SALT LAKE CITY — Within a galaxy that spans many light years and is over 13 billion years old, it makes sense that major astronomical discoveries come so few and far between.
Located in the Milky Way is Omega Centauri, a global cluster of millions of stars – so dense towards the center that it becomes impossible to distinguish individual stars – visible only as a tiny speck in the night sky from southern latitudes.
But within that cluster is something astronomers have been searching for and arguing about for nearly a decade, and something a new study led by researchers from the University of Utah and the Mac Planck Institute for Astronomy revealed: Omega Centauri is home to a central black hole. .
“This is a once-in-a-lifetime kind of discovery. I’ve been excited about it for nine months straight. Every time I think about it, I have trouble sleeping,” said Anil Seth, associate professor of astronomy. at the U. and co-principal investigator of the study.
‘At the level of Bigfoot’
The study, which was published in the journal Nature on Wednesday, explained that black holes come in different mass ranges.
Common black holes include stellar black holes, ranging from one to several tens of solar masses, and supermassive black holes, with masses up to billions of suns.
More notoriously elusive and undetected — until now — are intermediate-mass black holes, the type discovered by the research team.
“These intermediate-mass black holes are at the level of Bigfoot. Observing them is like finding the first evidence of Bigfoot – people are going to go crazy,” said Matthew Whittaker, a US undergraduate student and co-author. of study.
“Needle in a Haystack”
Omega Centauri appears to be the core of a small, separate galaxy whose evolution was interrupted when it was swallowed by the Milky Way, the paper said. The current state of galaxy evolution suggests that these earliest galaxies should have had intermediate-sized central black holes that would have grown over time.
But how do you go about finding one?
Seth and Nadine Neumayer, a group leader at the Max Planck Institute and principal investigator of the study, first began researching how to better understand the formation history of Omega Centauri in 2019.
They realized that if they found fast-moving stars around its center, they could finally solve the question about the central black hole of the cluster by measuring the black hole’s mass.
This search for the stars fell into the lap of Maximilian Häberle, a PhD student at the Max Planck Institute. Häberle led the charge of developing a giant catalog of the motions of stars in Omega Centauri, measuring velocities for 1.4 million stars by studying over 500 Hubble images of the cluster.
The challenge with this was that most of the images available to Häberle were taken to calibrate Hubble’s instruments, not to aid groundbreaking scientific discoveries.
However, with over 500 images, this unintentional dataset served its purpose.
“Searching for high-velocity stars and documenting their motion was the proverbial search for a needle in a haystack,” Häberle said. In the end, Häberle not only had the most complete catalog to date of the motion of stars in Omega Centauri, he also found seven needles in his archival haystack—seven fast-moving stars in a small region at the center of Omega Centauri .
DISCLOSURE
However, the work did not end with finding these seven stars. With seven stars, all with different speeds and directions of motion, the researchers were able to separate the various effects and determine that there is, in fact, a central mass in Omega Centauri, with the mass of at least 8,200 suns.
Furthermore, the images do not suggest any visible objects at the location of that central mass as expected for a black hole.
And more analysis led to more good news for the team. As the paper explained, a single high-velocity star in the image may not belong to Omega Centauri. It could be an out-of-group star passing just behind or in front of the center of Omega Centauri by chance. On the other hand, the observations of seven such stars cannot be a coincidence and leave no room for explanations other than the presence of a black hole.
checkmate
Moving forward
The team now plans to build on their monumental findings by further examining the center of Omega Centauri. Seth is leading a project that received approval to use the James Webb Space Telescope to measure the high-speed motion of stars toward or away from Earth.
As future instruments emerge that can determine the positions of stars with even greater precision than Hubble, the goal is to determine how stars accelerate and how their orbits curve—however, that project will fall into the hands of future generations. of researchers.
However, this discovery builds the case for Omega Centauri as the core region of what was once a galaxy engulfed by the Milky Way billions of years ago.
For people interested in hearing directly from the researchers, Seth will present the team’s findings on August 8 at 7:00 pm at the Clarke Planetarium IMAX Theater in Salt Lake City. Meanwhile, the full study can be found online.
“I think extraordinary claims require extraordinary evidence. This is truly extraordinary evidence,” Seth said.
