Sagittarius A* Black Hole

The sharp image of the Sagittarius A* black hole

Black are cosmic structures with a gravitational field so strong that not even light can escape. Supermassive black holes can have masses of millions or even billions of Sun and are typically found at the centers of galaxies. At the center of the Milky Way, the region known as Sagittarius A* (Sgr A*) has a mass of approximately four million solar masses and is located about 26,000 light years from World. Black holes cannot be observed directly, but they can be studied indirectly through their interactions with surrounding matter and the radiation they create around their event horizon. In 2019, the Event Horizon Telescope (EHT) collaboration obtained the first direct image of the supermassive black hole M87* at the center of the M87 galaxy. Following this success, the EHT team focused on observing Sagittarius A* at the center of the Milky Way and succeeded in capturing its first direct image in 2022. This discovery has provided crucial insights into the physical properties of black holes and enabled new tests of Einstein’s General Theory of Relativity.

Technical Characteristics of Sagittarius A*

The fundamental physical properties of Sagittarius A* can be summarized as follows:

• Location: Sagittarius constellation, center of the Milky Way,
• Distance: Approximately 26,000 light years,
• Mass: Approximately four million solar masses,
• Diameter: The event horizon’s diameter is approximately 24 million kilometers,
• Event Horizon: The Schwarzschild radius is approximately 12 million kilometers,
• Rotation Speed: It likely possesses a high angular momentum, though its exact value remains unknown,
• Motion of Surrounding Gas: Matter orbits the event horizon in just a few hours, making observation more challenging compared to M87*. The most distinctive feature of Sagittarius A* is its much smaller size relative to M87*. While M87* has a mass of about 6.5 billion solar masses, Sgr A* is only about four million solar masses. This results in much faster motion of surrounding gas and complicates the observational process.

First Image of Sagittarius A*

First image of the Sagittarius A* black hole – ESO

Event Horizon Telescope (EHT) and Techniques Used

The Event Horizon Telescope (EHT) was used to image Sagittarius A*. The EHT is a global network of eight radio telescopes synchronized across different regions of Earth. This network operates using very long baseline interferometry (VLBI) to create a virtual telescope the size of the planet.

The telescopes used in this network include:

• ALMA (Chile)
• IRAM 30m (Spain)
• JCMT (Hawaii)
• LMT (Mexico)
• SMT (Arizona, USA)
• SPT (South Pole, Antarctica)

This telescope array detected radiation emitted by the superheated plasma surrounding the black hole, using radio waves with a wavelength of 1.3 mm. The collected data were processed using advanced algorithms to produce the first direct image of Sgr A*.

Significance of the Sagittarius A* Image

The image reveals a bright ring formed by the bending of radiation from hot gas around the black hole, with a dark region at its center corresponding to the black hole’s shadow.

• Bright ring: This region is created by gravitational lensing of light emitted by gas orbiting the black hole.
• Dark central region: This is the black hole’s shadow, corresponding to the event horizon.
• Asymmetric brightness distribution: Indicates the presence of matter flows and magnetic fields around the event horizon.

This image largely agrees with the structure of the black hole shadow predicted by Einstein’s General Theory of Relativity.

Scientific Significance of the Discovery

The direct imaging of Sagittarius A* holds major scientific importance:

Testing General Relativity

The obtained image matches precisely the structure of black holes predicted by Einstein’s General Theory of Relativity.

It provides a critical testing environment for understanding how black holes warp spacetime.

Impact on Galaxy Evolution

Sagittarius A* is in a interaction relationship with the Milky Way and can influence the galaxy’s structure and evolution. Its interactions with surrounding matter may alter star formation processes and galaxy dynamics.

Magnetic Fields and Jets

The image provides new data on the nature of magnetic fields around Sagittarius A*. It will contribute to the development of new models explaining how supermassive black holes accrete matter and produce high-energy jets.