Recently, NASA’s Nuclear Spectroscopic Telescope Array (NuSTAR) has captured images of two galaxies colliding. Collectively known as Arp 299, these galaxies are located 134 million light-years away from Earth. The high-energy X-ray images provide a clear view of the ongoing interaction.
The black holes are located on the right side of the pair, actively gorging on gas, while their partner is either one of the two is active or obscured by gas and dust. In these images, X-rays with energies of 4-6 kiloelectron volts appear red, those with energies of 6-12 kiloelectron volts are green, and 12-25 kiloelectron volts are blue.
Image of two colliding galaxies, with the gas and dust from the left galaxy being pulled into the black hole at the center of the right galaxy.
NuSTAR has identified that the black hole on the right of this pair is attempting to absorb the gas and dust from the left galaxy. This discovery may help scientists better understand the process of galactic collisions, how black holes operate at the center of each galaxy, and the subsequent growth of galaxies. Previously, NASA had also detected signs of a supermassive black hole in Arp 299 based on low-energy X-ray traces.
However, scientists still do not fully understand the interaction between the two black holes of these galaxies, as each galaxy harbors a massive black hole at its center. It remains unclear whether both black holes are consuming gas from the other galaxy or if the larger black hole will engulf the smaller one. Current information is insufficient to provide definitive answers.
New X-ray data from NuSTAR – layered over visible light images from NASA’s Hubble Space Telescope – shows that the black holes on the right are, in fact, very active. As they consume gas, the energy process near the black holes heats electrons and protons to hundreds of millions of degrees, creating an extremely hot plasma, or corona, that increases visible light to high-energy X-rays.
Light emitted from the active black hole on the right indicates it is extremely active, with temperatures reaching hundreds of millions of degrees Celsius.
NASA scientists combined images from the Hubble Space Telescope to observe the light from these two galaxies. They discovered that the black hole on the right is very bright, indicating that its temperature is rising significantly. Meanwhile, the black hole on the left shows no remarkable signs and is even obscured by a massive cloud of gas moving toward the right black hole.
As a result, scientists speculate that only the right black hole is active and consuming the left galaxy. They are also investigating what will happen as these two galaxies move closer together, where the two black holes will eventually meet at the center.
There is a hypothesis that the larger black hole will consume the smaller one, resulting in the formation of a new supermassive black hole. However, there is also speculation that as the two black holes approach each other, tidal forces at the mouths of the black holes could cause them to repel and push both black holes apart.
Scientists continue to observe this phenomenon to find answers. This is also the first time scientists have been able to observe the collision of two galaxies through high-energy X-ray images. Previously, observing black holes at the centers of galaxies was quite challenging due to low-energy X-ray images and light being obscured by dense clouds of gas and dust.
