A Milky Way merger with a dwarf galaxy about 11.8 billion years ago has been uncovered by astronomers using the Hubble Space Telescope and ESA’s Gaia mission. The discovery provides new evidence about how the Milky Way formed and identifies a distinct population of ancient globular clusters linked to the merger.

Our home galaxy, the Milky Way, contains hundreds of billions of stars today. It grew to this size over billions of years by pulling in smaller neighbouring galaxies and absorbing them. Now, astronomers using the NASA/ESA Hubble Space Telescope and ESA’s Gaia mission have found evidence of a major merger that occurred near the very beginning of the Milky Way’s history.

By combining precise stellar age and chemical-composition measurements from Hubble with motion-mapping data from Gaia, the team pushed back the known timeline of the Milky Way’s formation by roughly 1.8 billion years. The findings, led by Davide Massari of the Astrophysics and Space Science Observatory of Bologna, Italy, were published this week in Nature Astronomy.

Evidence of an Ancient Milky Way Merger

Reconstructing the Milky Way’s earliest history is difficult: in its youth, the galaxy was smaller, more chaotic, and closer in size to the dwarf galaxies it collided with, and many physical traces of those early mergers have since been erased.

To work around this, the researchers studied 39 globular clusters — dense, ancient groupings of up to a few million stars — in the inner 20,000 light-years of the galaxy, where evidence of the earliest mergers is most likely to survive. Using Hubble’s high-resolution imaging, the team measured each cluster’s age and metallicity (its abundance of elements heavier than helium) with what the researchers describe as unprecedented precision.

“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, a co-author on the study at the University of Bologna, in a release issued by ESA Hubble. “Coupled with measurements from Gaia, this made it possible to distinguish a population of globular clusters that are different from the others.”

Identifying LKH

Cross-referencing Hubble’s age and metallicity data with Gaia’s motion measurements, the researchers identified a distinct third population of globular clusters — older than the ones known to have arrived during the Milky Way’s collision with the Gaia-Sausage-Enceladus dwarf galaxy about 10 billion years ago, but younger than the stars that formed within the Milky Way itself.

That pattern pointed to a separate, earlier merger: the absorption of a dwarf galaxy roughly 11.8 billion years ago — about two billion years after the Big Bang — carrying a total stellar mass of around 500 million times the mass of the Sun, a significant share of the Milky Way’s total mass at the time.

The researchers named the dwarf galaxy Low-energy-Kraken-Heracles, or LKH, after three earlier papers that had proposed the idea of an early merger in the Milky Way’s history.

“Our home is the Milky Way galaxy, but we do not know how our house was built,” Massari said. “In this paper we discover where the first significant batch of bricks came from: a dwarf galaxy that we call LKH.”

Rewriting Early Galactic History

The finding challenges an earlier assumption that the Milky Way’s oldest stellar populations formed almost entirely in place, showing instead that external galaxies contributed to its structure far earlier than previously established.

The team plans to extend the analysis to additional globular clusters across the galaxy, aiming to build a more complete map of the mergers that shaped the Milky Way over cosmic history.

On August 12, the Moon passed between the Sun and Earth, producing a total solar eclipse. Along a narrow path, the Moon completely covered the Sun, briefly darkening the daytime sky. Much of Europe and parts of North America and northwestern Africa saw a partial eclipse.

A solar eclipse occurs when the Moon passes between the Sun and Earth and casts its shadow on Earth’s surface. Because the Moon’s darkest shadow covers only a limited area, an eclipse can be total in one region, partial in another and invisible elsewhere.

Why did some places go dark?

The Moon casts two main shadows during a solar eclipse. The umbra is the central shadow, where the Sun is completely blocked. People within it experience totality.

The penumbra extends beyond the umbra. People in this larger region see only part of the Sun covered and therefore experience a partial eclipse.

This is why the same eclipse looks different from different locations. A place inside the path of totality can experience a few minutes of daytime darkness, while a location farther away may see only a portion of the Sun covered.

Where was the eclipse visible?

Totality was visible across parts of Greenland, Iceland, northern Russia, Spain and northeastern Portugal, as well as parts of the Atlantic and Arctic oceans.

A much larger area experienced a partial eclipse. This included much of Europe, parts of North America and northwestern Africa, along with areas over the Atlantic, Arctic and Pacific oceans.

For mainland Europe, the event was particularly notable because it brought totality to the region for the first time since 1999.

Why couldn’t India see it?

India was outside the eclipse’s visibility zone. The eclipse’s path of totality was concentrated much farther north, and India was not within the region from which the August 12 event could be observed.

This illustrates an important point about solar eclipses: an eclipse may occur over Earth without being visible from a particular country. The Moon’s shadow covers only a limited part of the planet.

How often do solar eclipses occur?

Solar eclipses are not exceptionally rare. There are generally two to five solar eclipses somewhere on Earth each year.

However, a total solar eclipse at a particular location is much rarer. A 2026 analysis by timeanddate estimates that, on average, a total solar eclipse occurs at a given location about once every 373 years. The actual interval can vary considerably between locations.

The reason is the geometry of the Moon’s orbit. It is tilted by about five degrees relative to Earth’s orbit around the Sun, so the Moon usually passes above or below the Sun rather than directly in front of it. Only when the alignment is sufficiently close does its shadow fall across Earth.

Why are total solar eclipses scientifically important?

During normal daylight, the Sun’s bright surface makes its faint corona difficult to observe. During totality, the Moon blocks the bright disk, revealing the corona around it.

