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January 1, 2026<\/p>\n
4 min read<\/p>\n
Add Us On Google<\/span>Add SciAm<\/span><\/span><\/p>\n The Pleiades Star Cluster Has a Secret Stellar Family Scattered across the Milky Way<\/p>\n The \u201cSeven Sisters\u201d of the Pleiades are part of a much larger complex that can help reveal our galaxy\u2019s deep history<\/p>\n By Phil Plait edited by Lee Billings<\/span><\/p>\n A view of the Pleiades, a star cluster about 440 light-years from Earth.<\/p>\n ROBERT GENDLER\/SCIENCE PHOTO LIBRARY\/Getty Images<\/p>\n The sun wanders the Milky Way alone; our star orbits the galaxy\u2019s distant center without any stellar siblings. But it wasn\u2019t always this way. The solar system was very likely born in a tremendous gas cloud that also birthed thousands of other stars, forming a large, loosely bound stellar family called an open cluster.<\/p>\n These stars may have remained enshrouded in that nebula for 10 million years or more, until their combined stellar winds and light pushed away the surrounding nebulosity. No longer embedded in the gas, the cluster gradually disintegrated as its internal motions flung away some of its members. Throw in collisions with other huge clouds of gas and dust, as well as interactions with the galaxy\u2019s gravitational field, and the cluster\u2019s fate was sealed: its stars dispersed, eventually mixing with the background \u201cfield\u201d stars in the Milky Way.<\/p>\n Our solar kin may be long lost, but that\u2019s not the case for all stars. Some groupings are younger than the sun\u2019s 4.6-billion-year age\u2014and are still in the process of eroding away. Interestingly, we see such loose affiliations of stars (called associations) all over the sky, and they often share similar characteristics, such as age and velocity, through the galaxy. Astronomers now suspect that many of these scattered associations formed in the same gas cloud, where they were born as part of a single, sprawling structure that has since broken up. But we might yet glimpse parts of such long-lost clusters that are still intact because stars from their close-packed cores should be tightly bound to each other via gravity and thus able to survive as a tight-knit group for much longer.<\/p>\n If you’re enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.<\/p>\n Finding such surviving clusters is important; they can tell us about when and where many of the Milky Way\u2019s stars formed and how our galaxy\u2019s stellar populations and structures evolved over billions of years. In short, studying these stellar relics can lead to a better perception of the galaxy as a whole.<\/p>\n So where are they?<\/p>\n If you\u2019re in the Northern Hemisphere and go outside on a clear winter\u2019s night, you might notice a fuzzy clutch of stars not too far from Orion. This is the Pleiades (pronounced \u201cPLEE-uh-deez\u201d), a lovely cluster that is about 440 light-years from Earth and located in the constellation Taurus. Six stars can be seen by the unaided eye, although many cultures\u2019 ancient myths indicate there are seven. It\u2019s possible two of the stars have moved closer together in the sky over time, making it hard to separate them; we still call these stars the Seven Sisters.<\/p>\n Binoculars reveal many dozens of stars in the Pleiades, and hundreds can be seen in deep astronomical images. The cluster doesn\u2019t have a sharp boundary, but most of the stars are found in a volume that is about 40 light-years across.<\/p>\n It\u2019s about 125 million years old, give or take several million years. If it was once part of a bigger structure, this estimated age would align with our expectation that that structure\u2019s outer stars would have been shaken loose. Could the Pleiades be the leftover core of a long-gone cluster?<\/p>\n Finding any far-flung stars that once were anchored by the Pleiades is not an easy task. The sky is big, and the Pleiades\u2019 swath of the Milky Way also contains millions of other stars. Astronomers took this on, however, and published their results on November 12 in the Astrophysical Journal.<\/p>\n They were clever, reasoning that any stars that used to hang out with the Pleiades would have similar ages and chemical compositions, and would probably still have close to the same motion through the galaxy, as the cluster\u2019s current members. By cross-referencing known Pleiades members and a vast stellar database from the European Space Agency mission Gaia, the team pinpointed a selection of stars hurtling through the Milky Way within five kilometers per second of the galactic velocity of the Pleiades.<\/p>\n To firm up this connection, the researchers next estimated the ages of these stars\u2014a difficult task but one that was made easier by the knowledge that younger stars tend to rotate faster than older ones. (This effect exists because a star\u2019s magnetic field can sweep up surrounding material and act like drag on a parachute, slowing the star\u2019s spin.) A star\u2019s rotation can be determined by looking for tiny variations in brightness as dark star spots\u2014which are like the sun\u2019s sunspots but appear on other stars\u2014rotate in and out of view. Using data from NASA\u2019s Transiting Exoplanet Survey Satellite, which can precisely measures stellar brightness, the astronomers found stars that rotated with periods shorter than 12 days, which is roughly the expected spin rate for stars as old as the average Pleiades member.