavy its increasing speed all the time. by the time the small object has reached the heavyer object and is about to do a orbit like turn its speed has become so great that it shots away from the heavy object at great speed because of the centrifugal force. they use the same techniek to give space probes some extra speed inside our solar system, aspecialy if they are going for the planets on the outside of our system.

Re:Does anyone know...

[EvilTwinSkippy]

Theoretically, decellerating.

Observationally, we don't know. It required a lot of observations to gauge its proper speed. It is going to require a lot more to gauge how much that speed is changing.

One moment of insight I had into how much we don't know about our universe was fooling around with some software from NASA. (Perks of working in a science museum with a planetarium.) One of the items you could toggle on you flights around the solar system and surrounds and ... well just about anywhere in the observable universe... was paralax error.

That's a neat orange strip that shows all of the possible values that the paralax, the difference between the angles observed at different places. It's used to calculate distance. Even on nearby stars, we have paralax errors that place them over ranges of hundreds of light years.

We can measure the relative direction of a star easily. Determining the distance is largely voodoo. Especially when you throw in "proper motion." What we see as the constellations are changing slowly above our heads as the stars themselved move relative to one another and Sol.

Re:1.5 million miles per hour!!

[j1bb3rj4bb3r]

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

huh... I just posted something about this to another comment...
that's not actually correct... it's not acceleration that kills, it's jerk (change in acceleration)

Re:Any astronomers out there?

[another_henry]

So why would a black hole produce a greater gravitational force at a distance than any massive star?

It doesn't, but the black hole is very massive - considerably more massive than any star in the galaxy.

And why would a great force at the centre of the galaxy be inclined to spit out stars at huge velocities?

It's tricky to explain and not terribly easy to get your head around, but I think the principle is similar to this demonstration [grand-illusions.com] (check out the video). The grav. potential energy of the companion star due to its attraction to the black hole is transferred into kinetic energy in the ejected star.

IANAPyet so please correct me if I'm wrong.

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:What if there were planets orbiting it?

[EvilTwinSkippy]

Depends on how close the system came to the large gravitational mass that flung them off. If they passed really close, and the pull of the larger body exceeded the pull of the star, then yes, a lot of stuff would transfer orbit to the larger body, or been slingshotted off into space.

If the approach wasn't that close, then the planets would still have been a lot more attracted to the "traveling star" than anything else. Their orbits may have been altered slightly by the influence of the larger mass, but they would have stayed.

Re:1.5 million miles per hour!!

[LurkerXXX]

Really? I bet if we put you in a rocket, and had it accelerate and the acceleration built up very very very slowly, you would still turn to jelly when the acceleration finally hit 20 G's.

Re:Little relativistic phenomena

[OOGG_THE_CAVEMAN]

1.5 million miles per hour is only 671,000 meters/second [google.com], or 0.00224 the speed of light. Relativistic effects are basically negligible.

Re:Moving

[eutychus_awakes]

While witty, that scenario doesn't hold up if you consider that either the star or the galaxy had to undergo a (relatively) brief period of acceleration in order to exhibit the behavior we currently see. The probability of every star in the galaxy except this one undergoing that kind of acceleration is minuscule - however, the probability of one star meeting the conditions of the proposed hypothesis is quite high.

That's how we solve these kinds of paradox problems in relativity. The classic "Twin Paradox" is solved in a similar manner. For those who need a refresher, it is the 'paradox' whereby one twin takes a trip at some substantial fraction of the speed of light and returns to find the other several decades older than himself (or herself) due to the time dilation effects encountered during the trip. The paradox is: From the point of view of the twin on the trip, it is the twin on Earth and everything else that ends up going very fast. Why shouldn't they be the ones to experience time dilation? The answer is, a deliberate acceleration is applied to the twin on the spaceship (reaction mass burning, converting energy to momentum). This defines the reference frame for the experiment, resulting in the correct application of the time dilation effect.

For our wayward star, its reference frame was defined by its proximity to our galactic center, and the probability that a super-massive black hole smacked it out of the galaxy's gravitational hole.

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:Any astronomers out there?

[Tired and Emotional]

You don't get a slingshot effect from the black hole at the centre of the galaxy in the same way as you do from a planet because the black hole is at rest. The presence of a companion was crucial.

Its more like a satelite performing a rocket burn near the sun in order to gain velocity. Because the exhaust comes out moving more slowly (relative the the far away observer) than it would if the satellite was in higher orbit, the satelite gets much more boost.

In the case of a binary system and the black hole, I expcect what happens is the tidal forces break appart the binary system. The component that was travelling in the direction of motion (relative to the black hole) gets ejected with increased velocity while the unfortunate companion gets swallowed up - or goes into a much tighter orbit.

I wonder how much boost you get from the black hole at the centre of our galaxy as a result of frame dragging? Does frame dragging in fact produce a boost? (I would expect so) Do we have any estimates of the effect for the galactic centre?

