Astronomy/cosmology questions...

[Lorizael]

I was hoping for something other than another black hole-black hole merger this time, but apparently detecting this many in so short a period of time has some scratching their heads. That is, stars and other dots in space rarely ever collide, because space is so big compared to the size of gravitationally collapsed objects, unless those objects basically started out next to each other anyway. And if these black holes started out next to each other, why did it take until they had both lived their entire lives as stars and then collapsed into black holes before they merged?

[Geo]

I was hoping for something other than another black hole-black hole merger this time, but apparently detecting this many in so short a period of time has some scratching their heads. That is, stars and other dots in space rarely ever collide, because space is so big compared to the size of gravitationally collapsed objects, unless those objects basically started out next to each other anyway. And if these black holes started out next to each other, why did it take until they had both lived their entire lives as stars and then collapsed into black holes before they merged?

Maybe the collapse also released huge amounts of stellar gas, creating a denser environment in which at least one of the stars 'brakes' into an ever closer orbit?
In any case, the gravitational equilibrum changes when a massive object occupying a certain space 'suddenly' becomes a pinpoint. The tides become different.

[Rusty Edge]

I read it and think that there's some kind of kernel for a Larry Niven story. Weaponized gravity wave communication transmitters in a Pak Protector war or something.

[Geo]

I read it and think that there's some kind of kernel for a Larry Niven story. Weaponized gravity wave communication transmitters in a Pak Protector war or something.

The closest I can remember to that is a human-descended Pak Protector and his sidekick sling around a neutron star to change course and during the manoeuver the human Pak fires some bullets which somehow would intersect with the trajectory the nearest of their native Pak pursuers follows.

[Lorizael]

Okay, so I clearly bungled this whole plan. Sorry for not actually giving you guys lengthy responses to your questions. BU, I'm working on a post about gas and dust. In the mean time, here's something about Newton and gravity.

http://anomalous-readings.blogspot.com/2017/07/from-earth-to-moon.html

[ColdWizard]

I dislike horseshoe orbits.

[Lorizael]

What'd they ever do to you?

[ColdWizard]

Made me frantically search for gifs while my feeble brain melted trying to understand. Brain goo is very difficult to get out of carpet, fyi.

[Lorizael]

The thing to remember about horseshoe orbits is that the horseshoe shape only looks that way relative to the Earth, which is also moving around the sun. If you look at an object in a horseshoe orbit relative to the sun, it will look just like any old asteroid with a slightly elliptical orbit. Relative to the earth, though, it speeds up and slows down and ends up looking weird.

Calling it a horseshoe orbit is something of a misnomer. It would be like if we said that planets have a loop-the-loop orbit because, from the earth's perspective, they sometimes loop backwards. No, planets are just orbiting in ellipses, and because they orbit at different speeds, more distant planets will appear to move backward when closer, faster planets pass them up.

(The difference, though, is that a horsehoe orbit object does weird stuff because it is close to the earth and being affected by its gravity. But the end result is still basically just an ellipse from the perspective of the sun.)

[ColdWizard]

Unfortunately, everything I first saw/read was all from the earth perspective and was very unhelpful to me. A proper non-geocentric gif helped a lot.

[Geo]

Be glad you didn't start with lissajous curves/orbits then.

[Rusty Edge]

I thought this was interesting. It makes sense now that I think about it. Still, it kind of amazed me that one would neither freeze, nor boil, nor explode, at least in the short term.

http://www.webcitation.org/68Aef3glC?url=http%3A%2F%2Fimagine.gsfc.nasa.gov%2Fdocs%2Fask_astro%2Fanswers%2F970603.html

[gwillybj]

Be glad you didn't start with lissajous curves/orbits then.

You had to make me look, didn't you?
https://en.wikipedia.org/wiki/Lissajous_orbit

[ColdWizard]

That one didn't bother me. Maybe there's nothing left to melt.

[Geo]

Be glad you didn't start with lissajous curves/orbits then.

You had to make me look, didn't you?
https://en.wikipedia.org/wiki/Lissajous_orbit

Not particularly you.