Space is Filled with Giant Pancakes

The Cosmic Companion
Aug 13 · 1 min read

Galaxies are distributed throughout the Universe along massive pancakes, or cosmic sheets, stretching millions of light years across. Between layers, vast stretches of space between galaxies are filled with the intergalactic medium (IGM) — gas (mostly hydrogen and helium) — which remains largely free from control by large bodies. This tenuous material makes up most of the “normal matter” in the Universe.

Yale University astronomers recently carried out computer simulations, simulating the behavior of the clouds of gas moving between these sheets, finding these formations could shatter due to temperature instabilities. Researchers also confirmed theories that material from these clouds, mostly hydrogen, might “feed” galaxies, promoting the birth of new stars.

A temperature map of the IGM, with hot regions in red and cooler areas in blue. Image credit: Screenshot from video by Yale University.

“The reason galaxies are able to form stars continuously is because fresh gas flows into galaxies from the IGM. It is clear that galaxies would run out of gas in very short order if they didn’t accrete fresh gas from the IGM,” Nir Mandelker, postdoctoral associate at Yale University, explained.

Tall, Dark, and Mysterious…

Everything we see in the Universe around us — stars, planets, galaxies — makes up less than five percent of the total matter/energy in the observable Cosmos. Dark matter makes up 27 percent of “everything,” while dark energy accounts for the remaining 68 percent.

Still, it is this “normal matter” — atoms, molecules, and “stuff” with which we are most familiar. This simulation revealed the behavior of most of the normal matter of the Universe on the grandest scale, with detail never before seen.

The intergalactic medium is both exceedingly sparse and stupendously hot. This near-vacuum, containing just one atom per cubic meter (on average) of gas, radiates at temperatures of millions of degrees Celsius.

The largest of these massive clouds of gas contain as much mass as hundreds of trillions of stars like our Sun.

A computer simulation showing how clumps of dark matter can draw material from the IGM into galaxies, fueling star formation. Image credit: NASA, ESA, and T. Brown and J. Tumlinson (STScI)

In addition to being attracted to galaxies through the gravitational interaction of galaxies, gas from the IGM can also be pulled into galaxies by large clumps of dark matter within groupings of stars.

“Normal dwarf galaxies near the Milky Way contain 10 times more dark matter than the ordinary matter that makes up gas and stars. In ultra-faint dwarf galaxies, dark matter outweighs ordinary matter by at least a factor of 100,” NASA explains.

This process could feed not just star birth within galaxies, but can also result in the formation of new dwarf galaxies.

I’m on a Metal-free Diet

“Tell me what you know.”
“I’m awake and you’re not pancakes.”
― Seanan McGuire, Once Broken Faith

This new study also examined whether the composition of the gas may be altered by star formation in galaxies, polluting the IGM with metals (elements heavier than helium). The simulation determined these clouds, far from galaxies, are nearly free from heavy elements.

Strings placed in a complex series or twisted lines, like spilled spaghetti.
Strings placed in a complex series or twisted lines, like spilled spaghetti.
A computer simulation of the distribution of IGM over an area of space 2.7 billion light years wide, and 0.3 light years deep. Image credit: James Wadsley (McMaster U.) et al.

Unlike matter in stars, the IGM does not glow with light of its own, apart from X-rays generated by the enormous temperature of the gas. This radiation, however, is difficult to measure, due to the extremely low density of the gas. The IGM can best be studied through its absorption of light from stars, providing information on the density and chemical makeup of these clouds.

Clouds in the IGM were thought to only form near galaxies, where gas is denser. This new simulation suggests these formations, the result of inefficient heating in the gas, can also form deep within the intergalactic medium. Here, the gas would be kept largely free of contaminants from star formation.

A shockwave moves between two hot (red) areas on in the IGM. Video: Yale University

This new study, detailed in The Astrophysical Journal Letters, could help explain the presence of large, metal-free, clouds of matter seen between galaxies.

Between pancakes of galaxies hides chunky clouds of intergalactic matter, like comic dabs of butter, floating in the hot syrup of the IGM medium. I’m getting hungry.

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    The Cosmic Companion

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    James Maynard is the author of two books, and thousands of articles about space and science. E-mail:

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