Just like T-shirts, black holes come in many sizes. The size of a black hole mostly depends on how massive the star was before it ran out of fuel, exploded and collapsed under its own extreme gravity. The bigger the black hole, the stronger and larger its effect on the fabric of space and time. Here is the twist!

In a recent study, astronomers found that even tiny black holes have immense power to shape galaxies—far more than previously thought.

Black holes can rip apart a star that moves close by, even the tiniest ones, known as stellar-mass black holes. Sometimes this meet and greet releases massive energy in the form of powerful invisible jets, appearing just like the water jet used by firefighters to put out a fire.

Unlike water jets, the jets from black holes can travel through space for many light years. These jets move super fast and interact with the surrounding gas as they travel, creating massive shockwaves, known as bow shocks. Discovering these bow shocks is therefore a good indication of black hole jet activities and their long term effects in shaping far away galaxies. 

Recently, an international team of astronomers found massive bow shocks caused by the jets from two stellar-mass black holes, GRS 1915+105 and Cygnus X-1 (the first stellar-mass black hole ever discovered), using the MeerKAT radio telescope in South Africa. 

Whereas before, only supermassive black holes were considered to have far-reaching effects on their host galaxies, astronomers now have solid evidence that even small black holes can significantly impact their galactic environments, potentially shaping the galaxy's evolution through cosmic time. 

With the new MeerKAT discovery, scientists think that similar shockwaves may be hiding in our Milky way galaxy. Scientists are now actively looking for bow shock structures in our galaxy caused by the central black hole activities from thousands of years ago, so as to trace the history of our galactic black hole.

Image: Artist impression of a black hole system generating powerful jets and a massive bow shock structure. Credits: Artist impression by Danielle Futselaar, ASTRON