Updated

Updated · Universe Today · Jul 24

Omega Centauri Yields 4.46-Solar-Mass Black Hole After 20 Years of Hubble and Webb Data

Updated

Updated · Universe Today · Jul 24

Omega Centauri Yields 4.46-Solar-Mass Black Hole After 20 Years of Hubble and Webb Data

Q: How did astronomers prove a 4.46-solar-mass black hole exists in Omega Centauri without seeing X-rays or radio signals?

Astronomers proved it by measuring gravity, not radiation. Using precision astrometry from Hubble data taken from 2002 to 2023, plus newer infrared observations from the James Webb Space Telescope, they tracked the tiny side-to-side motion of a visible 0.78-solar-mass main-sequence star in Omega Centauri. That star was clearly orbiting an unseen companion. From the star’s motion, the team reconstructed the binary’s orbit and calculated how much mass the invisible object must have to produce it. The key was that the system was observed near periastron, the point where the visible star moves fastest, which let researchers tightly constrain the companion’s gravity even though they have not yet seen the full 94-year orbit. The result was an unseen companion with a mass of about 4.46 times that of the Sun. That is too massive to be a neutron star, making a stellar-mass black hole the only plausible explanation. The object was named oMEGACat BH-2. That is why no X-rays or radio signals were needed. Those signals usually come from black holes actively feeding on gas, but this one appears quiet. Instead of catching the black hole glowing, astronomers detected its gravitational pull directly through the star’s long-term wobble, measured down to fractions of a pixel by Hubble and Webb. This made the case strong enough to confirm the first stellar-mass black hole in Omega Centauri.

3 articles · Updated · Universe Today · Jul 24

A Utah-led team identified oMEGACat BH-2 as the first stellar-mass black hole found in Omega Centauri by tracking a visible companion star orbiting an unseen object.
Twenty-plus years of Hubble astrometry, sharpened with James Webb NIRCam data, showed the star completes one orbit every 94 years and pinned the companion's mass at 4.46 solar masses—too heavy to be a neutron star.
That 94-year cycle makes it the longest-period black hole binary yet discovered and suggests the black hole likely captured the 0.78-solar-mass star inside the cluster rather than forming together with it.
The find addresses Omega Centauri's long-standing lack of detected stellar-mass black holes despite models predicting about 10,000, and its unexpectedly low mass in a metal-poor environment could reshape black-hole formation models.
Researchers estimate the binary will survive less than 1 billion years in the 12-billion-year-old cluster, and say future searches with Hubble, Webb and the Roman Space Telescope could uncover more of the cluster's 'missing' black holes.

Sources

Universe Today18h ago

Utah Team Discovers First Stellar-Mass Black Hole, oMEGACat BH-2, in Omega Centauri Cluster

The Watchers18h ago

Hubble and Webb Uncover First Stellar-Mass Black Hole, oMEGACat BH-2, in Omega Centauri

YouTube18h ago

The Hidden Black Hole in Omega Centauri - YouTube

6 Sources

Does one 94-year black hole orbit finally reveal the thousands of hidden black holes long predicted inside Omega Centauri?

How did astronomers prove a 4.46-solar-mass black hole exists in Omega Centauri without seeing X-rays or radio signals?

What can a doomed binary in Omega Centauri tell us about how star clusters create future gravitational-wave sources?

Discovery of oMEGACat BH-2: The First Confirmed Stellar-Mass Black Hole in Omega Centauri Reveals a 94-Year Binary and Challenges Black Hole Formation Models

Overview

For decades, traditional methods failed to find stellar-mass black holes in Omega Centauri because they relied on visible activity, which is rare in such a dense cluster. A University of Utah team broke this stalemate by using astrometry, tracking a star’s tiny movements over 20 years of Hubble and Webb data. This revealed the star’s 94-year orbit around a hidden 4.46-solar-mass object—oMEGACat BH-2, the cluster’s first confirmed black hole. Its unexpectedly low mass in a metal-poor environment challenges existing models, and future wide-field surveys with the Roman Space Telescope will help uncover many more hidden black holes across the galaxy.

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