The diameter of the Milky Way is between 100,000 and 180,000 light-years, but the “halo” surrounding the entire Milky Way is as large as a million light-years. Astronomers recently discovered more than 200 distant variable stars in the outer halo of the Milky Way, one of which is 1.04 million light-years away from the center of the Milky Way, and is likely to reach the farthest boundary of the Milky Way.
RR Lyrae variable stars (RR Lyrae) are periodic variable stars whose characteristic pulsation and brightness often make them used as “candles” to measure the distance of galaxies. A new study has used this type of variable stars to track the boundary of the Milky Way’s outer galactic halo.
The diameter of the Milky Way ranges from 100,000 to 180,000 light-years (there are differences in the calculation methods). Basically, we can divide the territory of the Milky Way into three major blocks: the spiral arms and the disk of the Milky Way that accumulate a large amount of dust and gas and stars and galaxies; The raised area surrounded by the inner halo in the center of the plane contains the oldest stars in the Milky Way; and the wider outer halo surrounds the entire Milky Way, which is also the most difficult part of the Milky Way to study, because it is mainly filled with dark matter, and the boundary is too fuzzy and far away .
Previous model studies have calculated that the outer galactic halo should extend about 1 million light-years from the center of the galaxy, and the University of California, Santa Cruz team used the data from the NGVS survey of nearby galaxies to track 208 RR Lyrae variable stars in the hazy light, and calculated The results show that the outer galactic halo is indeed about 1 million light-years away from the galactic center, and one of the variable stars is 1.04 million light-years away from the galactic center, which is probably located at the farthest boundary of the Milky Way.
In short, astronomers believe that the territory of the Milky Way extends more than 1 million light-years from the center, almost half the distance from our nearby neighbor, the Andromeda Galaxy.
(The first picture is a schematic diagram, source: pixabay)
