Empty bits, basically. They’re regions where there’s significantly less stuff than average. Because there’s less stuff there, surrounding stuff gets pulled away from that region in every other direction by gravity, so it looks like the empty region is pushing stuff away from it. It’s actually just failing to pull things towards it as hard as everywhere else is, but that’s why they’re called “repellers”
It seems like the issue has been confused a lot by a couple of things. First is a theory that if antimatter and matter gravitationally repulse each other it could explain dark energy, so voids like this might be full of antimatter pushing everything else away. Consensus has, however, generally settled on gravity attracting matter and antimatter to each other just as it would matter to matter. CERN is able to produce antimatter and experiments seem to have confirmed the consensus.
Second, the scientist that led the project that identified the dipole repeller seems to be very insistent on referring to it as actually pushing things, rather than an apparent pushing that arises from pulling less than everything else. Now, to be clear, I’m no expert. I’m a qualified mechanical engineer so I have a decent grasp of physics, but I’m still a complete amateur and outsider in the world of astrophysics. I also don’t know anything about the scientist in question. I say this so that you can take it in to account when I say that it really, really looks to me like the guy is doing it deliberately to grab headlines because “big patch of space emptier than expected” isn’t easily understood to be as much of a discovery as it actually is
But basically, yellow bits on the map = big patches with less stuff in them than usual
That’s my understanding, yeah. There’s not a hard lìne of “must have below x density to be a void” but apparently around a tenth of the average density across the observable universe is typical. The largest known void is about three billion light years across and contains over 100,000 entire galaxies. I have absolutely no way to put measurement of that magnitude in to context, but “has 100,000 galaxies in it and is still considered to be notably empty” is wild to me
Empty bits, basically. They’re regions where there’s significantly less stuff than average. Because there’s less stuff there, surrounding stuff gets pulled away from that region in every other direction by gravity, so it looks like the empty region is pushing stuff away from it. It’s actually just failing to pull things towards it as hard as everywhere else is, but that’s why they’re called “repellers”
It seems like the issue has been confused a lot by a couple of things. First is a theory that if antimatter and matter gravitationally repulse each other it could explain dark energy, so voids like this might be full of antimatter pushing everything else away. Consensus has, however, generally settled on gravity attracting matter and antimatter to each other just as it would matter to matter. CERN is able to produce antimatter and experiments seem to have confirmed the consensus.
Second, the scientist that led the project that identified the dipole repeller seems to be very insistent on referring to it as actually pushing things, rather than an apparent pushing that arises from pulling less than everything else. Now, to be clear, I’m no expert. I’m a qualified mechanical engineer so I have a decent grasp of physics, but I’m still a complete amateur and outsider in the world of astrophysics. I also don’t know anything about the scientist in question. I say this so that you can take it in to account when I say that it really, really looks to me like the guy is doing it deliberately to grab headlines because “big patch of space emptier than expected” isn’t easily understood to be as much of a discovery as it actually is
But basically, yellow bits on the map = big patches with less stuff in them than usual
I’m guessing here, but- ‘less stuff than usual’ means ‘still galaxies with hundreds of billions of stars, just fewer of them.’
That’s my understanding, yeah. There’s not a hard lìne of “must have below x density to be a void” but apparently around a tenth of the average density across the observable universe is typical. The largest known void is about three billion light years across and contains over 100,000 entire galaxies. I have absolutely no way to put measurement of that magnitude in to context, but “has 100,000 galaxies in it and is still considered to be notably empty” is wild to me