Astronomers in the US have discovered some of the most distant stars which have been found in galaxy us, specifically in the galactic halo, i.e. the extended spheroidal region surrounding the main body of the galaxy. Thanks to these new observations, scientists now have a better picture of the outer limits of the halo.
Specifically, they were found 208 variable stars of the RR Lyrae typewith the most distant of these being more than a million light-years from Earth and to be almost halfway to our neighboring Andromeda galaxy, which is about 2.5 million light-years away. The ancient stars in question are, as reported by APE-MPE, of predictable changing brightness (it fluctuates within a repeating cycle) and are thus considered ideal as reference points for measuring galactic distances.
“The new research redefines what constitutes the outermost limits of our galaxy. In fact, our galaxy and Andromeda are both so large that there is almost no gap between the two galaxies,” said University of California, Santa Cruz astronomy and astrophysics professor Raja Guha Thakurta, who made the announcement in American Astronomical Society Conference in Seattle.
Astronomers pointed out that the surrounding halo, made up of various scattered stars, is much larger than the main disc of our galaxy, which does not exceed 100,000 light-years in diameter. Our solar system with Earth is located in one of the spiral arms of the disk. In the middle of the disk is a central “bulge” and around it is the halo containing the oldest stars in our galaxy, which stretches hundreds of thousands of kilometers in every direction.
Halo is difficult to study because it is so far from Earth and furthermore its stars are very sparse compared to those in the central galactic disk. On the other hand, the halo is dominated by dark matter and thus contains most of the total galactic mass.
Based on previous estimates, the halo extends up to 300 kiloparsecs, or about one million light-years from the galactic center (one kiloparsec is 3,260 light-years), but the new study extends the halo’s outer limit to at least 320 kiloparsecs.
Source: News Beast
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