Understanding the formation and evolution of galactic centers is a major challenge facing astrophysicists. For some time, astronomers have known that the supermassive black holes (SMBHs) at the centers of galaxies and the densely packed nuclear star clusters that surround them play a major role in star formation and other processes. Alas, scientists were still missing some of the pieces of this particular puzzle. By understanding the mechanics that govern galactic centers, scientists will be able to track how the Universe itself has evolved since the first galaxies emerged.

Using a state-of-the-art galaxy simulation, a team led by researchers from Leibniz Institute for Astrophysics Potsdam (AIP) has gained new insights into these processes. Their results, described in a study published in Astronomy & Astrophysics, indicate that nuclear star clusters and stellar discs found in the inner core are not independent processes, as previously thought. These findings are bridging the gap between theory and observation, improving our understanding of how galaxies evolve.

The research was led by SungWon Kwak, a postdoctoral researcher from the AIP. He and his colleagues were joined by researchers from the Observatoire de la Côte d’Azur (OCA), the SNU Astronomy Research Center, the Università di Bologna, the Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, the Kavli Institute for Astrophysics and Space Research at MIT, the University of California, Riverside, Tsinghua University, and the Institut für Physik und Astronomie at the Universität Potsdam.

The diffraction spike in the center of NGC 1365 is a telescope artifact caused by an enormous amount of light in a compact region. Credit: NASA, ESA, CSA, STScI, Janice Lee (STScI), Thomas Williams (Oxford), PHANGS Team

The team hoped to learn more about the physical processes that led to the formation of two features that surround the SMBHs at the centers of most galaxies in the Universe: nuclear star clusters and nuclear stellar discs. Such features have been observed for only about a decade in the Milky Way and other galaxies, and were thought to be products of separate formation processes. However, observational surveys found no clear correlation between their masses and sizes, and simulations could not realistically reproduce the processes.

Resolving this mystery is the purpose of the Stellar Feedback in Galaxies and its Effects, or SMUGGLE-Ring, project, an advanced physics framework used in astrophysical simulations to model how stars and stellar feedback shape galaxies. Through their high-resolution hydrodynamical simulation, the team demonstrated that a barred galaxy (like the Milky Way) could naturally form both nuclear star clusters and nuclear stellar discs together, while simulating their growth over billions of years.

For the first time, the simulation directly reveals an evolutionary link between their formation, showing that they grow together. The simulation also shows that the galaxy’s stellar bar plays a central role in this process, funneling gas inward toward the center. As gas accumulates in the center of a galaxy, where the supernovae of dying stars generate shock waves that repeatedly trigger the formation of new stars. Over several billion years, hundreds of millions of solar masses’ worth of stars form in the galactic center.

“Our simulation achieves this by showing how the galactic bar acts like a cosmic conveyor belt, channeling gas inward to feed both structures simultaneously from the exact same reservoir,” explains SungWon Kwak. The results also explain why previous observations failed to find a clear connection between nuclear star clusters and nuclear stellar disks. “The apparent disconnection does not mean that the stars themselves differ fundamentally in age, chemical composition, or motion,” added Dr. Cristina Chiappini, also a scientist from AIP and co-author of the study.

In addition, the simulation showed that the structural relationship between the two processes naturally evolves. During periods of sustained growth, the relative masses and sizes of the cluster and disk begin to differentiate. Despite the shared underlying growth mechanism, the clusters and stellar disks appeared remarkably different when observed at different stages in their evolution. However, the results proved that the dynamics of this co-evolution are even more complex than all that.

Barred spiral galaxy known as NGC 1300 viewed nearly face-on. It’s thought the Milky Way is a barred spiral like this (Credit: NASA, ESA, and The Hubble Heritage)

At one point in their simulations, a star cluster of 30 million solar masses spiraled into the galactic center and merged with the nuclear star cluster. This was particularly fascinating, since recent observations of NGC 1365 revealed a massive star cluster inside the galaxy’s bar. This cluster is expected to spiral into the galaxy’s center and merge with its nuclear star cluster, causing it to grow in size and mass. This could also affect the mass of the SMBH inside the nuclear star cluster over time.

A key advantage of these types of astronomical simulations is how it allows researchers to observe processes that cannot be seen directly. In addition, simulations allow scientists to monitor the evolution of galaxies over billions of years. From this, they can observe the formation of a galaxy’s stellar bar, trace the inward flow of gas, witness the birth of new stars, and see how the nuclear stellar disk gradually grows outward from the center.

Another interesting part of the team’s simulation was the way they included dark matter, which played a crucial role in the results. As co-author Dr. Ivan Minchev said:

Previous studies rely on fixed background potentials for the galactic bar and dark matter halo, but the realistic dynamical treatment between stars and the dark matter halo using live particles in our model allows us to form a realistic bar that evolves in time and then naturally forms nuclear structures. Furthermore, our model also exhibits a ‘dark gap’ around the bar region, which is found in many observations and is known as evidence of the interaction between stars and dark matter by the rotation of the stellar bar.

These findings could expand our understanding of the connection between galactic components, helping astronomers interpret future observations.

Further Reading: AIP, Astronomy & Astrophysics

Daniel Flores, the LAPD officer who set off a political firestorm when he reported some of his police colleagues for making racist, sexist and homophobic comments behind closed doors, broke his silence on Tuesday.

Flores, whose only public comments had for months been filtered through his legal team, agreed to speak with The Times, detailing the toll that the prior year and a half had taken on him.

