NASA/ESA Hubble Space Telescope scientists spotted a black hole one billion times more massive than the Sun being expelled from its parent galaxy, becoming what astronomers define as a “rogue” black hole.

Many black holes are known to habit the center of galaxies, just like in our Milky Way. For galaxy 3C186, its black hole was classified as a quasar for it being extremely luminous and being surrounded by an orbiting accretion disk of gas.

Galaxy 3C186. Image credit:  NASA, ESA, and M. Chiaberge (STScI/ESA) /
Galaxy 3C186. Image credit: NASA, ESA, and M. Chiaberge (STScI/ESA) /

When Hubble astronomers saw that 3C186’s quasar was not located in the galaxy’s center, they hypothesized that it had to be kicked out from its original location.

The most likely scenario is that the black hole was ejected due to gravitational waves, having traveled at least 35,000 light-years from its original location. Now, the black hole is moving at a speed of 7.5 million kilometers per hour.

Telling a supermassive black hole to bug off

Astronomers propose that 2 billion years ago, two galaxies merged, with their massive black holes colliding with each other. As this new 3C186 galaxy formed, gravitational waves were produced, just like ripples on a pond after circling our fingers in it, but instead with two black holes encircling each other at blinding speeds. Because the black holes were not equal in their mass and rotational speed, the gravitational waves were irregular, being of a higher magnitude when traveling in a particular direction. In the final stages of the galaxy’s formation, a final wave occurred and flung away the resulting black hole, B3 1715+425, out of its center.

In comparison, the energy that caused the black hole to move is equivalent to 100 million supernovae exploding at the same time.

To further investigate the events, the black hole must be observed from the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, alongside other observatories. This will allow astronomers to have more precise measurements of the speed of the black hole and its accretion disk.

Luckily, the event was spotted thanks to the black hole at hand being a quasar. Otherwise, they would not be able to see anything because black holes absorb light and even gravity.

The highlight of this observation is the effect of gravitational waves, whose existence had not been confirmed until early 2016.

Gravitational wave: Undetected at first, now, they move black holes

The first evidence of the existence of gravitational waves occurred in September 2015. After the evidence had been documented, a scientific paper with 1,004 contributing authors was released for peer review.

A common analogy for gravitational waves is imagining a bowling ball rolling over a trampoline. The result is that the trampoline mat is warped as the bowling ball moves on its surface. The trampoline represents spacetime, and the bowling ball represents an object with a very high mass. This results in much lighter objects that cannot warp the trampoline as much, such as marbles, to be affected by the gravitational pull of massive objects, making it so the marbles go towards where the bowling ball resides on the trampoline.

What’s shocking is that the existence of gravitational waves was first proposed by Albert Einstein, almost 100 years ago. He believed that massive objects should cause gravitational waves, but that the most powerful of these events had to occur when two or more of these objects collide with each other.

The existence of gravitational waves was first proposed by Albert Einstein, almost 100 years ago. Image credit: R. Hurt/Caltech-JPL / NASA
The existence of gravitational waves was first proposed by Albert Einstein, almost 100 years ago. Image credit: R. Hurt/Caltech-JPL / NASA

According to LIGO scientists, any object with mass that accelerates produces gravitational waves, including humans, cars, and white sharks, but gravitational waves produced on Earth are too small to detect, and perhaps even impossible to recreate. The only way to study them is to look for massive objects in space, and apparently, the best ones for this purpose are black holes.

There are several types of gravitational waves. A massive spinning object produces continuous gravitational waves. Any imperfection on the object will generate gravitational waves as it spins. If the rotation is constant, so are the gravitational waves it emits, just like a singer holding a sharp note. Researchers have even tried to convert continuous gravitational waves into sound. A simulation is available here.

Another type of gravitational wave is compact binary inspiral gravitational waves, produced by orbiting pairs of massive but dense objects. Apparently, the events of 3C186 enter in this category if the theory is proven. The mechanism that generates the gravitational waves occurs as thousands of years pass by. As the black holes orbit each other, they speed up and lose energy, getting closer as time passes by. This causes the system to emit stronger gravitational waves.

So far, scientists were not sure about what happened after the encircling black holes finally stopped orbiting each other and merged into a single supermassive body. The most plausible theory would be that in the end, both objects collapse into each other and cause a massively strong gravitational wave, which is apparently able to kick off the resulting object out of its place in spacetime.

Source: Space Telescope