A machine learning system that looked at both the location and energy of gamma-ray photons has weakened a key argument in favor of the pulsar explanation. The study doesn't prove that dark matter creates the radiation, but it shows it's still too early to rule out the possibility.
It could be that the mysterious glow of gamma rays at the center The Milky Way It still stems fromdark matterA new study, based on Machine learning And over a million simulations show that it is still too early to rule out this possibility.
An international team of researchers led by scientists from the University of Vienna and the Lawrence Berkeley National Laboratory has reexamined the radiation known as the "excess bthe center of the galaxy" – Galactic Center Excess, or GCE for short. This is a faint, almost spherical glow of gamma rays, extending thousands of light-years around the center of the Milky Way.
Since its discovery, astrophysicists have been trying to figure out what creates it. One explanation is the mutual annihilation of dark matter particles – a hypothetical process in which two particles meet, disappear and convert some of their mass into energy, including gamma rays.
A competing explanation is that the central region of the galaxy contains a large population of pulsars of milliseconds. These Neutron stars Rotating hundreds of times a second, they emit beams of radiation. If they are faint and far enough away, telescopes may not be able to detect each one individually, and their combined radiation will appear as a diffuse glow.
Neither explanation has yet been proven.
A crowded and noisy area with gamma radiation
The signal is particularly difficult to interpret because the center of the Milky Way is one of the densest and brightest regions in the gamma-ray sky. The region is home to many radiation sources, gas clouds, supernova remnants, stars, and compact bodies.
To identify the excess, researchers first need to estimate the expected radiation from all other sources. Any error in the background model could affect the shape and strength of the remaining signal.
"The interpretation of the signal is particularly difficult because the center of the galaxy is an unusually bright and dense region in the gamma-ray sky," explained Florian List of the University of Vienna, one of the study's authors.
Previous statistical analyses have often supported an explanation for unresolved point sources, including pulsars. However, some of these analyses were based primarily on the location of gamma-ray photons in the sky, without fully exploiting information about the energy of each photon.
Machine learning examined both location and energy
To overcome this limitation, the researchers developed an inference method based on a neural network. They trained it using more than a million simulations of the gamma-ray sky, which included different models of the background and possible sources of the excess.
The model simultaneously analyzed both the location of each photon and its energy. Energy adds information because different sources may create different distributions of photons across the gamma-ray spectrum.
Using the simulations, the researchers were able to examine what the signal would look like if it originated from diffuse and relatively smooth radiation, as might be expected from the annihilation of dark matter particles, and what it would look like if it originated from a population of faint point sources.
Adding information about the photon energy significantly changed the result.
If these are pulsars, there must be very many of them.
Previous studies suggested that the glow could be explained by a few hundred to a few thousand pulsars that are not seen individually. The new analysis shows that the point sources should be much fainter.
If the excess is indeed created by pulsars, more than 35,000 of them are required at a 90% confidence level. The model's median estimate is even higher, approaching 100,000 sources in the galactic center.
As each source becomes weaker, it becomes harder to statistically distinguish between a vast population of weak sources and a smooth, diffuse radiation. In the extreme case, each source produces on average a very small number of photons, and the aggregate picture resembles the radiation expected from dark matter annihilation.
"Our analysis shows that the sources should be so faint that it would be almost impossible to distinguish them from the radiation expected from self-annihilating dark matter," said Nicholas Rudd of Lawrence Berkeley National Laboratory.
This does not mean that such a population of pulsars does not exist. However, the explanation requires a much larger number of fainter bodies than some of the previous studies had assumed.
Dark matter has not been discovered.
The findings are not direct evidence of the existence of dark matter at the center of the Milky Way, nor do they prove that the excess is caused by the annihilation of its particles.
They also do not prove that the pulsar explanation is wrong. It is possible that there is indeed a very large population of faint pulsars in the center of the galaxy that have not yet been discovered. In addition, the result depends on the accuracy of the models used to describe the complex background radiation in the region.
The study mainly weakens a previous argument: that the non-uniform structure of the radiation necessarily indicates a relatively small number of point sources, and therefore contradicts the possibility of diffuse radiation from dark matter.
In the background model that best fit the data, the excess was largely consistent with diffuse emission of the kind expected in a dark matter annihilation scenario.
"The origin of the excess at the center of the galaxy is one of the longest-running debates in astrophysics," said List. "Our study does not show that dark matter is responsible for the signal, but it does suggest that it is still too early to rule out this possibility."
The debate is expected to continue.
More information will be needed to decide between the explanations. Direct detection of a large number of pulsars at the center of the galaxy would strengthen the astrophysical explanation. On the other hand, detection of a signal with similar characteristics in other galaxies or in objects rich in dark matter but poor in pulsars could strengthen the dark matter hypothesis.
Improved models of the background radiation, longer observations, and machine learning methods that combine spatial and spectral information could reduce uncertainty.
For now, the gamma-ray glow at the center of the Milky Way remains a mystery. The new study doesn't solve it, but it brings dark matter back to the center of the debate.
Questions and Answers
What is the excess at the center of the galaxy?
This is a gamma-ray glow observed in the region surrounding the center of the Milky Way, beyond the radiation expected from conventional models of gamma-ray sources and the galactic background.
How might dark matter create gamma rays?
In some models, dark matter particles are their own antiparticles. When two particles meet, they may annihilate each other, creating particles and radiation, including gamma rays. Such a process has not yet been directly observed.
What are millisecond pulsars?
These are dense neutron stars that rotate very rapidly, sometimes hundreds of times per second. They can emit gamma rays, and a large population of them may appear as a diffuse source of radiation.
Has the study proven that dark matter is at the center of the Milky Way?
No. The study showed that the data is still consistent with the possibility of dark matter radiation, but a very large population of faint pulsars could also explain them.
What did machine learning add?
The system analyzed both the location of the photons and their energy, after being trained on more than a million simulations. This allowed for a more complete comparison between diffuse radiation and populations of point sources.
How many pulsars are needed to explain the glow?
According to the analysis, more than 35,000 sources are required at a 90% confidence level. The model's median estimate is on the order of 100,000 sources.
The scientific article
Article publication date: June 12, 2026
For the scientific article: Opening the scientific article
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