The proverb “You are what you eat” has motivated many people to eat healthier. If you want to live long and enjoy an active lifestyle, you must be disciplined and mindful of what you consume.
What is true for the human body is also true for spiral galaxies. For a variety of reasons, advanced life is only possible in a spiral galaxy that maintains highly symmetrical spiral arms for billions of years. However, for the spiral structure of a galaxy to be maintained, it must receive frequent infusions of gas. Those gas infusions come from small gas-rich galaxies.
In every cluster of galaxies, the dwarf galaxies far outnumber the large and medium-sized galaxies. In our Local Group galaxy cluster (see figure 1), there are two large spiral galaxies—the Milky Way Galaxy (MWG) and Andromeda Galaxy; one small spiral galaxy—the Triangulum Galaxy; and over 100 dwarf galaxies. Billions of years ago the number of dwarf galaxies in the Local Group was much higher.
Figure 1: The large and medium-sized galaxies in the Local Group of galaxies.Our Milky Way Galaxy is pictured in the lower right corner. Situated above it are the Large and Small Magellanic Clouds. In the upper left corner is the Andromeda Galaxy, with the Triangulum Galaxy below it. Image credit for the individual galaxies: NASA/ESA/ESO/JPL-Caltech (R. Hurt)
Dwarf galaxies, unlike their larger cousins, are very gas rich. Thus, if the gravitational pull of a spiral galaxy is strong enough to draw dwarf galaxies into its bulge (its central core), it will receive the gas it needs to sustain its spiral structure. However, if the spiral galaxy draws in a large dwarf galaxy, or several smaller dwarf galaxies all at once, it will receive so much gas that it will “burp.” As they are consumed by the spiral galaxy, the gravity of the large dwarf galaxy, or set of smaller galaxies, will distort the structure of spiral arms beyond what advanced life can tolerate. Furthermore, the infusion of gas will generate such an aggressive burst of star formation that the newly formed stars will endanger existing advanced life with deadly radiation and additional gravitational disturbances.
A team of astronomers from China, Germany, Russia, and Ukraine studied what would happen if a galaxy like ours merged with dwarf galaxies ranging in size from one-eighth to one-seventieth the mass of the MWG. They then created a computerized reenactment and published their findings in the June issue of the Astrophysical Journal.1 The team’s primary goal was to determine changes in the spiral galaxy’s metallicity gradient—its abundance of elements heavier than helium with respect to its distance from the galaxy’s center—when induced by a merger with a dwarf galaxy. Secondarily, their study revealed spiral disk perturbations resulting from the merger.
The team’s computer simulations showed first that the MWG’s central bar (see figure 2) is not a perturbation or a short-lived phenomenon. As long as our galaxy frequently consumes dwarf galaxies no larger than one-seventieth the mass of our galaxy, its central bar remains a stable feature of its bulge. Second, the team demonstrated that if our galaxy had consumed dwarf galaxies significantly larger than one-seventieth its mass throughout the past 10 billion years, not only would there be a substantial change in its metallicity gradient but its spiral arm structure and disk shape would have suffered severe distortions.
Figure 2: Map of the Milky Way Galaxy’s structure. This map of the Milky Way Galaxy’s structure was constructed from the integration of images of various parts of the galaxy across a wide range of wavelengths of observation. NASA released this latest and most detailed map in June 2015. The yellow dot represents the position of our solar system. Image credit: JPL-Caltech (R. Hurt)
Advanced life is able to exist in our galaxy because our galaxy has possessed highly symmetrical spiral arms, with only a few spurs and feathers between the arms, throughout the past 10 billion years.2 The new study shows that this fine-tuned spiral structure has been maintained for many billions of years because our galaxy has been on a strict diet. It has consumed dwarf galaxies no larger than one-seventieth of its mass at a sufficiently frequent rate to sustain its spiral structure, but not so frequent or irregular a rate as to disturb the spiral structure or warp the shape of its spiral disk.
In their published paper the research team did not speculate as to why the MWG has such an extraordinarily fine-tuned and extremely stable spiral structure. Other research teams have suggested that the MWG’s unique environment probably plays a significant role.3 In particular, the masses and the positions of the Small and Large Magellanic Clouds (see figure 3)—two large dwarf galaxies that are situated 160,000 and 200,000 light years away from Earth—likely operate to shepherd a regular stream of smaller dwarf galaxies into the MWG’s bulge.
Figure 3: Map of the Milky Way Galaxy and the Large and Small Magellanic Clouds. Our Milky Way Galaxy is to the lower right. Situated above it are the Large and Small Magellanic Clouds. Image credit for the individual galaxies: NASA/ESO/JPL-Caltech (R. Hurt)
How much longer will our MWG maintain its amazingly symmetrical and stable spiral structure? Astronomers have determined that nothing in the near future—meaning the next billion years—will generate a significant disturbance. However, the MWG’s gravity is slowly drawing the Large Magellanic Cloud toward it. A merger event between the MWG and the Large and (perhaps) Small Magellanic Clouds is calculated to occur about 4.5 billion years hence. In addition, the mutual gravitational attractions of the Andromeda Galaxy and MWG are causing them to rush toward one another. Astronomers calculate that their merger date is about 4.5 billion years into the future. These future merger events definitely will disrupt, if not completely destroy, the MWG’s spiral structure.
Today, we humans are living at the best, actually the only possible, time in the MWG’s history for launching and sustaining a highly technological civilization. We know of no other galaxy within the vast universe that is endowed with the MWG’s marvelously designed spiral arm symmetry, spiral disk size and shape, minimal spurring and feathering, and stability of structure that is necessary to make advanced life and advanced civilization possible.
Have you thanked God for your galaxy today?