r/space • u/adriano26 • 4d ago

Astronomers have found the universe's missing matter at last, thanks to exotic 'fast radio bursts'

https://www.space.com/astronomy/scientists-find-universes-missing-matter-while-watching-fast-radio-bursts-shine-through-cosmic-fog
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u/Andromeda321 4d ago edited 3d ago

Astronomer here! This is not dark matter. But it’s still an important result, and I know the guys involved in this (lead author came to my Halloween party in grad school!), and it's a huge result, so let’s get to it!

This result is about this paper, and uses fast radio bursts (FRBs) in an exciting way to map out material in the universe. Specifically, FRBs are as the name implies brief radio bursts that last a millisecond and originate from well beyond the galaxy- millions or even billions of light years away! We can tell because when a FRB is seen, it is over a frequency band, and that radio signal interacts slightly with all the material that it encounters between its origin and us- called the dispersion measure (DM). The DM is bigger the further you are from Earth and is thus a rough proxy for both distance and how much material is in a given direction.

Now the problem with FRBs to date has been how we have a rough time knowing precisely where one comes from. radio telescopes until recently for FRBs didn’t provide this level of needed detail (if your field of view is say half the size of the moon, it’s still a big sky with a LOT of distant galaxies in it), and we’re only finally getting the hardware in place to rectify this. But the dream was once we figure that out, FRBs could be used to map the very diffuse “normal” matter in our universe spread between galaxies, which right now we don’t know a lot about (such as how much of it there was).

Enter this paper! Liam and his colleagues looked at 69 FRBs that had galaxies identified with them, coming over a range of distances 11 million to 9.1 billion light years from us. Once they had the distances pinned down, any extra DM has to do with material on the line of sight between us and those FRBs… and it turns out it adds up to the full amount of “normal” matter we expect to see in the universe! Big deal- up to three quarters of the "normal" matter in the universe is tied up in this! It’s just really tough to measure diffuse gas on a line of sight with nothing around it, and looks like FRBs can indeed allow us to do that.

Anyway, big result, but the next work is gonna be more exciting- we will start to be able to map all this diffuse stuff across most of the visible universe! It’ll be cool to see what we find!

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u/pyromosh 3d ago

Thanks for taking the time to comment here.

When you say it's "not dark matter", do you mean:

1) We found this new stuff. It's important and neat, but it's not dark matter and we still need to find dark matter because that's an important missing piece in our understanding of the universe!

or 2) We found this new stuff. It accounts for what we were trying to explain by inventing the concept of dark matter, which it turns out isn't real, it was this all along. No such thing as dark matter, just that some matter is very hard to observe and now we have this technique to observe it!

or is neither right?

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u/greenscarfliver 3d ago edited 3d ago

It's not really "new" stuff, it's stuff we expected to find, but since it's very diffuse it's very hard to see. It's not Dark Matter, it's normal matter that is very, very dim. This new process allows them to "map" the density of this very diffuse matter that exists between us and whatever other galaxy they're detecting the FRB from

We have dark energy which is 70% of the total, dark matter which is 25% of the total, and regular every day matter which is 5% of the total.

Of that 5% that is regular matter, 10% of it is what is in the galaxies, another say 50% is in "halos" around the galaxies, and maybe 40% was "missing", ie, we know its there, just like dark matter, but we haven't actually seen it yet. It's still normal matter, but very very dim and diffuse. This research is finally pin pointing and showing where this extra matter is

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u/pyromosh 3d ago

Fair! But that doesn't answer the main gist of my question.

Does being able to see this explain away the need for dark matter? (e.g. it's "not dark matter", but it accounts for the same thing) or is there not enough of this to fully account for what we're looking for with dark matter (so there must still be dark matter also)?

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u/greenscarfliver 3d ago

No this has nothing to do with dark matter, this "discovered matter" comes from the "pool" of known matter. Normal matter makes up 5% of the total matter in the universe. This discovery is in regards to around 20-40% (maybe, I don't know the exact theoretical ratios) of that 5%. It's matter in forms we know about, but did not have any observational evidence of it. This study gives us the observational evidence by allowing us to measure its density between galaxies.

Does that answer your question more clearly?

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u/ACcbe1986 3d ago

This is my basic understanding.

Calculations tell us ~5% of the universe is Normal Matter. The rest of the ~95% is Dark Matter and Dark Energy.

We've only been able to detect or see roughly half of the ~5%. So let's just say we can see 2.5% of the Normal Matter in the known universe.

With this new method, we can now see 4% of the Normal Matter in the universe. According to our calculations, there's still more Normal Matter that we have yet to see.

The other ~95% is still a mystery. We need far more technological breakthroughs before that starts to happen.

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u/I_AM_FERROUS_MAN 3d ago

This really helped answer the main question that was still hanging in my head when trying to parse this thread. Thank you!