Record-breaking faint and light companion to the Milky Way discovered (which may be packed with dark matter)


Astronomers have discovered a record-breaking galaxy. The Milky Way satellite is so light and small that scientists wonder how it is possible that it still exists. The answer: the new discovery is probably packed with dark matter.

The new supervisor’s name is: Ursa Major III/UNIONS 1in other words UMa3/U1 and is a so-called Milky Way satellite: the system orbits our galaxy. UMa3/U1 is located in the constellation ‘Great Bear’ and is relatively close at a distance of 30,000 light years from the sun. The galaxy is also very small: from top to bottom it measures only 10 light years. UMa3/U1 contains a total of about 60 stars, which together weigh sixteen times more than the Sun. Scientist Will Cerny contributed to the research. He explains: “UMa3/U1 is so small that it is very surprising that it still exists today. It would have made sense if the Milky Way Galaxy’s strong force had pulled the galaxy apart. The fact that this has not yet happened leads to two possibilities: or UMa3/U1 is a small galaxy that is held together by a lot of dark matter, or this is a star cluster that will soon die. Given that all stars have approximately the same speed, we think this is probably the first option: a galaxy packed with dark matter.” The results of the research have been published in the journal The Astrophysical Journal.

For the study, the researchers used two observatories in Hawaii: W. M. Keck Observatory and Canada-France-Hawai’i Telescope (CFHT). UMa3/U1 was first spotted by the Ultraviolet Near Infrared Optical Northern Survey (UNIONS) by CFHT. The scientists then chose to investigate the galaxy further by using the other observatory, which is the Deep Imaging Multi-Object Spectrograph (DEIMOS) houses. Fellow scientist Marla Geha also contributed to the research. She explains: “UMa3/U1 contains so few stars that it could well be a coincidental grouping of similar stars. The measurements of DEIMOS however, clearly show that this is not the case. Thus, all stars move at more or less the same speed and share similar chemical compositions.”

Credit: CFHT/S. Gwyn (right) / S. Smith (left)

Big bang
The results of the study are potentially significant, because they may be Lambda Cold Dark Matter (LCDM)model could support. This theory predicts that galaxies like the Milky Way are surrounded by faint and old companions that are packed with dark matter. And UMa3/U1 can be the textbook example of this; Researchers suspect that it even harbors 7,000 times more dark matter than ‘normal’ matter. It is still unclear whether that is really the case. This requires very detailed measurements of the movements of the stars in UMa3/U1. But the researchers actually expect that this will show that the system contains a particularly large amount of dark matter. UMa3/U1 moves through the innermost regions of the Milky Way, where the galaxy is being pulled heavily and you would expect it to be completely torn apart in the absence of the binding agent called dark matter. “Without dark matter, it is not clear how UMa3/U1 has survived for so many billions of years,” said researcher Raphaël Errani.

Although more research is desperately needed, the researchers are very pleased with their discovery. “Whether future observations confirm that the system harbors a large amount of dark matter or reject that idea; We are very excited because this object could be the tip of the iceberg: a first example of a new class of extremely faint stellar systems that have managed to escape detection until now,” says Cerny.

The article is in Dutch

Tags: Recordbreaking faint light companion Milky discovered packed dark matter


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