Astronomers release new images of black hole M87

The second-ever images of the event horizon around a black hole are out — and they’re stunners.

In 2019, we got our first good glimpse of a supermassive black hole, revealing the dark silhouette of the gaping maw at the center of galaxy Messier 87 (M87), surrounded by a fiery halo of material. But on Wednesday, The Event Horizon Telescope (EHT) collaboration — the international team behind the original image — released two new images of M87 that shows it in polarized light.

The latest images show the black hole surrounded by polarized light that “swooshes” around it in a heated sweep, showing the magnetic field's size and strength around the black hole.

The findings from the images were detailed in three studies published Wednesday in The Astrophysical Journal Letters.

WHAT’S NEW — The new images are constructed using the same datasets from 2019. However, the team was able to construct data on the direction of the light, revealing polarization.

Light is polarized when it is emitted in high temperatures in areas where there are magnetic fields. This reveals a few things about the M87 supermassive black hole.

• The light around the M87 black hole is produced in a synchrotron process, where electrons gyrate around the magnetic field lines.
• This helps reveal the shape and strength of the black hole’s magnetic field. The EHT team is still working to determine constraints on the strength.

Andrew Chael, a fellow at the Princeton University Center for Theoretical Science and co-author of one of the new studies, says that the previous data only told part of the story of M87.

“Now we're looking at sort of an extra dimension,” Chael tells Inverse.“We are adding the direction of the light that we see to the total brightness.”

Monika Mościbrodzka, assistant professor of astrophysics at Radboud University in the Netherlands and coordinator of the EHT Polarimetry Working Group, says that the new images are a way to learn about the physics taking place within the ring.

“From the polarization pattern, we can learn about the shape of magnetic field lines close to the black hole,” Mościbrodzka tells Inverse. “And we can have a deeper understanding about how exactly the ring emission visible in the images is produced.”

HERE’S THE BACKGROUND — On April 10, 2019, a team of international researchers unveiled the first-ever direct image captured of a black hole. Before this, images of black holes captured the effects of a black hole on its surrounding region rather than the object itself — for instance, seeing only the jets emitted.

The Event Horizon Telescope collected a massive amount of data on M87 through radio antennas worldwide to produce the 2019 image. It revealed a crescent of hot gas and debris orbiting the black hole's event horizon, the region of space directly surrounding the singularity of a black hole, the “point of no return” from which nothing can escape.

The M87 black hole is around 6.5 billion solar masses, or times the mass of the Sun. For comparison, Sagitarrius A* — the black hole at the center of our galaxy — is only about 2.6 million solar masses.

HOW THEY DID IT — To capture the images of the black hole, an object otherwise shrouded in darkness, the team had to simulate a telescope the size of the Earth.

The EHT combined an array of eight telescopes located on five continents. Together, they aimed at the core of M87, which is located 55 million light-years away from Earth, over the course of seven days in April 2017.

Synchronized by custom-made atomic clocks, they collected incoming radio signals from the distant black hole and logged the data on super-fast data recorders built for this one task.

The telescopes gathered 5,000 terabytes of data, with around 350 terabytes collected every day of the observation period.

WHY IT’S IMPORTANT — Since its release in 2019, the first image of a black hole has helped scientists confirm theories about its nature, including its size and the amount of material surrounding it.

But there is still a lot that we don’t understand about the mechanisms that govern black holes.

“The image that we're seeing is only a little bit bigger than the solar system, but from that very small region, it's launching this huge jet of material outside the entire galaxy tens of thousands of light years on,” Chael says. “The mechanism that launches the jet and takes all the energy and puts it out into this big column of matter is not completely well understood.”

Most matter that gets close to the edge of a black hole ends up being swallowed up by the massive object. However, some of the surrounding particles escape just moments before they are captured and are emitted in the form of high-speed jets.

But the new images of the black hole in the polarized light hold precious information about the structure of the magnetic field that lies just outside the black hole where this process takes place.

The latest observations suggest that the magnetic field is strong enough to help this material resist the strong tug of the black hole’s gravitational pull, pushing it out into space. This helps construct the mechanism by which jets form, which is only partially understood.

Priyamvada Natarajan, an astronomy professor at Yale University, who was not involved in the study, says this will have a huge effect on subsequent black hole observations.

“It's a very exciting result,” Natarajan tells Inverse. “And a harbinger of new directions.”

WHAT'S NEXT — Following up with their recent images, the EHT team is getting ready to observe M87 in two weeks to see how the black hole evolved in the period of time since the first image of it was captured. They also plan on observing Sagitarrius A* during that time.

“We can learn a lot about properties of the black hole by looking at how matter around them changes in time,” Mościbrodzka says. “We hope to discover how M87 evolved in the time since the year 2017.”

EHT is also adding more telescopes to the array to create higher resolution images of black holes that will allow the team to probe closer at these objects.

“Right now, we're only sensitive to the brightest emission,” Chael says. “So I think if we have more sensitivity, what we hope to see is the connection between the black hole and the jet. That’d be very exciting.”

Abstract: In April 2017, the Event Horizon Telescope observed the near-horizon region around the supermassive black hole at the core of the M87 galaxy. These 1.3 mm wavelength observations revealed a compact asymmetric ring-like source morphology. Such a structure originates from synchrotron emission produced by relativistic plasma located in the immediate vicinity of the black hole. Here we present the corresponding linear-polarimetric images of the center of M87. We find that only a part of the ring is significantly polarized. The resolved fractional linear polarization has a maximum located in the south-west part of the ring, where it rises to the level of ⇠15 %. The polarization position angles are arranged into a nearly azimuthal pattern. We perform quantitative measurements of relevant polarimetric properties of the compact emission and find evidence for the temporal evolution of the polarized source structure over one week of EHT observations. The details of the polarimetric data reduction and calibration methodology are provided. We carry out the data analysis using multiple independent imaging and modeling techniques, each of which is validated against a suite of synthetic datasets. The gross polarimetric structure and its apparent evolution with time are insensitive to the method used to reconstruct the image. These polarimetric images carry information about the structure of the magnetic fields responsible for the synchrotron emission. Their physical interpretation is discussed in an accompanying publication.