sounds like the work to rule out false-positives would be huge. This is putting a lot of weight on a technique that is not fully described in the paper (i might have missed, just glanced at them for now, and i am an amateur that just like to fiddle with similar data).
The third team took a different approach [1], with results that are both more accurate, less prone to FP, and generally agree with the other findings.
> Here we report observations of two absorbers of highly ionized oxygen (O VII) in the high-signal-to-noise-ratio X-ray spectrum of a quasar at a redshift higher than 0.4. These absorbers show no variability over a two-year timescale and have no associated cold absorption, making the assumption that they originate from the quasar’s intrinsic outflow or the host galaxy’s interstellar medium implausible.
After my understanding of the stacking technique as used in other contexts in astrophysics and without going into too much details :
The problem they were facing is that the signal to noise of the images of the filaments was too low to say that they had detected anything in any individual images. However by stacking (adding) images they were able to detect it because the signal grows roughly with N (N being the number of images) and the noise grows with sqrt(N). So by stacking enough images you'll get the signal to noise necessary to say you've detected sth.
Now, my hypothesis is that "between all two bright lights, there is third, dimmer one, hidding". And then i prove it by filtering X from the two bright light halo, and prove that Y is left proving that the third light is there.
Now, how can i be sure Y is really a third dimmer light? and not just noise on the function i used to try to clean up the halo of the two bright light?
I notice that Oumuamua happened to pass within some 20 million km of earth within a decade or so of having systems in place to spot it. Wouldn't this imply there are an awful lot of them?
[t]he energy released by a cosmic collision increases as the
square of the incoming object's speed, so a comet could pack
nine times more destructive power than an asteroid of the
same mass. (https://www.space.com/26264-asteroids-comets-earth-impact-risks.html)
With a single observation we can't deduce much of anything concrete except to floor the incidence of these interstellar objects at greater than 0. I'm no astronomer, but I assume models of interstellar objects as they reflect actual risk to Earth wouldn't be very useful without more observations. Whatever the average density in galactic space, I'm betting they're not uniformly distributed. Our solar system is speeding through space that could be littered with clouds of objects.[1] Are we entering a cloud? Leaving a cloud? We can't know without more observations.
[1] There are theories that posit that the ~30- and ~225-million year cycles we see in extinction events are a function of our solar system's orbit in the galaxy, which takes about 200-250 million years. Shorter cycles could relate to the inclination of our orbit (and other stars' orbits) relative to the galactic plane.
The kinetic energy of objects is proportional to the square of the velocity (Ke = (mv^2)/2), so an object going 4 times faster than a solar system object has 16 times the energy for the same mass. This makes it possible to have extinction level events from rocks that are 1/4 the size of planet killing asteroids.
Oumuamua interstellar asteroid. 230x35x35m, ~= 280000 m^3
Density assumption: 2 x water. => mass is ~500,000 metric tonnes.
Spotted only after passing the Sun. Assume we'd spot such objects only if they came within the orbit of mercury so are well illuminated. Assume one such object every 10 years (we've not been searching very long with automated telescopes), and we spot all of them.
Mean mercury orbit radius ~ 60,000,000 km
Area of mercury's orbit: 1.1 x 10^16 km^2
Mercury's orbital area x path length in 10 years = volume swept by one visible object in 10 years.
Asteroid velocity ~100,000 km/h
Path length in 10 years = 100,000 x 10 x 24x365. Swept volume ~ 10 x 10^25 km^3
Distance to Alpha Centauri: 4.37 light years = 4.37 x 9.5 x 10^12 km = 4.15 x 10^13km
Sol's "cube of influence" ~= 7 x 10^40 km^3
Cube of influence / swept volume = rough estimate of number of asteroids in cube of influence. Number of asteroids: 7 x 10^14
Mass of asteroids: 3.5 x 10^20 tonnes. Mass of sun: 2 x 10^27 tonnes.
Conclusion: dark interstellar asteroids like Oumuamua are a tiny fraction of the visible mass of the galaxy.
Finding one in a decade's span within 20 million km would imply there are "an awful lot of them"?
It's an observation, so it sets some level of constraints on the rate. Though it's true that an estimate of that rate would have large uncertainties.
Either way, the energy required to maintain operations anywhere near Jupiter means you probably want to find your hydrogen somewhere else.
Seems like we are somewhat validating Vernor Vinge's "zones of thought" idea
I'm not really good at physics at this level so it throws me off. It makes it very difficult to really understand what they are talking about.
You would think physicists would be very precise with their language, by I guess they mostly write for people who are know what they are talking about.
edit: excuse my french ;)