Astronomers find the edge of the Milky Way | Hacker News Reader

Astronomers find the edge of the Milky Way

skyandtelescope.org

159 pointsbookofjoe44 comments

Better, adblocker-friendly article (original press release): https://www.um.edu.mt/newspoint/learn/2026/theedgeofthemilky...

Paper: https://www.aanda.org/articles/aa/full_html/2026/04/aa58144-...

Thanks. Cloudflare took so long to determine whether or not I was bot-shaped that I just came to the comments.

Title: "Astronomers find the edge of the Milky Way"

First sentence in the article: "Astronomers have located the edge of the Milky Way’s star-forming disk for the first time"

Wouldn't you expect someone from a publication called "Sky & Telescope" to know that these two are different things?!

Also, in diagrams showing our galaxy, I would greatly appreciate a "you are here" marker which points out the location of our solar system...

> Also, in diagrams showing our galaxy, I would greatly appreciate a "you are here" marker which points out the location of our solar system...

What would that mean?

Try locating France on this map: https://en.wikipedia.org/wiki/File:T_and_O_map_Guntherus_Zin...

Ok, I would be happy with an approximate location too. On that map, I would place France in Europa right beside the mediterraneum, pretty much on the Occidens side (although not at the very edge).

Well, to ask you again, what do you think "an approximate location" would mean? How would the labeling be done?

It's easy enough to take the rob74 position of "I'm going to choose an arbitrary point on this artist's conception and paste a 'you are here' sticker over it", but what would be the point?

Well, we’re clearly not in the center, for one thing.

It’s right where the V (Latin U) symbol is.

Do we not know where we are in the galaxy? I would have thought that was well established.

Is this a non-sequiter or just poorly phrased?

  > Disk galaxies like the Milky Way form stars “inside-out” — starting from the center and working outwards through the disk. So, as a general rule, the farther out astronomers look, the younger the stars are.

Do they meant looking out from Earth (which is actually nearer to the center of a spiral arm than to either end) or out from the galactic bulge. Either way doesn't make sense.

It is beyond obvious what they mean.

Poorly phrased. The most recent stars are on the edges. The inner stars were first, hence the “working outwards”.

But why? Star forms when enough hydrogen (or maybe also helium) clusters together with gravity to spark fusion IIRC. The center of Milky way ain't some ultra dense place where stars are just trillions of kms from each other to support somehow earlier star formation.

Or did ie dark matter/energy somehow coalesce on the outer edge later? Milky way is supposed to be very old place, almost as old as universe itself so one would expect more homogeneous distribution, at least as a layperson.

You need certain density to start formation progress. Then you get more density as it drags more stuff via gravity from intergalactic void. So new stars form at edges when there is finally enough stuff pulled by gravity of whole galaxy to there for the formation to happen.

It seems that you need quite large concentrations(as in scale of whole universe average) to actually get to star formation. Otherwise stars would be uniform trough the universe.

Then again I am not astronomer.

> Then you get more density as it drags more stuff via gravity from intergalactic void.

The pre-stellar cloud has the same mass, and thus the same gravitational impact, as the stars that form from it.

> You need certain density to start formation progress.

Aren't fluids (such as a hydrogen gas cloud) densest at the bottom of a gravity well? It would be expected that the nearer one is to the galactic center, the denser the intergalactic medium would be.

I actually am not following what the ambiguity is - stars farther out from the center are younger, no?

The Earth isn't the center of the galaxy, so this feels confusing/confused:

> So, as a general rule, the farther out astronomers look, the younger the stars are.

The father out from the center of the galaxy they look, the younger the stars are.

The location of the Earth is completely irrelevant. "closer" and "farther" refer to the center of the galaxy.

When does "starting in the center" mean anything besides "starting in the center"?

The earth is not the center of the galaxy

He didn't say that. He said earth is nearer to the center of a spiral arm.

the location of earth has precisely zero to do with the topic

And your reply has zero to do with what I'm talking about.

What does the center of a spiral arm have to do with the center of the galaxy?

I don't know but that's not what I'm talking about.

The Earth is where the astronomers are. If they are looking outward (away from the center) then the further they look, the younger the stars.

Try: "the farther out [from the center] astronomers look"

Looking from Earth at the stars closer to the center of a galaxy, they are found to be older. Looking from Earth at the stars closer to the edge of a galaxy, they are found to be younger.

To use an analogy, to add to everybody else: it's like rings on a tree stump. The innermost part of the stump is the oldest; the outer the youngest. Earth is on one of those in-between rings, neither the oldest nor the newest - doesn't matter which of the in-betweens, to be honest.

Suppose now that you're an ant on the middle ring of that tree stump. No matter which way you're looking from Earth's middle-ring, either the rings will get gradually older and then younger with increasing distance (if you're looking towards the center-ish), or the rings will get strictly younger (if you're looking away from the center-ish).

This analogy obviously breaks down if you delve into details but that should give a better intuition to what's going on.

From Earth (where astronomers are) looking "out"ward (away from the bulge).

Earth isn't relevant. The stars at the center of the galaxy developed first, and development proceeded from the inside out, so the youngest stars are on the edge ... then they get older from there on out, as the stars beyond the edge broke away from the galaxy. The bottom of the age U is the location of the formative edge.

They don't mean that the stars migrate out (then further stars would be older), they mean that stars further away from the center start forming later (so further stars are younger).

I agree that the phrasing can be confusing.

Just the daily post that makes me feel small and insignificant.

I prefer that feeling much more than the modern sense from social media where everyone is abnormally important

Seriously. Being meaningless and insignificant gives you more freedom, and nowhere to hide from what you do with it. I’ve never understood cosmic dread. It feels like a release valve instead of a threat.

I'm still searching for the location of the Restaurant at the end of the universe.

It's not a search problem it's a grammar problem: https://pages.cs.wisc.edu/~param/quotes/guide.html

Oh thank goodness, I've been looking for that.

How are claims like these verified?

Looking up.

Incredible. "Hi honey, what did you do at work today? Casually discovered the edge of the galaxy. How are you?"

I think they have been looking for the edge for years, and the discovery had come gradually over some time. So I don't think that "casually" fits there and "today" doesn't make things better.

Great. Next Laniakea

Reply on news.ycombinator.com