I think the article headline is somewhat misstating the conclusion of the actual paper (linked to by alex_young). The actual paper says the stellar mass density will reach a maximum only 5% higher than its current value. But the stellar mass density is affected by two processes: star formation and star destruction. As the paper notes, the process of star destruction "recycles" some fraction of the mass of the destroyed star, making it available for new star formation. So the stellar mass density reaching a maximum does not mean that all star formation stops, which is what the article headline implies.
> the stellar mass density is affected by two processes: star formation and star destruction
Hang on, it sounds like you're talking about the total stellar mass, not density. I'm not an astronomer, but assuming they use the normal definition of "density" there are two things that affect it: total stellar mass (which, as you said, can be further broken down into formation and destruction) and the volume it's contained within.
Isn't the universe expanding? (Again, I'm not an astronomer.) If the density is going to remain similar to now then that means that the total stellar mass is going to continue increasing too. That's consistent with what your comment literally says but is quite different from how I think most people would interpret it.
On the other hand, this one is incorrect, so it's a bad trade-off no matter how you put it.
Besides, the meaning of "stellar mass density" ought to be obvious to anyone who's gone through high-school level science classes, even if they're not "into" astronomy. Even if that weren't the case, it's pretty easy to look up a simple explanation of the term. I doubt someone who isn't willing to put even that tiny amount of effort into it would even bother reading popular science articles in the first place.
To put it another way: it takes less time and effort to figure it out if you don't know what it means that it takes to even read the article. The overlap between "people reading the article" and "people who don't know what SMD is, can't figure it out from the name, and aren't willing to look it up" is unlikely to be too high.
Optimizing for lazy readers isn't good scientific journalism, it just makes the experience worse for interested readers -- the ones who are willing to do things like pay for a subscription, for example. It's a bad trade-off to make.
If you assume that interestingness of headlines is somewhat randomly distributed, and that for each article there are more misleading headlines than accurate headlines, your relation is bound to be true, even if being misleading by itself doesn't help.
You can email the mods (well, currently just dang) with concerns and/or alternate suggestions (splices from subheads/content are strongly preferred). He's appreciative and responsive. hn <at> ycombinator <dot> com
I think there are two ways to understand that. One is that the total number of stars probably won't ever be much higher (which is iffy, given that I'm not clear if average stellar mass is going to stay the same) and one is that there is very little formation of new stars, so the ones we have right now are all that they're going to be.
I think they were going for the former interpretation and I'm not clear that this interpretation is actually supported by the paper.
> One is that the total number of stars probably won't ever be much higher
I don't see how the article title supports that interpretation. "Has made almost all the stars it will ever make" doesn't seem to me to be consistent with "more stars will continue to be made but the total number of stars won't get any higher".
This appears to be the paper actually stating the headline [0].
Interestingly the statement is a bit different:
"The star formation activity over the last ∼11 Gyr is responsible for producing ∼95 per cent of the total stellar mass density observed locally, with half of that being assembled in 2 Gyr between z = 1.2 and 2.2, and the other half in 8 Gyr (since z < 1.2). If the star formation rate density continues to decline with time in the same way as seen in the past ∼11 Gyr, then the stellar mass density of the Universe will reach a maximum which is only 5 per cent higher than the present-day value."
To me, this says a lot more about the expansion of the universe, in that we have an ever smaller window into the observable universe, than anything about black holes.
Is that a reasonable interpretation or am I missing something?
> To me, this says a lot more about the expansion of the universe, in that we have an ever smaller window into the observable universe
I don't think that's what the actual paper is saying. The "stellar mass density" it talks about is by definition homogeneous across the entire universe; it's not something that is affected by how much of the entire universe we can actually see.
We can only make direct observations of stellar mass density locally. We have no direct way of knowing what the stellar mass density is "now" a billion light years away; all we can see is what it was a billion years ago. We have to reconstruct what things are like "now" elsewhere based on past data, which is all we can see.
> isn’t it at least more likely than not that there is relatively normal distribution?
No, because that would make our particular spatial location in the universe special, and that is an additional hypothesis that would require some kind of evidence in its favor, and we have none. The simplest hypothesis is that the universe is pretty much the same everywhere, and that means the average stellar density "now" should be pretty much the same everywhere.
"Research over the past 30 or so years has revealed that the formation of stars across the universe reached an extended peak of activity roughly 10 to 11 billion years ago."
"... it appears that the great majority of stars that the universe will ever make—perhaps 95 percent of them—have already been made."
Not sure it matters on human timescales, but still feels like we're late to the party.
We look up at the night sky and see tons of bright upper main-sequence stars like our Sun, destined to live for billions of years. But this is a fleeting early period, the first 0.1% of the stelliferous era. Red dwarf stars are both more numerous and long-lived, like 10 trillion years! And red dwarfs seem habitable? [1]
So it's very surprising that we find ourselves orbiting an upper main-sequence star in a universe less than 15 billion years old. By chance the universe ought to be older and our star more common.
It would be interesting to check if M class stars actually can support habitable planets. Could significantly increase the lifespan of planets like earth.
The article hints at problems in the process of early planetary creation. Although there was this Chinese sci-fi movie that I actually liked about putting giant boosters on the planet... don't remember the name, but I believe it was on Netflix.
Aren't class G stars quite common? Not as common as class M perhaps, but I always though about the sun as being quite "normal".
