NANOGrav confirms gravitational wave sighting

June 28, 2023 5:32 PM

I hadn't heard of NANOGrav before today, but they've announced exciting findings. NPR puts it like this:

What they found is a pattern of deviations from the expected pulsar beam arrival timings that suggests gravitational waves are jiggling space-time as though it's a vast serving of Jell-O.

While the LIGO observaory on earth can measure gravitational waves with a wavelength comparable to its size (4km), NANOGrav's neutron star observations work on a scale of light years, so they see an entirely different "slice" of gravitational waves, much like the difference between visible light and radio waves.
posted by the antecedent of that pronoun (21 comments total)

Are gravitational waves damped as they pass through matter or do they just keep going forever?
posted by hypnogogue at 5:44 PM on June 28, 2023 [2 favorites]

Yesterday, in anticipation of this, Hank Green had a good bit on his TikTok about this such that I was able to (mostly) understand it.
posted by The Wrong Kind of Cheese at 5:52 PM on June 28, 2023 [3 favorites]

On Twitter, cosmologist Katie Mack has a nice Q&A.

Q: Give me a nice analogy.
A: The Earth is a ship on a cosmic sea. Every once in a while, we’re hit by a wave, and we know something went by. But now, for the first time, we can start to see the choppiness of the entire ocean, and we’re learning what else lives in our sea.
12/n

posted by Jeanne at 6:24 PM on June 28, 2023 [11 favorites]

NANOGrav's neutron star observations work on a scale of light years

Someone had a sense of humor.
posted by ChurchHatesTucker at 6:41 PM on June 28, 2023

I don't think it's supposed to be funny. The "nano" in NANOGrav's name is there because they're looking for gravitational wave signals that are measured in nanoHertz.
posted by teraflop at 6:51 PM on June 28, 2023 [5 favorites]

Ligo is most sensitive around 300Hz or a wavelength of 1000km. It's sensitivity to wavelengths of only a few km is far worse, which is a bit unfortunate as these higher frequencies could be informative for understanding neutron stars and supernova. But yes NANOGrav is in a different part of the spectrum.
posted by mscibing at 7:26 PM on June 28, 2023

(Hi, I don't visit much any longer.)

The NANOGrav results are getting lots of press, but if you'd like it straight from the horse's mouth, our collaboration members are doing a public briefing at the National Science Foundation HQ on Thursday at 1 PM US/Eastern. It will be live streamed on YouTube (potentially here, but the previous link is safer), and available after the fact.

There's also a gorgeous animation that should be out around then.
posted by RedOrGreen at 8:03 PM on June 28, 2023 [50 favorites]

Ligo is most sensitive around 300Hz or a wavelength of 1000km.

He is Ligo! Your stars are like the buzzing of flies to him.
posted by snuffleupagus at 8:36 PM on June 28, 2023 [7 favorites]

NPR hints at this in their report, but in addition the report from NANOGrav, teams from India, China, Australia and Europe are all announcing highly similar findings. So, not only are we getting new information but it has already been independently verified through separate studies by teams from around the world.
posted by Big Al 8000 at 9:26 PM on June 28, 2023 [2 favorites]

The different scales are throwing me off a bit...

NANO because nanoHertz? But the waves they're detecting have wavelengths of lightyears and thus frequencies of, um... periods of years, right? Ohhh, nanoHertz is a very little tiny bit of Hertz, not a whole lotta Hertz. Right. Okay! 1 / (1 nanoHertz) = 31.7 years. That meshes.

But then they're doing this by measuring millisecond pulsars. Why do they use the fast pulsars? The internet tells me "the majority of pulsars spin at a rate of about once per second," though, so I guess millisecond pulsars aren't that far off from the norm. But still, why millisecond vs any other pulsars? Just to get more samples?

And then just to check my understanding: do they have to use years of measurements because they need to sample from roughly one full period of a wave to properly measure/detect it?
posted by whatnotever at 10:07 PM on June 28, 2023 [1 favorite]

NASA CHIEF: Mr President, we have detected a large number of waves. I must brief you on the full implications, which we have been expecting for some time. We believe that this wave data represents the fourth...

BIDEN: No, man, not the fourth...

NASA CHIEF: I'm afraid so. The Fourth Wave Of Ska has arrived.
posted by Fiasco da Gama at 10:10 PM on June 28, 2023 [20 favorites]

Scientists figure out how to detect when cthulhu puts a quarter in the motel bed.
posted by allium cepa at 11:11 PM on June 28, 2023 [6 favorites]

The WaPo's longtime NASA/astronomy writer Joel Achenbach (w/ science editor Victoria Jaggard) as usual did a great job of making this accessible to a casual reader. Gift link, free to read.

(BTW, the WaPo just announced that the whole site is free to read until the end of the month. So I guess the gift link was unnecessary. But whatever.)
posted by martin q blank at 6:30 AM on June 29, 2023

The WaPo's longtime NASA/astronomy writer Joel Achenbach (w/ science editor Victoria Jaggard) as usual did a great job of making this accessible to a casual reader.

From the article:
“What we measure is the Earth kind of moving in this sea. It’s bobbing around — and it’s not just bobbing up and down, its bobbing in all directions”

This is an oddly terrifying thought when considered on a human scale, even though the article notes that these waves aren't felt on our lower range.
posted by Brandon Blatcher at 6:54 AM on June 29, 2023

On Twitter, cosmologist Katie Mack has a nice Q&A.

Thanks for that link!
posted by They sucked his brains out! at 6:58 AM on June 29, 2023

My tiktok feed has been basically nothing but (a) this and (b) people doing the Happy Birthday Grimace smashcut cosmic horror meme and I refuse to believe that's a coincidence.
posted by cortex at 7:53 AM on June 29, 2023 [2 favorites]

I assume the phrase “gravitational wave background” was chosen to recall the cosmic microwave background. I like the analogy, is it accurate?

I didn't love this quote in the NYTimes article

The findings carry a confidence level in the range of 3.5- to 4-sigma, just shy of the 5-sigma standard generally expected by physicists to claim a smoking-gun discovery. That means the odds of seeing a result like this randomly are about 1 in 1,000 years, Dr. Mingarelli said. “That’s good enough for me, but other people want once in a million years,” she said. “We’ll get there eventually.”

I'm sympathetic to the expert's personal confidence in the result but the point of having a simple standard numerical test for statistical significance is that it removes personal confidence from the discussion.

Still an amazing feat of signals analysis. Such a delicate thing to detect! And not even "extract from the noise", more like detecting the noise at all.
posted by Nelson at 8:00 AM on June 29, 2023 [2 favorites]

Are gravitational waves damped as they pass through matter or do they just keep going forever?

Technically yes, but not remotely on any scale that ever matters even on the grandest of timescales.
posted by edd at 8:04 AM on June 29, 2023

But still, why millisecond vs any other pulsars?
Millisecond pulsars are way more stable than slower pulsars in terms of rotation speed, so they're much more useful here.
posted by edd at 8:12 AM on June 29, 2023

NASA CHIEF: I'm afraid so. The Fourth Wave Of Ska has arrived.

BIDEN: Your scientists are certain of this?

NASA CHIEF: That’s the impression that I get.
posted by dephlogisticated at 4:06 PM on June 29, 2023 [6 favorites]

All the publications are listed/linked here.
posted by neuron at 8:35 PM on June 29, 2023