Last of universe's missing ordinary matter found-in dark about dark matter



We Just Found The Missing Matter In The Universe, And Still Need Dark Matter
Many hoped we could do without dark matter. On cosmic scales, the evidence has finally spoken.
Forbes
 We Just Found The Missing Matter In The Universe, And Still Need Dark Matter
Starts With A Bang The Universe is out there, waiting for you to discover it Opinions expressed by Forbes Contributors are their own.
Ethan Siegel Ethan Siegel , Contributor
Spectrum: NASA/CXC/Univ. of California Irvine/T. Fang. Illustration: CXC/M. Weiss
The warm-hot intergalactic medium (WHIM) has been seen before, along incredibly overdense regions, like the Sculptor wall, illustrated above. But it's conceivable that there are still surprises out there in the Universe, and our current understanding will once again be subject to a revolution.
For over 40 years, scientists have argued over dark matter's existence.
Wikimedia Commons user Stefania.deluca
The extended rotation curve of M33, the Triangulum galaxy. These rotation curves of spiral galaxies ushered in the modern astrophysics concept of dark matter to the general field. The dashed curve would correspond to a galaxy without dark matter, which represents less than 1% of galaxies.
Big questions arose from the motions inside galaxies, clusters of galaxies, and along the cosmic web.
Ralf Kaehler, Oliver Hahn and Tom Abel (KIPAC)
The cosmic web is driven by dark matter, with the largest-scale structure set by the expansion rate and dark energy. The small structures along the filaments form by the collapse of normal, electromagnetically-interacting matter.
From their gravity, we can infer the total mass in the Universe.
NASA, modified by Wikimedia Commons user 老陳, modified further by E. Siegel
The matter and energy content in the Universe at the present time (left) and at earlier times (right). Multiple lines of evidence indicate that normal (atomic) matter can only compose 1/6th of the total matter in the Universe; the remainder must be dark matter.

Yet multiple sources indicate that only 15% of that mass can be baryonic: made of normal matter.
Chris Blake and Sam Moorfield
The density fluctuations in the cosmic microwave background provide the seeds for modern cosmic structure to form, including stars, galaxies, clusters of galaxies, filaments, and large-scale cosmic voids.
If there were more, the:
  • temperature imperfections in the cosmic microwave background,
  • galaxy correlations in large-scale structure,
  • and abundances of the light elements,
Recommended by Forbes
would be different.
NASA / WMAP Science Team
The predicted abundances of helium-4, deuterium, helium-3 and lithium-7 as predicted by Big Bang Nucleosynthesis, with observations shown in the red circles. This indicates that 5% of the total energy density, and ~15% of the total matter, is in normal matter, and no more.
Many nevertheless wondered: could normal matter be hiding — and gravitating — entirely without dark matter?
NASA, ESA, and A. Feild (STScI)
An illustration of a slice of the cosmic web, as viewed by Hubble. The missing matter we can detect through electromagnetic signals is the normal matter alone; the dark matter is unaffected.
Scientists set out to measure all the normal matter in the Universe, including stars, planets, gas, dust, and more.
A 3D, reconstructed map of the total mass distribution in the cosmos. There wasn't enough normal matter to account for this, so new search techniques needed to be devised to discover where, and how much, normal matter is truly, totally out there.
Only ~20% was within galaxies and clusters; about another 35% was found along filaments and in cosmic voids.
Illustris Collaboration / Illustris Simulation
The formation of cosmic structure, on both large scales and small scales, is highly dependent on how dark matter and normal matter interact. Despite the indirect evidence for dark matter, it's vitally important to count up all the normal matter and make sure it cannot account for what's assumed to be missing.
Still, nearly half the normal matter remained missing, assumed hiding in heated, intergalactic plasmas.
Vid Iršič
A depiction of hydrogen gas within the intergalactic medium, or IGM, with bright areas indicating high gas density.
Missing normal matter was theorized: the warm-hot intergalactic medium (WHIM).
Illustrations and composition: ESA / ATG medialab; data: ESA / XMM-Newton / F. Nicastro et al. 2018; cosmological simulation: Princeton University/Renyue Cen
Astronomers have used ESA’s XMM-Newton space observatory (lower right) to detect the WHIM. The white box encloses the filamentary structure of the hot gas that represents part of the WHIM. It is based on a cosmological simulation extending over more than 200 million light years. The red and orange regions have the highest densities & the green regions have lower densities. The oxygen detection is how the baryon abundance was reconstructed.
X-ray scientists finally announced evidence for the hot part of the WHIM in precisely the predicted amounts.
Ed Janssen, ESO
The light from ultra-distant quasars provide cosmic laboratories for measuring not only the gas clouds they encounter along the way, but for the intergalactic medium that contains warm-and-hot plasmas outside of clusters, galaxies, and filaments. The X-ray emission from quasars enabled this newest detection by XMM-Newton.
If the results are universal, the mystery is solved: the missing normal matter has been found.
ESA
By examining stars, dust, and gas in galaxies and clusters, scientists had found only 18% of the normal matter. But by surveying intergalactic space, including along filaments and in cosmic voids, scientists found not only gas, but ionized plasmas of all temperatures, that lead us to 100% of what's expected. There is no more; and therefore, dark matter is still absolutely necessary.
The conclusion? Dark matter is absolutely necessary.
Mostly Mute Monday tells the astronomical story of an object, phenomenon, or process in images, visuals, and no more than 200 words. Talk less, smile more.
Astrophysicist and author Ethan Siegel is the founder and primary writer of Starts With A Bang! His books, Treknology and Beyond The Galaxy, are available wherever books are sold.



















No comments:

Post a Comment

Subscribe to: Post Comments (Atom)