A group of researchers from Japan’s National Astronomical Observatory (NAOJ) has suggested that the image of the supermassive black hole at the center of the Milky Way, known as Sagittarius A*, may not be accurate. The original image was produced by the Event Horizon Telescope Collaboration and released in May 2022. It depicted the black hole as a dark region surrounded by a bright ring, which represents the accretion disk. However, the NAOJ team posits that the disk is more likely elongated, as detailed in their paper published in the Monthly Notices of the Royal Astronomical Society.
The image of Sagittarius A* reveals a massive black hole, approximately four million times the mass of the Sun. This was the first depiction of the black hole at the core of the Milky Way and the second black hole image produced by the Event Horizon Telescope (EHT), following the 2019 release of the image of the black hole Messier 87 (M87).
Black holes are areas in spacetime characterized by intense gravitational fields, preventing light from escaping once it crosses a boundary known as the event horizon. Surrounding this horizon is a field of superheated material, called the accretion disk. The recent study by the NAOJ team concentrated on this accretion disk, proposing an alternative shape than what was previously depicted.
The EHT is an extensive radio observatory linking multiple radio telescopes worldwide. It captures the silhouette of black holes against the brightly shining accretion disks. Miyoshi Makoto, an astronomer at NAOJ and co-author of the recent study, stated in a Royal Astronomical Society release that the ring seen in the original image could have resulted from errors in EHT’s imaging analysis, creating an artefact instead of depicting the true astronomical structure.
The NAOJ researchers re-examined the 2017 data used for the EHT’s initial image, employing a different analytical method. Their findings suggest an elongated disk rather than the doughnut shape depicted in the 2022 release. The M87 black hole also appears ring-shaped in EHT’s imagery; subsequent research developed a polarized image revealing its magnetic field structure.
In August, the EHT introduced an updated method designed to enhance the resolution of their black hole images, potentially leading to clearer and more accurate observations of black holes, including Sagittarius A*. Furthermore, there are plans for a future space-based mission that could sharpen EHT’s images. This concept involves a $300 million mission to investigate the photon rings of black holes, dubbed the Event Horizon Explorer.
Advancing knowledge of black holes and other extreme cosmic phenomena, such as neutron stars and their collisions, is essential for deepening the understanding of gravitational dynamics and the core of the Milky Way.
