The meetings of the American Astronomical Society never disappoint astronomy and universe enthusiasts, as many scientists take advantage of them to present their latest findings. And the 241st meeting being held these days in Seattle, Washington, was no exception. Two talks, the first on January 9th and the second today, the 11th, have taken center stage this time, because at them, Yuting Feng and Guha Thakurta, astronomers at the University of California, Santa Cruz, announced the discovery of the most distant stars in our galaxy. Some 200 distant variable stars, known as RR LYrae, are located more than a million light-years away from us, at the outer edges of the Milky Way's halo. This is truly incredible, given the size of our galaxy, about 100,000 light-years across, which is almost half the distance from Andromeda, our neighboring galaxy 2.5 million light-years away. The characteristic pulsations and brightness of RR Lyrae stars make them excellent 'standard candles' for measuring galactic distances. So these new observations allowed Feng and Thakurta to discover how far the Milky Way's halo really extends. "This study," says Thakurta, "is redefining what constitutes the outer limits of our galaxy. The Milky Way and Andromeda are so large that there is barely any space between the two galaxies." Related News standard No Two growing black holes found together, the closest ever observed J. de J. The two objects are only 750 light-years away from each other, a cosmic 'step' away During his talk, Thakurta explained that our galaxy's stellar halo is much larger than the disk, which is about 100,000 light-years across. Our solar system resides in one of the disk's spiral arms. In the middle of the disk is a central bulge, and surrounding it is the halo, which contains the galaxy's oldest stars and extends for hundreds of thousands of light-years in all directions. "The halo," the astronomer lauded, "is the most difficult part to study because its outer limits are very far away. Stars there are very few compared to the high stellar densities of the disk and the bulge, but the halo is dominated by dark matter and actually contains most of the galaxy's mass." A theory confirmed Feng, for his part, highlights that previous studies had already calculated that the stellar halo should extend around 300 kiloparsecs (or 1 million light-years) from the galactic center. (One kiloparsec is equivalent to 3,260 light-years.) And now, those distances are confirmed, as the 208 RR Lyrae stars detected by Feng and his colleagues were between 20 and 320 kiloparsecs away. “We were able to use these variable stars as reliable tracers to pinpoint the distances,” says Feng. “Our observations confirm theoretical estimates of the halo size, so this is an important result.” “The way these stars vary their brightness,” explains Thakurta, “is similar to an electrocardiogram. They’re like the heartbeat of the galaxy, so the brightness increases rapidly and decreases slowly, and the cycle repeats perfectly in this very characteristic way. Moreover, if you measure their average brightness, it turns out to be the same from star to star.” And this combination is fantastic for studying the structure of the Galaxy." As astronomers know very well, the brightness of a star can be deceptive. Some are brighter than others, but a star can appear bright because it is actually very luminous or because it is very close to us, and it can be difficult to tell the difference. But astronomers can identify an RR Lyrae star from its characteristic pulsations, and then use its observed brightness to calculate how far away it is. The procedures are not simple, and sometimes the most distant objects, such as quasars, can pass themselves off as RR Lyrae stars. MORE INFORMATION news No Dust storms and the first halo on another planet: everything a Spanish instrument has detected during a Martian year news No The major scientific advances expected for 2023 "Only astronomers know how painful it is to obtain reliable markers of these distances," Feng said. And now, this robust sample of distant RR Lyrae stars gives us a very powerful tool to study the halo and test our current models of our Galaxy's size and mass.
