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What we see in our universe only accounts for roughly five per cent of what’s out there. The remaining 95 per cent is invisible.
But now, a researcher at the University of Tokyo says he’s seen at least part of that invisible universe.
It’s believed that roughly 68 per cent of our universe is made up of dark energy, which is causing the universe to expand at an accelerating rate, and the remaining 27 per cent is dark matter, which keeps galaxies from flying apart.
The only problem is, we can’t see dark matter or dark energy: we only see how they interact with other objects, like galaxies.
In 1933, astronomer Fritz Zwicky wondered why galaxies in a cluster weren’t flying away from one another, based on ordinary matter. He proposed that there was an invisible form of matter holding them together.
We can actually see the effects of dark matter in galaxy clusters, which warps space-time. The streaks of light are galaxies hidden behind the cluster. (NASA, ESA, and J. Lotz and the HFF Team [STScI])
Then, in the 1970s, researcher Vera Rubin was also puzzled as to why stars in spiral galaxies were kept together rather than flying apart. She proposed that there was invisible matter that prevented this from happening: dark matter.
Since then, scientists have been struggling to “see” the dark matter in some form.
Now, astronomer and professor Tomonori Totani from the department of astronomy at the University of Tokyo says he has captured an image of dark matter using data from the Fermi Gamma-ray Space Telescope.
It’s not in visible light, but rather in gamma rays, a type of radiation.
Totani said he was skeptical when he first encountered what looked like a halo of gamma rays. “But when I took the time to check it meticulously and felt confident it was correct, I got goosebumps,” he said in an email. His findings were published in the Journal of Cosmology and Astroparticle Physics on Tuesday.
Questions remain
Astronomers don’t really know what dark matter is. But there is a theory that it is made up of something called weakly interacting massive particles, or WIMPS. These particles are heavier than protons but interact very little with other matter. The idea is that when these particles collide, they will annihilate each other, releasing other particles which include gamma rays.
It’s also believed that a good place to search for dark matter would be at the centre of our galaxy.
Using data from Fermi, Totani claims he has captured gamma rays from the centre of the Milky Way.
While he has written several studies about dark matter over the past 20 years, he only began to look for gamma rays from dark matter in early 2024. The research spun out of an earlier study of gamma rays using Fermi satellite data.
“A part of the Fermi data showed a peculiar excess that our model couldn’t explain, leading me to suspect it might be due to radiation originating from dark matter,” said Totani.
NASA’s Fermi Gamma-ray Space Telescope, illustrated here, scans the entire sky every three hours as it orbits Earth. (NASA’s Goddard Space Flight Center/Chris Smith [USRA/GESTAR])
But, as the great astronomer Carl Sagan once said, extraordinary claims require extraordinary evidence.
How does this hold up?
“I think the paper — the hype around the paper — doesn’t quite match up with the analysis,” said Renée Hložek, cosmologist and associate professor at the University of Toronto’s Dunlap Institute for Astronomy and Astrophysics.
This is a finding from a single author, which is rare. While Hložek said it’s not “inherently bad,” she noted that the paper also ignores quite a few other analyses that have tried to more accurately model the sort of “noise” that comes from our own galaxy, or the astrophysical foreground.
“So, if you’re making a giant claim about detecting the dark matter signal and you don’t either cite those papers or do a really careful analysis of the foregrounds, that’s what starts to make me worry that the analysis is not as rigorous as the claim.”
Hložek isn’t the only one questioning the claim.
While Totani is confident in his findings, he knows there’s more work to be done.
“If this radiation truly originates from dark matter, its scientific impact would be so immense that many researchers would likely proceed with caution in their assessments,” he said.
“I am confident in my own work, so I look forward to other researchers independently analyzing and confirming these results.”
