Curiously hollow-centred galaxy

https://www.legacysurvey.org//viewer/?ra=343.0926&dec=-0.9511&layer=hsc-dr2&zoom=15

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collisional ring?

it certainly looks disturbed, but I cannot see what would have caused it.

Its definitely had some sort of interaction, but there’s no obvious bullet component for a collisional ring.

Perhaps we have found evidence of a roaming black hole having punched right through it?!

There’s nothing visible anywhere near it that could have caused this disturbance.

It’s certainly an enigma - I’ve never seen anything like it before.

Best guess would be a dwarf galaxy colliding with it and breaking up in the process.

It’s also possible that it’s a normal collisional ring and that this is our culprit, as it looks to have a very similar photometric redshift and be at the correct angle to have caused the ring:

image

Could be. I didn’t look that far away!

yeah, that could be the bullet, they seem pretty close to us, so the angular separation is high, and that could be the reason they don’t appear to be interacting from our POV here on Earth.

there’s also an asteroid near it:
image

If they are both the components of the interaction, it would have been a while since they interacted, which is why they would appear so far apart. Assuming the photometric redshift is somewhat accurate, they are over a billion light years away, so angular separation wouldnt be affected much by POV.

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If these are the two galaxies that were involved in the disturbance, it must be an extremely rare event for a small galaxy to pass right through the middle of a larger one and continue on its way seemingly unscathed, while the larger galaxy is so clearly disturbed. There also doesn’t appear to be any debris trail between the two, which is a notable characteristic of all the other interactions I’ve seen, so it remains puzzling to me.

I think this one is really worth some further study, if anyone can suggest it to someone working on galactic collisions? I’ve given AstroRobin a nod…

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My understanding is that the density waves that are caused by these kinds of collisions are quite strong and could be strong enough to cause the victim galaxy to hold on to material that would otherwise have been dragged in the wake of the other galaxy. I haven’t looked in to the physics of collisional rings deeply enough to be sure though, so Robin taking a look isn’t a bad idea.

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I also found a possible collisional ring;
image
and I also don’t see the ‘bullet’ galaxy.

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I think they’re unlikely to be collisional rings, but for sure they are low-mass dwarf galaxies and they’ve probably had a close fly-by interaction with another galaxy.

Another, possibly more extrapolating scenario, is that given this galaxy is undergoing a recent burst of star formation, the subsequent supernovae explosions may have carved out this hole. Pretty extreme and you would maybe hope to see some radio emission to back this up, but alas not.

Great find!

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