Sagittarius A*
There’s nothing in the whole universe as mysterious and fascinating as black holes. These dense, dark and elusive objects have been researched and studied for decades, capturing the interest of some of the world’s greatest physicists.
Sagittarius A*: The Mysterious Heart of Our Galaxy
The idea of black holes has been around for a while. Back in the late 1700s, John Michell and Pierre-Simon Laplace thought up the idea of “dark stars” with gravity so strong that not even light could escape. Fast-forward to 1967, and physicist John Archibald Wheeler coined the term “black hole”. Even earlier, in 1916, Karl Schwarzschild came up with the first modern description of what we now call a black hole, using Einstein’s theories.
It's only in recent years, however, that scientists started gazing towards the supermassive black hole nestled at the heart of our galaxy: Sagittarius A. This elusive giant is hanging quietly out about 26,000 light-years away from us, right in the centre of our galaxy, in the direction of the constellation Sagittarius. Don’t let the “quietly” part fool you, though. The forces at play around this black hole are anything but peaceful!
At the heart of our galaxy, Sagittarius A* whispers dark secrets
With a mass equivalent to about 4 million Suns, it exerts an undeniable gravitational influence over its surroundings. The region surrounding Sagittarius A*, in fact, pulses with unseen energies, as matter spirals inexorably towards its dark embrace. Here, violent processes unfold, creating phenomena that challenge our understanding of the universe.
It's this tumultuous phenomenon that in the end gave up Sagittarius A*, enabling astronomers to capture its first-ever image. But how did this happen?
On May 12, 2022, the Event Horizon Telescope (EHT) team revealed the first-ever image of this enigmatic black hole. This wasn't just a snapshot; it was a groundbreaking achievement. The image showed a glowing ring of gas surrounding a dark central region, the black hole’s shadow, giving us a glimpse of this behemoth's event horizon—the point beyond which nothing, not even light, can escape.
Getting an image of a black hole is no small feat. The EHT isn't a single telescope, but a network of radio observatories scattered around the globe, working together to form a planet-sized telescope. This technique, called very long baseline interferometry (VLBI), allows astronomers to capture incredibly detailed images. Think of it as combining the power of multiple telescopes to create one super-telescope.
Since the groundbreaking observations of M87 (the first black hole ever captured in an image) and Sgr A*, more telescopes have been added to the Event Horizon's network. But does this expansion suffice to produce sharper images or capture black holes located even farther away? After all, Sgr A* and M87 were prioritized due to their larger angular sizes in the sky, whereas black holes in distant galaxies appear much smaller from our vantage point.
To achieve higher resolution and enhance imaging capabilities, the EHT would require further expansion of its aperture. However, given the constraints of Earth's size, a potential solution lies in augmenting the array with a space-based component. While this is only an idea for now, imagine the possibilities that would open up with such an addition!