In July 2011, the spacecraft Dawn arrived at the asteroid Vesta and took the photograph shown in Figure 3. Vesta is about 530 kilometers across, or about the size of Wyoming. This beautiful image shows the varied texture on Vesta’s surface. Vesta has craters like the moon, but also ridged bands along the upper left. In fact, there are craters on top of the ridged bands! Just from looking at the surface, it is clear that Vesta has a history, in which the bands formed first, and after that small asteroids hit Vesta to make the craters on top of the bands.
Astronomers now know the orbits of nearly half a million individual asteroids in the asteroid belt. The asteroids are grouped into families that have similar chemical composition and similar orbits. College students with whom I work have programmed computers to run the orbits back in time under the laws of gravity. The students find the same thing that professionals do: asteroids in the same family have orbits that converge at a certain time in the past, millions of years ago. This was the time when two asteroids collided, breaking off many smaller asteroids. The new smaller asteroids are seen as a family today.
Charting the origins of asteroids is an excellent example of historical science: by using the evidence we see today, we can deduce what must have happened in the past. Very few assumptions go into the orbit calculation, just Newton’s laws of mechanics and gravity. Even though no one was there to see the collision, the orbits today show that a collision occurred millions of years ago. God gives us a glimpse of how he created the asteroid belt. The idea that something happened millions of years ago may seem startling to you. Christians disagree about the age of the earth, solar system, and universe. Some Christians believe the solar system is only 10,000 years old, in agreement with the genealogies recorded in the Bible. Other Christians believe the solar system is 4.6 billion years old, in agreement with many lines of evidence from astronomy and geology, including asteroid collisions.
Since God has revealed himself in both scripture and nature, we need to take both revelations seriously. Both revelations require human interpretation: scientists interpret the evidence in the natural world, and Christians interpret the Bible every time they read it. Many biblical scholars say that the best interpretation of Genesis indicates that it was never intended to teach scientific information about the age of the universe, but it was intended to teach truths about God’s sovereignty and the goodness of creation. A full discussion of age is beyond the scope of this essay, but resources on this topic are listed under Further Reading (at the end of this three-part series).
When you look at the night sky, the space between the stars looks black. Figure 4, however, shows that the space between the stars is actually filled with rich complexes of dust and gas. The Carina Nebula is located 7,500 light-years away. A light-year is the distance that light travels in one year, so that means the light we see left the nebula 7,500 years ago. This image is about thirty light years across. The beautiful colors represent different types of gas: blue for nitrogen, green for hydrogen, and red for sulfur. The dark clumps and filaments are regions where dust clouds absorb the light.
The resulting picture is as elegant as an abstract painting, truly a display of God’s artistic creativity. This nebula was around long before human history, but only in the last decade or two have we had telescopes and cameras to make images like this. We’ve found nebulae throughout our own galaxy and in other galaxies; God appears to have filled the universe with an extravagance of beauty, even where no human is there to see it.
This nebula displays God’s creative nature in another way: in this region God is creating new stars. It is an active “stellar nursery.” The smallest dark globules in the lower center of the picture are similar in size to our own solar system. Each globule will likely become a star with planets of its own. Our own solar system probably had its origin in a nebula like this. God brought together the dust and gasses in a swirling cloud to make the sun, earth, and planets. The very nitrogen in our bodies was once glowing in a beautiful nebula. God made us from stardust.
This nebula illustrates an important truth: a scientific explanation does not replace God. Some atheists say, “Scientists can explain this, so there’s no need for God.” And some Christians say, “Scientists can’t explain this, so God must have made it.” Both statements make the error of assuming that a scientific explanation is somehow a substitute for God. Yet in other areas—gravity or photosynthesis or chemical reactions—we view God as upholding the laws of nature. We don’t say that natural laws indicate God’s absence. For a Christian, a scientific explanation doesn’t diminish God’s role; it gives additional insight into God’s action and increases our praise of him.
Since the Chandra X-ray Observatory was launched into orbit in July 1999, it has been sending back amazing pictures of the universe in X-rays. As with the sun, this galaxy cluster looks very different in visible light and X-ray light. On the top in Figure 5 is a visible light image f rom the Hubble Space Telescope of galaxy cluster Abell 1689, located 2.3 billion light years away. You can see hundreds of yellow galaxies, each containing billions of stars. Many of these galaxies are larger than our own Milky Way galaxy.
Before X-ray telescopes, astronomers had no idea that there was more to a galaxy cluster—we thought the space between the galaxies was basically empty. On the bottom in Figure 5 is an image from the Chandra X-ray Observatory of the same region of space. Instead of individual galaxies, the image shows X-rays coming mostly from a huge cloud of hot gas filling the space between the galaxies. In fact, there is much more mass in the gas than in the galaxies!
Yet even this isn’t the whole story. Astronomers have found that most of the cluster mass is not in galaxies, and not in gas, but actually in a mysterious substance called dark matter. Dark matter is stuff that has mass but doesn’t emit light. Astronomers are not sure what dark matter really is, but the best guess is that it’s some bizarre elementary particle that doesn’t exist on earth except in particle accelerator experiments. Only 2% of the cluster mass is actually in the galaxies! I love how modern telescopes show a reality beyond what our eyes can see. Without optical telescopes, we couldn’t see the galaxy cluster at all. Without X-ray telescopes, we wouldn’t know about the hot gas. And without particle accelerators, we would be even more confused than we are about what dark matter is.
I study galaxy clusters like Abell 1689 in my own research program. My students and I are investigating how the hot gas interacts with the galaxies, specifically how the central bright core of the gas interacts with the big galaxy at the center of the cluster. My students and I share the joys of discovering new things about the universe, and suffer the daily frustrations of calibrating data and computer analysis. We contribute a small piece of the puzzle within a community of hundreds of astronomers around the world who study galaxy clusters.