Astrophysicists May Have Just Discovered the Hidden Matter of the Universe

Cosmic Web Concept

Using a novel statistical analysis of two-decade-old data, scientists might have identified hidden matter for the first time.

Astrophysicists consider that around 40% of the ordinary matter that makes up stars, planets, and galaxies remains undetected, concealed in the form of a hot gas in the complex cosmic web. Today, scientists at the Institut d’Astrophysique Spatiale (CNRS/Université Paris-Saclay) may have detected, for the first time, this hidden matter through an innovative statistical analysis of 20-year-old data. Their findings are published on November 6, 2020, in Astronomy & Astrophysics.

Hidden Matter of the Universe

© Tanimura, Aghanim (CNRS/Univ. Paris-Saclay)

Galaxies are distributed throughout the Universe in the form of a complex network of nodes connected by filaments, which are in turn separated by voids. This is known as the cosmic web. The filaments are thought to contain almost all of the ordinary (so-called baryonic) matter of the Universe in the form of a diffuse, hot gas.  However, the signal emitted by this diffuse gas is so weak that in reality, 40 to 50% of the baryons[1] go undetected.

These are the missing baryons, hidden in the filamentary structure of the cosmic web, that Nabila Aghanim, a researcher at the Institut d’Astrophysique Spatiale (CNRS/Université Paris-Saclay) and Hideki Tanimura, a post-doctoral researcher, together with their colleagues, are attempting to detect. In a new study, funded by the ERC ByoPiC project, they present a statistical analysis that reveals, for the first time, the X-ray emission from the hot baryons in filaments. This detection is based on the stacked X-ray signal, in the ROSAT[2] survey data, from approximately 15 000 large-scale cosmic filaments identified in the SDSS[3] galaxy survey. The team made use of the spatial correlation between the position of the filaments and the associated X-ray emission to provide evidence of the presence of hot gas in the cosmic web, and for the first time measure its temperature.

These findings confirm earlier analyses by the same research team, based on indirect detection of hot gas in the cosmic web through its effect on the cosmic microwave background.[4] This paves the way for more detailed studies, using better quality data, to test the evolution of gas in the filamentary structure of the cosmic web.


  1. Baryons are particles consisting of three quarks, such as protons and neutrons. They make up atoms and molecules as well as all the structures that can be seen in the observable Universe (stars, galaxies, galaxy clusters, etc). The ‘missing’ baryons, undetected until now, should not be confused with dark matter, which is made up of non-baryonic matter of unknown nature.
  2. ROSAT was a German space telescope designed for the observation of X-rays.
  3. The Sloan Digital Sky Survey (SDSS) is a program for surveying celestial objects using a dedicated 2.5-meter optical telescope located at Apache Point Observatory (New Mexico, USA). It began collecting data in 2000.
  4. See the article: Density and temperature of cosmic-web filaments on scales of tens of megaparsecs, Tanimura, H.; Aghanim, N.; Bonjean, V.; Malavasi, N.; Douspis, M. Astronomy & Astrophysics, Volume 637, A41 (2020).

Reference: “First detection of stacked X-ray emission from cosmic web filaments” by H. Tanimura, N. Aghanim, A. Kolodzig, M. Douspis and N. Malavasi, 6 November 2020, Astronomy & Astrophysics.
DOI: 10.1051/0004-6361/202038521

15 Comments on "Astrophysicists May Have Just Discovered the Hidden Matter of the Universe"

  1. John Beckman. (Professor of Astrophysics, Instituto de Astrofísica de Canarias) | November 9, 2020 at 3:43 am | Reply

    The headline is totally misleading. We know that the baryons cannot make up more than around 4to 5 % of the total matter in the universe. So if the researchers have found a significant fraction of the baryons, they cannot possibly have found more than 5% of the mass of the universe, and in fact this figure must be a strong upper limit. The vast quantity of missing rest mass is in “dark matter” which cannot be baryonic, and even this can only be around 20% of the total gravitational mass of the universe. So the title is really very bad, and very misleading indeed

    • Torbjörn Larsson | November 9, 2020 at 4:45 am | Reply

      @John Beckman: “The headline is totally misleading.”

      It is perhaps misleading to those unfamiliar with the problem, perhaps. (I have a recollection of having to familiarize myself with it a few years back, and I’m not a cosmologist.)

      But dark matter is not considered to be “missing” – it has been robustly observed to the amounts predicted by the cosmic background spectra (which itself constitutes an independent observation.

      The “missing baryon problem” is what cosmologists has long labeled the 40 % discrepancy [“Missing baryon problem” @ Wikipedia]:

      “The missing baryon problem was a problem related to the fact that the observed amount of baryonic matter did not match theoretical predictions. The density of baryons can be constrained according to Big Bang nucleosynthesis and the cosmic microwave background. Observations by the Planck spacecraft in 2015, yielded a theoretical value for baryonic matter of 4.85% of the contents of the Universe.[1] However, directly adding up all the known baryonic matter produces a baryonic density slightly less than half of this.[2] The missing baryon problem is distinct from the dark matter problem, which is mainly non-baryonic in nature.[3]

      The missing baryons are believed to be located in the warm–hot intergalactic medium (WHIM) (hot intergalactic gas), with recent observations providing strong support.[4][5]”

      • Torbjörn Larsson | November 9, 2020 at 4:54 am | Reply

        I should perhaps add that today, with precision cosmology at 1 % uncertainty [eBOSS galaxy survey 20 year summary cosmological paper @ arxiv], 40 % discrepancy is *huge*. For comparison largest outstanding parameter tension is the 10 % Hubble rate tension between largely low-z* and largely integrated high-z observations.

