A cosmic buzz (6/29/23)

Good afternoon, and happy Thursday. If you’ve been tuned in to astrophysics Twitter this week, you already know it’s been a completely hectic, jam-packed week in space science. Let’s unpack it, shall we?

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It’s Wavy, Baby

Space and time aren’t constant. They ripple and stretch, manipulated by the motion of ultradense, supermassive black holes as they orbit one another, and those ripples pass constantly across the universe, forming a wobbly, shaky cosmic backdrop to everything we can see out in space.

These ripples—called gravitational waves—are subtle, elusive, and very hard to find. Until now, the background of waviness in spacetime had never been directly measured.

Over the last two decades, a team at the NANOGrav center and several international teams of researchers turned a collection of pulsars into a giant sensor half a galaxy wide in order to sense the constant cosmic backdrop of gravitational waves pulsing through the universe. Their findings were published yesterday as a collection of eight papers in The Astrophysical Journal Letters.

The cosmic backdrop: Gravitational waves were first theorized by—who else?—Albert Einstein in 1916 as a key part of the theory of relativity, unifying space and time.

They weren’t confirmed until nearly one hundred years later, when the Laser Interferometer Gravitational-Wave Observatory (LIGO) directly detected gravitational waves for the first time.

• LIGO, which consists of two detector sites in Washington and Louisiana, picked up on a short-wavelength wave coming from a collision between two black holes a few times the size of the Sun.

• Longer wavelengths of gravitational waves, theorized to start with the orbit of pairs of supermassive black holes and cover the breadth of the universe, had never been detected.

Sensing the waves: In order to pick up on these very faint pulses coming from across the cosmos, researchers needed a sensor bigger than anything they could possibly build on Earth. The solution: millisecond pulsar timing arrays.

Pulsars are dense remnants of dead stars that emit concentrated jets of radiation. They spin incredibly rapidly, as often as 1000 times each second. As they spin, from our perspective, those jets flash by like the spinning beam of a lighthouse. This happens with remarkable regularity, the flashes keeping nearly perfect time.

That is, until something gets in the way. Gravitational waves, as they’re defined, create ripples in the fabric of spacetime that delay the beat being kept by the pulsars. By measuring that infinitesimal change in the otherwise steady beat of radio waves coming from a large sample of pulsars—in this case, 68 total signals—the researchers were able to detect long oscillations passing through the group.

Over more than 15 years, those precise, meticulous observations of this group of cosmic timekeepers yielded evidence that these long oscillations in spacetime were, in fact, passing through.

A caveat: The team is stopping short of calling its results a “discovery.” Statistically speaking, there’s only a one in 1000 chance that the observed patterns are a coincidence, which is lower than the usual threshold. The team felt comfortable making this announcement because of the consistency of results across multiple different arrays and teams collecting data and because the signal has gotten stronger as time has worn on.

The next wave: "While our early data told us that we were hearing something, we now know that it’s the music of the gravitational universe," NANOGrav co-director and OSU astrophysicist Xavier Siemens said in a release. "As we keep listening, individual instruments will come to the fore in this cosmic orchestra."

It’s a poetic way of saying there’s still work to be done to tease out data from individual wave sources (i.e., theorized pairs of supermassive black holes around one another). The NANOGrav team is looking now to use the widespread background of waves they’ve detected to trace back the location of individual pairs across space—or to discover whether parts of that cosmic background have other, unexpected sources.

Other News from the Cosmos

• JWST captured starlight from two galaxies with supermassive black holes at their centers dating from less than a billion years after the Big Bang.

• Mars Sample Return has nearly doubled in cost since its inception, making NASA stakeholders a little antsy about continuing the program.

• An extra planet up to the size of Uranus (ha ha) may be lurking in our solar system somewhere in the theorized Oort cloud of asteroids beyond the known planets’ orbits.

• Martian gullies found on the sides of craters look similar to ones on Earth formed by meltwater from glaciers. New models show that the Mars gullies may have formed the same way under specific conditions.

• Blue supergiants, a class of stars in a sort of stellar “adolescence,” have been mapped by a team of researchers across our region of the Milky Way.

• China’s Zhurong Mars rover found a surprisingly weak magnetic field in the Utopia Basin.

• Perseverance doubled the oxygen output of its MOXIE instrument on Mars.

• Methyl cation, a molecule known to initiate growth of complex carbon molecules, has been spotted by JWST in a planet-forming disc in the Orion Nebula.

Rachael's Recs

👻 Going ghost: Earth is constantly being bombarded with neutrinos, a type of high-energy particle, affectionately nicknamed “ghost particles” for their ability to pass through us totally undetected. Neutrinos are abundant throughout the universe, but this quality makes them tough to detect. The IceCube Neutrino Observatory in Antarctica is dedicated to studying these particles, and now, it’s released the first map of the neutrinos of the Milky Way.

💡 Lights out: This weekend, ESA is launching its Euclid space telescope. Euclid is the first of its kind, on a mission to unravel the mysteries of dark matter by creating a 3D map, with time as the third dimension, of billions of galaxies up to 10 million light-years away from Earth. In an article for Science magazine, physics reporter Daniel Clery walks readers through everything we know and believe about dark matter so far—and what Euclid may help us to understand.

The View from Space