In 2022, the first real image of Sagittarius A* (Sgr A*), the central supermassive black hole of the Milky Way, located about 27 thousand light-years away from Earth, was revealed.
Although it is at least a thousand times smaller and less massive than M87*, the first black hole photographed in history (both by the project Event Horizon Telescope – EHT), observations revealed that the two are quite similar, which led scientists to wonder whether these cosmic monsters shared common characteristics beyond appearance.
To find out, a team of scientists from the European Southern Observatory (ESO) decided to study Sgr A* in polarized light – resulting in the first detection of the object’s spiral magnetic fields, a very important discovery reported this Wednesday (27). in the scientific journal The Astrophysical Journal Letters.
What the study revealed about Sgr A*:
- Astronomers have announced the detection of a strong, organized magnetic field twisted into a spiral shape around Sagittarius A*, the Milky Way’s central supermassive black hole;
- They used polarized light to arrive at this discovery;
- Only a single black hole, M87*, has had its magnetic field previously detected;
- Comparison between the two reveals a striking similarity, which could mean that the existence of ordered magnetic fields could be essential for the interaction of black holes with their surroundings.
Previous studies of the light around the M87* black hole revealed that the magnetic fields around it allowed it to launch powerful jets of material into the surrounding space. New images have now revealed that the same may be true for Sagittarius A*.
“What we are seeing are strong, twisted, organized magnetic fields near the black hole at the center of the Milky Way,” said Sara Issaoun, a PhD researcher in the NASA Hubble Fellowship Program at the Harvard-Smithsonian Center for Astrophysics in the US. and co-leader of the project. “If we add to this the fact that Sgr A* has a polarization structure very similar to that observed in the much larger and more powerful black hole M87*, it seems to us that strong and ordered magnetic fields are fundamental to the way black holes interact with the gas and matter that surround them.”
Polarized light allows detection of magnetic field in black hole
Light is composed of oscillating (or moving) electromagnetic waves, which allow us to see objects. Sometimes, light oscillates in a preferred orientation, when we classify it as “polarized”.
This is how, for example, 3D glasses work – the two lenses have different polarizations that allow only part of the light to enter so that our brains can create a 3D image in our head.
Because polarized light helps reduce glare from bright light sources, this allowed the team to get a clearer look at the edges of Sagittarius A* and map the magnetic field lines there.
“For the first time, we have obtained event horizon-scale polarimetric images of the black hole at the center of our galaxy, Sgr A*,” said researcher Mariafelicia De Laurentis, deputy lead scientist at the EHT and professor at the University of Naples Federico II, in Italy, in a statement.
“Thanks to the polarization of light, these images reveal a surprisingly detailed and ordered magnetic structure around the black hole. It is important that these images are offered in polarized light because it allows us to ‘see’ and understand the geometry of the magnetic field around the black hole, a crucial aspect that cannot be captured with unpolarized light alone,” explained De Laurentis.
In the plasma that surrounds these mysterious colossal objects, the particles that revolve around the magnetic field lines give it a polarization pattern perpendicular to the field, which allows astronomers to observe in great detail what is happening in those regions and map the lines magnetic field of these cosmic monsters.
“Polarization is important in the study of black holes because it provides us with information about the geometry and dynamics of the magnetic fields around the black hole,” said the researcher. “These fields play a fundamental role in accretion processes and jet emissions, directly influencing the observation of black holes and our understanding of the physics that govern these extreme objects.”
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Compared to other black holes, Sagittarius A* is very quiet and calm, which is great, because at such a long distance, an active supermassive black hole can have a significant impact, with the ability to shape the fate of an entire galaxy.
In the case of M87*, for example, magnetic fields are essential for the release of powerful jets. It has been observed releasing jets of particles at nearly the speed of light for about five thousand light years in length. Seeing in the Milky Way’s central black hole the same magnetic structures that power long-range events in M87 suggests that these are underlying mechanisms shared by them all.