        [*Oddly, a just published z < 0.2 raw data galaxy survey gets the middle ground of 70 km s^-1 Mpc^-1 that independent tip of the red giant branch and gravitational binary neutron star mergers get, but at much smaller data sets. And some supernova group has recently published that the field has a problem: they are looking at two different populations of events.]

    • The dark mass & dark matter are continuously changing. There is a new universe beyond the one we know of. It also consists of planets, stars, gases but of a different biometric pressures and matter. It’s like highly unlikely that it would react as if it has it own orbits, planets, stars and gravitational pull etc but it does along with existence of life…but of a different life form. Astrophysicists will be discovering new phases as well as mis-naming them which will sound uncanny or absurd.

      • Torbjörn Larsson | November 9, 2020 at 5:00 am | Reply

        @RM Rodrigues: “The dark mass & dark matter are continuously changing.”

        There is no “dark” mass, famously mass is a unipolar charge of gravity. And dark matter is observably a constant mass fraction of the universe.

        As for the rest, relevance et cetera – see my other response to you.

  2. Fascinating…& there’s more to discover. The voids in the web are actually dimensions where life exists. The emissions being transmitted are that of gases & unknown substances…most of it relatively invisible energy with surges of heat, water, plasmas of different forms. You will notice another change in the universe with a different but amazing atmosphere as of Nov 8 2020 & days to follow.
    New “livable” planets & universe does exist as well the blackhole close to earth…amongst many recently created. You should be able to see activity like that of a fire ball with a tail over DFW in TX. No, it not a comet or meteor etc. It’s a flame with burning stars within looking almost like a candlestick created today for your fascination.

    • Torbjörn Larsson | November 9, 2020 at 4:57 am | Reply

      @RM Rodriguez:


      Science is based on evidence. Your wildly speculative, hardly readable comments are not.

      • Once again….uncanny or absurd.
        However, new discoveries are being revealed or unveiled. Whether you’re on the same level of knowledge or not.

        • Torbjörn Larsson | November 11, 2020 at 9:50 am | Reply

          Only science gives knowledge. You are indulging in personal fantasies.

          There is a huge difference, and the latter is not really a topic for science site comment threads.

  3. Torbjörn Larsson | November 9, 2020 at 4:36 am | Reply

    The paper discuss only hot gas, so their only comparison is with other X-ray as well as weak lensing and thermal Sunyaev–Zeldovich effect (CMB boost by collisions with galaxy cluster electrons) surveys which supposedly find the right amount of hot gas in the filaments.

    Else there has been an interesting fast radio burst method seeing the right amount of missing normal matter in the filaments since 2016. “New fast radio burst discovery finds ‘missing matter’ in the universe” @ Phys Org leading up to “Mysterious radio bursts reveal missing matter in cosmos” @ Science:

    “Roughly half of the “normal” matter in the universe—the stuff that makes up stars, planets, and even us—exists as mere wisps of material floating in intergalactic space, according to cosmologists. But astronomers had no good way to confirm that, until now. A new study has used fast radio bursts (FRBs)—powerful milliseconds long pulses of radio waves coming from distant galaxies—to weigh intergalactic matter, and the results match up with predictions.”

    “So far, astronomers can see the glowing galaxies that make up the web, but not the gas between them. The ASKAP researchers hope to build up a collection of about 100 FRBs with known sources over the next year, so they will know not just that the normal matter is there, but exactly where it is hiding.”

  4. Extraordinary observations require extraordinary theories to explain them. “Leakage” gravity from other galaxies located elsewhere along a geometric axis “W” (a fourth dimension that we cannot access) could certainly create the illusion of missing mass in our own galaxy. If those galaxies are positioned along W so as to be perpendicular to our X, Y, and Z, it would also naturally create the halo shape that we see from measurements. Furthermore, the gravity that becomes “entrapped” in our three-space would appear “from nowhere” and then dissipate normally, per the inverse square law, just as light from an external source can become entrapped between two glass plates and dissipate with the inverse of distance. Particle physicists might be looking for something that isn’t really where they are looking.

    • Torbjörn Larsson | November 11, 2020 at 9:56 am | Reply

      You are reversing Sagan’s advice: “extraordinary claims require extraordinary evidence” [“Sagan standard” @ Wikipedia].

      But X-ray emission from hot gas and/or the hot gas are not extraordinary observations. Further, it was expected – see the article. And explained by mundane theory.

      FWIW on your speculations, there are no observations of extra dimensions.

  5. … business as usual…

  6. Howard Jeffrey Bender | November 9, 2020 at 1:22 pm | Reply

    So how did this cosmic web form? I think the view in this article is backwards – the cosmic web formed because the matter in the universe is where it is.

    Another possibility, from a view of String Theory, is that Dark Matter appears to us as an effect of string/anti-string annihilations. As you may know, quantum mechanics requires that strings must be formed as pairs in the quantum foam – a string and an anti-string – that immediately annihilate each other. Quantum mechanics also requires both the string and anti-string to be surrounded by “jitters” that reduce their monstrous vibrating energies. What if this jitter remains for a fraction of an instant after their string/anti-string annihilations? This temporary jitter would be seen by us as matter for that instant before it too returns to the foam. That’s why we never see it – the “mass” lasts only for that instant but is repeated over and over and over, all over. Specifics on this can be found in my YouTube at

    • Torbjörn Larsson | November 11, 2020 at 9:59 am | Reply

      It isn’t “a view” – it is the result of the cosmological process, see simulations of the web formation during the observable universe history.

      String theory is becoming unpopular. But you know that since you always comment with that as basis no matter what the science says.

      Finally, the usual observation: you post self promotion links. That is not nice.

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