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Milky Way’s central black hole erupted surprisingly recently
New observations of light echoes reflecting through the Milky Way point to when our galaxy’s supermassive black hole erupted violently in the recent past.
With a mass of 4 million suns, the supermassive black hole – named Sagittarius A* – might seem fearsome, but it’s oddly timid in the grand scheme of the universe. Despite a fairly typical size, Sagittarius A* appears far dimmer and less active than most other supermassive black holes we’ve found. But this wasn’t always the case, according to a new study published January 15, 2026.
The research reveals that not only was Sagittarius A* once shockingly explosive, but this violent activity could have been seen from Earth as recently as a few hundred years ago.
That’s according to new data from the XRISM space telescope, a joint venture of NASA, ESA and JAXA. Researchers from Michigan State University said on January 7, 2026, they used this telescope to study X-ray emissions coming from a giant cloud of gas near our galaxy’s center. But these emissions, they said, actually originated in a dramatic bout of flaring from Sagittarius A*. The cloud is acting as a cosmic mirror, reflecting the black hole’s X-ray blast with a centuries-long delay.
It’s a remarkable finding, and one that shocked the researchers. Lead author Stephen DiKerby of Michigan State University said:
Nothing in my professional training as an X-ray astronomer had prepared me for something like this.
The researchers published their peer-reviewed results in The Astrophysical Journal Letters on January 15, 2026.
A black hole is both dark and bright
Black holes – and particularly supermassive ones – are inconceivably dense. That’s why they appear dark; their gravity is so strong that not even light can escape their clutches. But just outside the light’s point of no return – the event horizon – black holes are anything but black.
As gas and dust spiral around a black hole, friction superheats the material to millions or even billions of degrees. This causes the material to blaze astonishingly brightly, both in visible light and across the electromagnetic spectrum, including high-energy X-rays. Actively feeding black holes are among the brightest objects in the universe, easily outshining entire galaxies. And this feeding process – known as accretion – often involves sudden flares or outbursts of particularly intense radiation.
We do see occasional flares from our galaxy’s supermassive black hole. But on the whole, Sagittarius A* is exceedingly dim and quiet. That’s because this beast has very little gas around it to consume. No food, no fireworks.
But it seems our supermassive black hole had a good meal more recently than we thought. Within the last few hundred to a thousand years, the researchers said a ferocious outburst made Sagittarius A* shine in X-rays 10,000 times brighter than it does today.
Written in the clouds
When the astronomers talk of an outburst a few hundred years ago, they mean the light reached us at that time. Sagittarius A* lies about 26,000 light-years away, so the black hole actually had this outburst a little more than 26,000 years ago.
But there’s an even more interesting time delay at work here. The XRISM telescope is picking up these X-rays now, not a few hundred years ago. So why are the researchers dating the outburst to a few centuries ago?
The answer is that the researchers are seeing light echoes. Much like an auditory echo, this phenomenon is the result of a signal bouncing off a surface and reaching an observer with a delay.
When Sagittarius A* had its violent outburst some 26,000 years ago, it sent out a volley of X-rays that eventually reached Earth. These arrived, entirely unnoticed, a few hundred years ago. But some of the X-rays from the black hole also hit a nearby cloud of gas, and then bounced off that cloud in our direction.
These X-rays traveled farther than those that came to Earth directly, so the journey took longer. That’s why astronomers are only now seeing these X-rays arrive.
Co-author Shuo Zhang of Michigan State University said:
This remarkable measurement shows just how powerful XRISM is for uncovering the hidden history of the center of our galaxy.
New detail brings a new conclusion
This is not the first time astronomers have observed the X-rays coming from this gas cloud. But until now, telescopes have lacked the precision to be confident about what produced them.
XRISM has changed that. Launched in 2023, this telescope is able to study X-rays with unprecedented resolution. That means it can better distinguish between X-rays with different levels of energy.
And this new level of detail allowed the researchers to rule out the alternative explanation that cosmic rays actually triggered these X-rays. XRISM has given them confidence that they are really seeing the echoes of a violent outburst from our galaxy’s supermassive black hole.
DiKerby said:
We’re just the lucky scientists who got to solve the problems with handling this data in this brand-new way. One of my favorite things about being an astronomer is realizing I’m the first human to ever see this part of the sky in this way.
Bottom line: New observations of “light echoes” reflecting through the Milky Way point to a surprisingly violent recent past for our galaxy’s supermassive black hole.
Source: Resolving the Fe K alpha Doublet of the Galactic Center Molecular Cloud G0.11-0.11 with XRISM
Via Michigan State University