For decades astronomers have struggled to find their so called "missing baryons" which has been considered to be separate from "dark matter" by the way.By extrapolating from these observations of oxygen to the full set of elements, and from the observed region to the local universe, the researchers report they can account for the complete amount of missing matter. At least in this particular case, the missing matter had been hiding in the WHIM after all.
"We were thrilled that we were able to track down some of this missing matter" said co-author Randall Smith, also of CfA. "In the future we can apply this same method to other quasar data to confirm that this long-standing mystery has at last been cracked."
Based on the LCDM model, astronomers estimated that they should be finding a specific amount of baryonic mass based on luminosity oriented mass estimation techniques of galaxies, but they've been consistently finding only about half of the expected amount of ordinary baryonic mass based on those luminosity oriented techniques. They knew that something was wrong, but they hadn't been able to locate the missing baryons and find the problem in their baryonic mass estimate techniques. This baryonic mass estimation technique was used in the now infamous Bullet Cluster study in 2006 when astronomers claimed to "prove" the existence of "dark matter" by estimating the total mass of the galaxy clusters based on a lensing technique associated with General Relativity and then subtracting the amount of baryonic mass in those galaxies that is estimated based on luminosity:
The Bullet Cluster – A Smoking Gun for Dark Matter!
This luminosity oriented baryonic mass estimation technique is based upon an IMF (initial mass function) of stars, and their expected luminosity. Only the largest stars in distant galaxies produce enough light to be seen on Earth, whereas smaller stars simply do not emit enough light to contribute much to the overall brightness of galaxies at large distances. They use an "estimation" process that essentially estimates the number of smaller stars that we cannot see on Earth compared to the larger sized stars which emit enough light to contribute to the overall galaxy brightness which we observe. They categorize the stars into different groups based on size, small red dwarfs being the most abundant but emitting the least amount of light, stars the size of our own sun which emit more light than red dwarfs, yet still too little light to be observed on Earth, and the largest stars in galaxies that emit enough light to contribute to the overall brightness.
Numerous assumptions are made in that baryonic mass estimation technique relating to the maximum size of massive (large) stars, the number of them found in various galaxies, the percentage of smaller sun size stars compared to larger stars, and the percentage of smaller sized red dwarfs compared to larger stars. They also estimate the amount of stars found between galaxies in various galaxy clusters. All of these 'assumptions' have recently (within the past 11 years) been shown to be incorrect:
Over the past 11 years. numerous problems have been identified in those luminosity oriented mass estimation techniques, and a *lot* of new 'normal' matter has been found:
In 2008, they figured out that distant galaxies are actually twice as bright as first suspected. About half of the light from ordinary stars has been absorbed/blocked by ordinary dust which surrounds every galaxy:
Universe shines twice as bright
The authors of that paper assumed that the larger stars in galaxies must be bigger and more massive than originally estimated by the IMF calculations. That assumption was confirmed last year when they discovered that the size of massive stars can actually be considerably larger than first estimated and the number of larger stars can be considerable greater than expected:
This massive star discovery could rewrite astrophysics
They found that the massive stars in 30 Doradus were actually larger and considerably more numerous than has been estimated in the luminosity oriented mass estimation techniques we've been using. In essence the two studies confirmed that we've been systematically underestimating the ordinary baryonic mass that is found in larger stars in every galaxy in those luminosity calculations.
In 2009 they also discovered that their luminosity oriented mass estimation techniques had been systematically underestimating the number of smaller sized stars like our own sun in various galaxies, which do not emit enough light to be seen on Earth, compared to the number of larger stars which can be observed on Earth. In fact we've been underestimating the number of such stars by a factor of four!
NASA - Galaxies Demand a Stellar Recount
The following year in 2010, they discovered that they've been underestimating the most *common* sized star (dwarf stars) in various galaxies by a *whopping* factor of between 3 and 20 times depending on the galaxy type. Again, they've been grossly underestimating the *normal baryonic material* that is present in galaxies.
Scientists Find 200 Sextillion More Stars in the Sky
In 2012 NASA reported that it had found a hot plasma halo around our galaxy and presumably every galaxy which is so massive that by itself that hot plasma halo might explain the entire missing baryon problem:
Milky Way is Surrounded by Huge Halo of Hot Gas | ChandraBlog | Fresh Chandra News
In 2014 it was discovered that there might be as many stars *outside* of galaxies in a galaxy cluster as the number of stars found in the galaxies themselves.Data from NASA's Chandra X-ray Observatory was used to estimate that the mass of the halo is comparable to the mass of all the stars in the Milky Way galaxy. If the size and mass of this gas halo is confirmed, it could be the solution to the "missing-baryon" problem for the Galaxy.
A Universe of Stars May Exist Outside Galaxies | RealClearScience
In 2017 a *second* massive halo of cooler baryonic hydrogen gas was also discovered around our galaxy which also potentially holds enough ordinary baryonic mass to account for the so called "missing" baryons."If confirmed, these observations reveal an unexpected stellar population, with as many as half the stars in the local universe being outside galaxies," NASA astronomer Harvey Moseley commented. "It is remarkable that such a major component of the universe could have been hiding in plain sight as an infrared background between the stars and galaxies."
Galaxy’s hydrogen halo hides missing mass | Cosmos
Today's Chandra announcement marks the third time now in the last 7 years that astronomers have reported finding their 'missing baryons', first they reported finding them in a hot million degree plasma halo in 2012, again they claimed to find them in a cooler hydrogen gas halo in 2017, and a third time today in a "hot/warm" plasma medium found in the filaments connecting galaxies. This is *on top of* all of the of the stellar mass underestimates discovered since 2008. Astronomers no longer have a 'missing baryon" problem, they have an *excess* of baryon problem on their hands in 2019. The have now reported to have found triple the number of missing baryons inside of a hot plasma halo, again inside of a cooler gas halo, and for a third time in the hot/warm filaments between galaxies, *plus* they've reported a bunch of baryon underestimation problems related to their stellar IMF calculations!Drilling through the data, Zaritsky and Zhang confirmed not only the existence of the gas, but also that its mass matches that missing in the baryonic-to-dark-matter equation.
There is no absolutely no evidence of any need for exotic forms of "dark matter", and there is now plenty of evidence to suggest that our baryonic mass estimation techniques have never been worth the paper they've been printed on.