If you’ve never seen a gigantic electric-orange donut made of neatly ordered spiraling magnetic fields, spinning around the edges of a supermassive black hole in the Milky Way galaxy, this is your lucky click of the day. The mega-monster black hole, called Sagittarius A* (Sgr A*), is just 26,700 light-years away — and its astonishing mass is about 4.3 million times greater than our Sun. In a milestone discovery that promises to rock the entire astronomical study of black holes, scientists just served up the first images ever seen of a mesmerizing portal right at the heart of our home galaxy.
There are two things even freakier than seeing vibrating magnetic fields of plasma-light around our galaxy’s black hole. First, we’ve known about Sgr A*’s parabolic space-donut since 2022, but had no idea it was literally just vibing (magnetically speaking). And second, Sgr A* isn’t even the fattest hole we’ve seen. In fact, the reason Sgr A*’s magnetic spiral-field is shaking up the astrophysics world is because it looks just like the one scientists found around an even bigger black hole in 2021 about 55 million light-years away, called M87.
While the credit for capturing these priceless images most often goes to just one or two research teams, the astonishingly powerful Event Horizon Telescope (EHT) is so technologically sophisticated that it actually has to be operated by several teams around the world. And this scientific power tool is more than just a big lens on a big camera — the tsunami of data it captures for scientists is so massive that it demands the creation of unique software, tools and frameworks just to become functional. On top of all this, those frameworks have to snap a clear picture amid astronomical chaos, as the plasma-frenzied Sgr A* refuses to sit still.
“Sgr A* is like a frenetic toddler,” Dr. Avery Broderick explained in an emailed university statement.
Broderick is a professor in the physics and astronomy department at Canada’s University of Waterloo and an associate faculty at the Perimeter Institute. He and other Canadian EHT collaborators created the data-to-space-donut framework for the EHT, a hypercomplex process called THEMIS. They’re the reason you see an actual picture at the top of this webpage, rather than just an incomprehensible scramble of space data and binary code.
“The polarized light we see from Sgr A* is striking,” he said. “Not only is it highly polarized, at three times more polarization than the black hole at the centre of the M87 galaxy, but it’s also highly organized. This new image limits the density of the plasma orbiting Sgr A* and reveals the magnetic fields that govern its fate.”
Let me give you an idea of how much data we’re talking about: As the Harvard Gazette noted during the discovery of the M87 field in 2021, “the impressive resolution obtained with the EHT is equivalent to that needed to image a credit card on the surface of the moon.”
Yeah. Whoa.
“We’re seeing for the first time the invisible structure that shepherds the material within the black hole’s disk,” said Broderick, and which “drives plasma to the event horizon, helping it to grow.”
“It is exciting that we were able to make a polarized image of Sgr A* at all. The first image took months of extensive analysis to understand its dynamical nature and unveil its average structure,” said astrophysicist Paul Tiede in a Wednesday release from Harvard University.
“Making a polarized image adds on the challenge of the dynamics of the magnetic fields around the black hole. Our models often predicted highly turbulent magnetic fields, making it extremely difficult to construct a polarized image. Fortunately, our black hole is much calmer, making the first image possible,” said Tiede.
How is all this polarization even possible? In a bite-sized Twitter animation, the Event Horizon Telescope team explains that all the random hot-gas plasma rocking around in space is actually emitting raw, unpolarized light waves — akin to how our sun throws down a full spectrum of different light waves, some we can see and some we can’t, like UV light. Just like we can filter out some types of sunlight with the polarized coating on our sunglasses, the magnetic field around Sag A* becomes a polarizing filter for all that raw plasma light.
When the black hole sucks all that light-producing plasma toward its cosmically horrific maw, the magnetic field around the black hole whips the unpolarized plasma-light chaos into a tight and orderly rhythm, polarizing it. But black holes also bend gravity, and thus magnetic fields — and when magnetic fields get bent, so does the polarization of that light, letting us catch an eye-full.
It’s a bird! It’s a plane! It’s a …hidden plasma jet?
“What we’re seeing now is that there are strong, twisted and organized magnetic fields near the black hole at the center of the Milky Way galaxy,” said Sara Issaoun.
Like Tiede, Issaon is an astrophysicist with the Smithsonian Astrophysical Observatory. Issaon is the co-lead of the EHT project on Sgr A* and a NASA Einstein Fellow.
“Along with Sgr A* having a strikingly similar polarization structure to that seen in the much larger and more powerful M87* black hole, we’ve learned that strong and ordered magnetic fields are critical to how black holes interact with the gas and matter around them,” she said.
OK, so there’s a spiraling magnetic donut around our black hole. Now what?
Glad you asked. Now that we’ve got hard-won images of two different black holes — and can see that both have similar spiraling magnetic fields — we can begin to figure out whether they’ve got more in common. Specifically, astronomers are aiming to discover whether Sgr A* has the same sort of propulsive plasma jets we can see in M87.
If it does, then we may be able to understand something critical about the entire astronomical study of black holes across the board — how these light-devouring space monsters are actually fueled and sustained. And knowing that much, would open the door to a tidal wave of knowledge about how the universe works.
Sgr A*’s 15 minutes of fame is far from over. The EHT already has a planned expansion in the works for the next decade that will enable high-fidelity movies of Sgr A*. Not only might the Sgr A* starlet’s movie debut reveal the hypothesized hidden plasma jet — the tech could also allow astronomers to observe other black holes, and spot these kinds of polarizing features and jets elsewhere. In the meantime, the EHT will be poking its lens further and further into space, with a global team probing a universe of data to solve the mystery of the swirling monster at the heart of our galaxy.
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