Hello,

We noticed you're browsing in private or incognito mode.

To continue reading this article, please exit incognito mode or log in.

Not an Insider? Subscribe now for unlimited access to online articles.

Emerging Technology from the arXiv

A View from Emerging Technology from the arXiv

Flukeprints and Hydraulic White Holes

The patterns whales leave on the surface of the ocean are the time-reversed equivalent of hydraulic black holes, says the researcher who has measured them with laser imaging for the first time

  • June 20, 2012

Flukeprints are the giant circular patterns that whales leave on the surface of the ocean as they disappear beneath the waves. Researchers have long known that they are caused by turbulence from the whale’s tail or fluke.

But exactly how  this turbulence creates these beautiful patterns has never been properly understood.

Now Germain Rousseaux at the Universite de Nice-Sophia Antipolis in France says he’s solved the mystery using the results from a unique set of experiments in which he uses an artificial fluke in a tank of water to recreate the patterns. 

He then videoed the way these patterns form and disperse using a laser imaging technique called particle imaging velicometry. This shines a laser beam off tiny particles in the water to see how they move. The result is a 3D video image of the resultant flow.

Flukeprints tend to be circular or ovoid and contain a central region that is smooth compared the surrounding water. It’s almost as if something is flattening the water in this region, preventing the nearby surface waves from penetrating.

The explanation turns out to be remarkably simple and fascinating. The key is to think about the pattern of water that forms in a kitchen sink when you leave the tap on. The steady stream of water hits the sink surface and spreads out in a circular pattern surrounded by a rim called a hydraulic jump, like the one below.  

Rousseaux says flukeprints are essentially hydraulic jumps caused by jets of water from beneath the surface. 

As the whale submerges, its flukes generate powerful vortices in the water. In the centre of the vortices, water is forced upwards hitting the surface from below, like a jet. This creates the jump, which is the circular rim around the flukeprint. 

One of the curious properties of hydraulic jumps is that they are ‘white holes’, the time reversed equivalent of black holes.  

White holes are special because they can emit waves and particles but do not allow them to enter, as we discussed in this post a couple of years ago. It’s exactly this process that creates the region of perfect calm at the centre of the flukeprint.

That’s a fascinating explanation. It means that the flukeprints whales leave behind are white holes on the surface of the ocean. Amazing!

Ref: arxiv.org/abs/1206.3893: The Flow Induced By A Mock Whale : Origin Of Flukeprint Formation

Be the leader your company needs. Implement ethical AI.
Join us at EmTech Digital 2019.

Register now
Want more award-winning journalism? Subscribe to Insider Plus.
  • Insider Plus {! insider.prices.plus !}*

    {! insider.display.menuOptionsLabel !}

    Everything included in Insider Basic, plus the digital magazine, extensive archive, ad-free web experience, and discounts to partner offerings and MIT Technology Review events.

    See details+

    Print + Digital Magazine (6 bi-monthly issues)

    Unlimited online access including all articles, multimedia, and more

    The Download newsletter with top tech stories delivered daily to your inbox

    Technology Review PDF magazine archive, including articles, images, and covers dating back to 1899

    10% Discount to MIT Technology Review events and MIT Press

    Ad-free website experience

/3
You've read of three free articles this month. for unlimited online access. You've read of three free articles this month. for unlimited online access. This is your last free article this month. for unlimited online access. You've read all your free articles this month. for unlimited online access. You've read of three free articles this month. for more, or for unlimited online access. for two more free articles, or for unlimited online access.