Scientists studying a mysterious signal from distant galaxies have not found dark matter as they expected. But the new inventive technique they used to detect this strange signal, which uses our own galaxy to hunt dark matter, could elevate the hunt for elusive material.
For decades, scientists have been looking for dark matter, an invisible material that does not interact with light but permeates our entire universe. And a signal from a nearby galaxy spotted in a 2014 study gave scientists hope it was long-sought-after evidence of dark matter.
Some current models predict that dark matter particles slowly decompose into ordinary matter, a process that would produce low photon emissions that X-ray telescopes could detect. And in 2014, scientists spotted an emission of X-rays from a galaxy while hunting for dark matter, as dark matter is known to accumulate around galaxies.
Researchers believe that the emission, known as the “3.5 keV line” (keV stands for kiloelectronvolts), likely consists of sterile neutrinos, which have long been considered a candidate for dark matter, co – study author Chris Dessert, of the University of Michigan, said Space.com.
Sterile neutrinos are hypothetical particles that are a close relative of the neutrino, a neutral subatomic particle with a mass very close to zero. They are released in nuclear reactions like those of nuclear power plants on Earth and in the sun. Because the small amount of mass in neutrinos cannot be explained by the standard model of particle physics, some believe that sterile neutrinos could constitute this mysterious mass which is actually dark matter.
But in this new study of objects in the Milky Way, which analyzed a mountain of raw data over the past 20 years from the XMM-Newton space telescope, the researchers found evidence that this signal seen in the 2014 study did not come from dark matter. In fact, looking for dark matter with their new technique, they didn’t see the signal at all. However, that does not rule out sterile neutrinos as a strong candidate for dark matter, the researchers said.
To reach this conclusion, the researchers looked for the 3.5 keV line in the sky. Since we live in the dark matter halo of the Milky Way, any observation made through the halo must contain dark matter.
So when the team found no trace of a 3.5 keV line in the data, they determined that “the 3.5 keV line was not due to dark matter,” said Dessert.
Now, while the 3.5 keV signature is likely caused by sterile neutrinos, this might seem to rule out the hypothetical particle as a candidate for dark matter. But it is always possible that different sterile mass neutrinos, which would not emit the same signal, could explain the elusive material.
“Even if you find this evidence convincing, that this 3.5 keV line is not necessarily there or is not necessarily dark matter, that does not exclude sterile neutrinos as candidates for dark matter”, Kerstin Perez, an assistant professor of physics at the Massachusetts Institute of Technology who was not involved in this study, said Space.com. There are “still many different masses that sterile neutrinos may have and which may still constitute all or part of the dark matter in the universe.”
New techniques for hunting dark matter
While Dessert admitted that it was quite disappointing that the researchers had not observed a 3.5 keV line, the technique they developed could aid in the search for the elusive material.
“Although this work unfortunately throws cold water on what looked like what might have been the first evidence of the microscopic nature of dark matter, it opens up a whole new approach to dark matter research, which could lead to a discovery in the near future, “said co-author Ben Safdi, assistant professor of physics at the University of Michigan, in a statement.
“In the past, people said,” Well, let’s look at a part of the sky that contains a huge amount of dark matter and see if we see [dark matter] over there, “said Perez.
But, with this team’s technique, which is similar to a technique that Perez uses in his own work, they use our place in the universe to their advantage because, “If this signal is really dark matter, it should to be everywhere in the sky with some varying intensity because we live in the halo of dark matter. ”
“I think this is a really exciting way to think about this research because it allows you to basically use the open sky,” added Perez. “Before, we were sort of taking snapshots of the sky and looking at them separately. ”
While researching the dark halo of the Milky Way for this signature helped the team determine that the signal was not from dark matter, it had additional benefits. “By looking through the halo of dark matter in the Milky Way, you don’t actually lose any sensitivity,” said Dessert.
“The previous techniques basically consist in directing your X-ray telescope towards a cluster of galaxies or simply a galaxy which has a halo of dark matter, and you are looking for the signal of disintegration of dark matter which will appear in the form of a line, ”Dessert continued. He added that with their technique in which they look through the dark matter halo of our galaxy, they are able to get better results in their research.
“The halo of dark matter around our galaxy is much closer to us, and that means you are more likely to get the photons resulting from the decomposition of dark matter in our galaxy than you are if you look at a cluster away. ”
Dessert added: “This technique that we have developed can be used in other research, for example for this 3.5 keV line. ”
This work was published today (March 26) in the journal Science.