I have no doubt something so blindly obvious has already been considered and accounted for by astronomers but in all of my reading on this stuff I’ve never seen it mentioned and am curious about the answer.
To the best scientists can figure today the Universe seems to be lacking some 80% (?give or take?) of the matter necessary to account for what is observed. Hence the notion of ‘dark matter’ that accounts for the rest of the mass of the Universe but is so far invisible to us.
As I understand it our sun is likely a third or fourth generation star. That is, the stuff in our sun (and you and me as well) has been inside three or four other suns in the past.
Considering in the early Universe everything was closer together I would assume (understanding the dangers of ass/u/me…mostly me) that there were a helluva lot of stars around. Probably big ones to…lots and lots of hydrogen nearby to grab onto. Big stars have markedly lower lifespans than smaller stars. They have more fuel but their greater size causes them to eat it all up at a much faster rate. Get big enough and their lifespans can be measured in a few millions of years rather than the billions of a star like our sun.
So…where are all of these stellar remnants? Whether they went supernova or not should not matter…even supernova stars leave behind a core. If that core collapses into a black hole no big deal…the gravitational effect will still be there. By now I doubt any of these early stars would be visible to us as they cooled over the last several billion years. Would they now be dark hunks of matter floating about?
Do astronomers have an estimate for the number of stars that have lived and died already and take that into account when estimating the mass of the Universe? If so how much faith do they have in that number as it perforce has to be a guess (just how educated of a guess is it)?
I am certainly no expert on the subject of astrophysics and the like, but I’ve done some reading on the subject before. As stated in the subject, dark matter does not necessarily mean remnants of supernova explosions. And as stated in your article, dark matter is a kind of matter that is invisible to us. If you are interested in this subject, then you probably know of the possibility of neutrinos (actually i think they have been proven to exist already). Neutrinos have been great notion of a cure to this ‘missing matter’ problem. I have read that neutrinos are nearly impossible to detect, because they pass directly through other matter without affecting it. Neutrinos could be passing through your skin right now and you wouldn’t know it. It is becuase they are so incredibly small.
As for the supernovae byproducts, they are always detectable. Supernovae explosions give birth to other new stars, dwarf stars (which come in a variety of types, these being the chunks of matter you talk about after a supernova explosion), and black holes. I don’t believe supernovae give birth to any kind of matter that is not observable.
The thing is stellar remnants wouldn’t be visible.
We only observe objects here on earth because an object emitted energy or reflected energy from another source towards us.
In the case of a remnant star we would have no way to detect it.
Consider our own star. After some moderate violence for a star (swelling, expelling material in explosions and so on) it will settle down as a white dwarf where it will cool over the next billion years or so.
Even a White Dwarf star in its early stages is difficult for astronomers to pick out of the sky. They are very hot and emit x-rays like mad but they are also quite small (our sun will end up about a millionth the size it is now but will still retain a much more significant portion of its mass than the size suggests). Eventually it will cool to be a lump of material floating in space and would be practically impossible to detect except by its gravitational influence.
You now have this great lump of stuff merrily orbiting the galaxy with practically nothing to give itself away. Eventually over an incredibly long period of time it will ‘evaporate’ but if our universe is only 10-15 billion years old there hasn’t been enough time for that to really be a significant issue. I would assume most of these remnants should still be around and was wondering if their gravitational influence was actually accounted for in models speculating on how much ‘stuff’ there should be in the Universe.
Heck, Brown Dwarfs are speculated to be as numerous as stars and we have only seen a few of those (a Brown Dwarf is about the size of Jupiter but much more dense such that it glows a bit…not quite a planet and not quite a star…sort of a star wannabe that never made it).
Basically, yes. In fact, this is the sort of issue you can come at from several different directions.
For a start, you can put limits on the total baryon density. One of the great triumphs of modern cosmology was explaining the observed amounts of the lighter elements in the universe: we see so much matter in the form of hydrogen atoms, so much as helium etc. These were all produced via nuclear reactions from protons and neutrons during the Big Bang and these processes have been modelled in detail. One of the things the results you get depends on is the density of protons and neutrons you start with. By comparing the models with the observed abundances of the light elements, you can put limits on this density. I don’t have up-to-date numbers, but typically it usually comes out as between 1 and 20% of the critical density.
Now you can have all sorts of stuff happen to the neutrons and protons, but they pretty much have to stay neutrons and protons. And it these that you’re supposing are making up once-upon-a-time stars and hence the unobserved stellar remnents. So even if there are unobservable black holes or whatever out there, they’re still included in this stuff and so can’t account for more than perhaps 20% of the critical density.
(To simplify the discussion, I’m assuming that we need dark matter to get to the critical density. If that’s not a requirement, the amount of dark matter required, for example, to explain galaxy rotation curves is somewhat less.)
There are also arguments relating to heavy elements, the ones produced in the early generations of stars and their supernovae. If you have too many of these stars, you produce too many heavy elements. So looking at the adundancies of the different elements can also put limits on how many such stars there were and hence how many remnents there might be.
Then you can look for them directly via gravitational lensing. As a far away dark, heavy object passes in front of a even more distant star, it can briefly and roughly focus some of the star’s light towards us. We’d observe the star brightening for a few days. People have looked for such flare-ups and the observations place limits on what sorts of unobserved dark, heavy objects there can be. I don’t know how useful these are for limiting, say, black holes formed from massive stars in the early universe, but they place good limits on objects in the sub-solar-mass range like brown dwarves. In particular, only a few percent of the mass of the galactic halo (the stuff round our galaxy) can be made up of such objects.
Given recent progress, I’d expect most of these limits are being reviewed and refined right now.
Also most of the white dwarfs that have been created by the death of large bright stars have not have had time to cool down yet.
Smaller stars that have not turned into dwarfs yet are still shining…
I think there are a great many practically invisible brown dwarfs ansd rogue isolated planets out there but they are all low mass so don’t add up to much.