Supermassive Black Holes on a Collision Course!
Let’s first start with a brief description of Black Hole: A black hole is an astronomical object with extremely strong gravitational forces that prevent anything, including light, from escaping once it enters a region called the event horizon. It is formed when a massive star runs out of fuel and collapses under the influence of its own gravity.
As the star collapses, it becomes denser and its gravitational field becomes stronger, eventually becoming so powerful that nothing can escape from it. Black holes come in different sizes, from those that are a few times more massive than the Sun to supermassive black holes that are millions or billions of times more massive than the Sun and are found at the center of most galaxies, including our own Milky Way.
In the early Universe, there were a large number of dwarf galaxies present just a few hundred million years after the Big Bang. As these galaxies merged with each other, they grew in size and mass, while the giant black holes inside them also merged. This process is believed to be the key to the growth and evolution of galaxies, and likely played a role in the early history of our own galaxy.
Astronomers have now discovered the first evidence of giant and potentially supermassive black holes in dwarf galaxies that are on a collision course. This is going to be exciting as they will be able to observe dwarf galaxy collisions closer to home to gather insights into this process.
What this event is all about?
This release includes two composite images presented side by side, separated by a thin white line. The image on our left features two colliding dwarf galaxies in the late stages of merging into one larger galaxy. The image on our right features two colliding dwarf galaxies in the early stages of merging.
Astronomers have made a ground-breaking discovery, identifying two pairs of dwarf galaxies that are featuring giant black holes that are heading towards a collision with each other. One of the pairs is in the advanced stages of merging in a galaxy cluster called Abell 133, located around 760 million light-years away from Earth.
The researchers have named this merging pair “Mirabilis” after a species of endangered hummingbird. The other pair is in the early stages of merging in the galaxy cluster Abell 1758S, located about 3.2 billion light-years away from Earth. The connection between the two galaxies is forming a bridge of stars and other materials, which is acting as the leading edge of the cosmic collision.
While astronomers have previously observed black holes on a collision course in large galaxies that are relatively close by, it is the first time such giant black holes have been discovered at the center of dwarf galaxies. Although finding black holes in dwarf galaxies is much more challenging, this discovery opens up new possibilities for further research.
How was it detected?
Dwarf galaxies, which contain stars with a total mass less than 3 billion Suns, or about 20 times less than the Milky Way, are believed to merge in order to grow into larger galaxies. However, due to their faintness at great distances, observing the first generation of dwarf galaxy mergers has been impossible with current technology. Previous attempts to observe dwarf galaxy mergers closer to Earth had also been unsuccessful.
To overcome these challenges, astronomers conducted a systematic survey using deep Chandra X-ray observations and combined them with infrared data from NASA’s Wide Infrared Survey Explorer and optical data from the Canada-France-Hawaii Telescope. Chandra was particularly useful in identifying pairs of bright X-ray sources in colliding dwarf galaxies, as material surrounding black holes can be heated up to millions of degrees, producing significant amounts of X-rays. Through this method, the team discovered two examples of dwarf galaxies featuring pairs of bright X-ray sources, indicating the presence of two black holes.
Effects of Mergers
The hierarchical theory of galaxy evolution suggests that small galaxies merged in the early Universe, forming larger and larger ones through multiple mergers. If these early galaxies contained black holes, which we know existed at that time, then those black holes should have also merged. These observations not only help determine if this process occurred in the early Universe, but also provide insight into the history of our own galaxy. Dwarf galaxies are in some ways like the ancestors of our galaxy, evolving over billions of years to eventually create larger galaxies such as the Milky Way.
The Milky Way is still cannibalizing dwarf galaxies today, some 13.6 billion years after it first began to form. Currently, astronomers know that about 50 dwarfs surround the Milky Way. Our galaxy is ingesting some of them, like the Sagittarius Dwarf. Fortunately, Milky Way isn’t set to collide with another galaxy, of similar or even bigger than ours, any time soon.
But if you do happen to be around in 4 billion years, heads up for the impact with Andromeda.