印度天文學家在宇宙黎明時期發現令人驚嘆的銀河系相似天體

Indian astronomers have made a remarkable discovery that could change what we know about the early universe. They found a massive spiral galaxy, named Alaknanda, that looks very similar to our own Milky Way. What makes this discovery so special is that Alaknanda is located 12 billion light years away, meaning we are seeing it as it was when the universe was only about 1. 5 billion years old. Since the universe is estimated to be 13. 8 billion years old, this galaxy formed when the cosmos was just a tenth of its current age.

The discovery was made by Rashi Jain, a PhD researcher at the National Centre for Radio Astrophysics in Pune, India. She was studying images and data from the James Webb Space Telescope, which was launched in 2021 by the US, European, and Canadian space agencies. Jain examined details of 70,000 objects, but only one stood out as a grand design spiral galaxy. Alaknanda spans about 30,000 light-years in diameter and has two symmetrical arms that wrap around a bright central bulge. These arms show a 'beads-on-a-string' pattern, which means there are clusters of stars along the spiral arms, similar to what we see in nearby spiral galaxies today.

Professor Yogesh Wadadekar, Jain's supervisor, was initially skeptical about the discovery. He explained that it is astonishing for such a large galaxy with spiral arms to exist just 1. 5 billion years after the Big Bang. Alaknanda had to gather 10 billion solar masses of stars and form a large disc with spiral arms in only a few hundred million years, which is extremely fast by cosmic standards. Scientists used to believe that galaxies in the early universe were small, irregular, and chaotic. However, Alaknanda is one-third the size of the Milky Way and is forming new stars at a rate 20 to 30 times faster than our galaxy does today. This challenges previous ideas about how galaxies formed and evolved.

Since the James Webb Space Telescope began its work, astronomers have found more distant and sophisticated galaxies. The discovery of Alaknanda adds to the evidence that the early universe was more creative and mature than previously thought. Jain says that finding such a well-formed spiral galaxy so far back in time is rare, but it forces scientists to rethink their understanding of the universe's early history. The information we have about Alaknanda comes from 12 billion years ago, as its light has traveled that long to reach us. Jain explains that we can only see a snapshot of the galaxy's past, not its entire life. For now, researchers plan to use the James Webb Space Telescope and other observatories to study Alaknanda further and learn how it formed its spiral arms. They believe that understanding galaxies from the past can help us unlock secrets about the present and future of the universe.