The proximity of Veterans Day made me think of the American flag and then, about stars. Astronomers like to think about the properties of stars, including their nuclear burning histories, in order to appreciate how they gave us the life-friendly conditions we enjoy today. Part of that stellar history involves detection of neutral hydrogen in galaxies more than 8 billion light-years away. Now, a team of astronomers has employed an innovative telescope technique to detect this hydrogen, a find that helps us understand star formation history and the conditions conducive to life today.

A Just-Right Time for Life
Using anthropic principles (there’s a weak and a strong type), which is the knowledge that humans exist in the universe today, astronomers have determined what the history of star formation in the universe looked like. Stars produce the elements needed for humans to efficiently function over several decades and for a planetary home on which to thrive. However, aggressive star formation in the universe today would shower those humans with deadly radiation and gravitationally disturb their home planet. For human beings to possibly exist, star formation must begin early in the universe, roughly 200 million years after the cosmic creation eventThen it must ramp up to a peak star formation rate per unit volume of the universe that lasts from about 2.5–4.5 billion years ago, and then exponentially decline to where it is today. Star formation is now about 10 times less than what it was at its peak.

Astronomical observations have affirmed much of what astronomers have derived from anthropic principles. Measurements of the stellar content in galaxies over a distance range of 13 billion years (look-back times spanning the past 13 billion years) establish that about half of all stars in the universe formed when the universe was between 2.5 and 4.5 billion years old.1 During the last 10 billion years, the star formation rate per unit volume has decreased to about 10 percent of what it was when the universe was 4 billion years old.2

Based on observations of ongoing star formation in our galaxy, astronomers have discerned that stars form as a result of diffuse clouds of neutral hydrogen that cool and collapse into dense clouds of molecular hydrogen (H2). What astronomers have lacked, however, are observations of neutral hydrogen in galaxies sufficiently distant to correspond to the epoch of peak star formation to determine exactly how star formation rates are linked to the properties of neutral hydrogen clouds.

Observations of Distant Neutral Hydrogen Gas
This lack is understandable given how feeble neutral hydrogen emission is in galaxies located 8–13 billion light-years away. Presently, there is no radio telescope powerful enough to detect neutral hydrogen (even at concentrations tens of times greater than any source in our galaxy) in galaxies more distant than 8 billion light-years. However, researchers have overcome this deficiency thanks to a novel technique developed by a team of five astronomers led by Aditya Chowdhury.

Chowdhury’s team used what’s called a stacking analysis of the individual 21-centimeter radio observations of neutral hydrogen in 7,653 star-forming galaxies located between 9.4 and 6.7 billion light-years away. The observations were recently obtained with the upgraded Giant Metrewave Radio Telescope (near Pune, India), an array of 30 45-meter-diameter (150-foot-diameter) radio telescopes (see figure 1). They stacked the radio spectra of the 7,653 galaxies on top of one another. This stacking enhanced the sensitivity of their observations by the square root of 7,653. That is, they gained a factor of 87.5 times greater detectability of neutral hydrogen.

Though it was impossible for Chowdhury’s team to detect neutral hydrogen in any individual galaxy, they did achieve helpful results thanks to the enhanced detectability from their stacking. They were able to determine that, on average, the 7,653 galaxies contained about 2.5 times more neutral hydrogen gas relative to total stellar mass than galaxies do today. The team’s detection established that, indeed, excess neutral hydrogen gas explains the high star formation in galaxies 9.4–6.7 billion years ago. They showed that the amount of neutral hydrogen gas they measured in these distant galaxies implies that the hydrogen gas would have been consumed by star formation in only 1–2 billion years. This rapid rate of transformation of neutral hydrogen gas into stars explains the exponential drop-off in the star formation rate that occurred thereafter.

The stacking technique only reveals how much neutral hydrogen gas, on average, resides in the 7,653 galaxies. It gives no information as to where in the galaxies the hydrogen gas resides or where star formation is most aggressively occurring within the galaxies.

