Mathematically speaking, they’re all singularities — but this particular black hole is really one of a kind.
Astronomers, including researchers from the University of Utah, have discovered one of the only confirmed intermediate-mass black holes, a long-sought astronomical object whose detection helps illuminate the process of galaxy formation while offering further testimony of mankind’s insatiable ambition to comprehend the cosmos.
“This is an important step in understanding the process of galaxy assembly, the process of how we got from the Big Bang to having a sun with a planet around it in a galaxy like the Milky Way. We’re seeing the fossils of that type of assembly here and that’s what makes it exciting,” said Anil Seth, professor of physics and astronomy at the University of Utah and co-author of the findings published in The Astrophysical Journal.
The new black hole, going by the official if un-catchy name of B023-G078, tells the story of what happens when stars collide. In this case, when big and little galaxies meet. The hole is what’s known as a “stripped nuclei,” comprised of the remnants of a small galaxy that’s fallen into a bigger one, leaving the dense nucleus in orbit around the larger galaxy.
It contributes to the field by confirming the presence of a scarcely known phenomenon that falls between two extremes in the world of black holes and helps inform theories about the creation of supermassive black holes at the center of many galaxies.
“There are two different types of black holes that we know about in the universe. There’s the ones that are formed when stars blow up as supernovae and leave behind a mass similar to the mass of our sun. Then there’s these really massive black holes we find at the centers of galaxies, and they’re typically more than a million times the mass of the sun,” explained Seth.
“The most exciting result is that this black hole is in the gap between those. And that is most likely telling us that it was the center of a galaxy, which is also shown because of the wide variations of elements within the star cluster” surrounding the black hole, said Seth.
The hole was discovered in the galaxy Andromeda, which, despite its relative cosmic proximity, remains a mind-warping 2.5 million light-years away, a distance whose visual apprehension testifies to the prowess of modern optical technology. But that technology is highly coveted, and the limited supply of big telescopes needed for research has resulted in a bottleneck of proposals from astronomers eager to test their theories of space.
More than star gazing
The hole was discovered with data collected from the Hubble Space Telescope and the Gemini Observatory at the Mauna Kea summit on the big island of Hawaii.
In addition to the massive, 8.1-meter-diameter optical mirrors, the Gemini telescope is equipped with “laser guide star adaptive optics,” which corrects for atmospheric wobble, the twinkling tendency favored by romantics but best avoided for astronomers peering eons into the past.
These capabilities make the Gemini the apple of many an astronomer’s eye, which makes for a highly competitive field for research proposals. For instance, Seth first submitted a proposal to look for the intermediate mass B023-G078 over 10 years ago, then waited another four years for approval before the project could begin.
Of course, gathering the light data is just the beginning, as the field of astronomy increasingly relies on post observational technology and analysis. Astronomers looked at light emission data gathered from HST to determine the mass and composition of the B023-G078 cluster, a process called spectrography, before turning to Gemini data to measure the cluster’s velocities.
Renuka Pechetti, a postdoctoral research scholar at Liverpool John Moores University who was a Ph.D. student with Seth during the study, helped make the discovery by running the observation data through different models meant to determine the relationship between two primary measurements — mass and velocity — showing how modern astronomy requires more than a view of the open sky.
“We cannot just give the observed data directly. It contains a lot of dust and you have to remove that. And then sometimes it contains foreground stars, like Milky Way stars, and you have to mask those out as well. You change one parameter of the model then see what happens to the platform, then change another and so on until you take all of those biases into account and consider all errors,” said Pechetti. “What I found most exciting was, despite all the biases I considered for this cluster, the black hole didn’t go away and it was still there. It’s a robust detection. Before there have not been robust detections. And we need this to know more about the evolution of black holes along with their galaxies.”
Science or art?
Discoveries like B023-G078 are enabled by public funding in institutions like NASA. And though field astronomy receives consistent funding, Seth says, researchers still hope for more investment to boost telescope inventories and grant projects in a field where fewer than 1 in 8 research proposals are approved.
Even as recent years have seen increased political appetites for American research and development, spending on astronomy projects are dwarfed by other research priorities with immediate application at institutions like the Department of Defense. But unlike traditional applied sciences, astronomy seems to fulfill a different mandate.
“It’s hard to argue that astronomy is practical, right? So that’s not how you justify the funding,” said Seth. “It’s a lot like art in the sense that it provides a fundamental understanding of where we are in the universe, who we are, and how we got here. It engages the public in a way very few other sciences do.”
For Pechetti, who plans to continue research into intermediate mass black holes, astronomy is about satisfying a fundamental human inquisitiveness. Inquiry comes first, practicality follows.
“I think curiosity drives everything for us. And whether it’s astronomy or any kind of applied science, a lot of discoveries are made because someone was curious about something. Even though it was not applied science at the time, it’s got an application later. I think in the future all these discoveries will improve our knowledge and only make the sciences better,” said Pechetti.