“It’s definitely been a roller coaster of a struggle,” he said. “As you know, I didn’t see this coming or turning out like this.”

Last month, L.A. County Dist. Atty. Nathan Hochman charged Flores with 16 felonies, alleging he violated a state eavesdropping law by secretly recording his fellow LAPD officers. The charges could have carried a sentence of 13 years in prison, but last week, after facing criticism from Mayor Karen Bass and others, Hochman downgraded the counts to misdemeanors with a diversion agreement that will probably allow Flores to avoid any time behind bars.

Internal LAPD documents reviewed by The Times raise new questions about the timing of Flores’ prosecution.

The files show that the department originally presented the case to prosecutors on July 1, 2025. Ten days later, the district attorney’s office declined to bring charges.

The case sat dormant for about a year, before Flores filed a whistleblower lawsuit against the city in L.A. County Superior Court, alleging he faced retaliation for speaking out about misconduct. Less than three weeks later, the district attorney’s office announced that it would move forward with the prosecution.

Flores and his attorney allege the case was further retaliation for his decision to file a lawsuit.

On Tuesday, the district attorney’s office said that it didn’t pursue charges against Flores in July 2025 because it lacked the evidence to “definitely establish” that he had made the recordings and sent the case back to the LAPD for further investigation.

“That changed when Flores filed his own civil lawsuit against the City of Los Angeles,” the office said in a statement. A spokesperson said that even though Flores had admitted to making the recordings, the LAPD didn’t release that information to the district attorney until after Flores filed his lawsuit.

Hochman said last week that he wanted to thread the needle between punishing the illegal recording and not dissuading whistleblowers from coming forward.

“If you go ahead and illegally eavesdrop in our community, you will face criminal prosecution for doing it, so don’t take out your cellphones and or your smart glasses or anything else,” he said, while encouraging whistleblowers to work with the district attorney’s office to gather evidence in the future.

Flores told The Times that he initially filed an anonymous Internal Affairs complaint against members of his LAPD unit in February 2025. Flores worked in a recruitment division, which handles job applications from aspiring officers.

According to Flores’ complaint, he heard officers make jokes and racial comments about Black candidates who interviewed for the department, focusing on their “failures and adverse histories, which prevented them from being hired as Los Angeles Police Officers.”

LAPD Officer Daniel Flores, left, listens as his attorney Alan Jackson, center, speaks to reporters at the Superior Court building in downtown Los Angeles this month.

(Libor Jany / Los Angeles Times)

A few days after filing the complaint, he said, he received a call from Internal Affairs investigators who notified him that someone had accused him of making racist remarks. Flores vehemently disputes this, saying that it was clearly an attempt to discredit him. When he reached out to the police union for legal representation, he said, he was told that there was a conflict of interest because one of the union’s attorneys was already representing some of the accused officers.

Ten days after filing his anonymous complaint, he submitted a letter to the inspector general’s office, along with a USB drive with the 122 recordings, which he’d made over a span of about six months.

According to Flores, he began surreptitiously recording his colleagues after their inappropriate commentary got so bad that one day a police lieutenant warned them that if they continued, they would “bring down the whole department.”

Flores said he taped his fellow officers making racial slurs, along with homophobic and sexist comments. In one conversation about Latino immigrants, a colleague was heard saying, “F—ing deport them, call ICE.”

Flores’ attorney Greg Smith said that his client tried to report misconduct by going through the proper channels but still ended up being targeted by the department and, later, prosecutors.

“He was trying to fix things, not trying to create publicity or any kind of public outrage,” Smith said.

Almost from the outset, it appeared as though the outcome of the department’s investigation into the allegations was “predetermined,” according to Flores. Investigators assigned to the case were asking some of the accused officers leading questions, which seemed designed to soften their actions, he said.

“I know from the beginning that they were going to try to swing the investigation, and I knew from the beginning that they were going to try to come after me,” Flores said.

California is a “two-party consent” state, meaning it is a crime for someone to record a conversation without the permission of other participants, unless there is a court order granting authority to do so. Flores’ attorneys have argued that his actions were allowed under the California Invasion of Privacy Act because he was acting in the course of his duties as a police officer.

Flores has kept his job with the LAPD since filing the initial complaint and facing criminal charges, but remained away from the department on medical leave.

He described the months since the complaint became public as “painful” and isolating.

“No cop will talk to me at all,” he said. No one from the department has reached out to check on him since the scandal broke; he suspects it’s because people are worried about getting entangled in his criminal or civil cases.

“The things I see on the internet: The other cops are calling me rat, snitch, [saying], ‘Snitches get stitches,’” he said. He recalled one Facebook post, made by a current LAPD officer, that drew scores of comments from officers criticizing him.

“It’s hurtful, because the people who are calling me rat and snitch, they’re all officers,” he said. “The people on my side, they’re all citizens.”

He was reluctant to report the wrongdoing, he said, because one of the lieutenants had boasted that he knew a lot of people in Internal Affairs.

He said that during his time with the department, he had heard of other reports of wrongdoing that ended up going nowhere. The conversations he recorded were “apparently normal for the LAPD,” he said.

“When I brought it to their attention, I think the reason they retaliated against me as much as they did was because there was evidence, so it was no longer to be under the table,” he said.

Asked whether he regretted coming forward at all, Flores paused before saying that he did.

“I do because it ruined everything, it ruined my life,” he said. “My face is all over the internet. They painted me as the criminal. They didn’t even care about the bigotry, they just painted me as the criminal.”