Four Astronomical Discoveries of "Missing Matter" Support Cosmic Creation

During my graduate school days at the University of Toronto I had the privilege of taking a short course from Princeton University astronomer and cosmologist Jeremiah Ostriker. In that course Ostriker spoke about the "missing mass" of the universe. The mass he referred to was not the dark matter (also known as cold dark matter or exotic dark matter), comprised of particles that do not interact, or only weakly interact, with photons. Rather, he was concerned about missing atomic matter, matter comprised of protons, neutrons, and electrons, which interact strongly with photons. Detection of such matter carries significant implications for the reliability of models for the beginning of the universe, often called big bang models.

Astronomers began to refer to this problem as the "missing baryons" problem, given that baryons—predominantly protons and neutrons—comprise the atomic matter we most commonly experience. (Electrons contribute a trivial amount to the total mass of the universe's atomic matter.)

Back in the 1970s, the missing baryons posed a significant challenge to the set of big bang cosmic origin models. The models predicted the existence of many more baryons in the universe—nearly ten times more—than astronomers at that time had been able to inventory. This dilemma led to lingering doubts about the validity of the biblically anticipated model1 for the origin of the universe.

In the 1970s Ostriker hypothesized that many of these missing baryons lurked in the hot diffuse gas spread across the otherwise empty voids between galaxies. He also opined that these baryons would be extremely difficult to detect.

Measuring Absorption Spectra to Detect the Missing Baryons

In 1999 Ostriker and his Princeton colleague Renyue Cen published computer simulations they had run on gas movements within and between galaxies.2 They concluded that hot gas accumulates along filaments between galaxies. These filaments, they proposed, most likely contained the missing baryons. However, this hot gas would remain undetectable until a new generation of X-ray telescopes, then being planned or scheduled for launch into Earth orbit, could reveal the absorption spectra (see Figure 1) of quasars at X-ray wavelengths.

The gas between Earth and a bright quasar or galaxy will absorb some of the light of the quasar or galaxy if that gas is not too hot. Typically, astronomers would determine the mass of this gas by measuring the absorption spectra of the two most abundant elements comprising intergalactic gas, namely, hydrogen and helium. (Hydrogen and helium make up 98–99 percent of the baryons in intergalactic gas.) However, this option offered no help because the intergalactic gas is so extremely hot that it completely strips away all the electrons normally attached to hydrogen and helium nuclei. The resulting plasma of free electrons plus hydrogen and helium nuclei absorbs no light.

After hydrogen and helium, oxygen is the third most abundant element in the universe (see Figure 2).3 Oxygen atoms have eight electrons, compared to two for helium and one for hydrogen. It takes a lot more heat to strip away all the electrons of an oxygen atom than of a helium or hydrogen atom. Ostriker and Cen calculated that the heat of intergalactic gas would be able to strip away five, six, or seven of oxygen's electrons, but not all eight. The remaining electrons would allow for an absorption spectrum measurement sufficient to determine the mass of the previously unmeasurable intergalactic gas.

Finally, in 2018, astronomers gained the necessary instrumentation and observing time to detect (more than marginally) the oxygen absorption spectra of hot intergalactic gas. A team of 21 astronomers led by Fabrizio Nicastro performed a very long duration observation on the brightest known X-ray blazar, IES 1553+133,4 with the X-ray multi-mirror Newton telescope (see Figure 3).5 They detected the absorption spectrum of OVII, oxygen atoms with six of their eight electrons stripped away by the hot intergalactic gas. Thanks to their long observing time, Nicastro's team achieved a signal-to-noise ratio high enough to conclude from their absorption spectra measurements that they had found all of the missing baryons.

Because the conclusion by Nicastro's team was based on a single object, a question mark remained. Perhaps the density of the hot intergalactic medium varies, at least slightly, from one location to another. To be certain that they had found all the missing baryons, astronomers needed confirmation based on measurements from at least one other bright extragalactic source, and preferably accomplished with a different X-ray telescope.

In a recent submission to the Astrophysical Journal, a team of six astronomers led by Sanskriti Das reported that they had achieved OVII absorption line measurements on the spiral galaxy NGC 3221 (see Figure 4) using the Suzaku X-ray telescope.6 Though the signal-to-noise ratio of their measurements achieved a little less clarity than that realized by Nicastro's team, the Das team's measurements were notably consistent with the conclusion that all the missing baryons have been found.

