New revelations on dark matter and relic neutrinos

New revelations on dark matter and relic neutrinos
Temperature map of the relic radiation (bottom left), and close-ups showing, in relief, the polarisation of light in the 353 GHz channel (the colors correspond to the intensity of the thermal emission from galactic dust.) Credit: ESA – Planck collaboration

The Planck collaboration, which notably includes the CNRS, CEA, CNES and several French universities, has disclosed, at a conference in Ferrara, Italy, the results of four years of observations from the ESA's Planck satellite. The satellite aims to study relic radiation (the most ancient light in the Universe). This light has been measured precisely across the entire sky for the first time, in both intensity and polarisation, thereby producing the oldest image of the Universe. This primordial light lets us "see" some of the most elusive particles in the Universe: dark matter and relic neutrinos.

Between 2009 and 2013, the Planck satellite observed relic radiation, sometimes called (CMB) radiation. Today, with a full analysis of the data, the quality of the map is now such that the imprints left by dark matter and relic neutrinos are clearly visible.

Already in 2013, the map for variations in light intensity was released, showing where matter was in the sky 380,000 years after the Big Bang. Thanks to the measurement of the polarisation of this light (in four of seven frequencies, for the moment), Planck can now see how this material used to move. Our vision of the primordial Universe has thus become dynamic. This new dimension, and the quality of the data, allows us to test numerous aspects of the standard model of cosmology. In particular, they illuminate the most elusive of particles: dark matter and neutrinos.

New constraints on dark matter

The Planck collaboration results now make it possible to rule out an entire class of models of dark matter, in which dark matter-antimatter annihilation is important. Annihilation is the process whereby a particle and its antiparticle jointly disappear, followed by a release in energy.

The basic existence of dark matter is becoming firmly established, but the nature of remains unknown. There are numerous hypotheses concerning the physical nature of this matter, and one of today's goals is to whittle down the possibilities, for instance by searching for the effects of this mysterious matter on and light. Observations made by Planck show that it is not necessary to appeal to the existence of strong dark matter-antimatter annihilation to explain the dynamics of the early universe. Such events would have produced enough energy to exert an influence on the evolution of the light-matter fluid in the early universe, especially around the time relic radiation was emitted. However, the most recent observations show no hints that this actually took place.

These new results are even more interesting when compared with measurements made by other instruments. The satellites Fermi and Pamela, as well as the AMS-02 experiment aboard the International Space Station, have all observed an excess of cosmic rays, which might be interpreted as a consequence of . Given the Planck observations, however, an alternative explanation for these AMS-02 or Fermi measurements—such as radiation from undetected pulsars—has to be considered, if one is to make the reasonable hypothesis that the properties of dark matter particles are stable over time.

Additionally, the Planck collaboration has confirmed that comprises a bit more than 26% of the Universe today (figure deriving from its 2013 analysis), and has made more accurate maps of the density of matter a few billion years after the Big Bang, thanks to measurements of temperature and B-mode polarisation.

Neutrinos from the earliest instants detected

The new results from the Planck collaboration also inform us about another type of very elusive particle, the neutrino. These "ghost" particles, abundantly produced in our Sun for example, can pass through our planet with almost no interaction, which makes them very difficult to detect. It is therefore not realistic to directly detect the first neutrinos, which were created within the first second after the Big Bang, and which have very little energy. However, for the first time, Planck has unambiguously detected the effect these relic neutrinos have on relic radiation maps.

The relic neutrinos detected by Planck were released about one second after the Big Bang, when the Universe was still opaque to light but already transparent to these particles, which can freely escape from environments that are opaque to photons, such as the Sun's core. 380,000 years later, when was released, it bore the imprint of neutrinos because photons had gravitational interaction with these particles. Observing the oldest photons thus made it possible to confirm the properties of neutrinos.

Planck observations are consistent with the standard model of particle physics. They essentially exclude the existence of a fourth species of neutrinos, previously considered a possibility based on the final data from the WMAP satellite, the US predecessor of Planck. Finally, Planck makes it possible to set an upper limit to the sum of the mass of neutrinos, currently established at 0.23 eV (electron-volt).

