Most of the major galaxies in the universe host a supermassive black hole at their center. For instance, the one lurking at the heart of the Milky Way is known as Sagittarius A* (pronounced “Sagittarius A-star”). This monster black hole is about 4 million times more massive than the sun and was only recently confirmed following ground-breaking telescope observations, as the Inquisitr previously reported.
Even some dwarf galaxies are known to have a central supermassive black hole, per the Inquisitr.
When these galaxies — dwarf or otherwise — find themselves on a collision path with one another, something happens to the black holes nestled within. Similar to their host galaxies, which crash into each other and ultimately morph into something more grandiose, these supermassive black holes also collide and go on to form bigger objects.
This spectacular phenomenon — black holes on the brink of collision within merging galaxies — was recently observed with great clarity in what NASA describes as the “best view yet” of a black hole merger.
This is the first time that astronomers have been able to spot pairs of black holes interacting during the final throes of a galactic merger. Since coalescing galaxies are typically shrouded by a dense cloud of galaxy-forming material, taking a peek at their cores during the last stage of collision has proven difficult in the past, notes Phys.org.
These new and unique sightings are the result of an extensive survey of nearby galaxies, published yesterday in the journal Nature. Unlike previous observations of galactic mergers, which only managed to photograph earlier phases of the phenomenon, this survey captures the final stage of the union between different pairs of galactic cores, or nuclei — in this case, the black holes at the center of galaxies.
In each of these cases, the galactic cores are imaged in a tight embrace that brings them as close as 3,000 light-years from each other. By comparison, in prior observations of colliding galaxies, the inner black holes were still circling each other, photographed at 10 times the distance observed in the new survey.
“Seeing the pairs of merging galaxy nuclei associated with these huge black holes so close together was pretty amazing,” said study lead author Michael Koss, an astronomer at Eureka Scientific Inc. in Washington.
As NASA explains, finding galaxy cores that are so close to each other is a rarity. This incredible work owes its success to the sharp vision of NASA’s Hubble Space Telescope and the W.M. Keck Observatory in Hawaii. Endowed with infrared instruments, these observatories were able to peer through the thick walls of gas and dust surrounding the cores of merging galaxies and take high-resolution images of supermassive black holes on the verge of blending into “mega black holes.”
The merging galaxies caught the team’s attention due to their very luminous cores — brighter than what astronomers usually see in similar galaxies without an active nucleus. This is because the supermassive black holes at their center are constantly gorging on gas kicked up by the galactic collisions.
This makes the black holes grow faster and larger as the galactic merger progresses and emit beacons of X-rays that alerted the astronomers to their location.
“People had conducted studies to look for these close interacting black holes before, but what really enabled this particular study were the X-rays that can break through the cocoon of dust,” Koss said in a statement. “We also looked a bit farther in the universe so that we could survey a larger volume of space, giving us a greater chance of finding more luminous, rapidly growing black holes.”
According to NASA, this is “the largest-ever survey of the cores of nearby galaxies” based on high-resolution images from Hubble and Keck. The astronomers combed through the vast archives of the two observatories and looked at almost 500 galaxies located around 330 million light-years from Earth — all about the size of the Milky Way.
“Computer simulations of galaxy smashups show us that black holes grow fastest during the final stages of mergers, near the time when the black holes interact, and that’s what we have found in our survey,” said study co-author Laura Blecha of the University of Florida in Gainesville.
As she points out, this phenomenon could shed new light into how some of the supermassive black holes at the center of galaxies “got to be so monstrously big” in the aftermath of a galactic merger.