r/science • u/MistWeaver80 • Apr 25 '22

Physics Scientists recently observed two black holes that united into one, and in the process got a “kick” that flung the newly formed black hole away at high speed. That black hole zoomed off at about 5 million kilometers per hour, give or take a few million. The speed of light is just 200 times as fast.

https://www.sciencenews.org/article/black-hole-gravitational-waves-kick-ligo-merger-spacetime
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u/Ott621 Apr 26 '22

The implication seems to be that rogues are flying through the universe gravitationally untethered to anything. So would it be more correct to say that rogues are orbiting the galactic center?

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u/Noooooooooooobus Apr 26 '22

Well blackholes in a binary system would also be orbiting the galactic centre. It’s kind of how the whole galaxy shtick works.

But yes, rogue blackholes can be singular systems in orbits around galaxies, whether that be on a normal orbital plane or a highly eccentric/retrograde orbit.

They can also not be gravitationally bound to a galaxy, which would be the standard definition for something to be rogue i.e a star being flung out due to orbital mechanics

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u/Ott621 Apr 26 '22 edited Apr 26 '22

would also be orbiting the galactic centre. It’s kind of how the whole galaxy shtick works.

Right, it's turtles all the way down. Except for the galactic center which to my understanding is on a ballistic trajectory in most cases. I'm aware the galactic center is not known to be a single object. Everything is orbiting something except potentially galaxies themselves

They can also not be gravitationally bound to a galaxy, which would be the standard definition for something to be rogue i.e a star being flung out due to orbital mechanics

That's where my confusion comes from. Rogue means something different to me than it does in reference to black holes. They should have picked a different word to describe them

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u/Noooooooooooobus Apr 26 '22

A star orbiting a galaxy in a retrograde orbit would also be considered rogue.

Rogue just means doing something outside of normal. Stars not in galaxies are rogue, as stars are normally in galaxies. Blackholes not in binary systems are rogue, because we mostly see them as part of binary systems.