The full data set for the mission, along with associated articles that will be submitted to the journal Astronomy & Astrophysics (A&A), will be available December 22 on the ESA web site.


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Researchers report on data analysis from Planck spacecraft

Journal information: Astronomy & Astrophysics

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Citation: New revelations on dark matter and relic neutrinos (2014, December 5) retrieved 26 August 2019 from https://phys.org/news/2014-12-revelations-dark-relic-neutrinos.html
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Dec 05, 2014
"photons having gravitational interaction"

I never quite understood how massless photons interact with gravity. Someone told me they aren't interacting with gravity but just following the curvature of space-time. However, this is exactly what normal matter with mass does and then we do call it gravity... right?

Dec 05, 2014
I never quite understood how massless photons interact with gravity.

Photons have zero rest mass but they have energy, and energy has mass: m=E/c², so photons do interact with gravity. ('Following the curvature of space-time' is interacting with gravity.)

Dec 05, 2014

Quoting del2, "Photons have zero rest mass but they have energy, and energy has mass: m=E/c², so photons do interact with gravity. ('Following the curvature of space-time' is interacting with gravity.)"

Would we then conclude that neutrino's with less energy/mass would not follow the curvature of space-time as much?


Dec 05, 2014
Would we then conclude that neutrinos with less energy/mass would not follow the curvature of space-time as much?

If the (relativistic) mass of the neutrinos is less than that of the photons, then yes, that would be so.

Dec 05, 2014
"photons having gravitational interaction"

I never quite understood how massless photons interact with gravity. Someone told me they aren't interacting with gravity but just following the curvature of space-time. However, this is exactly what normal matter with mass does and then we do call it gravity... right?


Photons are not massless. Because of e=mc^2, they have mass. Normal matter's path curves more in a gravitational field than does light for the same reason that a fastball's trajectory isn't as flat as that of a bullet. Matter moving at near light speed curves in pretty much the same way as light.

Dec 05, 2014
First of all, photons *are* massless. They have no mass. Zero. They are "pure energy." The only "mass" that makes any sense in relativity is so-called, rest mass.

Second, gravity is not a force in general relativity (GR). Gravity is the effect we see when the presence of a gravitational source produces curvature of spacetime.
GR can be summarized as,
"Matter tells space how to curve; space tells matter how to move."

All objects free of forces, follow geodesics of spacetime. That's so whatever the mass, including 0.
Where spacetime is flat, geodesics are straight lines (constant vector velocity == straight world-line). Where it is curved, they're the straightest lines possible.
Objects with mass follow time-like geodesics.
0-mass objects follow light-like geodesics (local speed=c, as measured in any inertial frame).

Dec 05, 2014
Illustration that mass is not velocity-dependent:
The usual rule for this is that
m = γm₀ where m₀=rest-mass, γ=1/√(1-[v/c]²)
This allows us to continue using
p = mv
for the momentum. But now if you try to do the same with kinetic energy, T, you'll find that the "velocity-dependent mass" has a different dependence on velocity, because
T ≠ ½γm₀v²
instead,
T = (γ-1)m₀c²

The truth is, that momentum simply does NOT equal mass times velocity; it is
p = γmv, where m=rest-mass
It all does become mathematically simpler again, p = mv, if you write it all in 4-vectors.

As for photons etc., energy doesn't have mass; although it can be converted to mass.
Mass, energy and stress are all sources of gravitation, however; each affects the curvature of spacetime.

Note that a photon doesn't have an inherent value of its energy, stuck to it like a price tag; its energy is different in different-velocity inertial frames.

Dec 05, 2014
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Dec 05, 2014

As for photons etc., energy doesn't have mass; although it can be converted to mass.

Energy does have mass, the binding energy of a nucleus is the difference between the mass of the nucleus and the sum of the masses of its nucleons. It is not 'converted' to mass. E=mc².

Note that a photon doesn't have an inherent value of its energy, stuck to it like a price tag; its energy is different in different-velocity inertial frames.

The energy of a photon is governed by its frequency. E=hf

Dec 06, 2014
From the perspective of SR is the amount of dark matter constant or identical in all non-inertial systems?

