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When two black holes collide, they don’t smash into each other the way two stars might. A black hole is an intensely curved region of space that can be described by only its mass, rotation, and electric charge, so two black holes release violent gravitational ripples as merge into a single black hole. The new black hole continues to emit gravitational waves until it settles down into a simple rotating black hole. That settling down period is known as the ring down, and its pattern holds clues to some of the deepest mysteries of gravitational physics.

Gravitational wave observatories such as the Laser Interferometry Gravitational-Wave Observatory (LIGO) have mostly focused on the inspiral period of black hole mergers. This is the period where the two black holes orbit ever closer to each other, creating a rhythmic stream of strong gravitational waves. From this astronomers can determine the mass and rotation of the original black holes, as well as the mass and rotation of the merged black hole. The pattern of gravitational waves we observe is governed by Einstein’s general relativity equations, and by matching observation to theory we learn about black holes.

General relativity describes gravity extremely well. Of all the gravitational tests we’ve done, they all agree with general relativity. But Einstein’s theory doesn’t play well with the other extremely accurate physical theory, quantum mechanics. Because of this, physicists have proposed modifications to general relativity that are more compatible with quantum theory. Under these modified theories, there are subtle differences in the way merged black holes ring down, but observing those differences hasn’t been possible. But a couple of new studies show how we might be able to observe them in the next LIGO run.

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The modified Teukolsky equation. Credit: Li, Dongjun, et al

In the first work, the team focused on what is known as the Teukolsky Equation. First proposed by Saul Teukolsky, the equations are an efficient way of analyzing gravitational waves. The equations only apply to classical general relativity, so the team developed a way to modify the equations for modified general relativity models. Since the solutions to both the Teukolsky and modified Teukolsky equations don’t require a massive supercomputer to solve, the team can compare black hole ring downs in various gravitational models.

The second work looks at how this would be done with LIGO data. Rather than focusing on general differences, this work focuses on what is known as the no-hair theorem. General relativity predicts that no matter how two black holes merge, the final merged black hole must be described by only mass, rotation, and charge. It can’t have any “hair”, or remnant features of the collision. In some modified versions of general relativity, black holes can have certain features, which would violate the no-hair theorem. In this second work, the authors show how this could be used to test general relativity against certain modified theories.

LIGO has just begun its latest observation run, so it will be a while before there is enough data to test. But we may soon have a new observational test of Einstein’s old theory, and we might just prove it isn’t the final theory of gravity after all.

Reference: Li, Dongjun, et al. “Perturbations of spinning black holes beyond General Relativity: Modified Teukolsky equation.” Physical Review X 13.2 (2022): 021029.

Reference: Ma, Sizheng, Ling Sun, and Yanbei Chen. “Black hole spectroscopy by mode cleaning.” Physical Review Letters 130.2 (2023): 141401.

The post When Black Holes Merge, They’ll Ring Like a Bell appeared first on Universe Today.

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The Best Backpacking Gear for the John Muir Trail

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June 5, 2023

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By Michael Lanza

So you’re planning to thru-hike the John Muir Trail and making all of the necessary preparations, and now you’re wondering: What’s the best gear for a JMT hike? Having thru-hiked the JMT as well as taken numerous other backpacking trips all over the High Sierra—mostly between late August and late September, which I consider that the best time to walk the Sierra, to avoid snow and the voracious mosquitoes and blazing hot afternoons of mid-summer—I offer the following picks for the best lightweight backpacking gear and apparel for a JMT thru-hike.

Indisputably one of the best backpacking trips in America—and among the very best I’ve taken over three decades of backpacking, including 10 years I spent as Northwest Editor and lead gear reviewer for Backpacker magazine and even longer running this blog—the JMT meanders for 211 miles through the magnificent High Sierra, from Yosemite Valley to the summit of the highest peak in the Lower 48, 14,505-foot Mount Whitney (where backpackers must then descend another 11 miles to finish the trip at Whitney Portal trailhead). See my story about thru-hiking the JMT in seven days.

With few opportunities to resupply along the trail—and given the generally dry weather in the Sierra in summer—you can easily and should hike the JMT with the lightest gear that works for you (or that you can afford). Maximum pack weight will depend on how many days you spend on the trail and your food weight, but it’s quite feasible to keep your base pack weight (everything but food and water) within 15 pounds or less—and certainly no more than 20 pounds—without compromising safety or comfort in camp.

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Hi, I’m Michael Lanza, creator of The Big Outside. Click here to sign up for my FREE email newsletter. Join The Big Outside to get full access to all of my blog’s stories. Click here for my e-guides to classic backpacking trips. Click here to learn how I can help you plan your next trip.