<\/p>\n Finally, after applying various statistical techniques to look for other stars, the researchers wound up with a list of more than 10,000 possible members of what they called the Greater Pleiades Complex. Mapping these members in three dimensions, they found that the stars fall in a slightly elongated grouping that is about 1,600 by 2,000 light-years in size. This includes stars that belong to at least seven previously known associations. Among these associations is the AB Doradus group, which contains a few dozen stars that are only about 70 light-years from the sun. Another, called UPK 303, had been proposed to be a \u201ctidal tail\u201d of the Pleiades, stars torn away from the cluster by the galaxy\u2019s gravity, and the new study supports that conclusion. In fact, looking at the stars\u2019 motions and running the clock backward, the astronomers found that they were all within about 200 light-years of the central Pleiades about 75 million years ago, which is consistent with all of these stars being part of a larger structure that is now well into the process of \u201cevaporating\u201d into the galaxy.<\/p>\n This delights and amazes me. I\u2019ve had my eye on the Pleiades ever since I first started looking at the sky as a wee lad, and I cannot say how many times I\u2019ve gawked at them through various telescopes and in dramatic images. If you go out sometime to look at them\u2014and I really hope you do\u2014gaze upon that tight little cluster and consider that there\u2019s still so much we don\u2019t know about these stars\u2014and so much more they can tell us about the cosmos.<\/p>\n If you enjoyed this article, I\u2019d like to ask for your support. Scientific American<\/span> has served as an advocate for science and industry for 180 years, and right now may be the most critical moment in that two-century history.<\/p>\n I\u2019ve been a Scientific American<\/span> subscriber since I was 12 years old, and it helped shape the way I look at the world. SciAm <\/span>always educates and delights me, and inspires a sense of awe for our vast, beautiful universe. I hope it does that for you, too.<\/p>\n If you subscribe to Scientific American<\/span>, you help ensure that our coverage is centered on meaningful research and discovery; that we have the resources to report on the decisions that threaten labs across the U.S.; and that we support both budding and working scientists at a time when the value of science itself too often goes unrecognized.<\/p>\n In return, you get essential news, captivating podcasts, brilliant infographics, can’t-miss newsletters, must-watch videos, challenging games, and the science world’s best writing and reporting. You can even gift someone a subscription.<\/p>\n There has never been a more important time for us to stand up and show why science matters. I hope you\u2019ll support us in that mission.<\/p>\n","protected":false},"excerpt":{"rendered":" January 1, 2026 4 min read Add Us On GoogleAdd SciAm The Pleiades Star Cluster Has a Secret Stellar Family Scattered across the Milky Way The \u201cSeven Sisters\u201d of the Pleiades are part of a much larger complex that can help reveal our galaxy\u2019s deep history By Phil Plait edited by Lee Billings A view<\/p>\n","protected":false},"author":1,"featured_media":40044,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[58],"tags":[12803,2906,21602,537,622,21603],"class_list":{"0":"post-40043","1":"post","2":"type-post","3":"status-publish","4":"format-standard","5":"has-post-thumbnail","7":"category-science","8":"tag-cluster","9":"tag-family","10":"tag-pleiades","11":"tag-secret","12":"tag-star","13":"tag-stellar"},"_links":{"self":[{"href":"https:\/\/naijaglobalnews.org\/index.php?rest_route=\/wp\/v2\/posts\/40043","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/naijaglobalnews.org\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/naijaglobalnews.org\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/naijaglobalnews.org\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/naijaglobalnews.org\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=40043"}],"version-history":[{"count":0,"href":"https:\/\/naijaglobalnews.org\/index.php?rest_route=\/wp\/v2\/posts\/40043\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/naijaglobalnews.org\/index.php?rest_route=\/wp\/v2\/media\/40044"}],"wp:attachment":[{"href":"https:\/\/naijaglobalnews.org\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=40043"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/naijaglobalnews.org\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=40043"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/naijaglobalnews.org\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=40043"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}On supporting science journalism<\/h2>\n
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