Hubble Solves Merger Mystery From Milky Way’s Early Years - UNIVERSE

About 12 billion years ago, a dwarf galaxy known as LKH collided with a young Milky Way and merged with it. This artist’s concept portrays that collision. NASA’s Hubble Space Telescope uncovered definitive evidence of this collision by studying globular star clusters.

Illustration: NASA, ESA, Joseph Olmsted (STScI)

Our home galaxy, the Milky Way, grew to its current size in part by consuming smaller galaxies. Now, new data from NASA’s Hubble Space Telescope shows definitive evidence of a dwarf galaxy merging with the young Milky Way galaxy in the earliest phases of its evolution. This finding extends our knowledge of our galaxy’s history 1.8 billion years farther back in time than before.

The results published Monday in the journal Nature Astronomy.

The Milky Way today is a massive spiral galaxy home to hundreds of billions of stars. However, our galaxy wasn’t always so large; it has grown by forming new stars from its gas clouds as well as collecting stars, gas, and dark matter from other galaxies through mergers.

The most recent massive merger in our galaxy’s history took place with the Sagittarius dwarf galaxy, beginning over 6 billion years ago and still ongoing today. Looking back into the even more distant past, researchers learned that the Milky Way galaxy consumed another dwarf galaxy called Gaia-Sausage-Enceladus 10 billion years ago. This ancient merger greatly affected the structure of our galaxy’s disk of stars. Other, smaller mergers occurred between these two.

But our galaxy’s history doesn’t stop there. Both observations and simulations have suggested that another large merger preceded these two, though the specifics of the event have been heavily debated. Now, Hubble has uncovered definitive evidence of an earlier merger that occurred about 11.8 billion years ago, or just 2 billion years after the big bang.

“Our home is the Milky Way galaxy, but we do not know how our house was built,” said Davide Massari, lead author, Astrophysics and Space Science Observatory of Bologna in Italy. “In this paper we discover where the first significant batch of bricks came from: a dwarf galaxy that we call LKH.”

Cosmic archaeological sites

Immense astronomical surveys and precision data from spacecraft like ESA’s (European Space Agency’s) Gaia mission have been instrumental in piecing together the history of our galaxy. The farther back into our galaxy’s history that scientists attempt to look, the more difficult it becomes to tell what happened. When our galaxy was young, it was smaller and much closer in size to the galaxies it clashed with. It was also more chaotic, and it’s possible that the signs of mergers have been erased over billions of years.

It’s into this murky past that Hubble peered. Researchers used Hubble to study some of the Milky Way galaxy’s globular clusters: immense, roughly spherical collections of tens of thousands to a few million stars. Globular clusters contain some of the oldest stars in our galaxy, and they can act as cosmic archaeological sites that preserve stars from other galaxies the Milky Way galaxy has collected.

“Thanks to the high resolution and depth of Hubble imaging, we could measure the age and the metal content of these clusters with unprecedented precision,” said Chiara Zerbinati, study co-author, University of Bologna in Italy. “Coupled with measurements from Gaia, this made it possible to distinguish a population of globular clusters that are different from the others. These are the clusters that were born in LKH, and they tell us when that galaxy was devoured by ours, and how massive it was.”

The team analyzed Hubble observations of 39 globular clusters in the inner 20,000 light-years of our galaxy, where evidence of the most ancient mergers should be preserved. They expected this sample to contain globular clusters that formed within the young Milky Way galaxy as well as those collected from the Gaia-Sausage-Enceladus dwarf galaxy about 10 billion years ago.

Using Hubble’s sensitive observations to determine each cluster’s precise age and associated metallicity — the abundance of elements heavier than helium — they determined there was a third population of globular clusters in the inner regions of our galaxy. The team found that these clusters are older than the group collected in the Gaia-Sausage-Enceladus merger, but younger than those born in the Milky Way, regardless of their metal content. These  clusters, therefore, came from a separate and even earlier merger — in which the Milky Way galaxy absorbed a dwarf galaxy containing roughly 500 million times the mass of the Sun in stars, a significant fraction of our galaxy’s mass at the time. They named this dwarf galaxy Low-energy-Kraken-Heracles, or LKH, in honor of three earlier research papers that championed the idea of a merger early in our galaxy’s history.

Such a large merger so early in the Milky Way galaxy’s formation has profound implications for the evolution of our galaxy.

