Galactic Archaeology: Uncovering the History Written in the Stars

How can the earth and the universe be very young if both show so many signs of great age? This is a crucial question for young-earth creationism (YEC), the belief that the natural world came into existence about 10,000 years ago. Young-earth researchers have been making attempts to deal with modern scientific findings under this constraint. For starters, they have argued that the laws of nature have changed radically over time,^[1] along with catastrophic effects which (they claim) accompanied the biblical events of the Fall and the Flood. Beyond that, YEC thinkers have also recognized that some degree of “mature creation” is necessary for their paradigm.^[2] This is the belief that certain features of the earth and universe were created mature and “fully functional” during the first week of Creation.

One major problem with mature creation is that it ends up including evidence of event histories that never happened. To their credit, YEC thinkers have acknowledged this and have tried to temper it. For instance, the YEC ministry Answers in Genesis (AiG) asserts that Adam and Eve were created as adults but without belly buttons, because these would have indicated a natural birth. They have also distanced themselves from the proposal that light rays could have been created already travelling on their way to earth (“in transit”) as an explanation for distant starlight. AiG has rejected this possibility because such light would have to contain fake recordings of past events. This acknowledgement is very important to keep in mind as we proceed, because it places a useful limit on young-earth theorizing.

The idea that the natural world was created “mature” only 10,000 years ago becomes increasingly questionable when we consider the record of cosmic history written in the heavens, which astronomers have been able to study in great detail. As it turns out, separating the maturity of the universe from its event history is exceedingly difficult or, to put it more precisely, impossible. For example, “mature” relativistic jets show evidence of histories stretching across millions of years. Even our universe itself has a “belly button” that is still visible to this very day.

Partial relief from this problem of false history might be found in a class of young-earth models that rely on tweaking the passage of time. These models generally posit that billions of years have passed in places far away from our Earth, while only about 10,000 years have passed on Earth since the initial six days of Creation. In the recent documentary “Is Genesis History”, Danny Faulkner of AiG described his proposal of appealing to a miracle that made the clocks run faster. Unfortunately, that brings us back to a form of deception on God’s part, but this time one in which billions of “physical” years are compressed into a few miraculous days. It actually boils down to a form of day-age theory, in which the days of Genesis are taken to correspond with excessively long periods of natural time in the universe. This is surprising because AiG has critiqued day-age theory strongly in the past.

Looking beyond ad-hoc appeals to miracles, some have attempted to tweak the passage of time in a physical way, using the concept of time dilation from Einstein’s theory of Relativity. The most notable example is the White Hole Cosmology^[3] of Russell Humphreys. His proposal places the earth inside a black hole, slowing the passage of time on earth for the first days of the Creation week. Much can be critiqued about this approach,^[4] but let us take it at face value for the sake of the argument. Time-dilation models still have to take into account that our planet is located amidst many stars of our own galaxy: the Milky Way. The size of our galaxy is negligible compared to the distance to other galaxies. Because of this, young-earth cosmologists like John Hartnett have recognized that even time-dilation models are forced to assume mature creation of our host galaxy, and at least some neighboring galaxies. Do nearby galaxies contain evidence of past events beyond the time scales that fit in the young-earth paradigm? The answer is a loud “yes!”

Uncovering the rich past of our Milky Way

For this, we need to dive into the wonderful topic of galaxy formation. How did those hundred billion stars of our Milky Way come together to form such beautiful features? The current scientific picture involves the mixing of many smaller galaxies, due to their gravitational attraction. Such occurrences are called merger events, because the dwarf galaxies are literally merged into a larger whole. At some point, the Milky Way itself became so big that merger events started looking more like crumbs being gathered onto a loaf of bread. Or, in a more gruesome analogy, a sort of galactic predation in which the greater galaxy consumes the smaller one. This picture produces very specific predictions. Let’s go through a few of them.

Firstly, we know exactly what kind of features such events should leave behind: stellar streams. Imagine a dwarf galaxy as a clump of about 100 million stars, entering close to the Milky Way. All of its stars are getting pulled into orbits around the center of our galaxy (which consists of a  supermassive black hole). The orbit of every individual star ends up being very similar to, yet a little bit different from its brothers and sisters. The result is that these stars start smearing out across space, forming streams of stars draped around the galaxy. Because they started out as a single clump, you should still be able to see from their movement and other properties that they used to belong together.

Secondly, if this picture is correct, we know how many of such events have taken place in the past. We know the current mass of our Milky Way (100 billion solar masses) and the typical mass of those galactic snacks (about 100 million solar masses). It’s a straightforward calculation to estimate how many merger events have taken place. Based on this number (~1,000), the leftovers from recent galactic dinners should be all over the place in the form of stellar streams!

Do we observe such streams? Yes, dozens of them have been observed and more are being found as we launch better space telescopes. We are essentially looking at all the scars our galaxy has from its dynamic history. This field of study has been labeled “galactic archeology.” From the laws of gravity, computer simulations can directly trace back how those streams originated in small dwarf galaxies, and even how much time ago those dwarf galaxies were devoured by our Milky Way. One notable example is the Aquarius stellar stream, its size on the sky is 1300 times (!) the size of the moon. It turns out this stream is the aftermath from a meal our galaxy had 700 million years ago; and this is a relatively recent one! The positions and velocities of the stars of the much older Sagittarius stream (~3 billion years) were measured so precisely that astronomers were able to use them for estimating the overall shape of our galaxy. The animation below shows an actual simulation of such events: