Signature of the Universe’s First Stars and Dark Matter

If you are familiar with the legends of King Arthur or the famous Monty Python movie that spoofed those legends, the holy grail is a cup or vessel with miraculous powers that gallant knights would spend decades in their fruitless quests to find. In science, the term “Holy Grail” is used for a difficult-to-achieve potential discovery of great significance.

One of the Holy Grails of modern cosmology is to find, identify, and date the very first stars that formed in the history of the universe. Another is to discover and identify the particles that comprise cosmic dark matter, the exotic matter that makes up about 5/6 of all the matter in the universe and possesses the properties that its particles do not interact or very weakly interact with light. Both of these Holy Grails are linchpins in the big bang creation model that the Bible predicted more than two thousand years ago.¹

Both of these Holy Grail quests have proved very challenging over the past three decades of astronomical research. However, a recent sky-averaged radio spectrum has brought both of these quests within sight.²

First Holy Grail Quest
What makes the first Holy Grail quest so challenging is that astronomers know that when the first stars formed, the only elements that existed in the universe were hydrogen and helium. While astronomers have found low-mass stars with extremely low abundances of elements heavier than helium, lower than a hundred-thousandth the abundance measured in the Sun,³ they have yet to find a metal-free star, that is, a star containing only hydrogen and helium.

Astronomers have concluded that the low-mass stars with extremely low abundances of elements heavier than helium are firstborn stars that have been slightly polluted by the ashes of very high-mass firstborn stars. While low-mass stars take tens of millions, some even hundreds of millions of years to form, stars more massive than 30 times the Sun’s mass take less than a hundred thousand years to form.⁴ Stars more massive than 30 times the Sun’s mass go through their entire nuclear burning phase and explode as supernovae in less than 10 million years.⁵ Thus, firstborn low-mass stars are polluted by the ashes of firstborn high-mass stars before their formation is completed.

Astronomers see star-filled galaxies as distant as 13.4 billion light-years away. Since the high-mass firstborn stars stop shining just several million years after they form, for astronomers to see these stars and determine that they only contain hydrogen and helium they need to measure the spectra of individual stars that are more distant than 13.4 billion light-years. Currently, astronomers lack the telescope power and the technology to measure spectra of stars at such great distances.

Second Holy Grail Quest
Just a few weeks ago, I wrote and posted a blog⁶ updating the search for dark matter and the particles that comprise dark matter. In that blog I cited and explained four different observational tools that now leave no doubt that cosmic dark matter exists and that it comprises about 5/6 of all the matter the universe contains. I also cited and explained how the detection of a 3.5-kilo-electron volt feature in the soft X-ray spectrum of the Perseus Galaxy Cluster could well be the long-sought signal of dark matter particles absorbing and reemitting photons.

Signature of Metal-Free Stars
Decades ago, astronomers had calculated that the absorption of ultraviolet radiation emitted by the universe’s firstborn stars—the high-mass metal-free ones—by nearby clouds of hydrogen gas would lower the spin temperature of neutral hydrogen in those clouds by a predictable amount.⁷ A team of five astronomers measured this spin temperature, averaged over much of the sky, throughout a continuous range of radio frequencies. The team found a dip in the spin temperature of neutral hydrogen that was centered at 78 megahertz^.8

Each radio frequency that the five astronomers observed corresponds to a different time in the universe’s past. The low frequency edge of the dip centered at 78 megahertz corresponds to the time when the universe was 180 million years old. The observed dip, therefore, signals the advent of stars in the universe. It shows that stars first formed when the universe was 180 million years old. Such a date is consistent with predictions from the best big bang creation models.

Signature of Cosmic Dark Matter
The dip in the spin temperature of neutral hydrogen that the astronomer team detected was too low by at least a factor of two and the frequency profile of the dip much too flat-bottomed to be explained solely by the advent of the universe’s firstborn stars. In the same journal issue that the five astronomers reported their detection of the 78 megahertz dip in the neutral hydrogen spin temperature, theoretical astrophysicist Rennan Barkana published a companion paper where he offered an explanation for the extra neutral hydrogen spin temperature dip.⁹

Barkana pointed out that cosmic dark matter may be responsible for the extra cooling of the hydrogen. Specifically, he showed that the excess cooling of the hydrogen gas would be well explained by scattering between baryons (protons and neutrons) and the particles that comprise cosmic dark matter—with two important conditions. First, the cosmic dark matter particles must be less massive than a few times the mass of a proton. Second, the cosmic dark matter particles must be at least moderately cold; that is, manifesting velocities that are nonrelativistic.

Barkana concluded his paper by pointing out that measurements of the neutral hydrogen spin temperature provide astronomers with a powerful probe of the attributes of cosmic dark matter. The current result published by the astronomical researchers soon will be complemented by several other independent experiments aimed at measuring what has now been labeled the “cosmic dawn signal.” Astronomers and the rest of us soon can look forward to many more insights into the nature of the universe’s firstborn stars and of the nature of cosmic dark matter.

What Does It All Mean?
The significance was not lost on Marc Kamionkowski, an astrophysicist at Johns Hopkins University, who was not part of either of the two studies. He wrote concerning the discoveries, “This therefore is about as important as you can get in cosmology.”¹⁰

Underscoring that importance is the philosophical implication that it puts to rest charges lobbed at the biblically predicted big bang creation model by a few atheists and nearly all young-earth creationist scientists that the big bang model has failed because astronomers have not detected metal-free stars or the particles that comprise the majority of cosmic dark matter. All the empirical evidence that astronomers possess about the universe, including evidence for the first stars and for cosmic dark matter, supports the big bang creation model. Thanks to the recent discoveries reported here, the empirical evidence for the big bang creation model has grown. Such growth is in accord with the biblical principle that the more we learn about the realm of nature the more evidence we will accumulate for the supernatural, super-intelligent handiwork of God.