[The Epoch Times, January 28, 2023](The Epoch Times reporter Linda compiled a report) Scientists say that by tracking the “heartbeat” of a special kind of star in the Milky Way, it may be possible to find the boundary of the Milky Way.
Trying to visualize the size of the universe is not only difficult and disturbing, but also full of paradoxes. In a sense, the scope of the universe is both finite, because it has not existed forever, and infinite, because it is constantly expanding in all directions. However, one can start by answering some more elementary and specific questions, such as understanding the size of the various celestial bodies in our universe.
So what celestial range is a better place to start than our own Milky Way? In two scientific presentations on Jan. 9 and 11 at the annual meeting of the American Astronomical Society in Seattle, astronomers said they may have finally pinpointed where the farthest boundary of the Milky Way is.
In short, astronomers estimate that our Milky Way is more than a million light-years from center to edge, half the size of our neighboring galaxy, Andromeda.
“This study redefines where the edge of the Milky Way is,” co-author Raja Guha Thakurta, a professor of astronomy and astrophysics at UC Santa Cruz, said in a statement. said the statement. “Both the Milky Way and Andromeda are so large that there is almost no spatial separation between them.”
A light-year is equivalent to about 6 trillion miles, and at a steady speed of 3,000 miles per hour (which is roughly the speed of the Artemis 1 lunar spacecraft), it would take more than two billion hours to travel that far, let alone a million Light years away.
Basically, the territory of the galaxy consists of three parts. First, several iconic spiral arms (our solar system is in one of them) make up the so-called “thin disk” (thin disk), which is scattered with stars, planets and moons, and is about 10 in diameter. million light years. Second, the bulging area at the center of the Milky Way is wrapped in an “inner halo” that contains some of the oldest stars and extends hundreds of thousands of light-years in every direction. Finally, there is an “outer halo”.
This elusive outer halo region floating around the inner halo is dominated by dark matter, which makes up most of the Milky Way’s mass. However, it is “the hardest part to study because the outer edge is so far away,” Sakata said. “Compared to the high star density in the disk and bulge regions, the stars here are fairly sparsely distributed.”
However, Sakata and other researchers have figured out a way to figure out where the Milky Way’s outer halo ends.
They tracked down the so-called RR Lyrae stars that live in the hazy light. This is a special kind of star whose brightness pulsates and whose size also expands and contracts regularly. It can be seen on astronomical instruments on Earth that its brightness changes over and over again between strong and weak.
“The brightness of this star looks like an electrocardiogram, and the pulsation is like the heartbeat of the Milky Way, with a rapid rise in brightness and a slow fall back, repeating perfectly with this characteristic curve,” Sakata said. “Also, if you measure the average brightness, every star is equally bright. This situation is great for studying the structure of the Milky Way.”
In other words, RR Lyrae is better for measuring distances because its average brightness can be measured. In contrast, other types of stars may appear bright because they are so close, but they may also be bright because they are not so close. RR Lyrae does not have this uncertainty, and its brightness is easily directly related to its distance, so it can help scientists measure and calibrate the structure of the entire universe.
“Only astronomers know how difficult it is to obtain these distances,” Yuting Feng, a doctoral student at UCSC and lead author of the study, said in a statement.
Feng and Sakata had great success in revisiting data collected by the Next Generation Virgo Cluster Survey, which imaged a large group of galaxies in the Milky Way’s vicinity, which also happened to capture a cluster of galaxies in the same field of view. Foreground stars – 208 of which are RR Lyrae stars.
“The data we used was a by-product of that investigation,” Feng explained. “This robust sample from the distant RR Lyrae star provides us with a powerful tool for studying halos and testing models of the size and mass of the Milky Way.”
Moreover, according to Feng, the team’s findings confirm long-held theoretical estimates of the boundary of the Milky Way’s outer halo. These estimates suggest that the outer halo is about 300 kiloparsecs, or 1 million light-years, from the center of the Milky Way — the team’s research found the star RR Lyrae to be between 20 and 320 kiloparsecs away, the latter being just over a hundred kiloparsecs from the center of the Milky Way. million light years. ◇
Editor in charge: Ye Ziwei