“Some past studies have argued that the earliest phases of our galaxy’s evolution were defined by stars born only in our galaxy,” says Massari. “Here, we have shown that stars born in external galaxies also need to be considered.”

The team plans to continue their work to unravel the history of the Milky Way galaxy by studying its globular clusters, aiming to characterize all the massive mergers that our galaxy has experienced across cosmic history.

“Hubble is observing globular clusters that have never been studied before, and this will help us characterize the merger events that are far back in time in the Milky Way galaxy’s history,” said Fernando Aguado-Agelet, co-author, University of Vigo and the University of La Laguna in Spain.

The Hubble Space Telescope has been operating for more than three decades and continues to make ground-breaking discoveries that shape our fundamental understanding of the universe. Hubble is a project of international cooperation between NASA and ESA (European Space Agency). NASA’s Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope and mission operations. Lockheed Martin Space also supports mission operations at Goddard. The Space Telescope Science Institute in Baltimore, which is operated by the Association of Universities for Research in Astronomy, conducts Hubble science operations for NASA. 

Source: Hubble Solves Merger Mystery From Milky Way’s Early Years - NASA Science 

The Enzyme Trapped in a Vicious Circle: How ETH Zurich’s “Compound 10” Could Slow Alzheimer’s

Alzheimer’s research moves at a punishing pace. Because the disease is age-related, scientists have to work with old mice, and each experiment can take a year and a half to two years before it even yields conclusions worth building on. “It’s all a great deal slower than in cancer research,” says Ursula Quitterer, Professor of Molecular Pharmacology at ETH Zurich. Her team has spent almost twenty years chasing a single culprit and they may have finally found a way to disarm it.

An enzyme with a split personality

The story starts with GRK2, an enzyme found throughout the body that normally helps cells respond to stress and signalling. In the brain, it supports the day-to-day function of nerve cells. But GRK2 comes in two forms: a healthy, active one, and a version that cellular metabolism has switched off.

Working with brain tissue samples collected from patients in Cairo, some with dementia, some without, and with a mouse model of Alzheimer’s, Quitterer’s team found that the inactive form of GRK2 piles up in dementia brains. Worse, it doesn’t stay harmlessly out of the way. It clumps together into aggregates that latch onto mitochondria, the cell’s energy factories, and physically block their pores. Energy production drops, and the cell is thrown into a state of chronic stress.

A feedback loop that feeds itself

Here’s where it gets nasty. The stressed mitochondria push nerve cells to produce more amyloid beta, the sticky protein fragment long implicated as a driver of Alzheimer’s. Amyloid beta then stresses the cells further, and that stress generates still more inactive, aggregating GRK2. Cause becomes effect becomes cause again, a self-perpetuating cycle that keeps the disease advancing.

Breaking a loop like that means finding the right point to intervene. The team synthesized a series of candidate compounds and tested them in cell cultures and in mice. One of them, referred to simply as “compound 10,” stood out: it stopped GRK2 molecules from aggregating in the first place. With the aggregates cleared out of the way, mitochondria worked properly again, amyloid beta deposits dropped, and nerve cells stopped dying off at their usual accelerated rate. Treated mice survived longer than untreated ones.

An unexpected bonus

Compound 10’s effects weren’t confined to the brain. Treated mice also showed better heart function and slower signs of ageing overall, including, notably, fewer grey hairs in old age. It’s a reminder that GRK2 dysfunction and mitochondrial stress aren’t purely a neurological story; they touch aging biology more broadly.

Why this matters

Current Alzheimer’s medications don’t cure the disease, at best, they delay its progression by a few months. What makes compound 10 interesting isn’t just that it worked in mice, but that it works through a completely different mechanism than existing drugs, by targeting GRK2 rather than amyloid beta directly. That opens the door to combination therapies down the line. Quitterer’s team has filed a patent on the compound and is now looking for a pharmaceutical partner willing to carry it through the long process of drug development. Given how slowly this field moves, that next stage could itself take years, but the basic science, two decades in the making, is done.

Original paper: Abd Alla J, Perhal A, Fu X, Langer A, el Faramawy Y, Quitterer U. Analysis of GRK2 aggregation in the pathology of Alzheimer disease in animal models. Cell Reports Medicine, 2026. 

Source: The Enzyme Trapped in a Vicious Circle: How ETH Zurich’s “Compound 10” Could Slow Alzheimer’s