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An international team of astronomers found that the Milky Way is not just a flat disk, but it contains several concentric ripples. As a result, the new findings reveal that our galaxy may be at least 50 percent larger than previously thought.
During their research, the astronomers sifted through the huge amounts of data collected in 2002 by the Sloan Digital Sky Survey, which has provided us so far with the most detailed 3-D maps of the Universe.
The research team was led by Heidi Jo Newberg, a professor of physics and astronomy at the Rensselaer Polytechnic Institute’ School of Science in Troy, New York. To their surprise, scientists found that the reviewed data was pointing out several rings of stars that may substantially enlarge the current known size of the Milky Way.
“In essence, what we found is that the disk of the Milky Way isn’t just a disk of stars in a flat plane–it’s corrugated. As it radiates outward from the sun, we see at least four ripples in the disk of the Milky Way,”
briefly explained Prof Heidi Newberg.
However, Prof Newberg acknowledged that the four ripples were detected only in the visible part of the Milky Way. So, the idea that there may be more and that the pattern repeats thought the disk is currently just an assumption.
Yan Xu, a Chinese scientist from the Academy of Science’s National Astronomical Observatories of China in Beijing and lead-author of the findings, said that the bulging rings of stars had been previously detected, but astronomers thought that they weren’t parts of the Milky Way. However, the new data shows that the rings are important components of our galaxy since they extend its previously known width of 100,000 light-years to 150,000 light-years.
Mr. Xu also explained how his team managed to draw the new conclusions. He said that, while sifting through previous data, astronomers noticed that the number of stars in Milky Way suddenly dropped at about 50,000 light-years from its center, but at 60,000 light-years from the galaxy’s core there was a ring of stars.
So, astronomers assumed that the ring is not separate from the galaxy. Instead, it is a ripple in its disk, Mr. Xu said. He also said that more ripples may inhabit the Milky Way, but more research needs to be done.
The paper on the new discovery was entitled “Rings and Radial Waves in the Disk of the Milky Way” and published March 11 in the Astrophysical Journal.
Prof. Newberg, Mr. Xu and their team started from the Sun looking for so-called ripples in the disk. Then, as they were looking outward from the center of our galaxy, they saw that the mid-plane of the galactic disk had corrugated design, going up and then down then up and finally down again.
In 2002, Prof. Newberg found the “Monoceros Ring,” a very dense ring of stars in the outer parts of our galaxy, which was like a bump on the galactic plane. Additionally, the professor found other over-dense clusters of stars between Monoceros and our sun, but she couldn’t identify them as ripples in the galactic disk. But the data from the SDSS helped scientists take a deeper insight into the phenomenon.
Prof Newberg said she started the new study to learn more about the mysterious over-dense and concentric clusters of stars. She explained that other scientists classified them as disk stars, but their density was at odds with the definition of a disk star. So, the team suspected that the clusters may be either rings of stars or a disrupted dwarf galaxy.
While gathering more data, the research team found four ripples in the galactic disk. The Monoceros Ring was identified as the third ripple. Also, scientists learn ed that the rings were lined up with the Milky Way’s spiral arms.
The new model of a corrugated Milky Way
In the end, the team reached the conclusion that a dark matter lump or a dwarf galaxy crossing the Milky Way was responsible for the ripples in its otherwise flat disk. Additionally, researchers currently try to use the ripples to measure the dark matter lumps in our galaxy.
Prof. Newberg compared the galactic ripples with the waves that irradiate on a lake surface when somebody throws a pebble into it. She said that a dwarf galaxy acts like the pebble by pulling the disk up when entering it and pulling it down as it goes through the disk. As a result, a very dense dwarf galaxy’s gravitational pull would form a pattern of ripples that propagates outward.
But researchers acknowledged that their current theory was backed by other research conducted over the past two to three years. That research helped them substantially to get a bigger picture on the galactic ripple effect.
The latest research was funded by the U.S. government through its National Science Foundation (NSF) and the Chinese government via its National Natural Science Foundation and 973 Program.
Image Source: Chapter Masters, Science Daily
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