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three years ago, Filippo Fraternali and his colleagues discovered six mysterious diffuse galaxies that look like huge stars and gas cities. But unlike almost all other galaxies we’ve seen—including our own Milky Way—they don’t seem to be enveloped by large amounts of dark matter, which usually uses their gravity to gather these stellar metropolises together. The scientists selected a medium-sized galaxy about 250,000 light-years away to zoom in, and they pointed the 27 radio telescope antennas of the New Mexico Very Large Array at it.
After collecting 40 hours of data, they mapped the stars and gas and confirmed what the earlier snapshots suggested: “We inferred that the amount of dark matter in this galaxy is much smaller than you expected,” said Fraternali, an astronomer at the Kaputan Institute of Astronomy, University of Groningen, the Netherlands. If the team or their competitors discover other such galaxies, this may pose a challenge to scientists’ research. the opinion of dark matter, The dominant perspective in this field for at least 20 years. Fraternali and his team Published their findings December at Monthly Bulletin of the Royal Astronomical Society.
Based on decades of telescope observations and computer simulations, scientists have begun to regard dark matter as the hidden skeleton of the universe; its “joints” are huge clusters of invisible particles that carry large and small galaxies. But Fraternali is not the first to see an exception to this rule.A few years ago, astronomer Pieter van Dokkum of Yale University and his colleagues Find Similar galaxies Hubble Space Telescope It also seems to lack dark matter. “The galaxies we discovered in 2018 were unexpected and difficult to explain, which caused a lot of controversy, discussion and follow-up work,” van Dokkum said.
Those other galaxies live in crowded environments, where larger neighboring galaxies often fly by and may take away dark matter. In contrast, Fraternali’s galaxy is very isolated and has no such troublesome neighbors, so the lack of dark matter cannot be explained in this way. “This can be very important,” van Dokkum said. “Without the help of dark matter, how would you gather the stars and gas in that place?”
These strange objects are called “super-diffused galaxies.” They are extreme outliers: in terms of their mass, they are small, but they are distributed far away. Some are as big as the Milky Way, but only one percent of the stars-or even fewer. They are almost transparent, so that it is difficult to snoop in the night sky. “They are slightly weaker in the center, so they are difficult to spot. Now, with better telescopes and deeper observations, they become more well-known,” astronomers at the Baltimore Space Telescope Institute of Science and experts in such galaxies. Miria Montes said.
Beginning in the 1960s, when American astronomer Vera Rubin and others measured the speed of stars in a galaxy around the center, they first revealed that there may be invisible matter or “dark” matter, indicating internal stars It travels at a different speed from the outer star. Based on the rotation of these stars, scientists calculated how much mass the galaxy must have to keep them orbiting instead of being thrown into space. For many galaxies, this mass is many times greater than the sum of the masses of all stars. Scientists solved this problem by inferring the existence of certain dark matter, which does not emit or reflect light, and must constitute the rest of the mass that holds the galaxies together.
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