Magnetic mysteries – a new photo of our supermassive black hole Sagittarius A*

In an astonishing leap forward in space exploration, scientists part of the Event Horizon Telescope (EHT) collaboration have recently unveiled a groundbreaking image of the supermassive black hole at the center of our Milky Way galaxy, known as Sagittarius A* (Sgr A*).

Imagine a place where gravity pulls so much that even light cannot escape. This is the reality at the heart of our galaxy, where the supermassive black hole Sgr (Sagittarius) A* resides. Although it’s located a staggering 27,000 light-years away, astronomers’ latest efforts have brought it closer to view than ever before.

Polarised light

For the first time, scientists have captured this black hole in polarised light, revealing the presence of strong, organized magnetic fields spiralling from its edge. These magnetic fields are similar to those observed around the M87 black hole, a giant residing in another galaxy. This similarity hints at the possibility that strong magnetic fields might be a common feature among all black holes, regardless of their size or the galaxies they inhabit.

The Event Horizon Telescope (EHT) collaboration, which produced the first-ever image of our Milky Way black hole released in 2022, has captured a new view of the massive object at the centre of our Galaxy: how it looks in polarised light. This is the first time astronomers have been able to measure polarization, a signature of magnetic fields, this close to the edge of Sagittarius A*. This image shows the polarised view of the Milky Way black hole. The lines overlaid on this image mark the orientation of polarisation, which is related to the magnetic field around the shadow of the black hole.

What makes this discovery even more fascinating is the method used to observe these magnetic fields. Light, as we know, is an electromagnetic wave that usually oscillates in various orientations. However, around these cosmic giants, the light becomes polarized, meaning it oscillates in a preferred direction. This special light gives scientists a unique tool to map the magnetic fields around black holes, offering new insights into how these mysterious objects interact with their surroundings.

Two “cousin” blackholes, M 87 and Sgr A*

The imagery of Sgr A* in polarised light is a significant achievement. Unlike its more stable cousin, M87*, Sgr A* is much more dynamic, constantly moving and changing, making it a challenging subject for astronomers.

Size comparison of the two black holes imaged by the Event Horizon Telescope (EHT) Collaboration: M87*, at the heart of the galaxy Messier 87, and Sagittarius A* (Sgr A*), at the centre of the Milky Way. The image shows the scale of Sgr A* compared to M87* and other elements of the Solar System, such as the orbits of Pluto and Mercury. Also displayed is the Sun’s diameter and the current location of the Voyager 1 space probe, the furthest spacecraft from Earth. M87*, which lies 55 million light-years away, is one of the largest black holes known. While Sgr A*, 27,000 light-years away, has a mass roughly four million times the Sun’s, M87* is more than 1000 times more massive. Because of their relative distances from Earth, both black holes appear the same size in the sky.

And an observatory the size of planet Earth

The success of this endeavour showcases the ingenuity and persistence of the global scientific community. Employing a network of eight telescopes around the world to act as a single Earth-sized observatory, the project has been a success.

A global map showing the radio observatories that form the Event Horizon Telescope (EHT) network used to image the Milky Way’s central black hole, Sagittarius A*. The telescopes highlighted in yellow were part of the EHT network during the observations of Sagittarius A* in 2017. These include the Atacama Large Millimeter/submillimeter Array (ALMA), the Atacama Pathfinder EXperiment (APEX), the IRAM 30-meter telescope, James Clark Maxwell Telescope (JCMT), Large Millimeter Telescope (LMT), Submillimeter Array (SMA), Submillimeter Telescope (SMT) and South Pole Telescope (SPT). Highlighted in blue are the three telescopes added to the EHT Collaboration after 2018: the Greenland Telescope, the Northern Extended Millimeter Array (NOEMA) in France, and the UArizona ARO 12-meter Telescope at Kitt Peak.

This discovery is not just about the awe-inspiring images it produces; it’s about understanding the universe a little better. It teaches us about the properties of black holes, the structure and strength of their magnetic fields, and the processes that occur as they feed on gas and matter. It’s a glimpse into the cosmic dance of nature’s most powerful entities.

The EHT’s observations are proof of human curiosity and our relentless pursuit of knowledge. They are a great opportunity to spark interest in STEM and inspire the next generation.

A classroom resource about polarised sunglasses

This resource for teachers was created by the Exploratorium Museum in San Francisco. We like it also because it talks about how polarised glasses reduce glare, which is one of the effects of light pollution.

Polarizing sunglasses cut road glare better in some positions than in others. When light reflects from water, asphalt, or other nonmetallic surfaces, it becomes polarized—that is, the reflected light is usually vibrating more in one direction than others. Polarizing sunglasses reduce this reflection, known as glare, but only when the polarizing lenses are oriented properly.
https://www.exploratorium.edu/snacks/polarized-sunglasses