David DiMolfetta
Earth Science IH
Current Event #1
McKee, Maggie. "Little Galaxy Was Born of Two Colliding Galaxies." BBC Earth. BBC, 30 Oct. 2014. Web. 03 Nov. 2014. <http://www.bbc.com/earth/story/20141030-dwarf-galaxy-formed-in-collision>.
Astronomers are aware that larger galaxies with masses greater than one billion times that of our sun, such as the nearby Andromeda galaxy, are typically formed via collisions between smaller galaxies. Our own galaxy, the Milky Way, is predicted to collide with Andromeda to form an even larger so-called supergalaxy within the next four billion years. However, until now it has been difficult to find evidence that smaller galaxies are also formed via galactic collisions. Dr. Nicola Amorisco of the University of Copenhagen led a team to investigate the formation of Andromeda II, a minor galaxy (with a mass of approximately ten million suns) which orbits the Andromeda galaxy. A team of astronomers led by doctors Marla Geha and Nhung Ho found that the rotation of the galaxy was around its longest axis, which is not normal. Amorisco’s team looked more closely at the galaxy, and found that there was a group of stars moving together within Andromeda II, which suggested that those stars represented the remnants of another, smaller galaxy which had collided with another galaxy to form Andromeda II. They ran computer simulations which found that Andromeda II was probably formed from the collision of two smaller disc galaxies. The collision process began with the two galaxies approaching each other. From here, the heavy gravity from each galaxy pulls on one another, causing fluctuations in their form. Soon, they merged together to form one galaxy. The merging took place probably around three billion years ago. Due to coherent stellar flows and travelling light, we are only seeing this now. Amorisco, one of the astronomers, stated, "It was a very lucky finding – signs of mergers can disappear very quickly,"
This study has interesting implications for our theories of the formation of galaxies and dark matter. This evidence suggests that the first galaxies, which were formed by the collapse of gas bubbles to form concentrations of stars in the early days of the universe, were much smaller than previously believed. Without clear evidence that smaller galaxies were formed by galactic collisions, it was previously unclear whether or not galaxies with masses less than a billion suns were formed by collapsed gas clouds or collisions between even smaller galaxies, so astronomers did not know how large early galaxies were. This study suggests that since relatively small galaxies such as Andromeda II can be formed by collisions, early galaxies could have been smaller and collided to form larger galaxies. Another field the study has advanced is research into dark matter, a type of matter which is theorized to compose some 84.5% of the visible universe and does not interact with radiation or normal matter outside of exerting gravitational pull on them. Professor Christopher Conselice of the University of Nottingham believes that the the first galaxies were actually formed inside pockets of dark matter, because the gravitational pull of the dark matter initiated the collapse of gas clouds which created early galaxies. The speed of dark matter would have influenced the size of the resulting galaxies- faster dark matter particles would create larger early galaxies, while slower particles would create smaller galaxies - which is suggested by these results. Size of dark matter particles would also influence galactic formation; heavier particles would have formed galaxies faster, causing more galactic mergers, while smaller particles would have formed galaxies slower, resulting in fewer mergers. However, this individual result is not enough to form accurate conclusions about the mass and speed of dark matter. Dr. Amorisco has already begun analyzing other nearby dwarf galaxies in orbit around our own Milky Way to see if they too were formed by galactic mergers.
Dark matter is a hypothesized matter which results in what we might see as invisible mass. It does not emit any form of radiation, nor can it be seen through telescopes. The only true way to calculate the effects of dark matter is through rigorous testing in gravity experiments because dark matter results in invisible mass. Mass is the main factor of which gravity acts upon. In fact, the only information that could be inferred from dark matter is just from the gravitational effects on visible matter, radiation, and our current scale model of the universe. According to the Planck mission team, the standard model of cosmology, the total mass/energy of the known universe contains 4.9% ordinary matter, 26.8% dark matter and 68.3% dark energy. Therefore, we know that all dark energy and matter make up about 95.1% of the entire universe as we know. Other evidence of dark matter also comes from observations from WMAP and Planck indicates that around ⅚ of total matter does not interact with photons or ordinary matter. Jan Oort was the first to investigate the presence dark matter in the mid 1930’s.
Overall, the article proved interesting to me, as it gave me a newer perspective on our universe and other effects that act upon it. However, a few issues presented themselves in the article. For instance, the article assumed that many terms were known already, such as dark matter, which had to be further researched for better understanding of terms and theories. The article also lacked in diagrams, which would have proved helpful in better understanding the evidence behind the astronomers’ findings. Although, there were a few pictures to indicate the galaxy collision process. In general, however, the article empowered me with more knowledge about theories to the origins of our galaxies and anyone who may chose to read the article will be better off in their knowledge of astronomy.
I really liked David’s review about the recent study about colliding galaxies, and dark matter. One thing I liked about his article was that it was extremely detailed. It included in depth, such as measurements, theories, test procedures, results, and the collision of galaxies. For example, he stated that Dr. Nicola Amorisco looked extremely close at the galaxy, and discovered that there was a group of stars moving together within Andromeda II, which shows that Andromeda II was formed by two galaxies colliding. I also liked how David included some of his own knowledge into the article. For example, he included the current theory about dark matter: that it makes up 84.5% of the galaxy, and that it isn’t affected by the gravitational pulls of the galaxies all around it. Lastly, I liked how he had many critiques of the article, that were well constructed and reasonable. For example , he stated that there were some terms that were used and assumed were known by the reader, which is a downside to many articles found online or in newspapers.
ReplyDeleteAlthough, this was a great review, as always there were some errors. First of all, the article was about galaxies colliding, and although he did talk about our galaxy colliding with another one in billions of years, he did not mention the effect on us today. He could have included something about what galaxies are colliding, or could collide in the near future, and could these collisions produce amazing spectacles in the night sky for us to see. Also, David critiqued the article well, but he only mentioned how the article expanded his knowledge on the universe as a positive fact. He should have included at least one specific thing that he liked about the article.
Overall, this was a great review, and I learned some very interesting facts about galaxies and the universe. I learned about dark matter, and the definition I mentioned earlier. I also learned that galaxies can collide! Prior to reading this review, I believed that only planets, and other smaller celestial bodies could collide, but I had no idea that galaxies could also collide, because I thought the fact that they are made up mostly of dark matter, would not allow them to collide. This was a very cool review and I enjoyed reading it.