3 ms·

For what it's worth, there are friction-like processes that allow black hole and neutron stars to get captured into each other's orbits and then spiral in towar

For what it's worth, there are friction-like processes that allow black hole and neutron stars to get captured into each other's orbits and then spiral in toward each other. BH and NS mergers (such as seen by LIGO) are not direct head-on chance collisions between freely propagating objects in the Galaxy.

wyager 9y ago
Are these processes gravitationally mediated, like tidal energy transfer?
- AlanSE 9y ago
  Binary systems radiate out gravitational waves. Google image search for "binary system gravitational waves" and you will pretty easily identify the canonical graphical representation. While there are lots of problems with the "sheet" analogy for general relativity, there is still value in considering gravitational radiation to be waves in the sheet. From a layman perspective, the analogy is irresistible. The mental picture of the spiraling-in process is pretty easy to grasp, but the process of gravitational capture is a little more difficult. Gravitational radiation is extremely dependent on the distance of the mutual orbit, so the inward spiral progresses rapidly at short distances, but can take a very long time at greater distances. So I imagine the research comes down to the general statistics of the formation of binary systems, how often they will involve a neutron star with a black hole, and how often they form at distances close enough to create the collision.
  - jessriedel 9y ago
    This only works when the bodies are very close together, right before they coalesce. For most of the lifetime of binary BHs and NSs, the gravitational radiation is negligible.
- jessriedel 9y ago
  Yes, mostly, but it takes the form of significant gravitational wave emission only when the bodies are very close together. (Much less than an AU, I think, although don't quote me on that.) For larger distances, it's mostly a matter of ejecting dust and other matter in the vacinity. https://en.wikipedia.org/wiki/Dynamical_friction https://en.wikipedia.org/wiki/Dynamical_friction
raattgift 9y ago
Given that how common it is to find massive stars in multiple systems, it would be surprising not to find systems of compact massive objects that are remnants of these. OTOH, who knows about intermediate mass BHs and beyond. Aggregation of these multiple systems of CMOs? Let's look! - -- sec 3.5 and table 1, Duchêne & Kraus, https://arxiv.org/abs/1303.3028 https://arxiv.org/abs/1303.3028 multiplicity counts are all over the map: Eggleton & Tokovinin 2008 Guerrero et al. 2014 Lada 2006 but pretty much nobody thinks they're extremely rare.

wyager 9y ago

Are these processes gravitationally mediated, like tidal energy transfer?

AlanSE 9y ago
Binary systems radiate out gravitational waves. Google image search for "binary system gravitational waves" and you will pretty easily identify the canonical graphical representation. While there are lots of problems with the "sheet" analogy for general relativity, there is still value in considering gravitational radiation to be waves in the sheet. From a layman perspective, the analogy is irresistible. The mental picture of the spiraling-in process is pretty easy to grasp, but the process of gravitational capture is a little more difficult. Gravitational radiation is extremely dependent on the distance of the mutual orbit, so the inward spiral progresses rapidly at short distances, but can take a very long time at greater distances. So I imagine the research comes down to the general statistics of the formation of binary systems, how often they will involve a neutron star with a black hole, and how often they form at distances close enough to create the collision.
- jessriedel 9y ago
  This only works when the bodies are very close together, right before they coalesce. For most of the lifetime of binary BHs and NSs, the gravitational radiation is negligible.
jessriedel 9y ago
Yes, mostly, but it takes the form of significant gravitational wave emission only when the bodies are very close together. (Much less than an AU, I think, although don't quote me on that.) For larger distances, it's mostly a matter of ejecting dust and other matter in the vacinity. https://en.wikipedia.org/wiki/Dynamical_friction https://en.wikipedia.org/wiki/Dynamical_friction

raattgift 9y ago

Given that how common it is to find massive stars in multiple systems, it would be surprising not to find systems of compact massive objects that are remnants of these. OTOH, who knows about intermediate mass BHs and beyond. Aggregation of these multiple systems of CMOs? Let's look! - -- sec 3.5 and table 1, Duchêne & Kraus, https://arxiv.org/abs/1303.3028 https://arxiv.org/abs/1303.3028 multiplicity counts are all over the map: Eggleton & Tokovinin 2008 Guerrero et al. 2014 Lada 2006 but pretty much nobody thinks they're extremely rare.