Surprising new image of the Milky Way's supermassive black hole with its magnetic field released!

The EHT collaboration recently published a new image of the supermassive black hole at the centre of the Milky Way. In the image, it is possible to map the magnetic fields.

EHT collaboration releases new image of the supermassive black hole Sgr A*. Credit: EHT
EHT collaboration releases new image of the supermassive black hole Sgr A*. Credit: EHT

The EHT collaboration is responsible for imaging the black holes Sgr A* and M87* that inhabit the centre of the Milky Way and the M87 galaxy, respectively. Using radio astronomy techniques, they were able to observe the two black holes in campaigns carried out since 2017. The collaboration uses a set of telescopes spread across the Earth. In April 2019, EHT researchers stopped the world by showing the first photo of a black hole.

Years of work resulted in one of the most famous photos in Astronomy and an important milestone in the history of Science. To obtain more information and study in more detail, other observation campaigns have been carried out in recent years.

This week, the EHT collaboration showed another important result of the observations. They used the polarisation of light to map the magnetic fields that are in the environment of the Sgr A* black hole. Understanding the dynamics of magnetic fields is important as they are crucial in the physical processes that take place in the black hole environment

Sgr A*

The supermassive black hole in the Milky Way is called Sagittarius A* or Sgr A* as it is located in the constellation Sagittarius. This object has around 4 million solar masses and a diameter slightly smaller than that of Mercury's orbit. It is located at a distance of 26 thousand light years from Earth.

Despite its mass, Sgr A* does not gravitationally influence the Solar System. The central black hole can only influence a relatively small region around it, such as the orbit of the star S2.

Understanding Sgr A* can give us important insights into how the Milky Way evolved. The black holes that inhabit the centres of galaxies appear to have co-evolved with the galaxy itself. Furthermore, the habitability of a galaxy can be related to the supermassive black hole that controls processes such as the number of stars.

Event Horizon Telescope collaboration

The Event Horizon Telescope (EHT) collaboration emerged with the mission of taking the first photograph of a black hole in history. The first campaign took place in April 2017, which led to the photo of M87* released in April 2019. In the same campaign, Sgr A* was observed and the photo was released in 2022.

Black buraco Sgr A*
Photo of the Sgr A* black hole released in 2022 by the EHT collaboration. Credit: EHT

The EHT consists of 11 telescopes spread across 9 points on the Earth's surface. Some examples are the South Pole Telescope located in Antarctica, the ALMA located in Chile and the Submillimeter Telescope in the United States. The data is processed and analysed at MIT, also located in the United States.

Campos magnéticos do Sgr A*

On 27 March, 2024, the EHT collaboration released another image of Sgr A* containing the ambient magnetic fields. Mapping magnetic fields is a challenge for environments as variable and dynamic as Sgr A*. The team of researchers uses polarimetry techniques that consist of measuring the polarisation of light.

Comparison of the magnetic fields of black holes M87* and Sgr A*, respectively. Credit: EHT
Comparison of the magnetic fields of black holes M87* and Sgr A*, respectively. Credit: EHT

Light consists of an oscillating electromagnetic wave that can sometimes have a preferred orientation. By using instruments capable of observing certain orientations, it is possible to map how the magnetic field is distributed. This is possible because electric fields and magnetic fields are perpendicular.

Importance of magnetic fields

Magnetic fields play a crucial role in understanding black holes as they are involved in a variety of processes. One of them is the accretion process itself where the transport of angular momentum is caused by friction from magnetic fields causing material to spiral towards the black hole.

Another important process associated with magnetic fields is the production of relativistic jets. On the official site of EHT, the similarity of the magnetic fields of Sgr A* and M87* could indicate a hidden jet emitted by Sgr A*. Since the M87* has a well-known jet since the 2000s.

Open questions remain

Both the accretion process and the production of relativistic jets are still processes that have open questions. Computer simulations using equations of general relativity, electromagnetism and hydrodynamics attempt to answer these questions with theoretical models. However, observations are necessary for scientific basis.

Reference of the science news:

EHT Collaboration 2024. First Sagittarius A* Event Horizon Telescope Results. VII. Polarization of the Ring. The Astrophysical Journal Letters