Mysterious star movement in Omega Centauri may finally be explained

Could the decades-long mystery of unusual star movements in Omega Centauri, the largest star cluster in the Milky Way, finally be solved?

Located in the constellation Centaurus, Omega Centauri is a massive cluster containing nearly ten million stars. Astronomers have long puzzled over the unexpected high velocities of stars near its center. 

The debate centers on whether these movements are caused by an “intermediate-mass black hole” (IMBH), weighing around 100,000 times the mass of the Sun, or a cluster of smaller “stellar-mass” black holes, each just a few times the Sun’s mass.

A cluster or a singular giant?

Astronomers have theorized that Omega Centauri’s center might host a cluster of black holes, naturally forming through stellar evolution.

However, experts also speculated that most of these black holes would have been ejected over time due to gravitational interactions with other stars, which made the presence of a single intermediate-mass black hole more plausible.

The case for an IMBH gained further strength when new evidence suggested that certain fast-moving stars near the cluster’s center could only achieve such speeds through interactions with a massive black hole.

Formation of supermassive black holes

IMBHs are particularly intriguing to astronomers as they might represent a missing link between stellar-mass black holes and supermassive black holes. 

Stellar-mass black holes form when massive stars collapse, while supermassive black holes – millions to billions of times the Sun’s mass – dominate the centers of large galaxies.

Understanding how supermassive black holes form – possibly starting as IMBHs – remains one of astronomy’s greatest mysteries.

Star velocities in Omega Centauri

In a fresh approach to this enigma, researchers from the University of Surrey, the Instituto de Astrofísica de Canarias (IAC, Spain), and the Annecy-le-Vieux Laboratoire de Physique Théorique (France) examined the anomalous star velocities in Omega Centauri using a new type of data: pulsar accelerations.

Pulsars are remnants of dying stars, typically weighing up to twice the Sun’s mass but only about 20 kilometers in diameter. Spinning up to 700 times per second, they emit radio waves in a lighthouse-like pattern that sweeps past Earth. 

Acting as natural, highly precise clocks, pulsars allow scientists to measure their accelerations and, in turn, the gravitational forces acting on them.

For the first time, the team combined pulsar acceleration measurements with data on star velocities. This innovative approach enabled them to probe the gravitational field at the cluster’s center and differentiate between the effects of an IMBH and a cluster of stellar-mass black holes. 

The results leaned toward the latter explanation: a cluster of smaller black holes rather than a single IMBH.

The hunt for intermediate-mass black holes

“The hunt for elusive intermediate-mass black holes continues. There could still be one at the center of Omega Centauri, but our work suggests that it must be less than about six thousand times the mass of the Sun and live alongside a cluster of stellar-mass black holes,” noted study co-author Justin Read, an astronomer at the University of Surrey. 

“There is, however, every chance of us finding one soon. More and more pulsar accelerations are coming, allowing us to peer into the centers of dense star clusters and hunt for black holes more precisely than ever before.”

Significance of studying Omega Centauri

Study lead author Andrés Bañares Hernández, an astronomer at IAC, noted that we have long known about supermassive black holes at galaxy centers and smaller stellar-mass black holes within our own galaxy. 

“However, the idea of intermediate-mass black holes, which could bridge the gap between these extremes, remains unproven,” said Hernández.

“By studying Omega Centauri – a remnant of a dwarf galaxy – we have been able to refine our methods and take a step forward in understanding whether such black holes exist and what role they might play in the evolution of star clusters and galaxies.”

“This work helps resolve a two-decade-long debate and opens new doors for future exploration.”

Pulsars: A key to further discoveries

The researchers also highlighted Omega Centauri as a prime environment for studying the formation and behavior of pulsars, given the cluster’s density and gravitational complexity. 

The recent discovery of numerous pulsars within Omega Centauri has provided new opportunities to investigate their origins.

“The formation of pulsars is also an active field of study because a large number of them have recently been detected. Omega Centauri is an ideal environment to study models of their formation, which we have been able to do for the first time in our analysis,” Hernández noted.

While the mystery of an IMBH in Omega Centauri remains unresolved, this study represents a significant step forward. 

The new data and techniques for analyzing gravitational fields and pulsar accelerations could soon reveal whether intermediate-mass black holes exist and, if so, what role they play in the universe’s cosmic architecture.

—–

Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates.

Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.

—–