Dec 06, 2014
"the binding energy of a nucleus is the difference between the mass of the nucleus and the sum of the masses of its nucleons."

When p and n stick together, they release an amount of energy equal to their binding energy, in the form of photons. The resulting deuteron therefore has less mass than p + n individually. Mass has thus been converted to energy, not the other way round.
E=mc²

"The energy of a photon is governed by its frequency. E=hf"

Right. And both its energy and its frequency change with relative motion of the frame they are measured in.
It's called, the Doppler shift.

Dec 06, 2014
And since every inertial frame is just as valid as every other, a photon doesn't have an inherent energy or frequency; it has values of those quantities only relative to a particular frame.

This is essentially no different from the situation for any particle **with** mass, whose energy, momentum, and deBroglie wavelength are all different in different inertial frames.

Dec 06, 2014
"the binding energy of a nucleus is the difference between the mass of the nucleus and the sum of the masses of its nucleons."

When p and n stick together, they release an amount of energy equal to their binding energy, in the form of photons. The resulting deuteron therefore has less mass than p + n individually. Mass has thus been converted to energy, not the other way round.

There is no 'conversion'. The difference in mass of the particles is the mass of the released energy. Which is not photons in the case of fusion - this is not e/m but strong nuclear force - it's kinetic energy.

"The energy of a photon is governed by its frequency. E=hf"

Right. And both its energy and its frequency change with relative motion of the frame they are measured in.

Of course. Did I say otherwise?

Dec 06, 2014
Energy does have mass, the binding energy of a nucleus is the difference between the mass of the nucleus and the sum of the masses of its nucleons...


The highest binding energy per nucleon is ~ 9 MeV in iron, or only around 1% of the nucleon's rest mass, and, as fred_s points out, the mass of a nucleus is lower than that of free nucleons.

Is the example you want the binding of quarks inside a nucleon?
The proton's rest mass is much higher than the sum of the individual quarks, so the binding mass is positive and makes up ~99% of the proton's rest mass.

Dec 06, 2014
As for photons etc., energy doesn't have mass; although it can be converted to mass.

Energy does have mass, the binding energy of a nucleus is the difference between the mass of the nucleus and the sum of the masses of its nucleons. It is not 'converted' to mass. E=mc².


Note that a photon doesn't have an inherent value of its energy, its energy is different in different-velocity inertial frames.

.........exactly right as put forth in Einstein's Energy/Mass Equivalence Principle alias E=mc2. Einstein made no distinction between energy & mass realizing the two are simply transformed products of one another. If a 2 kg mass is transformed to energy resulting in a mass of 1 kg, the resulting force of gravity of the remaining mass will be 1/2 of the original. Gravity is conserved, it just doesn't disappear into oblivion because mass is transformed. Einstein proved in his GR proves photons passing near the sun from background stars are bent.

Dec 06, 2014
cont'd from above:

........So when a mass loses 1/2 its mass through transformation to energy, then in accordance to the Energy/Mass Equivalence Principle (E=mc2), half the gravity field was carried away by the energy field (alias the term: Relativistic Mass). Gravitational attraction occurs only when gravitational fields interact directly with one another as was proven by Einstein when he postulated starlight passing near the disc of the sun would bend, later observations proved him correct, thus proving gravity does not simply disappear into oblivion when mass is transformed into energy, proving that gravity is conserved within the energy field itself.

Dec 06, 2014
Dark matter physically occupies three dimensional space. Dark matter is physically displaced by the particles of matter which exist in it and move through it.

The Milky Way's halo is not a clump of stuff anchored to the Milky Way. The Milky Way is moving through and displacing the dark matter. The Milky Way's halo is the state of displacement of the dark matter. The Milky Way's halo is the deformation of spacetime.

What is referred to geometrically as the deformation of spacetime physically exists in nature as the state of displacement of the dark matter.

A moving particle has an associated dark matter displacement wave. In a double slit experiment the particle travels through a single slit and the associated wave in the dark matter passes through both.

Dec 06, 2014
From the article:
"They essentially exclude the existence of a fourth species of neutrinos"

Are they referring to sterile neutrinos?


Yes.

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