The article links to a paywalled source for the paper "The Closest Known Flyby of a Star to the Solar System" by Mamajek et al. Full text is freely available on arXiv at [1].
A coincidence of units makes interstellar distances easy to visualize. One light-year is ≈63,240 AU. One mile is 63,360 inches. So if Earth was an inch from Sol, Alpha Centauri would be four miles away. Voyager probes would be 100-ish inches away, traveling about 3 inches per year.
This also gives you some idea of how tiny parallax[1] is. Parallax to Alpha Centauri is equivalent to looking at something four miles away and moving your head two inches. This is where the parsec comes from. If moving 1 AU causes an object to have an arc-second of parallax, that means it's 3.26 light-years away. An arc-second is a tiny angle. There are 360 degrees in a circle, 60 arc-minutes in a degree, and 60 arc-seconds in an arc-minute. To give you another point of reference, an arc-minute would be about an inch separation at 100 yards. Current instruments can use parallax to measure distances up to 300 light-years. The Gaia mission should be able to measure angles as small as 20 millionths of an arc-second.[2]
And presumably the next star's own Oort cloud goes halfway to us, meeting ours in the middle?
I remember some people a while back playing with the idea that the practical way for humanity to colonize the stars was by very gradually "rock-hopping through the Oort cloud", as opposed to "One Giant Leap" approaches like generation ships or crossing our fingers and desperately hoping for hyperdrive.
> And presumably the next star's own Oort cloud goes halfway to us
I don't know that we have enough information about how the size of Oort-like clouds would relate to other observable cahracteristics of stars to have a reasonable basis for any conclusion about the size of "Oort clouds" of other nearby star systems.
We assume gravity, the speed of light etc are the same everywhere. What reason have we to suppose our own stellar neighborhood is the only one to have an Oort cloud? If we assume physics is the same everywhere, then this cloud would extend throughout the galaxy.
I don't think anyone's suggesting that only Sol has an Oort cloud, but the Oort is a (very extended) part of the Solar system, orbiting the Sun like the rest of us, not something spread evenly throughout the galaxy. Stars don't all have the same sort of planets; it'd be surprising if they all had the same sort of Oort.
Oort objects are ill-behaved (erratic orbits). Inevitably some would wander off. Neighboring stars would have at least some Oort objects? Or we need to imagine a mechanism that prevents this.
Again, I think we're in violent agreement. The question wasn't whether they're likely to have some, it was more about how many and how far out, and more specifically whether it's likely to be feasible to hop from our Oort to e.g. Centauri's without having to traverse a huge void in between.
The Oort cloud in fact extends far enough from Sol that some objects in it could be affected by nearby stars - that is, the stars could be sharing/trading Oort objects. In fact, they must be, because gravity. So to deny that our nearest neighbor has Oort objects, we'd have to invent some mechanism that prevented it.
The authors actually discuss this possibility in their paper. (Section 4 of [1].) The star is very faint (an M dwarf), so even at its nearest approach it would have been far too faint to be seen with the naked eye. However, M dwarfs do show occasional flares, so it is possible that it would have brightened to be visible to the naked eye for a few minutes to hours during a flare event.
Possibly a fairly dim point of light, moving slowly like a planet? It was a red dwarf star (with a brown dwarf companion) so not that bright in the first place, and very, very, very far away - that perspective diagram has a log scale. The sun seen from the outer planets isn't much more than a particularly bright star, and it's much bigger and hotter than Scholz's star.
Not sure why you're being down voted without comment since you directly answered the parents question with broadly accurate information:
Anatomically modern humans first appear in the fossil record in Africa about 195,000 years ago (see Omo remains), and studies of molecular biology give evidence that the approximate time of divergence from the common ancestor of all modern human populations was 200,000 years [1]
Migration out of Africa is estimated at around 125000 years ago for modern humans. [2]
I am wondering if we could predict those events, and then launch a space probe similar to Voyager I and II that would be hooked in the alien star's gravity and orbiting around it while it travels in the Milky Way, which would be a some free speed for the space probe to explore space further.
Now, since stars rarely get that closed, I guess it's a bit pointless but I am still curious about it.
I wonder if another civilization had this same idea, and dropped a probe off some 70,000 years ago. Or perhaps the probe has yet to arrive, since elsewhere in this thread I see that comets dislodged by the perturbations of the passing stars are yet to arrive at Earth.
I'm starting to wonder if a somewhat similar event could have occurred ~66 million years ago and triggered a series of events leading to the extinction of dinosaurs.
That's the basis of the Nemesis hypothesis [1]; that supposedly there's a star that roughly orbits the sun and causes havoc every few miillion years. However, it's been pretty much debunked at this point
Was gonna come in here to ask...will this explain Nemesis as not a recurring event but rather a one-time event caused by that trailing brown dwarf (or the star itself) flinging comets all over the place. It would also explain a lot of other crater-rich surfaces dating back to that time...
If that's true it'd be hard to identify the responsible star since in a few million years it would be thousands of light years away and difficult to measure precise kinematics of it.
Given the distances involved, anything that may have had its orbit altered by this event is extremely unlikely to have struck any solid surface in our system already. It may, however, lead to some additional bombardment a few million years from now.