Scientists study the corona to better understand the Sun’s atmosphere, magnetic activity and solar wind. These processes are also important to the study of space weather, which can affect satellites and communications.

The August 12 eclipse was therefore more than a striking change in the daytime sky. For observers along its narrow path, a few minutes of darkness provided a rare opportunity to see the Sun’s outer atmosphere—while much of the world saw only a partial eclipse or nothing at all.

Astronomers using NASA’s James Webb Space Telescope have identified a possible new type of object they call a “black hole star.” Roughly the size of the Solar System and powered by a black hole about 100,000 times the Sun’s mass, the object could help explain the mysterious little red dots appearing across JWST’s images of the early universe.

Astronomers led by a team at MIT have identified what they describe as an entirely new type of astrophysical object: a blindingly bright, deep-red point of light from the early universe that behaves like an enormous star but produces energy on a scale that only a black hole should be capable of. They are calling it a “black hole star.”

The object, spotted using NASA’s James Webb Space Telescope (JWST), spans roughly the size of our solar system and appears to be putting out about 100 billion times more energy than any known star could physically generate through nuclear fusion. The findings, published in the journal Nature, suggest the object is instead powered by a black hole embedded inside a dense cocoon of gas — a combination that has not been observed before.

A ‘Black Hole Star’ in the Early Universe

“Our picture of this object is evolving very rapidly,” lead author Rohan Naidu, a NASA Hubble Fellow and Pappalardo Fellow at MIT’s Kavli Institute for Astrophysics and Space Research, said in a statement released by MIT News. “We think there is a central black hole that is 100,000 times as massive as the sun. And around this black hole, there would be this very extended envelope of gas that looks like a star the size of the solar system. It’s huge.”

The discovery could help resolve one of the more persistent puzzles of the JWST era: the identity of so-called “little red dots” that have turned up in nearly every deep-field image the telescope has captured. “These little red dots seem to be everywhere in the early universe but essentially disappear by the present day,” Naidu said. “What exactly these objects are has been one of the most debated topics of the JWST era.”

MIT’s Robert Simcoe, director of the Kavli Institute and the Bruno B. Rossi Professor of Experimental Physics, and Wendy Sun, a member of the MIT class of 2026, are among the study’s co-authors, alongside collaborators from several other institutions.

A Search for Something Else Entirely

The team wasn’t looking for a black hole star when they found one. Naidu and his colleagues were using JWST to hunt for the earliest, most distant galaxies, as part of a survey they named “Mirage or Miracle” (MoM) — an effort to work out which unusually bright early-universe objects were genuine galaxies, and which were something else entirely masquerading as one.

“There’s been this puzzle of many bright galaxies showing up at extremely early times,” Naidu said in a statement released by MIT News. “What we found was that what looks like an extremely bright early galaxy, aka a ‘miracle,’ in some cases actually could be a ‘mirage.’”

While scanning JWST’s images for candidates, the team noticed a dot that stood out for being unusually red and unusually bright. A very red object in space is typically read as a sign that it is shrouded in dust. “When we see something very red in the universe, we often assume that it is surrounded by dust, like soot or ash,” Simcoe said in a statement released by MIT News. “The same way that the wildfire smoke from Canada recently made the sky in Boston look bright red, astronomical objects can also appear redder than their intrinsic colour when you see them through a veil of dust.”

But the light didn’t fully fit a dust explanation. The team found another unusual pattern: the object’s brightness dropped off sharply and almost completely below a certain wavelength — a signature known as a “Balmer break,” normally associated with dense gas absorbing light in the atmospheres of stars a few hundred million years old. “The break we observed in this object is the deepest break we have ever observed in any object, ruling out ‘ordinary’ stars as the source,” Naidu said. “But it made us wonder if we were seeing a new kind of ‘stellar atmosphere,’ but on a spectacular scale.” The object’s light also showed almost no trace of any element beyond hydrogen and helium.

Modelling an Impossible Star

To work out what could produce such a distinctive signature, the researchers ran simulations testing different combinations of astrophysical features. “We started to ask: could you make something that red using just hydrogen, without any dust?” Simcoe said in a statement released by MIT News. “To our surprise, it turns out you can, if you have an extremely dense screen of hydrogen, so dense that it looks more like the surface of an enormous star than a wispy interstellar nebula.”

A dense hydrogen cocoon around a powerful, hidden energy source could account for the Balmer break and the near-total absence of heavier elements. It could not, on its own, account for the object’s extreme brightness. “You have something that looks a bit like a star but is 100 billion times brighter,” Naidu said. “That means you can’t be powering this by nuclear fusion, which is the energy source that sits at the heart of all the stars we have.”

Black holes, by contrast, can generate energy at exactly that scale. When the team added an actively feeding black hole into their simulation of a hydrogen-cocooned star and adjusted its mass and other parameters, the closest match to JWST’s observations pointed to a central black hole roughly 100,000 times the mass of the sun, wrapped in a dense, star-like envelope of hydrogen about the size of the solar system.

The researchers have named the object MoM-BH*-1, after the survey that found it. They believe black hole stars, generally fainter than this one, could account for many of the other little red dots turning up across JWST’s images. “Every little red dot is consistent with being a black hole star, embedded in a generic early galaxy,” Naidu added. “But what is special about MoM-BH*-1 is, the black hole star is essentially completely outshining its surrounding host galaxy, such that we’re seeing pure black hole star light.”