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Astronomers Witness the Death of a Galaxy

How do galaxies die? What causes them to die? These questions have puzzled astronomers and astrophysicists for years. What they do know is that galaxies disappear when stars are no longer materializing. The hypothesis goes that galaxies initiate death by ejecting a massive amount of gas. This makes it impossible for new stars to form. Although astronomers have seen dead galaxies, they’ve never been able to observe the process. Until now.



How Astronomers Watched the Galaxy


An international team of astronomers used the Atacama Large Millimeter/sub-millimeter Array (ALMA) located in the desert region of Chile to watch a distant galaxy. According to the National Radio Astronomy Observatory, ALMA is located at the most complex astronomical observatory ever built on Earth. Its creation was the result of a collaboration between teams from North America, East Asia, and Europe. It is a transformative radio telescope that can study cosmic light that straddles the boundary between radio and infrared. It had to be built in the high Andes because of how dry the atmosphere is there. Signals from space get heavily absorbed by water vapor in the Earth's atmosphere, making wet areas useless.


The Story Behind ID2299


The light from this galaxy, known as ID2299, has taken about 9 billion years to reach Earth. The crazy thing is that astronomers are actually observing its appearance at 4.5 billion years old, while its actual age is 14 billion years old. They believe that the galaxy began ejecting cold has gas due to a collision between two other galaxies, which eventually merged to form ID2299. The main clue that points towards ID2299’s creation by collision is the fact its ejected gas has taken the form of a tidal tail. These elongated streams of stars and gas that reach into interstellar space are often too faint to see and are theorized to be the result of galactic mergers. On complete chance, astronomers caught wind of this bright tail. They quickly realized that neither the active black hole nor the strong star formation hosted in ID2299 were powerful enough to produce such a gas ejection. These two factors were believed to be the inhibitors of star formation on the past. Now, astronomers hypothesize that gas ejections may be produced by mergers instead.


The Future of ID2299 & Research


ID2299 is losing 10,000 suns worth of gas a year despite creating stars faster than our galaxy. Eventually, all the gas will be used up and ID2299 will cease to exist. Astronomers estimate that it’ll only take a couple million years. The chance to observe this phenomenon has prompted scientists to reconsider existing theories on the end of star formation in galaxies. Moving forward, astronomers plan to look for similar occurrences in other galaxies. Getting to witness a galaxy die in real-time is a huge step in the journey to solve the puzzle of galaxy evolution. If you want to learn more, check out the rest of the study in Nature Astronomy.


Until next time, keep on that STEM journey.

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