A backpacker hiking the John Muir Trail above Helen Lake in Kings Canyon N.P., High Sierra.
” data-image-caption=”Marco Garofalo backpacking the John Muir Trail above Helen Lake in Kings Canyon N.P. Click photo to learn how I can help you plan your JMT thru-hike.
” data-medium-file=”https://i0.wp.com/thebigoutside.com/wp-content/uploads/2022/10/JMT2-085-Marco-Garofalo-hiking-above-Helen-Lake-John-Muir-Trail-Kings-Canyon-N.P.-High-Sierra..jpg?fit=300%2C200&ssl=1″ data-large-file=”https://i0.wp.com/thebigoutside.com/wp-content/uploads/2022/10/JMT2-085-Marco-Garofalo-hiking-above-Helen-Lake-John-Muir-Trail-Kings-Canyon-N.P.-High-Sierra..jpg?fit=900%2C600&ssl=1″ decoding=”async” width=”900″ height=”600″ src=”https://i0.wp.com/thebigoutside.com/wp-content/uploads/2022/10/JMT2-085-Marco-Garofalo-hiking-above-Helen-Lake-John-Muir-Trail-Kings-Canyon-N.P.-High-Sierra..jpg?resize=900%2C600&ssl=1″ alt=”A backpacker hiking the John Muir Trail above Helen Lake in Kings Canyon N.P., High Sierra.” class=”wp-image-54840″ srcset=”https://i0.wp.com/thebigoutside.com/wp-content/uploads/2022/10/JMT2-085-Marco-Garofalo-hiking-above-Helen-Lake-John-Muir-Trail-Kings-Canyon-N.P.-High-Sierra..jpg?resize=1024%2C683&ssl=1 1024w, https://i0.wp.com/thebigoutside.com/wp-content/uploads/2022/10/JMT2-085-Marco-Garofalo-hiking-above-Helen-Lake-John-Muir-Trail-Kings-Canyon-N.P.-High-Sierra..jpg?resize=300%2C200&ssl=1 300w, https://i0.wp.com/thebigoutside
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CRS-28 Mission Control Audio

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June 5, 2023

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This is the vehicle trajectory and mission control audio without any additional commentary. There may be very long periods of silence. For our full hosted webcast, visit

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Photo Gallery: 36 Gorgeous Backcountry Lakes

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June 5, 2023

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By Michael Lanza

Water makes up about 60 percent of our bodies—and, I suspect, 100 percent of our hearts. We crave it not only physically, for survival, but emotionally, for spiritual rejuvenation. We love playing in it for hours as children and we paddle and swim in it as adults. We’re drawn by the calming effects of sitting beside a stream or lake in a beautiful natural setting, an experience that possesses a certain je ne sais quoi—a quality difficult to describe, but that we can all feel.

And nothing beats taking a swim in a gorgeous backcountry lake.

I’ve come across quite a few wonderful backcountry lakes over more than three decades of exploring wilderness—including about 10 years as the Northwest Editor of Backpacker magazine and even longer running this blog. I’ve just updated and expanded this list of my favorites to give you some eye candy as well as ideas for future adventures—and perhaps compare against your list of favorite backcountry lakes.

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Hi, I’m Michael Lanza, creator of The Big Outside. Click here to sign up for my FREE email newsletter. Join The Big Outside to get full access to all of my blog’s stories. Click here for my e-guides to classic backpacking trips. Click here to learn how I can help you plan your next trip.

Click on the links to my stories in these brief writeups to learn more about each of these trips. Much of this story is free for anyone to read, but reading the entire story requires a paid subscription. See my Custom Trip Planning page to learn how I can help you plan a trip to any of these lakes.

If you know some gorgeous lakes that are not on my list, please suggest them in the comments section below this story. I try to respond to all comments.

Here’s to your next peaceful moment beside a gorgeous lake deep in the mountains somewhere.

Elizabeth Lake in Glacier National Park.
” data-image-caption=”Early morning at Elizabeth Lake in Glacier National Park. Click photo to learn how I can help you plan your Glacier trip.
” data-medium-file=”https://i0.wp.com/thebigoutside.com/wp-content/uploads/2020/03/Gla6-018-Elizabeth-Lake-in-Glacier-National-Park.-2.jpg?fit=300%2C200&ssl=1″ data-large-file=”https://i0.wp.com/thebigoutside.com/wp-content/uploads/2020/03/Gla6-018-Elizabeth-Lake-in-Glacier-National-Park.-2.jpg?fit=900%2C600&ssl=1″ decoding=”async” width=”900″ height=”600″ src=”https://i0.wp.com/thebigoutside.com/wp-content/uploads/2020/03/Gla6-018-Elizabeth-Lake-in-Glacier-National-Park.-2.jpg?resize=900%2C600&ssl=1″ alt=”Elizabeth Lake in Glacier National Park.” class=”wp-image-38774″ srcset=”https://i0.wp.com/thebigoutside.com/wp-content/uploads/2020/03/Gla6-018-Elizabeth-Lake-in-Glacier-National-Park.-2.jpg?resize=1024%2C683&ssl=1 1024w, https://i0.wp.com/thebigoutside.com/wp-content/uploads/2020/03/Gla6-018-Elizabeth-Lake-in-Glacier-National-Park.-2.jpg?resize=300%2C200&ssl=1 300w, https://i0.wp.com/thebigoutside.com/wp-content/uploads/2020/03/Gla6-018-Elizabeth-Lake-in-Glacier-National-Park.-2.jpg?resize=768%2C512&ssl=1 768w, https://i0.wp.com/thebigoutside.com/wp-content/uploads/2020/03/Gla6-018-Elizabeth-Lake-in-Glacier-National-Park.-2.jpg?resize=1080%2C720&ssl=1 1080w, https://i0.wp.com/thebigoutside.com/wp-content/uploads/2020/03/Gla6-018-Elizabeth-Lake-in-Glacier-National-Park.-2.jpg?w=1200&ssl=1 1200w” sizes=”(max-width: 900px) 100vw, 900px” data-recalc-dims=”1″ />Elizabeth Lake in Glacier National Park.

Elizabeth Lake, Glacier National
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