It’s well understood black holes are powerful. What’s less understood is exactly why — and what causes these jets to erupt.
On Monday, science took a step forward. Researchers obtained the highest resolution images yet of these eruptive jets as they blasted from a nearby black hole.
The new images suggest black holes of different masses — ranging from three times the mass of the Sun to a billion solar masses — still behave similarly. Understanding black holes and their behavior can help scientists understand how the galaxies that house them evolved over time.
These images are detailed in a study published in the journal Nature Astronomy.
What’s new — Using the Event Horizon Telescope (EHT) — the same telescope used to capture the first-ever image of a black hole — the study team got up close and personal with the center of a nearby galaxy. This allowed them to observe its black hole in greater detail.
“We’re seeing these jets in a way that we’ve never seen them before.”
Centaurus A is a giant elliptical active galaxy 12 million light-years away from Earth. It is the nearest galaxy with a strong jet of plasma erupting from its center. This jet exists because the center is home to a black hole weighing 55 million times the mass of the Sun.
By pointing their radio telescopes at the center of Centaurus A, the scientists were able to zoom into as close as 0.6 lightyears away from the black hole itself.
Michael Janssen is a researcher at the Max Planck Institute for Radio Astronomy in Bonn, Germany and the lead author of the study. He chose to point the telescope at Centaurus A because it allowed him to see the jets in “very fine detail.”
“We’re seeing these jets in a way that we’ve never seen them before,” Janssen tells Inverse.
The resulting images reveal the black hole’s jets appearing as hollow bi-cones with bright edges. Here’s an example of one of the high-resolution images:
“We see an X-shaped structure,” Janssen says. “We have two bright arms from this edge. We think these are the altar arms of the jet that are producing radiation — it's moving toward us.”
A black hole will launch a jet in one direction, and another in the opposite direction. The emissions from the counter jet can also be seen in the image, right on the opposite side. The image of the emission is much fainter since the jet is moving away from our view on Earth.
The scientists then compared the images with those captured of a much larger black hole, M87.
EHT scientists are pretty familiar with M87 since it was the first, and so far only, black hole to be directly imaged. In 2019, an international team of more than 200 astronomers unveiled the first image of a black hole.
M87 sits at the center of the galaxy Messier 87, an elliptical galaxy located 55 million light-years away. The black hole itself is quite the monster, weighing at 6.5 billion times the mass of the Sun.
The analysis revealed that, although M87 and Centaurus A greatly vary in mass, their jets are quite similar. The study team found the geometry and other properties of both black holes’ jets are pretty much the same, confirming massive black holes are simply scaled up versions of their not-so-massive counterparts.
“There’s no hidden physics that makes these objects change fundamentally when they grow,” Janssen says. “They will just grow and grow. They will stay a black hole but they will just become more massive.”
How do jets escape black holes?
Black holes typically come in two sizes:
- Stellar-mass black holes, which are five to ten times the mass of the Sun
- Supermassive black holes, which are millions or billions of times the mass of the Sun
A black hole feeds on its surrounding material, gobbling up nearby stars and other objects in order to grow in size. The amount of material swallowed by a black hole largely depends on its environment.
During their feeding frenzies, some matter — like hot gas or dust — falls toward the center of the black hole. It then shoots out in the form of jets, or two short beams of material, from outside the boundary that surrounds the black hole. This boundary is also known as the event horizon.
“If I had an answer, I would probably also have a really fancy physics prize.”
These jets can sometimes reach the outside of the galaxy itself, traveling at nearly the speed of light.
But the process that causes these jets to erupt isn’t exactly known, explains Matteo Lucchini, a researcher at the Massachusetts Institute of Technology. Lucchini is not affiliated with the new imaging study.
“If I had an answer, I would probably also have a really fancy physics prize because it's one of the big questions in astrophysics,” Lucchini tells Inverse.
But Lucchini, along with other astrophysicists, does have some ideas of what it could be.
“You need something to push this plasma close to the black hole,” Lucchini says. “That something, we are fairly certain, is the magnetic field.”
It’s possible that, as the black hole’s magnetic exerts stress on the plasma, it ends up escaping the entire system instead.
“With these images, we're really trying to put more physics — more complex and advanced physics — in our theoretical computer models to really recreate the physical conditions close to the black hole,” Lucchini says.
What’s next — Following the most recent images of the black hole at the center of Centaurus A, the EHT scientists are now pointing their telescopes at a familiar, enigmatic target.
The team is now working on capturing a video of the black hole at the center of the Milky Way — Sagittarius A*. Ideally, the video will reveal movement taking place around the black hole, giving scientists a better idea of its surrounding conditions.
“We’re working on it, and there are still some challenges to overcome,” Janssen says. “It will most likely be the next big announcement from EHT.”
Abstract: Very-long-baseline interferometry (VLBI) observations of active galactic nuclei at millimetre wavelengths have the power to reveal the launching and initial collimation region of extragalactic radio jets, down to 10–100 gravitational radii (rg≡GM/c2 ) scales in nearby sources1 . Centaurus A is the closest radio-loud source to Earth2 . It bridges the gap in mass and accretion rate between the supermassive black holes (SMBHs) in Messier 87 and our Galactic Centre. A large southern declination of −43° has, however, prevented VLBI imaging of Centaurus A below a wavelength of 1 cm thus far. Here we show the millimetre VLBI image of the source, which we obtained with the Event Horizon Telescope at 228 GHz. Compared with previous observations3 , we image the jet of Centaurus A at a tenfold higher frequency and sixteen times sharper resolution and thereby probe sub-lightday structures. We reveal a highly collimated, asymmetrically edge-brightened jet as well as the fainter counterjet. We find that the source structure of Centaurus A resembles the jet in Messier 87 on ~500 rg scales remarkably well. Furthermore, we identify the location of Centaurus A’s SMBH with respect to its resolved jet core at a wavelength of 1.3 mm and conclude that the source’s event horizon shadow4 should be visible at terahertz frequencies. This location further supports the universal scale invariance of black holes over a wide range of masses5,6