What wobbling rocks can tell us about nuclear safety

Precariously balanced rocks, or PBRs, record a history of things that haven't happened
Precariously balanced rocks, or PBRs, record a history of things that haven’t happened

We’ve all seen them; we’ve even taken pictures of ourselves pretending to hold them up or to push them over.

These are the precariously balanced rocks on a hill or a coastal cliff. It’s as if the gentlest nudge would send them tumbling.

In truth, the disturbance needed to unsettle the blocks is quite significant, and that got husband and wife geologists Drs Dylan and Anna Rood wondering about how these great stones could be used to decipher earthquake history.

Think about it: if a precariously balanced rock has held its position for 10,000 years without tipping over, it means the land around the stone hasn’t experienced shaking above a certain level in all that time.

“The turn of phrase we’re trying to coin is that these precariously balanced rocks, or PBRs, are an ‘inverse seismometer’,” explains

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Black Hole From Iconic Image Appears to Be Wobbling

Black hole M87*.

Black hole M87*.
Image: EHT Collaboration

Scientists are learning important new things about the first-ever directly imaged black hole, including behaviors consistent with Einsteinian theory, but it’s also showing an unexpected feature in the form of a very wobbly ring.

Seems like forever ago, but we finally got to feast our eyes on the apparently unseeable back in April 2019, when this incredible image of a supermassive black hole was first released. Of course, we can’t actually “see” the black hole, because, as any 6-year-old will happily tell you, black holes have a habit of sucking up light. What the picture does show, however, is an asymmetric ring, known as the black hole’s shadow, of superheated gas swirling around the black hole’s event horizon—that boundary beyond which light cannot escape.

This particular black hole, with the mass of 6.5 billion Suns, is located 55 million light-years away

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Shadow of black hole in M87 galaxy is wobbling and has been for a while — ScienceDaily

Analysis of previously unpublished data from observations of M87* between 2009 and 2013 by scientists at the Event Horizon Telescope (EHT) has revealed that the crescent shadow of the black hole is wobbling, and has rotated significantly over the past ten years of observation. Published today in The Astrophysical Journal, and led by scientists from the Center for Astrophysics | Harvard & Smithsonian (CfA), the study focused on the morphology of the black hole over time, and was made possible by advances in analysis and understanding achieved as a result of EHT’s groundbreaking black hole photo in 2019.

“EHT can detect changes in the M87 morphology on timescales as short as a few days, but its general geometry should be constant on long timescales,” said Maciek Wielgus, an astronomer at CfA, Black Hole Initiative (BHI) Fellow, and lead author on the paper. “In 2019, we saw the shadow of

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