Thursday, 27 April 2017

W is for Wobble

Lots of things wobble. This is due to gravitational influence by something else.

Mass has gravity, and gravity is a very social thing. Two bits of mass spy each other across the room (or the universe) and try to get closer. If they get close enough, they end up in an orbit around each other, possibly in a spiral until they collapse together, though this doesn't always happen if the escape velocity is sufficient to keep them from falling into each other.  (That's what most orbits are: falling, but failing to hit the ground.)

The centre of gravity about which these object spiral about is called the barycenter.

Looks like this:
Do-si-do.  The barycenter is the red cross in the middle.
When the objects are of a similar size, the barycenter will be somewhere in between the two objects, as is the case with Pluto and Charon:

Pluto and Charon and their barycenter, the cross in the middle.
Pluto has a small orbit around the barycenter while Charon has a larger one. So they kind of wobble like an uneven barbell.  Because the barycenter is outside of Pluto, some people would like to call Pluto/Charon a double planet, rather than a planet and a satellite. I'm cool with that.

When one object is distinctly more massive than the other, the barycenter will be located within the larger object, such as the Earth and the Moon:

This gives the Earth a little bit of a wobble, instead of a full-on do-si-do.

We noticed our Sun has a bit of a wobble, due to the gravitational influence of the planets about it. In fact, the Sun's wobbled quite a bit:
Notice how sometimes the barycenter's inside the sun and sometimes its not?

Yeah, not surprising, considering what we know about gravity. Then some clever soul thought, if our Sun wobbles due to planets pulling on it, wouldn't other stars wobble for the same reason?

Whoa! Mind blown! So we started looking at nearby stars with this Wobble Method (also called Radial Velocity or Doppler Spectroscopy Methods) to see if they had a wobble.

Ohmigosh, they did! Thus, we discovered exoplanets.  And we said, "That's so cool!!!" (Then we felt slightly stupid because we hadn't figured something so simple out until now.)

Gamma Cephei Ab was the first exoplanet detected in 1989 (confirmed in 2002), and since then, we've uncovered evidence for thousands of exoplanets.

Nice to know we're not alone.

Now, there's lots of other methods for detecting exoplanets, but it all started with noticing how gravity made things wobble.

Wobbling isn't just for detecting exoplanets. Lots of other discoveries are due to the observation of wobbliness.  Go hardcore and check out wobbliness from asteroids with moons to entire galaxy clusters.  Even browsing through the list of titles is fascinating. Never be afraid to read an abstract. Save your freaking out for the paper itself.

Her Grace believes that love makes the world go round, but gravity rules the universe.


SlimExpectations said...

nice explaination:)
PS- I also wobble :P

FinnBadger said...

I didn't know that that was how exoplanets were first discovered. Loving your science posts.

Phillip | W is for White Shapes | What do you see?

sage said...

Great post... You're astronomy posts are a lot more technical than mine, although I had to get a little technical to write about W and Y.... My take-away from your post: the Cosmos is just a little tipsy!

Emily in Ecuador said...

Fascinating! Thank you for such interesting explanations and the diagrams that explain them well.

Emily | My Life In Ecuador | Water. Clean Drinking Water

Sue Bursztynski said...

I'd heard about the wobble thing, though not how extensive it is. I keep thinking of gravity between Earth and Moon as two people, hands held, maybe a parent and child, spinning around and laughing and yes, you'd probably wobble while you were about it!

cheryl lennox said...

As I read this my brain kept chanting, "Weebles wobble but they don't fall down". Silly toy!