A Spiral Structure in the Inner Oort Cloud
35 comments
·June 4, 2025doctoboggan
tristramb
You might also appreciate W. W. Morgan's account of his discovery of the Perseus Spiral Arm of our Galaxy in his observational data on OB stars:
"This was in the fall of 1951, and I was walking between the observatory and home, which is only 100 yards away. I was looking up in the sky ... just looking up in the region of the Double Cluster [in Perseus], and I realized I had been getting distance moduli corrected the best way I could with the colors that were available, for numbers of stars in the general region ... Anyway, I was walking. I was looking up at the sky, and it suddenly occurred to me that the double cluster in Perseus, and then a number of stars in Cassiopeia, these are not the bright stars but the distant stars, and even Cepheus, that along there I was getting distance moduli, of between 11 and 12, corrected distance moduli. Well, 11.5 is two kiloparsecs ... and so, I couldn’t wait to get over here and really plot them up. It looked like they were at the same distance ... It looked like a concentration ... And so, as soon as I began plotting this out, the first thing that showed up was that there was a concentration, a long narrow concentration of young stars ... There are HII regions along there too ... And that was the thing that broke [the problem] down."
Full article here: https://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_que...
YesThatTom2
The ads for Hayden Planetarium show mostly highlight that it’s narrated by Pedro Pascal.
But, yeah, the spiral thing is cool too.
AStonesThrow
The past few planetarium shows in my neck-of-the-woods have featured narration by the likes of David Tennant and Diego Luna.
As I understand it, these shows are sort of syndicated and shared among many locations. Some of them were several years old.
coke12
Our own solar system has what appear to be spiral arms. Very cool finding.
dotancohen
Yes, this is interesting, finding complex structures that are found at multiple scales is rather amazing.
The paper attributes the solar system's spiral structure to the galactic tide. If I'm not mistaken, and this might be outdated, the galactic spiral structure is attributed to massive clumping - massive particles attract.
("Massive" meaning particles with mass - not necessarily large. "Particles" meaning macroscopic particles, not subatomic.)
antognini
The basic theory of spirals is basically that you get spiral structure when the orientation of elliptical orbits shifts with semi-major axis. This leads to what appear to be spiral arms that have higher densities. In these high density regions you get collisions of gas clouds which leads to star formation. The star forming regions produce lots of bright, blue stars, which then make the spiral arms very visible in optical wavelengths.
In this case of the Oort cloud the galactic tides would be what are responsible for inducing the change in orientation of the elliptical orbits as a function of semi-major axis.
throwawaymaths
IIRC the galactic spiral is believed explicitly to be not due to gravitational attraction so much as shock wave/traffic jam dynamics (transmitted through gravitational force ofc) -- not sure if that's what you meant by clumping.
dachris
It's amazing, yes, and at the same time, it makes perfect sense.
(Somewhat) similar mechanisms are at work whether you're pulling together stars into a galaxy, hydrogen gas into a solar system or water towards the drain of your bath tub - a pull towards the center, the centripetal force, slight variations producing "artifacts".
dotancohen
Well, I would not call these two mechanisms similar, though the artifacts may be similar. I wonder if in fact the spirals are similar, for that matter if mathematicians even have terminology for different types of spirals.
The spirals shown in the paper do look like idealised spirals of very young galaxies, shortly after the bar phase. I wonder, other than spirals, what other artifacts such processes might cause.
Imagine an accretian disk undergoing fusion in spiral-shaped filaments!
AStonesThrow
It will be really exciting if we confirm one, then.
The spiral structure here is a hypothesis within a hypothesis. Whatever objects comprise the Oort Cloud, they haven't been directly observed. Scientists have inferred its existence from a variety of comets that seem related and have very, very long orbital periods, such as 200 years, or 2,000 years. So these comets are observed once-in-a-lifetime, or once-in-a-civilization, and the hypotheses say that they're being dislodged somehow from a "cloud of planetesimals" where a bunch more of them are found.
But this supposed cloud would be extremely sparse: plenty of space in-between the very small icy bodies, and individually, they're so much smaller, and so distant from the Sun, that they don't reflect enough light to our telescopes. They really don't send signals in other wavelengths, either, like a pulsar or quasar or something with an active powerplant.
This is beyond the Kuiper Belt, even; the Kuiper Belt, if it indeed be a belt, has offered us a couple of directly-observed objects, including Pluto and Charon.
So it's nice to conjecture and invent proposals for some kind of structure there, but the very existence and extent of the Oort Cloud is something that's been extrapolated and inferred from secondary evidence.
metalman
confirmation is unlikely, as imaging and detection out there is not a thing from the intro, "Here we discuss dynamics underlying the Oort spiral and (feeble) prospects for its observational detection." we need a whole new class of space based telescopes for this, and other things like direct observation of surface conditions on.exo planets
jajko
Do we know why ie Saturn rings are not spiral-like? Ie due to their age (some relatively recently broken down comets) or some other forces that keep them spread evenly? Or just gravity is too weak amongst them for those smaller pieces of rock
antognini
Moons close to the rings tend to keep the particles of the ring confined within a narrow band (which is why they are called "shepherd moons").
seanhunter
Just trying to understand what you're getting at here. About what axis would you expect them to spiral? From normal mechanics + gravity I would expect them to orbit more or less elliptically about the polar axis of Saturn rather than spiral, but I don't know much about astrophysics.
twic
They could really do with a 3D model of this, it's rather hard to visualise from the views from two different directions.
dedicate
I always pictured it as, like, a super scattered snowball fight way out in the boonies. How does something so delicate even hold that shape out there?
This completely change how we should think about the 'edge' of our solar system!
Eduard
could someone explain the significance of this finding? Is it remarkable for being a definable structure in a previously thought random distribution of bodies that make up the Oort cloud?
machenesonk
could universe have a spin?
girvo
Meta: I can't even get into the site, the hCaptcha shows an image (a table and chairs) that never shows up even after 20+ "Skip" clicks...
graemep
> I can't even get into the site, the hCaptcha shows an image (a table and chairs) that never shows up even after 20+ "Skip" clicks...
But someone's metrics are showing 20+ bot request blocked!
gs17
It's a really poor design. "Fits the theme", not "is this object". I had a lighthouse and it wanted me to click sharks, because they're both "water" themed.
I asked Gemini to solve this "puzzle" and it could do it. Whatever weird filter they're trying to apply to the images doesn't work well enough.
samyok
you have to click on the fruit cups, as it asks what fits the "theme" of the image.
here's the pdf, though: https://iopscience.iop.org/article/10.3847/1538-4357/adbf9b/...
w10-1
Also no access, even after passing human validation - screen dark.
dcassett
I've been using the links browser for HN and fall back to a full-fledged browser if I get blocked. Links (and Lynx) give me no problems with TFA.
recursive
I got the same thing. The correct answer for me was the fancy desserts, because they go on a fancy restaurant table I guess.
misja111
The bot doesn't believe you're human
curtisszmania
[dead]
> The spiral structure was first identified by examining the simulation in the Hayden Planetarium in preparation for a new space show that describes and visualizes the Oort cloud.
That's a pretty cool way to discover something like this. Here is the simulation animation:
https://drive.google.com/file/d/1TuacHdAeZ5J8wNAJvlYv435x9Oj...