No one really knows how probable abiogenesis is. The fact that we are complex, sentient life forms within 13.8 billion years of the beginning of the universe seems improbable, especially considering that life on earth spent 2.5 billion years of its 4 billion year history as single-cell organisms. However the complexity of life appears to be accelerating. The earth is only 4.5 billion years old, so it only took 500 million years for life to form on earth, even less when you consider that the cooling of the crust was necessary.
At universe-scale, does it makes sense to talk about a general "now"? I thought that, when large enough distances are involved, "now" becomes a local concept.
The data points to this but "Einsteins greatest blunder" and earth-centric universe come to mind.
Simply (and I'm sure many have thought of alternatives), it is based on what we see. If, as is commonly thought, the universe will expand till we are alone, then there is no guarantee that this hasn't happened already which means we may have no idea what lies outside the cosmological horizon.
In a certain sense, everything has existed since the moment of the big bang, since all the information necessary to define the universe's evolutionary trajectory needs to have existed since the very inception of the universe. In other words, our universe, and you and I, have incredibly small Kolmogorov complexity.
> everything has existed since the moment of the big bang
That's a very non-quantum view of things. For example, Hawking radiation [1] relies on brand new matter-antimatter pairs of particles popping into existence.
So the rate of star creation over time is b ^ x , where 0 < b <= 0.5 (i.e. exponential decrease) ? Or perhaps e ^ (-bx) , where x >= 1 (i.e. exponential decay) ? Sounds logical enough, considering that there was a lot more raw material for star creation immediately after the big bang, than there has been ever since then.
I've always wondered if it's possible for there to be a steady-state universe, where it expands continuously like it does now, but new matter is added at a matching rate, keeping the density constant.
I suppose metallicity measurements of the oldest stars would exclude any such scenario, but it's fun to think about anyway.
I'm not an astrophysicist, not even close (and I haven't read the article) but making a statement like this seems bold. Who can predict how the universe will evolve in the next 1000's of billions of years, there are just too many unknowns, no?
We don't know with certainty how the universe will change in the future, however we do have a decent understanding of how the universe works at a large scale. We can use that understanding to make hypothesis that are backed by both data and theory. This is one such hypothesis.
This is part of the scientific method. In astrophysics data is collected and new experiments are done to improve theory, and it helps us better understand the history of the universe and the future of the universe. Our understanding will change over time.
Yes and no. Mostly likely, no. We understand a lot of the big picture stuff pretty well, and the parts we don't have a full grasp on, like dark matter, don't really impact star formation, or like dark energy, have an impact that will make matter less concentrated, and thus stars less likely to form.
We're pretty confident in general that we know what the ultimate fate of the universe will be - entropy will increase. Stars will go out, ultimately fading into iron or collapsing into black holes, expansion will eventually push all the galaxies away from each other (though some galaxies are close enough they will remain gravitationally bound together until they eventually merge or potentially eject each other), black holes will slowly evaporate, and eventually the universe will be cooled down to absolute 0.
There are some gotchas here. We can't account for things like being in a false vacuum, the possibility that worm holes might be able to bridge into other universes (and the variety of potential outcomes there), quantum tunneling or other quantum effects potentially being able to cause a big bang type event, or some other exotic theory that the math says might potentially be possible but lacks much in the way of evidence. Maybe we'll master physics and be able to keep bringing new matter into our universe and prevent the heat death. If we can do that it'd probably be easier for everyone to just keep universe hopping, but maybe we'll be sentimental.
But a lot of that stuff is more likely to be science fiction than science fact. Our cosmological models today do a pretty good job of things at the large scale, and most of the most shocking discoveries don't do anything to fundamentally alter what we think the ultimate fate of the universe is. We've got to figure out a way to reconcile some models together, which will be no small feat, and maybe that will mean some universe shattering conclusions as to where things will all end up, but we don't have much reason to think that.
Of course, the universe and how it all works is a pretty big topic. Humans are pretty limited. So there's always the caveat that we might just be really really wrong about things. But I don't know if working from that assumption is particularly useful.
I always wondered, if quantumness looks like observing something is what solidifies it into being, then “almost all the stars” is really just reaching a critical mass of observation? Somewhere beyond what we can see could be a shit ton more stars in the making.
Well, I think you're kind of conflating two things here.
It's not necessarily wrong to say that observing something solidifies it into being, because it's not really a scientific term. There's too much philosophical about the term 'being'
But the overall star formation of the universe isn't likely to be too tied to having to observe or measure things at the quantum level. There's some caveats there, and it's theoretically possible that a huge amount of mass could just appear due to quantum tunneling, but isn't likely to occur in any place or time relevant to us, or even our observable universe before heat death.
As for the second bit, the observable universe is the key, and we're back to the philosophical. It's unlikely we'll be able to ever travel at the speed of light, or faster than light. Even assuming we can get pretty close to the speed of light, similar to what we see in relativistic jets, and could do so today, and didn't care about making it back, we could really only reach about 3% of the stuff we can see now before the expansion of the universe takes it forever out of our grasp. And the universe is expanding everywhere, so even if there was other stuff that is, without expansion, moving "towards" us outside of our view, it won't be able to overcome expansion.
So we'll never see it. Maybe somewhere out there in the cosmos is an area where there's a ton of star formation left to go. But unless we can somehow travel faster than light, it has zero ability to impact us. We won't ever be able to observe it or confirm it. At that point, does it even actually exist, as far as we are concerned? Does it make sense to even really think about it or consider the possibility?
If mass of universe remains the same, so should any form of energy within it (since they are interchangeable according to my layman's high school knowledge of Einstein's stuff). Or you meant something else?
