Stunning new images of the giant black hole at the center of the Milky Way galaxy revealed

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Black holes are among the most striking, popular and unknown astrophysical objects in the universe. Since their first prediction, a great collective curiosity has been formed about their nature, supported by famous recreations such as the one in the movie Interstellar. In 2022, the Event Horizon Telescope, an Earth-sized radio telescope, obtained the first image of Sagittarius A* in the heart of the Milky Way. A new study shows that the supermassive black hole has intricate magnetic fields with the potential to shoot matter at nearly the speed of light.

Size comparison diagram between black holes M87* and Sagittarius A*.
Size comparison between images of black holes M87* and Sagittarius A*. Credits: EHT Collaboration.

Planetary scale telescope

Studying black holes, and obtaining detailed images, requires different techniques than conventional ones. While James Webb and Hubble employ lens and mirror systems, the Event Horizon Telescope combines the power of several radio telescopes around the globe to provide an observatory with an aperture virtually the same size as the planet.

Map of the Event Horizon Telescope radio telescopes
Map of the locations of the various radio telescopes that are part of the Event Horizon Telescope, together obtaining an aperture equivalent to the size of the Earth. Credits: ESO/M. Kornmesser.
EHT sizing
The observing capability of the Event Horizon Telescope is equivalent to a telescope powerful enough to see an astronaut's glove on the Moon in quality from Earth.

In 2019 the first photograph of a black hole was shown to the public. M87* was chosen for its distance, activity and relative stability. It would not be until 2022 that the first image of M87* could be obtained, processed and shared. Sagittarius A*. Which, as its name indicates, is located in the direction of the constellation Sagittarius, is a black hole with a mass estimated to be on the order of 4.1 million times that of the Sun.

Image of the supermassive black hole Sagittarius A*.
First image of the black hole Sagittarius A* at the center of the Milky Way. Credits: EHT Collaboration.

Light ring

The Event Event Telescope collaboration, contrary to its name, is capable of observing a much larger area than the event horizon of a black hole.. Where the bright regions represent photons deflected by the intense gravity of the black hole, whose wavelengths were strongly stretched to the radius ranges.

Electromagnetic radiation

In 2021, the first public showing of the first image in polarized light from M87*which was obtained under more processing and observation than in the case of the first black hole representation. On the other hand, Sagittarius A* is a different case, since its relative proximity of 27,000 light-years shows greater motion and a clear difficulty in capturing images.. New techniques had to be applied to reveal the new perspective of the black hole.

Image of the supermassive black hole M87* in polarized light
Image of the supermassive black hole M87* seen in polarized light, indicating the presence of magnetic fields and their respective direction. Credits: EHT Collaboration.

Light, regardless of its wavelength, is a combination of oscillations in the magnetic and electric field, and in general has no preferential direction. When it interacts with the active plasma located in the vicinity of the black hole, a polarization effect is generated, forcing a form of oscillation in the electromagnetic radiation, which, when detected, allows estimating the intensity and direction of the field that affected it.

Zoology of black holes

The images of the black holes M87* and Sagittarius A* are, so far, the only ways we have to understand these objects on small scales and test the different models. Therefore, comparisons between the two specimens are fundamental to inferring the structure and behavior of all black holes in the universe.

sgra polarized
New view of the supermassive black hole Sagittarius A* in the core of the Milky Way in polarized light, indicating the presence of strong, intertwined, organized magnetic field lines. Credits: EHT Collaboration.

He new discovery evidence of strong magnetic field lines spiraling around Sagittarius A*.. In some ways, similar to those of M87*, indicating that this is a common or even crucial feature of the vast majority of black holes in the universe.

Despite the similarities, in the galaxy M87 the presence and location of a black hole was inferred from an extensive jet of material ejected from the center of the galaxy. Which is accelerated by the object's magnetic fields, driving the gas to near-light speeds.

Meanwhile, no such thing has been observed with the black hole at the center of the Milky Way galaxy, raising questions about what other processes may be key to having a relativistic jet or the possibility that it remains hidden from current instruments and observations.

Francisco Andrés Forero Daza