ALMA sees galaxy collision in early universe
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Thirteen billion years ago, two small galaxies crashed into each other. The ALMA observatory has now witnessed this collision. Never before have astronomers seen a galaxy smashup so early in the history of the universe.
The cosmic traffic accident happened when the universe was less than one billion years old. Back then, there were many small, irregular galaxies. Over time, they merged into larger systems like our own Milky Way galaxy. The new ALMA discovery reveals one of those early collisions.
ALMA was able to see what happened long ago because the merging galaxies are so far away. Their light takes thirteen billion years to reach us. As a result, astronomers see them as they were thirteen billion years ago.
The Hubble Space Telescope had already discovered that the remote system consists of two blobs of light. But because of the large distance, Hubble couldn’t make out any details.
ALMA has now detected hot gas and warm dust in the two blobs. By studying the faint submillimeter radiation of oxygen, carbon and dust particles, the astronomers could tell how fast the gas and dust is moving. It turned out that the two blobs have different velocities. This means that they are really two separate small galaxies, merging into one.
The resulting galaxy is still puny, compared to our Milky Way: its total mass is about ten times smaller. But it produces new stars at a prodigious rate – about one hundred times faster than the Milky Way does.
Remember, we are seeing things that were happening thirteen billion years ago. During the past thirteen billion years, it must have experienced many more mergers. If we could see the galaxy as it is now, it might be as large as our own Milky Way, or even much larger.
Likewise, by studying the early merger, we see what may have happened in the youth of our home galaxy.
What?
The galaxy merger studied by ALMA is known as B14-65666. It is located in the small constellation of Sextans (the Sextant – an historical astronomical instruments to measure star positions). Like all remote galaxies, B14-65666 appears to recede from us because of the expansion of the universe. From the apparent recession velocity, astronomers have deduced that the system is very far away. So far, in fact, that the galaxy’s light that we receive today must have started its journey some thirteen billion years ago.
Who?
The ALMA observations of B14-65666 were carried out by a large team of scientists. The team was led by Japanese astronomer Takuya Hashimoto (not to be confused with the Japanese professional basketball player with the same name!). Takyua works at Waseda University in Tokyo, at Osaka Sangyo University, and at the National Astronomical Observatory of Japan. Almost all of his colleagues in the team are also from Japan, but some are from the United States, Sweden, Denmark, and Switzerland.
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