Start with stars

The study of science should begin with the study of stars. They are the magical progenitors of everything we know, the first in a sequence that begins with physics and leads to chemistry, biology, evolution, and civilization. At the same time, they are a metaphor for deep mystery, for the spellbinding unknown.

In a star, the outward energy released by fusion in its core is pitted against the inward force of gravity. So long as the core is fusing hydrogen into helium, the star is said to be in the main sequence. What happens when all the hydrogen is fused depends on how massive the star is.

We didn’t understand fusion in stars—the cause of starshine—until the 1930’s. Only then did we resolve questions about the sources of light and heat that were first posed by the ancient Greeks. (They also speculated about star clusters, particularly the Milky Way. The Greek for “milky” is galaxias.)

The past hundred years have seen giant strides in our knowledge of stars. We’ve learned:

• The more massive a star is, the more luminous (intrinsically bright) it is, and vice versa.

•  The distance of a star can be calculated by measuring its parallax as the Earth orbits and by timing the brightness pulsations in Cepheid variables and supernovas.

• There are galaxies other than ours—Hubble’s stellar discovery. We now estimate their number at 100 to 200 billion in the observable universe.

• Stars have a life cycle. The more massive the star, the shorter its time in the main sequence.

• Stars of small or average mass expand into red giants when they exit the main sequence. They envelop nearby planets, as our sun will in 5 billion years or so. Finally, they shrink into white dwarfs.

• More massive stars may become red supergiants, then supernovas. The outer layers of supernovas give birth to new stars; the remains are almost entirely neutrons—namely, neutron stars.

• The most massive stars implode and become black holes. Most galaxies have a supermassive black hole at their centers.

When I think about this list—and it’s far from exhaustive—I imagine the night sky as one colossal crime scene investigation. What is visible, and what leaves invisible traces, is the ever-shifting evidence of an almost 14-trillion-year-old “crime,” the Big Bang. (It would be thrilling to view a TV series titled “CSI: Stars.”) Yet despite our accumulation of knowledge, despite all the evidence and retrograde analysis, the most profound mysteries remain. For example, the inescapable gravity of a black hole must mean it contains no atoms. There must be nothing inside but a stew of subatomic particles. But if a cosmic “seed,” something unimaginably compact, produced the entire universe, what kind of matter could it have possibly contained? And why did it go bang? Black holes never go bang, even though their gravitational strength is inestimably weaker. Clearly, we’re dealing with a form of matter/energy that has no counterpart in what we’ve detected in the universe, not even in our most advanced supercolliders.

Another example: Galaxies rotate at a much faster rate than should be produced by the collective mass of visible gas and stars. To account for the actual rotational rate, we’d have to multiply the collective visible mass by 10! Most scientists conclude the missing 90% is hidden in dark matter. You might ask, “If galaxies have all that extra mass, why are they flying apart from one another at an accelerating rate?” The answer, I’ve read, is dark energy. What do you think of the practice of labeling something “dark” to balance the books?

There is a great deal more in this crime scene to investigate, and we may never crack the case. But that’s another reason why science must start with stars: they engage our intellect and wonderment more than any other branch of scientific inquiry.