A young open cluster called NGC 2516 has a classical tidal radius of 10 parsecs (33 light-years) and a halo of stars spanning at least 500 parsecs (1,600 light-years), according to new research led by Princeton University astronomers.
The open star cluster NGC 2516. Image credit: Centre de Données astronomiques de Strasbourg / SIMBAD / DSS2.
NGC 2516 is an open star cluster located 1,217 light-years away in the southern constellation of Carina.
Also known as Caldwell 96, the Southern Beehive, and the Sprinter, it was discovered by the French astronomer Nicolas-Louis de Lacaille in the 1750s.
“Recent analyses of data from ESA’s Gaia mission have reported the existence of diffuse stellar populations surrounding nearby open clusters,” said Luke Bouma, a graduate student at Princeton University.
“It is important to verify that these halos, tails, and strings are of similar ages and compositions as stars in the denser part of the cluster.”
Bouma and his colleagues used data from NASA’s Transiting Exoplanet Survey Satellite (TESS) to precisely measure the rotation rates of stars that Gaia had assigned to NGC 2516.
The researchers demonstrated that many stars with similar masses are all spinning at — or very near — the same rate, confirming that they were born in the same stellar nursery.
“What’s so surprising about this work — what’s so exciting — is that we confirmed that Gaia, because it really precisely measures the positions and the motions of stars, can find these ‘needles in the haystack’ of the Milky Way,” Bouma said.
“Gaia can identify all the stars that are moving in the same direction, at the same rate. And we don’t have to just trust the machine learning algorithm saying that they’re related — we can verify it with TESS data, using our gyrochronological technique.”
“In retrospect, the existence of this large stellar stream is not too surprising,” he added.
“One interpretation could be that a cluster starts as a tight clump that expands through time to form tidal tails stretching in front of it and behind it, as it moves through the Milky Way.”
“The broader implication is that there are bound to be other enormous open clusters like this.”
“The visible part of the cluster, where we can easily see the stars close together, may be only a small part of a much, much larger stream.”
The scientists presented their results this week at the 238th meeting of the American Astronomical Society (AAS).
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L.G. Bouma et al. 2021. An open cluster spread across 500 parsecs. AAS 238, abstract # 227.05
