The Physics Factbook
Edited by Glenn Elert -- Written by his students
An educational, Fair Use website
|Kraan-Korteweg, Renée C. & Ofer Lahav. "Galaxies Behind The Milky Way." Scientific America. October 1998.||"These measurements, confirmed by the Cosmic Background Explorer satellite in 1989 and 1990, suggest that our galaxy and its neighbors, the so-called Local Group, are moving at 600 kilometers per second (1.34 million miles per hour) in the direction of the constellation Hydra."||600 km/s|
|Does the Milky Way move in space or does it just stay put? Archive of Ask the Space Scientist FAQs. NASA/GSFC.||"The total speed is about 300 kilometers per second or so."||300 km/s|
|AstroFile -- Future Fate of the Milky Way Galaxy. Association of Universities for Research in Astronomy. 21 October 1997.||"The Milky Way and the Andromeda galaxy are approaching each other with a speed of 300,000 miles per hour."||130 km/s|
As we all know, a galaxy is a massive ensemble of hundreds of millions of stars. The galaxy where we live in today is called the Milky Way. The name itself came from the ancient Greek galaxies kyklos, or ring of milk, due to its faint milky appearance. Our Milky Way is a large spiral galaxy. Its diameter is at least 100,000 light-years, and may contain as many as 200 billions stars today.
Ever since four hundred years ago the settlement that the Earth is moving about the sun, and one hundred and fifty years ago that the sun is moving about the center of the Galaxy, it shouldn't be surprising if we learned that the Galaxy is also moving. The Milky Way is part of a cluster of galaxies call the Local Group. Two chief members are the Milky Way and the Andromeda galaxy, the Andromeda galaxy is known to contain at least 300 billion stars. We can presume that in every cluster of galaxies, the individual galaxy itself move about some sort of center of gravity. However, how do the clusters themselves move?
In 1928, an American astronomer Milton La Salle Humason found a galaxy that was receding at a speed of 3,800 km/s, and by 1936, when he observed the same galaxy again, he found it receding at a speed of 40,000 km/s. It didn't make any sense that the galaxies be receding from us and yet the recessions would be faster as they get farther way from each other. "Was there something special about our galaxy? Did it repel other galaxies, and did this repulsion grow stronger with distance?
If our galaxy exerted a repulsive force, that force should be felt with the local groups, however it wasn't. Furthermore, a repulsive force that grew stronger with distance is highly unlikely. For example, as we've learned in the past, a magnetic pole can repel another magnetic pole like itself, and an electric charge can repel another electric charge like itself, but in each of the cases, the repulsion weakens with the increase of distance. Hubble, an American astronomer, concluded in 1929 that the "entire universe was steadily expanding"and that the galaxies were moving apart from one another as part of this expansion and not because of any repulsive force. In addition, in 1916, Albert Einstein as part of his general theory of relativity, had prepared a set of equations that were intended to describe the properties of the universe as a whole, that showed that the universe would have to be expanding.
In conclusion, galaxies experience neutral attractions on one other. Due to relativity, the speed of the Milky Way varies when compared with different objects in space. For example, I have learned from my research that the Milky Way and Andromeda galaxy are approaching each other with a speed of about 130 km/s, however the collision of these two galaxies will not occur for about 5 billion years (AstroFile). Another result I found was that our galaxy and neighbors are moving at 600 km/s in the direction of the constellation Hydra (Scientific American). Finally, I found that the Milky Way moves through space within the cluster of galaxies it is a member of, and this cluster in turn moves through space towards yet another larger cluster of galaxies off in the direction of the constellation Virgo. This speed is approximately 300 km/s (Ask the Space Scientist). Therefore, the speed of the Milky Way galaxy is not a single number, its value is relative to the speed of other objects.
Patricia Kong -- 1999
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