Measuring the Mass of Intergalactic Gas to Detect the Missing Baryons

Just as Nicastro's and Das's teams were finding the universe's missing baryons through the X-ray absorption spectra method, two other astronomy research groups found them using a completely different method. These teams looked for subtle distortions in the spectrum of the cosmic microwave background radiation, the radiation left over from the cosmic creation event.

As the radiation from the very early history of the universe streams across the cosmos, it can be slightly distorted as it passes through regions of gas. The electrons in the hot intergalactic gas interact with photons from the cosmic microwave background radiation in a manner that imparts a little extra energy to those photons. Thus, astronomers should be able to see these subtle distortions in their maps of the cosmic microwave background radiation.

The Planck spacecraft had yielded the most detailed map of the cosmic microwave background radiation (see Figure 5) available. However, even within this most detailed map, the distortions caused by these energized electrons in the hot intergalactic gas proved too subtle to be seen.

While the Planck spacecraft was unable to make this detection between any single pair of galaxies, astronomers figured out a way to enhance the signal by stacking images of different galaxy pairs on top of one another. First, they searched published galaxy catalogs and selected pairs of galaxies that were massive enough and appropriately far apart from each other that researchers could reasonably anticipate the presence of a dense web of hot intergalactic gas between them. Next, they went to the Planck map of the cosmic microwave background radiation and precisely identified the location for each galaxy pair. Then they used digital scissors to clip the region for each galaxy pair from the Planck map.

Finally, they stacked all the clipped regions on top of one another so that all the pairs of galaxies were aligned in the same exact position. This stacking of images allowed them to subtract out the light from all the gas known to be associated with the galaxy pairs, leaving only the signal from the intervening intergalactic gas. What they had not been able to detect based on a single pair of galaxies ultimately became visible when integrated over numerous pairs of galaxies.

A team of four astronomers led by University of Edinburgh's Anna de Graaff stacked pieces of Planck map images from a million pairs of galaxies, one on top of another.7 The remaining signal (after subtraction of the signal from all the gas associated with the million galaxy pairs) was strong enough to show de Graaff's team the mass of the hot intergalactic gas. That mass added up to the missing baryons.

An independent team of nine astronomers led by University of British Columbia's Hideki Tanimura stacked Planck map image pieces of 260,000 pairs of luminous red galaxies seen in the Sloan Digital Sky Survey Data Release 12.8 Their measured mass of the hot intergalactic gas also added up to the missing baryons.

All Four Measurements Agree

Astronomers have now produced four independent measurements of the mass of the hot intergalactic medium based on completely distinct methods using different telescopes and different databases of galaxies and quasars. The fact that all four measurements agree gives astronomers confidence that they really have found the missing baryons of the universe.

Thus, the missing baryons challenge to big bang cosmology has been resolved, and the scientific case for the validity of the biblically predicted big bang creation model is even more firmly established than before.9 We have one more reason to be confident that the God of the Bible exists and personally crafted the universe for our existence.

1. Hugh Ross and John Rea, "Big Bang—The Bible Taught It First!", Reasons to Believe (June 30, 2000):
2. Renyue Cen and Jeremiah Ostriker, "Where Are the Baryons?", Astrophysical Journal 514 (March 20, 1999):
3. Wikipedia, "Abundance of the Chemical Elements":
4. C. M. Raiteri et al., "Synchrotron Emission from the Blazar PG 1553+133. An Analysis of Its Flux and Polarization Variability," Monthly Notices of the Royal Astronomical Society 466 (April 21, 2017):
5. Fabrizio Nicastro et al., "Observations of the Missing Baryons in the Warm-Hot Intergalactic Medium," Nature 558 (June 21, 2018):
6. Sanskriti Das et al., "Discovery of Massive Warm-Hot Circumgalactic Medium around NGC 3221" (Oct. 31, 2018):
7. Anna de Graaff et al., "Missing Baryons in the Cosmic Web Revealed by the Sunyaev-Zel'dovich Effect" (Oct. 5, 2017):
8. Hideki Tanimura et al., "A Search for Warm/Hot Gas Filaments between Pairs of SDSS Luminous Red Galaxies" (Oct. 5, 2018):
9. Ross and Rea, ibid., note 1.

is an astrophysicist and the founder and president of the science-faith think tank Reasons to Believe (RTB).

This article originally appeared in Salvo, Issue #48, Spring 2019 Copyright © 2019 Salvo |