Through a small telescope, it looks no different from other so-called globular clusters; a spherical stellar collection so dense towards the center that it becomes impossible to distinguish individual stars. But a new study, led by researchers from the University of Utah and the Max Planck Institute for Astronomy, confirms what astronomers had argued about for over a decade: Omega Centauri contains a central black hole.The black hole appears to be the missing link between its stellar and supermassive kin—stuck in an intermediate stage of evolution, it is considerably less massive than typical black holes in the centers of galaxies. Omega Centauri seems to be the core of a small, separate galaxy whose evolution was cut short when it was swallowed by the Milky Way.

“This is a once-in-a-career kind of finding. I’ve been excited about it for nine straight months. Every time I think about it, I have a hard time sleeping,” said Anil Seth, associate professor of astronomy at the U and co-principal investigator (PI) of the study. “I think that extraordinary claims require extraordinary evidence. This is really, truly extraordinary evidence.” A clear detection of this black hole had eluded astronomers until now. The overall motions of the stars in the cluster showed that there was likely some unseen mass near its center, but it was unclear if this was an intermediate-mass black hole or just a collection of the stellar black holes. Maybe there was no central black hole at all.

A medium Level panel zoom of the Omega Centauri star cluster’s intermediate black hole likely position. PHOTO CREDIT: ESA/HUBBLE & NASA, M. HÄBERLE (MPIA)

“Previous studies had prompted critical questions of ‘So where are the high-speed stars?’ We now have an answer to that, and the confirmation that Omega Centauri contains an intermediate-mass black hole. At about 18,000 light-years, this is the closest known example for a massive black hole,” said Nadine Neumayer, a group leader at the Max Planck Institute and PI of the study. For comparison, the supermassive black hole in the center of the Milky Way is about 27,000 light-years away.

A range of black hole masses

In astronomy, black holes come in different mass ranges. Stellar black holes, between one and a few dozen solar masses, are well known, as are the supermassive black holes with masses of millions or even billions of suns. Our current picture of galaxy evolution suggests that the earliest galaxies should have had intermediate-sized central black holes that would have grown over time, gobbling up smaller galaxies done or merging with larger galaxies.

Such medium-sized black holes are notoriously hard to find. Although there are promising candidates, there has been no definite detection of such an intermediate-mass black hole—until now.

“There are black holes a little heavier than our sun that are like ants or spiders—they’re hard to spot, but kind of everywhere throughout the universe. Then you’ve got supermassive black holes that are like Godzilla in the centers of galaxies tearing things up, and we can see them easily,” said Matthew Whittaker, an undergraduate student at the U and co-author of the study. “Then these intermediate-mass black holes are kind of on the level of Bigfoot. Spotting them is like finding the first evidence for Bigfoot—people are going to freak out.”

Read more about the Discovery @TheU.

Neutrinos are also incredibly small and light. They have some mass, but not much and they rarely interact with other matter. They come in three types or "flavors": electron, muon, and tau.

Cosmic rays travel through space then crash into the earth's atmosphere and produce  air showers that Include neutrinos and many other types of particles. When neutrinos are produced and start traveling, they can change from one flavor to another. The atmospheric neutrinos are then detected by DeepCore, a denser array of sensors in the center of the IceCube detector at the South Pole.This process is called neutrino oscillation and the IceCube Detector, a massive neutrino detector buried deep in the ice at the South Pole, has a special area called DeepCore that can detect lower-energy neutrinos.

Scientists at the IceCube Neutrino Observatory in Antarctica have made a breakthrough in measuring neutrinos. Using advanced computer techniques, they've achieved the most precise measurements to date of how these particles change as they travel through space, helping us understand fundamental properties of the universe that could lead to new discoveries in physics.

Shiqi Yu

Shiqi Yu, a research assistant professor in the Department of Physics & Astronomy at the University of Utah and others who published their findings recently in Physical Review Letters analyzed data from over 150,000 neutrino events collected over nine years (2012-2021). They used advanced computer programs called convolutional neural networks (CNNs) to process this data. The team made the most precise measurements ever of two important properties related to neutrino oscillation: Delta m²₃₂ and sin²(θ₂₃). These numbers help describe how neutrinos change as they travel.

“We also carefully studied the systematic uncertainties that arise from our imperfect knowledge of our models and chose some to use as free nuisance parameters that fit together with the physics parameters for our data,” says Yu.

Using CNNs, which use three-dimensional data for image classification, Yu and co-lead of the study Jessie Micallef first developed use cases for the CNNs to focus on the DeepCore region and trained them to reconstruct different properties of particle interactions in the detector. They then used the CNN reconstructions to select qualified neutrino interactions that happened in or near the DeepCore region to produce a neutrino-dominated dataset with well-reconstructed energies and zenith angles.

Jessie Micallef

Yu notes that the CNN-reconstructed analysis-level dataset is already being used for other neutrino oscillation analyses, such as determining the neutrino mass ordering and non-standard neutrino interactions and for atmospheric tau neutrino appearance analyses.

“The atmospheric neutrino dataset from DeepCore exhibits relatively high energies in the oscillation analyses, which is unique compared to existing accelerator-based experiments,” says Yu. “Given our dataset and independent analysis, it is interesting to see agreement and consistency in physics parameter measurements.”

This research helps confirm and refine our understanding of how neutrinos — fundamental particles that can tell us a lot about the universe — behave. The techniques developed here, animated by machine learning, can be used in future studies to learn even more about neutrinos and the universe. Those future studies will be informed by IceCube which is planning an upgrade in 2025-2026 that will allow for even more detailed measurements of neutrinos.

By studying neutrino detection and the phenomenon of neutrino oscillation, scientists like Shiqi Yu hope to answer big questions about the nature of matter, energy and the cosmos.