By that time, we might have computers of sufficient power working from an astronomical catalog of sufficient completeness to reverse-propagate the catalog far enough to actually blame the passing stars for kicking out comets in our direction.
I rather thought that Nemesis had become a fairly untenable hypothesis in light of the the facts that:
(1) Insofar as there is a periodicity to extinctions to explain (what Nemesis was posited to explain), more recent analysis has shown that it is too consistent for any plausible orbit for Nemesis, and
(2) A sensitive enough survey to detect stars (including brown dwarfs) within the radius of Earth in which Nemesis would have to exist has been conducted and failed to detect any such star.
I'm not sure I understood point #1. Do you mean that the periodicity is too consistent to support the theory of an orbiting body, because an orbiting body would have a less consistent orbit? If so, that's very interesting.
Pertaining point #2, I'm not very confident in any empirical data observed at this point in human evolution. It's not to say that scientists aren't working very hard to learn things, but moments like http://www.theguardian.com/science/2015/feb/26/found-a-black... tell me that we're going to go through many more "we're absolutely sure / wait, we were wrong" moments, especially when pertaining astronomy and ontology, both fields with many more unknowns than true facts.
The current consensus is a Manhattan-sized asteroid. [0] The science behind this is pretty strong. What's come open for question is how fast this happened. A new theory posits that the dinosaurs were wiped out in a matter of hours in the resulting heat wave [1].
Now where did this asteroid come from, and how did it get here? That's another story entirely for which I don't have a good answer.
I meant that the gravity from the hypothetical star could have caused a disturbance in one of the asteroid belts and that's why that massive asteroid hit the earth.
There is no need for a disturbance in asteroid belts for asteroids to hit the earth.
The orbits of asteroids are in general not stable. There are currently some >7000 known earth-orbit-crossers, which, if their orbits would not be modified by something else and given enough time, would all hit us eventually (except one which shares our orbital period). And that's really just scratching the surface, as we still haven't mapped but a small fraction of asteroids.
The sky up there is still really chaotic, as space is really big and ~5B years is simply not enough time to produce a stable equilibrium.
Which makes me wonder in line with that thought, whether the alien star in question from this article caused any serious asteroid strikes on earth circa 70,000 years ago.
Well sure. Isn't everything a series of events leading to something? Even my own existence is a series of events: parents born, meeting at the right moment, having sex at the right time...
This reminds me of the story "A Pail of Air" [0] where a "dark star" passes through the inner solar system, and its gravity causes the Earth to be ejected from the Sun's orbit. The story features a family who can only survive by maintaining a fire and constantly fetching pails of frozen Oxygen to heat up to breathe and pressurize their living area.
I thought of it as one of those things that's extremely unlikely to happen, but we'd be screwed if it did.
A little surprising that other start passing through the outer Oort cloud might actually happen semi-regularly, on galactic timescales. Makes the idea sound a little less unlikely, though the inner Solar System seems to have been around for ~5 billion years, and hasn't been disrupted by any star-mass galactic bodies yet.
Note that a distant star's ability to "perturb" the inner solar system is basically tidal force: it's the difference in how much the star attracts the Earth vs. the Sun, because if they are pulled by exactly the same acceleration then nothing is changed from the Earth and Sun's viewpoint.
So, the effect is proportional to 1/(distance)^3. I guess anything that zips around at ~10,000 AU would basically have zero effect on the inner solar system. And if we reduce the expected distance, the "target area" gets incredibly small.
It's travelling at around 80km/s radially according to the paper so that sounds about right. Almost all the velocity is radial, only 3km/s is observed tangential to us.
In perspective, it's only around 4-5 times faster than Voyager 1 or New Horizons.
Since it is moving away from a large body of mass, namely, the day star, it's likely that it has been decelerating over the past 70k years, meaning it would have been moving more quickly when it passed by.
I'm curious about what, if any, gravitational effects this would've had on the earth? Seems like its a relatively small star and it was so far away that I'm guessing any pull would've been negligible.
> The effect of a passing star on the Oort Cloud is a function of the star's mass, speed and proximity. The worst case scenario for stirring up comets would be a slow-moving, massive star that came close to the Sun.
> Scholz's star came relatively close, but the binary system (the red dwarf and its brown dwarf companion) has a low mass and it was speeding by. These factors conspired to make its effect on the Oort Cloud very small.
As a starting point, the sun's absolute brightness is much higher than this star's, and this star supposedly came within .8 light years of us. That's 50,591 further than Earth is from the sun, which means it would be no brighter than most of the stars you see in the sky... unfortunate, huh :(
Someone should run an n-body simulation of the solar system and this star backwards in time to see if it had any perturbative effects on us. What if this star was responsible for ripping Pluto away from a planet or sending Phobos down into the inner solar system to be captured by Mars?
The Nature News article says:
"Because Scholz’s star is puny and sped by quickly, it would have had a negligible impact on the Oort cloud, Mamajek notes. And any comets that the star might have sent hurtling towards the inner Solar System will not arrive for another few hundred thousand years, says Tremaine."
[1] http://arxiv.org/abs/1502.04655