For years, astronomers have been puzzled by rare and dramatic flashes of blue and ultraviolet light that suddenly appear in distant galaxies and then fade within days.
These events are incredibly bright, visible across hundreds of millions or even billions of light-years, and are often followed by weaker X-ray and radio signals.
With only a little more than a dozen known so far, scientists have debated what could possibly create such intense but short-lived cosmic fireworks.
Now, a new study of the brightest event ever seen has finally revealed what is powering these mysterious flashes.
Astronomers report that they are caused by an extreme encounter between a black hole and a massive companion star—an encounter so violent that the star is completely torn apart in just a few days.
These events are known as luminous fast blue optical transients, or LFBOTs. They were once thought to be either a strange kind of supernova or gas falling into a black hole. The new research shows that they are neither.
Instead, they are the result of a rare and catastrophic process called a tidal disruption, in which a black hole’s gravity rips a nearby star to pieces.
The research team, led by scientists at University of California, Berkeley, focused on an event discovered in 2024 known as AT 2024wpp. This outburst was even more powerful than earlier examples and provided an unusually rich set of observations across many wavelengths of light.
The key clue came from calculating how much energy the event released. The total energy was about 100 times greater than what a typical supernova produces.
To explain that much power with a stellar explosion would require converting an unrealistically large fraction of the Sun’s mass directly into energy in just a few weeks. That made a supernova explanation impossible.
Instead, the team concluded that the source was a black hole up to about 100 times the mass of the Sun. This places it in a mysterious category known as intermediate-mass black holes.
These objects are especially interesting because, while even larger black holes are known to exist from gravitational wave detections by observatories such as LIGO, astronomers still do not know how black holes grow to such sizes.
In this case, the black hole appears to have been orbiting a massive companion star—more than 10 times the mass of the Sun—for a long time. Over that period, the black hole slowly siphoned material from the star, surrounding itself with a thick cloud of gas. When the star finally drifted too close, the black hole’s gravity shredded it completely.
As the star was torn apart, its material formed a rapidly spinning disk around the black hole. Fresh debris crashed into the older surrounding gas, producing intense bursts of blue, ultraviolet, and X-ray light.
Some of the gas was also funneled toward the black hole’s poles and blasted outward as powerful jets moving at nearly half the speed of light. When these jets slammed into surrounding gas, they produced the radio waves detected later.
The nature of the destroyed star also helps explain what astronomers observed. The companion was likely a Wolf-Rayet star, an extremely hot and evolved star that has already lost much of its hydrogen. This fits with the unusually weak hydrogen signals seen in the light from AT 2024wpp.
Like other LFBOTs, this event occurred in a galaxy where new stars are actively forming, making the presence of massive stars more likely. AT 2024wpp is located about 1.1 billion light-years from Earth and was several times brighter than the famous earlier event nicknamed “the Cow.”
To study it, astronomers used an impressive network of space- and ground-based telescopes, capturing everything from X-rays to radio waves. Looking ahead, scientists are especially excited about upcoming ultraviolet space telescopes, which will make it much easier to spot these flashes early.
With better tools, LFBOTs may soon go from rare curiosities to routine discoveries—offering a powerful new way to study black holes, massive stars, and some of the most extreme events in the universe.
Source: UC Berkeley.