Such information awaits the completion of the Square Kilometer Array (see figure 2). When completed, the Square Kilometer Array will consist of several thousand radio telescopes located in Australia and South Africa with a total lightcollecting area of 1 square kilometer. This collecting area will exceed by 21.5 times the collecting area of the Giant Metrewave Radio Telescope. The Square Kilometer Array will possess the capability of detecting neutral hydrogen gas emission in individual galaxies 8–12 billion lightyears away, including the emissions’ locations within the galaxies.

As astronomers eagerly await the new technique, they celebrate the detection by Chowdhury’s team. It is a breakthrough in understanding how and when hydrogen gas is taken up by galaxies to form stars. The discovery provides concrete evidence that the star formation rates throughout the history of the universe have been fine-tuned to make possible the existence of human beings.

Check out more from Reasons to Believe

  1. Piero Madau and Mark Dickinson, “Cosmic Star-Formation History,” Annual Review of Astronomy and Astrophysics 52 (August 2014): 415–86, doi:10.1146/annurev-astro-081811-125615.
  2. Madau and Dickinson, “Cosmic Star-Formation.”
  3. Aditya Chowdhury et al., “HI 21-Centimetre Emission from an Ensemble of Galaxies at an Average Redshift of One,” Nature 586 (October 15, 2020): 369–72, doi:10.1038/s41586-020-2794-7.


About The Author

Dr. Hugh Ross

Reasons to Believe emerged from my passion to research, develop, and proclaim the most powerful new reasons to believe in Christ as Creator, Lord, and Savior and to use those new reasons to reach people for Christ. I also am eager to equip Christians to engage, rather than withdraw from or attack, educated non-Christians. One of the approaches I’ve developed, with the help of my RTB colleagues, is a biblical creation model that is testable, falsifiable, and predictive. I enjoy constructively integrating all 66 books of the Bible with all the science disciplines as a way to discover and apply deeper truths. 1 Peter 3:15–16 sets my ministry goal, "Always be prepared to give an answer to everyone who asks you to give the reason for the hope that you have. But do this with gentleness and respect, keeping a clear conscience." Hugh Ross launched his career at age seven when he went to the library to find out why stars are hot. Physics and astronomy captured his curiosity and never let go. At age seventeen he became the youngest person ever to serve as director of observations for Vancouver's Royal Astronomical Society. With the help of a provincial scholarship and a National Research Council (NRC) of Canada fellowship, he completed his undergraduate degree in physics (University of British Columbia) and graduate degrees in astronomy (University of Toronto). The NRC also sent him to the United States for postdoctoral studies. At Caltech he researched quasi-stellar objects, or "quasars," some of the most distant and ancient objects in the universe. Not all of Hugh's discoveries involved astrophysics. Prompted by curiosity, he studied the world’s religions and "holy books" and found only one book that proved scientifically and historically accurate: the Bible. Hugh started at religious "ground zero" and through scientific and historical reality-testing became convinced that the Bible is truly the Word of God! When he went on to describe for others his journey to faith in Jesus Christ, he was surprised to discover how many people believed or disbelieved without checking the evidence. Hugh's unshakable confidence that God's revelations in Scripture and nature do not, will not, and cannot contradict became his unique message. Wholeheartedly encouraged by family and friends, communicating that message as broadly and clearly as possible became his mission. Thus, in 1986, he founded science-faith think tank Reasons to Believe (RTB). He and his colleagues at RTB keep tabs on the frontiers of research to share with scientists and nonscientists alike the thrilling news of what's being discovered and how it connects with biblical theology. In this realm, he has written many books, including: The Fingerprint of God, The Creator and the Cosmos, Beyond the Cosmos, A Matter of Days, Creation as Science, Why the Universe Is the Way It Is, and More Than a Theory. Between writing books and articles, recording podcasts, and taking interviews, Hugh travels the world challenging students and faculty, churches and professional groups, to consider what they believe and why. He presents a persuasive case for Christianity without applying pressure. Because he treats people's questions and comments with respect, he is in great demand as a speaker and as a talk-radio and television guest. Having grown up amid the splendor of Canada's mountains, wildlife, and waterways, Hugh loves the outdoors. Hiking, trail running, and photography are among his favorite recreational pursuits - in addition to stargazing. Hugh lives in Southern California with his wife, Kathy, and two sons.

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