Re:Supermassive black holes

[wayne606]

I'm guessing that a large part of the radiation from black holes is like synchrotron radiation - charged particles being accelerated in a magnetic field (i.e. temporarily in orbit) will give off radiation. This radiation (and plain old friction) is probably a big reason that the particles don't stay in orbit forever but spiral in eventually.

Stuff almost never falls directly into a black hole... Because of conservation of angular momentum it will generally go into orbit.

Re:nitpick

[Anonymous Coward]

just to add, kelvin is based on absolute 0.

0 degrees celsius is defined the temperature water turns into its solid state, 100 degrees celsius is defined as the temperature water turns boils at sea level.

farenheit is scaled off the temperature mercury turns to its solid state.

a 1 degree increase in celsius matches a 1 "degree" increase of kelvin, farenheit is all screwed up in how it scales (blame the english).

0 degrees kelvin == -273 celsius == -459 farenheit

Dengejaa Uveso

[Scarabaeus]

... that's the name of the black hole in the center of our galaxy, milky way. At least according to Perry Rhodan [proc.org].

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.

Re:Inertia & Momentum - Star Stampede

[Wraithlyn]

Well they say its trajectory is coming pretty much directly from the centre of our galaxy, which supports their galactic black hole slingshot theory.

It's still possible that it's an extra-galactic object that just happened to intersect with the centre, but that requires us to assume a large coincidence, and we know what Occam has to say about that.

Re:What about relativity?

[pclminion]

Motion is relative but acceleration is not. Although it is valid to choose the star as the frame of reference, it is a non-inertial frame and thus would require the introduction of fictitious forces to explain the behavior of the rest of the universe.

If I were working the equations, I would prefer a reference frame which did not introduce fictitious forces on a universal scale.

YA Gravity Assist

[starglider29a]

Mythbuster: "Delta-V" is a function of amount of propellant burned for a given type of engine. Period. It is not affected by velocity, orbital geometry.

But, I know what you're saying. It's not bullshit. But there are some misnomers and misconceptions. I will try to expound on what I know you are saying.

• In general we are talking about a probe escaping Earth. Say, off to Saturn...
• After that, we are escaping the sun, as in Pioneer and V'Ger (before the upgrade ;-). In those cases, maximum velocity for minimum propellant is the goal.
• Orbits whose ellipses are the same major axis have equal period.
• High eccentricity orbits reach out farther than circular orbits of same major axis/period
• High eccentricity orbits require higher velocity near the planet/sun
• Until you hit escape velocity (a parabola or hyperbola) you are in a long ellipse

If you want to get a probe "out there" you want to burn at periapsis (Earth: perigee or Sun:perihelion). That leaves the peri at the same point and raises the other end. Do that enough times and you get escape on the last pass. Delta-V at any other point on the orbit will raise the peri and lower the apogee/aphelion. Propellant wasted.

Often, satellites will burn at perigee, orbit around and repeat. This allows the same amount of propellant to get your there, but without the mass of a larger engine/structure. Smaller motor more often is more efficient, just takes longer. Nothing is free.

In short, you don't get more Delta-V, but you get it where you want it.
--
"Illustrative Myth: Once you are out of earth orbit, you are halfway to anywhere."

Re:Supermassive black holes

[mbrother]

Some of the energy is in the form of synchrotron, but this is more important in so-called radio-loud objects with jets, and is beamed along the jets. The vast majority of the radiation is thermal, either from the hot accretion disk or reprocessed radiotion from surround dust heated to a few hundred degrees kelvin. Quasars are my specialty.

Re:Relative speeds

[khallow]

Third, a slingshot-type approach such as the one we are contemplating will impart significant angular momentum (spin) to the star. Again, since we're dealing with such a gentle gradient, the star won't spin apart, but the spin will adversely affect the planet's rotation as tidal locking slowly takes effect. (Not sure just how much of an effect this would be, though...I'll leave more mathmetically adept readers to do the math.)

Actually, this isn't the scenario described in the article. The theory concerns binary systems where one of the partners is trapped by the black hole and the other is thrown out. The angular momentum (plus maybe a boost from the partner sliding down the gravity well) is converted to regular momentum.

Second, tidal locking wouldn't be significantly effected by a change in the star's spin. For example, the Sun spins faster than any of the planets (particularly Mercury). Instead, tidal locking comes from the star's tidal forces (which is significantly greater) acting on the planet rather than vice versa. The spin of the star aside from minor changes in the star's shape has no effect on the tidal forces the star exerts on a nearby planet.

Re:1.5 million miles per hour!!

[Dana P'Simer]

But you are forgetting that we are talking about sublight speed. The damage done by a photon torpedo can easily disrupt the fragile warp fields. Warp speeds are created by sucessive warp shells like those nesting dolls. To reach warp 9 you need 9 nested warp shells.

I guess I spend more time infront of the tube than you :P