1239: #ClassicKenCroswell: The mysteries of Halo Stars. Ken Croswell, Scientific American.

Published: March 1, 2021, 12:50 a.m.

Photo: Hot stars burn brightly in this image from NASA’s Galaxy Evolution Explorer, showing the UV side of a familiar face. At 2.5 million light-years away, the Andromeda galaxy is our Milky Way’s largest galactic neighbor. The bands of blue-white making up the galaxy’s striking rings are neighborhoods that harbor hot, young, massive stars. Dark blue-grey lanes of cooler dust show up starkly against these bright rings, tracing the regions where star formation is currently taking place in dense cloudy cocoons. The stellar halo is a nearly spherical population of field stars and globular clusters (https://en.wikipedia.org/wiki/Globular_cluster) . It surrounds most disk galaxies as well as some elliptical galaxies of type cD (https://en.wikipedia.org/wiki/Type-cD_galaxy) . A low amount (about one percent) of a galaxy's stellar mass resides in the stellar halo, meaning its luminosity is much lower than other components of the galaxy.  —WIkipedia (https://en.wikipedia.org/wiki/Galactic_halo#cite_note-6) "The Halo Stars is the name given to the ancient formation of stars which encircle the outer edge of the Milky Way Galaxy (https://warhammer40k.fandom.com/wiki/Milky_Way_Galaxy) , representing the last stellar clusters to be encountered before one enters the eternal, frigid night of the intergalactic void. The Halo Stars are believed to be the oldest stars in the galaxy and their circumference extends for approximately 200,000 light years around the Milky Way, usually grouped in a cluster formation. The Halo Stars may also be intermixed into the shroud of dark matter that is known to extend beyond the visible disk of the galaxy for several hundred thousand light years." https://warhammer40k.fandom.com/wiki/Halo_Stars http://JohnBatchelorShow.com/contact http://JohnBatchelorShow.com/schedules Parler & Twitter: @BatchelorShow #ClassicKenCroswell: The mysteries of Halo Stars. Ken Croswell, Scientific American. http://www.scientificamerican.com/article/ancient-halo-stars-cast-the-milky-ways-first-light/ "...The star is much older than a globular cluster with the same chemical composition, however. "I think there's a real age difference," VandenBerg says. The cluster, named M92, lies in the constellation Hercules and is only about 12.5 billion years old—some 1.5 billion years younger than the star. Both have the same low iron abundance, about one two-hundred-fiftieth that of the sun. "It's the same story for the other star, named HD 132475, which is younger and richer in iron. It is some 320 light-years away and around 12.6 billion years old—about a billion years older than globular cluster M5, whose iron abundance of about one thirtieth of our sun’s matches that of the lone halo star. Thus, as the astronomers report in the September 10 issue of The Astrophysical Journal, both stars apparently formed well before the clusters they resemble. "It makes sense astrophysically," Gilmore says. Early on, he explains, the galaxy probably couldn't make big clusters but instead only individual stars and small stellar groups. Stars form when clouds of gas collapse. But to collapse a cloud must cool; in the modern Milky Way carbon and oxygen atoms radiate heat, cooling clouds to frigid temperatures. But the early galaxy had little carbon or oxygen. As a result, Gilmore says, something as grand as a globular cluster could emerge only after supernovae had cast these two crucial elements into space. So the first objects the Milky Way formed were instead individual stars.