Astronomers have discovered a pair of previously unknown satellite galaxies orbiting the Milky Way. The location of these dwarf galaxies suggests that hundreds of other unknown mini-galaxies may be lurking around us – potentially challenging our understanding of the galactic edges.
A satellite galaxy is a cluster of stars, either circular or halo-shaped, that orbit the Milky Way independently of the rest of the galaxy. The largest known satellite of our galaxy is Large Magellanic Cloud, which holds about 30 billion stars and can be seen with the naked eye. Other known satellites contain only a few hundred thousand or a few million stars.
or Registration 2020 of known satellite galaxies suggests that scientists have found a maximum of about 60 satellite galaxies orbiting the Milky Way. However, there is some uncertainty about the true number of satellite galaxies, mainly because scientists disagree on how large these star clusters must be and how far they must extend from the galactic center to count as true satellites. , according to NASA.
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But most astronomers agree that there must be many more, currently unknown, satellite galaxies out there. Based on our current understanding of dark matter — which does not react with light, but interacts gravitationally with visible matter and it makes up about 27% of the mass of the universe — Researchers have long assumed that the Milky Way must have about 220 satellite galaxies. Our inability to distinguish many more of these is often referred to as the “missing satellites problem.”
In a new study, published June 8 in the journal Publications of the Astronomical Society of Japan, researchers discovered two new potential satellite galaxies, Sextans II and Virgo III. The satellites are located about 411,000 and 492,000 light-years from Earth, respectively, and are likely both ultra compact dwarf (UCD) galaxies – collections of old stars packed tightly together, making them brighter than other galaxies satellite.
However, the discoveries do not help solve the problem of missing satellites. Instead, the location and orientation of these possible satellites hint that there are even more satellite galaxies than scientists first realized. This raises a new problem, which the researchers have called the “many-satellite problem.”
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The researchers discovered the UCDs using the Hyper Suprime-Cam (HSC) attached to Japan’s Subaru Telescope at the Mauna Kea Observatory in Hawaii. This instrument has spent the last few years searching a region of space about 33 light years across. Based on the estimated 220 satellite galaxies assumed by the missing satellite problem, an area of this size should have an average of about four satellite galaxies, Universe Today recently reported.
However, the latest discoveries bring the total number of satellites found by the HSC in this area to nine. If this concentration of satellites is stable around the Milky Way, it means there could be at least 500 satellite galaxies around the Milky Way, the researchers write in a STATEMENT.
In the past, scientists have proposed multiple solutions to the problem of missing satellites, including that some satellite galaxies are hiding behind larger satellites and that others are so diffuse that they are almost impossible to detect with current technology. However, these factors are unlikely to be able to explain an abundance of stars, leaving scientists with no real way to explain the new results.
“The next step is to use a more powerful telescope that captures a wider view of the sky,” co-author of the study. Masahi Chiba, an astronomer at Tohoku University in Japan, said in the statement. This should help clarify how common satellite galaxies are, he added.
Such a telescope is forthcoming Vera C. Rubin Observatory — a modern facility equipped with the world’s largest digital camera, which is expected to come online in 2025, Chiba said. “Hopefully many new satellite galaxies will be discovered.”