In space, the gravitational pull of large objects is not inhibited by small ones. The moons are locked in the orbits of the planets. Planets, asteroids and comets orbit massive stars, and stars gather around supermassive black holes, forming galaxies.
Big star necks, like the neckattract small constellations. The area of our solar system spans 100,000 light-years and is between 100 billion and 400 billion stars. The Milky Way is so large that, over billions of years, its mass has captured many of the smaller galaxies, containing no more than a few billion stars, as satellites.
But how many satellite groups does the Milky Way have?
The number is changing as new telescopes and astronomical observations reveal ever-faint galaxies. But let’s start with the ones we can easily see. The two most prominent satellite constellations of the Milky Way are the Large Magellanic Cloud and the Small Magellanic Cloud. They orbit the Milky Way at a distance of about 160,000 light-years and are visible from the Southern Hemisphere without a telescope, according to NASA’s Goddard Space Flight Center.
However, such highly visible satellites are the exception, not the rule. Most satellite galaxies are so small and faint that they are invisible to all but the most powerful telescopes. Scientists find small galaxies by using instruments with a wide field of view to capture as much of the sky as possible. Or Starlingassociate professor of astronomy at the University of Portsmouth UK
“As telescopes get bigger and our instruments get better, we can get down to very faint galaxies, all the way down to what are now called ‘ultra-faint dwarfs,’ which have very faint stars.” only a few hundred, Graur told Live Science.
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Determining whether a small nearby galaxy is a satellite of the Milky Way involves spectroscopy – an analysis of the light it emits – to determine its motion and direction, it said. Marla Gehaprofessor of astronomy and physics at Yale University.
“Now you can tell if that object is subject to gravity, and if that cluster is still orbiting the Milky Way,” Geha told Live Science. “There is a satellite galaxy now – and it will always be around – a large galaxy.”
The latest Census, published in 2020 by The Astrophysical Journalit is estimated that there were about 60 satellites orbiting the Milky Way at a distance of about 1.4 light years. However, the exact number of galaxies in the Milky Way is difficult to determine, partly because not all proposed satellite groups have been definitively confirmed to be orbiting the Milky Way.
“There are probably five to eight objects that don’t have spectroscopy or spectroscopies that don’t make sense,” Geha said. In addition, new satellite options are being discovered, he added.
Geha studies the origin and evolution of young galaxies, and when he began his research more than two decades ago, the Milky Way had only 11 known satellites. That changed when the Sloan Digital Sky Survey began collecting data in the early 2000s, Geha said. Sloan produced the first digital map covering more than one-third of the night sky, and its digital camera improved astronomers’ chances of seeing faint constellations. Their dim light is often obscured by brighter stars closer to Earth.
Using Sloan’s digital images, the researchers could algorithmically remove foreground stars — something that was very difficult to do with analog photos and photographic plates, Geha said. This revealed many small, faint galaxies that were previously hidden.
“Each of these new discoveries has changed the game,” Geha said. “Technology is really driving all this data and the number of satellites we know about.”
From Sloan in the 2000s to the Dark Energy Survey in the 2010s, each study revealed many satellite galaxies orbiting the Milky Way. The Vera C. Rubin Observatory in Chile is likely to find hundreds more satellites, Geha said – that is, if the Milky Way doesn’t eat up galaxies first.
“Satellite galaxies are connected to the Milky Way,” Graur said. Slowly, it draws them in. As it draws them in, it begins to tear them apart and finish them.”
One such victim was a small galaxy now known as Gaia Enceladusthat was torn apart and swallowed up by the Milky Way and whose stars now shine in the Milky Way’s light, Graur said. Eventually, satellite constellations visible today will probably suffer the same fate, Geha added.
“If we wait a very long time, billions and billions of years,” he said, “those galaxies will collapse into the parent and merge and form an even bigger galaxy.”
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