Questions concerning hypervelocity stars

[Travito]

Hey everybody, I'm new here and what better way to start then jump right in!! I have a few questions concerning hypervelocity stars for a sci fi book that I want to write.

First of all, what is the agreed upon "average" speed of a hypervelocity star? I have done a bit of googling, but I have seen a lot of different numbers. Would 1000km/s be about right?

Secondly, I have read that some hypervelocity stars are thought to have originated in the Magellanic Clouds. Which one would be more likely to produce hypervelocity stars? The LMC or the SMC?

Thirdly and finally, given the speed and the distance of the LMC/SMC, how long would it take a hypervelocity star to reach Earth? I know this would never happen, but keep in mind it's just for a sci fi novel

Thank you all for your help and I look forward to being a member of these forums Merry Christmas!!!

Travito

[ronin]

Thirdly and finally, given the speed and the distance of the LMC/SMC, how long would it take a hypervelocity star to reach Earth? I know this would never happen, but keep in mind it's just for a sci fi novel.

Sorry, but Time = Distance/Velocity.

Work it out.

Why ask anyone on here this very basic question.

HV stars are most likely to come from interacting binary stars, where they interact and one is in effect thrown out with a sizeable chunk of the system momentum.

Alternatives are when an orbiting dwarf galaxy finally gets absorbed into the main galaxy. Again stellar interactions. Since the LMC and SMC are still seperate HV stars will not come from them yet. In a few billion years maybe but not until they merge with the milky way.

[ncjunk]

Sorry, but Time = Distance/Velocity.

Work it out.

Why ask anyone on here this very basic question.

Thats a bit of a Grumpy answer, dont reply if you dont want to be helpfull.

Here's an interesting link-

http://www.astro.uni-bonn.de/~mwhalo/proceedings/mwh-t28-brown.pdf

It seems they are stars that are no longer gravitationally bound to the galaxy or to put it another way can escape from the milkyway.

So the velocity would be >1000km/s

It would be nice to know if 1000 is the minimum required velocity to escape the milkyway...hopefully someone cam clear that up.

[Grunthos]

First of all, what is the agreed upon "average" speed of a hypervelocity star? I have done a bit of googling, but I have seen a lot of different numbers. Would 1000km/s be about right?

It depends on a variety of factors but 1000km/s might be deemed the right order of magnitude (I assume you pulled this number from Wikipedia - escape velocity from Milky Way at the distance of our Sun from galactic centre )

Secondly, I have read that some hypervelocity stars are thought to have originated in the Magellanic Clouds. Which one would be more likely to produce hypervelocity stars? The LMC or the SMC?

We don't really know. Astronomers have only discovered a small amount of HV stars. Too few to make any accurate measurement of the statistic you wish. Hey, you're writing a sci-fi book. Make up a plausible reason!

Thirdly and finally, given the speed and the distance of the LMC/SMC, how long would it take a hypervelocity star to reach Earth? I know this would never happen, but keep in mind it's just for a sci fi novel

Assume an HV star on a direct tangent from the LMC travelling at 1000km/s.

I'm not going to do the maths for you (it would spoil the fun) but here is the raw data

1) Distance to LMC approx. 160,000 light years

2) Light year = approx 9.46 x 10power12 km (i.e. 946000000000km)

3) Average HV velocity = 1000km/s

Time = distance/velocity = a very loooooooong time (are your sci-fi characters long lived?)

[Dave Dubya]

Hey everybody, I'm new here and what better way to start then jump right in!! I have a few questions concerning hypervelocity stars for a sci fi book that I want to write.

First of all, what is the agreed upon "average" speed of a hypervelocity star? I have done a bit of googling, but I have seen a lot of different numbers. Would 1000km/s be about right?

Secondly, I have read that some hypervelocity stars are thought to have originated in the Magellanic Clouds. Which one would be more likely to produce hypervelocity stars? The LMC or the SMC?

Thirdly and finally, given the speed and the distance of the LMC/SMC, how long would it take a hypervelocity star to reach Earth? I know this would never happen, but keep in mind it's just for a sci fi novel

Thank you all for your help and I look forward to being a member of these forums Merry Christmas!!!

Travito

1. Yep

2. Probably not a lot in it. There is already one HVS detected thought to be from the LMC. (Not entirely sure how/why, as I didn't think the LMC had much of a core which might eject a start.)

3. Somewhere in the region of a billion years or so. (My calculation may be slightly out, as I have had a lot of cider today)

While obviously in the realms of far speculation, it'd perhaps be interesting to consider a planetary system forming around such a star.

[Damo636]

Sorry, but Time = Distance/Velocity.

Work it out.

Why ask anyone on here this very basic question.

Not a very nice response to a new members first post

Welcome to the forum Travito and good luck with the book

[Travito]

Thanks everyone for the help

Time = distance/velocity = a very loooooooong time (are your sci-fi characters long lived?)

Yea...I'll have to toy around with some numbers, maybe make the star superhyperfast or something Or maybe make it so people don't discover it until it'll collide with Earth during their lifetime.

On that note, how difficult is it to detect such a star? Are they like black holes which are very difficult, or just like a regular celestial body?

[ScubaMike]

You could always get one HV star to get a slingshot from another. Maybe an UV (Uber-Velocity) star

[glowjet]

Hi Travito and welcome to SGL, thats an interesting question for a start, and I would disregard any curt comment which may been have made, as it does not fit in with the accepted friendly standard of this forum, " would you be able to detect such a star " as it could have many more sun masses than our own, I would think yes, you would see it coming, a bit better than our local bus service best of luck with your book

[rightguard]

Thats a bit of a Grumpy answer, dont reply if you dont want to be helpfull.

my thoughts exactly. given that the op states he is new here, its hardly the kind of impression we as a whole want to give is it. this is a friendly forum.

shame on you ronin

[Grunthos]

Yea...I'll have to toy around with some numbers

Or you could read the answer Graal gave you (56M to 75M years) over on the Physics forum where you placed an identical OP.

On that note, how difficult is it to detect such a star? Are they like black holes which are very difficult, or just like a regular celestial body?

If it emitted light we could detect it and (say by spectroscopic analyis) infer a velocity (this sort of thing commonly done).

If the HV star was not visible then the "easiest" way to detect it might be it's gravitational interaction with another visible body (bit of a long shot though...)

[Bukko]

Hi, Travito,

Interesting first post..

Just a thought...

The average velocity of the HV star is 1000km/s, so they could be faster.

I guess it depends on what you are trying to do with the book, such as we have a thousand years to solve something, or it just crept up on us and we have a week.

How about a rogue black hole brushing past Proxima Centauri, only 4.3LY away? This would still need over a thousand years to get us, but what if it sent a small Mercury-sized planet our way instead? This might be how the start is where it is now, but the planet took the hit. a Millenium ago, we would not have a clue about this star, so the storyline would stand up.

Anyway, we would not notice it until it was much closer and you would not have to worry about accellerating a whole star, so the planet could possibly be much faster.

If you are looking for a disaster, this would also do it.

If you want a star, then even a small red dwarf would still be discovered hundreds of years out, so the impact would need to be well into the future.

Good luck with the book !!

Gordon.