Three years ago, Filippo Fraternali and his colleagues discovered half a dozen mysterious diffuse galaxies, which look like cities full of stars and gas. But unlike almost every other galaxy ever seen – including our own Milky Way – they don’t appear to be encased in the massive clumps of dark matter that would normally hold cities. stars and their gravity. The scientists selected a galaxy to zoom in, a modestly sized galaxy about 250,000 light-years away, and they directed the 27 antennas of the Very Large Array’s radio telescope in New Mexico at it.
After collecting 40 hours worth of data, they mapped the stars and gas and confirmed what previous snapshots suggested: “The dark matter content we infer in the galaxy This galaxy is much smaller than you would expect,” says Fraternali, an astronomer at the Kapteyn Institute of Astronomy at the University of Groningen in the Netherlands. If the team or their rivals find other such galaxies, it could pose a challenge for scientists’ view of dark problem, the dominant opinion in the field for at least 20 years. Fraternali and his team publish their findings in december in Monthly Notice of the Royal Astronomical Society.
Based on decades of telescope observations and computer simulations, scientists have thought of dark matter as the hidden skeleton of the universe; Its “couplings” are large masses of invisible particles containing galaxies large and small. But Fraternali is not the first to see an exception to that rule. A few years ago, Pieter van Dokkum, an astronomer at Yale, and his colleagues discovered Similar galaxies to Hubble telescope also seems to lack dark matter. “These galaxies that we found in 2018 have generated a lot of controversy, discussion and follow-up because they are unexpected and difficult to explain,” said Van Dokkum.
Those other galaxies live in a crowded environment where larger, nearby galaxies frequently pass by, possibly dragging dark matter with them. In contrast, Fraternali’s galaxy is quite isolated, without such nasty neighbors, so its scarcity of dark matter cannot be explained that way. “It can be very important,” van Dokkum said. “How can you combine stars and gas at that location without the help of dark matter?”
These strange objects are known as “super-diffusion galaxies”. They are extremely unusual: In terms of mass, they are very small, but they are spread out over vast distances. Some are as large as the Milky Way, but only a hundredth of a star — or even less. They are so nearly transparent that they are difficult to spy on in the night sky. “They’re a bit fainter in the center so they’re hard to spot. Now, with better telescopes and deeper observations, they are better known,” said Mireia Montes, an astronomer at the Space Telescope Science Institute in Baltimore and an expert. about such galaxies, said.
Starting in the 1960s, American astronomer Vera Rubin and others first revealed the possibility of invisible, or “dark” matter, while measuring the speeds of stars. Stars in galaxies orbit around the center, suggesting that the inner stars rotate at a different rate than the outer stars. Based on the rotations of those stars, the scientists calculated how much mass the galaxy must have to keep them in orbit, rather than into space. For many galaxies, that mass is many times greater than the mass of all the stars combined. The scientists solved the problem by deducing the presence of some kind of dark matter, which does not emit or reflect light, and must make up the rest of the mass that is holding the galaxy together .
