As confusing as dark matter is, regular matter isn’t always cooperative about being understood either. We have understood from a variety of observations that 5% of our universe should be made of the same normal (baryonic) matter that we, our computers, and our tables are made of. But we could only account for half of that amount in surveys that added up the mass of stars, planets, and other stuff in and around galaxies. 

Now, a new study published in the Monthly Notices of the Royal Astronomical Society (MNRAS) in a trio of papers by four researchers — Carlos Hernández-Monteagudo, Jonás Chaves-Montero, Raúl Angulo, and Giovanni Aricò — looks purely at the velocities of galaxies to see how they gravitationally interact and uses this data to look for the pull of otherwise invisible gas. According to Jonás Chaves-Montero: Most of this ‘ordinary’ matter is invisible to us because it is not sufficiently hot to emit energy. However, by using maps of the redshifts of the galaxies we find that all of this matter fills the space between them. 

To distinguish between dark matter and regular matter, they looked for the signature of electrons scattering light. These results look good, and I feel safe saying, half of the regular matter is hiding in the space between galaxies. And I’m ok with this. The universe is what is, and we’re going to learn about it one instrument, spacecraft, and computer model at a time.

More Information

IAC press release

“Density weighted angular redshift fluctuations: a new cosmological observable,” Carlos Hernández–Monteagudo, Jonás Chaves-Montero, and Raúl E Angulo, 2021 March 25, Monthly Notices of the Royal Astronomical Society: Letters

“Measuring the evolution of intergalactic gas from z = 0 to 5 using the kinematic Sunyaev–Zel’dovich effect,” Jonás Chaves-Montero et al., 2021 March 25, Monthly Notices of the Royal Astronomical Society

“Tomographic constraints on gravity from angular redshift fluctuations in the late Universe,” Carlos Hernández–Monteagudo et al., 2021 March 25, Monthly Notices of the Royal Astronomical Society: Letters