"tracy" wrote in message oups.com...
| According to this article, the mysterious super-high speed stars are
| more numerous and fastest than previously though. What if one of these
| "hypervelocity" stars came through Sun's neighborhood?

In hypothetical sentences introduced by 'if' and referring to
past time, where conditions are to be deemed 'unfulfilled',
the verb will regularly be found in the pluperfect subjunctive,
in both protasis and apodosis.
-- Donet, "Principles of Elementary Latin Syntax"



| How dangerous
| it could be for life on Earth?

About the same as a bacterium in a crematorium. It might even be fatal.


|
| What would be safe distance a star moving at about 700 - 1000 km/s
| could get near Sun without disrupting the planetary system?

The speed is irrelevant, presence is.
You don't seem to grasp the scale of the Universe or even the scale
of the Solar System.
Suppose you have a cluster of 4 pixels (dots) in the middle of your
monitor screen to represent the sun, like this:

---- o ---- (Sun, drawn too big)

Then
|
|
|
| -- . ---- (Mercury)
|
|
|
|
| -- . -- (Venus)
|
|
|
|
| -- ' -- (Earth and Moon)


Jupiter (still a dot -- . --- ) is about where your ceiling is.
Saturn is then in your kitchen, the NEAREST star is at the end of the street,
and the imaginary black hole at the galactic centre is in the next city.
You have a far better chance of winning the lottery than meeting another
star up close and personal.
Androcles