The black hole at the centre of our galaxy, named Sagittarius A* (Sagittarius A-Star), has been an astronomical enigma for decades – we can clearly observe the effects of its enormous gravitational pull.
Yet, this same gravitational pull makes it impossible to see with typical observational techniques. This is precisely what makes the recent picture of Sagittarius A* captured by the Event Horizon Telescope (EHT) so significant.
The EHT is a collaboration of telescopes from across the globe, all working in tandem to observe specific objects, effectively forming an earth-sized radar dish and thus allowing for the collection of genuinely humongous amounts of data.
This is especially important in capturing images of black holes like the one captured three years ago of M87*, the black hole at the centre of the galaxy Messier 87.
However, the team of researchers faced a lot more problems this time around, largely due to Sagittarius being so much closer to Earth than M87*. Due to how far and large M87* is, the energy emitted by the objects orbiting around it doesn’t differ significantly over time, making its observation relatively easy.
In stark contrast, Sagittarius is not only closer but also smaller than M87*, which means that the energy emitted by the bodies orbiting Sagittarius can change on time scales as short as 5 to 15 minutes, with equivalent changes in M87* taking around a week.
This meant that instead of generating only one image of Sagittarius, the data led to the EHT team generating thousands of pictures, all of which averaged into the final image they released. The most prominent features of the image are the three brighter ‘knots’, as one researcher called them. The positions of these knots were actually different in each image, which highlighted the importance of averaging the photos.
One of the main observations that came from this imaging was the fact that we face the Blackhole face-on, especially because previous observations suggested the opposite. Since the EHT team successfully captured an image of a second black hole in Sagittarius, their next goal is to create a movie that allows them to discern its physical properties better and see what’s truly going on at the heart of our galaxy.
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