Black Hole Orbits

Black holes are interesting things. Interesting because they make relativity start to break. Strange things happen like apparent faster-than-light motion (caused by pieces of space-time itself being pulled faster than light). At close enough distances, all things (even light) start to form spirals as they get drawn inexorably towards the black hole. Basically, if something’s heavy enough, it forces everything else nearby to move with it by, clichéed as it may sound, warping the fabric of time and space.

An effect of this is that, until recently, objects orbiting black holes appeared to be totally random. Chaos theory in motion, figuratively speaking. Well, not quite. A couple of physicists have actually managed to compile a ‘periodic table’ of different orbits, classifying them by their geometry.

An object far from a black hole orbits in a long ellipse, much like a comet or eccentric planet. The difference is that as it gets drawn in close, it’s trapped into one or more tight circular orbits before being slung back out into another distant ellipse. The effect carries on as a stable orbit ad infinitum (or at least as ad infinitum as an orbit can be). Of course, the orbit actually forming a perfect repeating pattern is an idealised scenario which probably won’t ever happen in the real world. However, for every orbit that doesn’t quite connect, there’s a theorietical repeating orbit with very similar character. The cloverleaf pattern is quoted as consisting of a “repeating flower-like pattern with over 10 million overlapping petals”.

The full paper’s available on arXiv (link), the New Scientist article makes for an interesting read (link) and Dr Janna Levin, one of the physicists involved in all of this, seems like a rather interesting lady (link)…

The ultimate aim of all of this is to better understand these orbits to help in the search for gravitational waves and other such exotic astrophysical phenomena. It interests me for a few reasons though… for one, there’s a certain similarity between a few of these and some electron orbitals.

About Invader Xan

Molecular astrophysicist, usually found writing frenziedly, staring at the sky, or drinking mojitos.
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4 Responses to Black Hole Orbits

  1. invaderxan says:

    Ooo… Shock front fluctuations!

  2. invaderxan says:

    Yay for circly spinning nonsense! Spirographs are a little different though… They’re more like an arc from a larger circle that loops back on itself in a smaller circular shape. Mmmm… Lissajouslicious!
    The difference with these is that the radius for the projected arc varies with the radius from the centre of the gravitational well, making them essentially random in real world situations. Random, but potentially pretty!

  3. dr_psycho says:

    All spirographs to me -> Periodic point attractors tracing hypotrochoid patterns (like poi- all circley spinny nonsense), never was patient enough to get the bloody things to work properly (spirographs not poi), but I guess if you sat for long enough you could create hundreds of interesting orbits

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