24 Facts About Dark matter

Dark matter is called "dark" because it does not appear to interact with the electromagnetic field, which means it does not absorb, reflect, or emit electromagnetic radiation and is, therefore, difficult to detect.

Primary evidence for dark matter comes from calculations showing that many galaxies would behave quite differently if they did not contain a large amount of unseen matter.

The primary candidate for dark matter is some new kind of elementary particle that has not yet been discovered, particularly weakly interacting massive particles, Many experiments to directly detect and study dark matter particles are being actively undertaken, but none have yet succeeded.

Dark matter estimated the cluster had about 400 times more mass than was visually observable.

Dark matter attributed it to either light absorption within the galaxy or modified dynamics in the outer portions of the spiral and not to the missing matter he had uncovered.

Related searches

In standard cosmology, matter is anything whose energy density scales with the inverse cube of the scale factor, i e, This is in contrast to radiation, which scales as the inverse fourth power of the scale factor and a cosmological constant, which is independent of a These scalings can be understood intuitively: For an ordinary particle in a cubical box, doubling the length of the sides of the box decreases the density by a factor of 8 .

The mass-to-light ratios correspond to dark matter densities predicted by other large-scale structure measurements.

In particular, in the early universe, ordinary Dark matter was ionized and interacted strongly with radiation via Thomson scattering.

Ordinary Dark matter is affected by radiation, which is the dominant element of the universe at very early times.

Dark matter provides a solution to this problem because it is unaffected by radiation.

The resulting gravitational potential acts as an attractive potential well for ordinary Dark matter collapsing later, speeding up the structure formation process.

However, for the reasons outlined below, most scientists think the dark matter is dominated by a non-baryonic component, which is likely composed of a currently unknown fundamental particle .

However, baryonic Dark matter encompasses less common non-primordial black holes, neutron stars, faint old white dwarfs and brown dwarfs, collectively known as massive compact halo objects, which can be hard to detect.

Candidates for non-baryonic dark matter are hypothetical particles such as axions, sterile neutrinos, weakly interacting massive particles, supersymmetric particles, geons, or primordial black holes.

Categories are set with respect to the size of a protogalaxy : Dark matter particles are classified as cold, warm, or hot according to their FSL; much smaller, similar to, or much larger than a protogalaxy.

Mixtures of the above are possible: a theory of mixed dark matter was popular in the mid-1990s, but was rejected following the discovery of dark energy.

Cold dark matter leads to a bottom-up formation of structure with galaxies forming first and galaxy clusters at a latter stage, while hot dark matter would result in a top-down formation scenario with large matter aggregations forming early, later fragmenting into separate galaxies; the latter is excluded by high-redshift galaxy observations.

The best candidate for hot dark matter is a neutrino.

Cold dark matter offers the simplest explanation for most cosmological observations.

Predictions based on warm dark matter are similar to those for cold dark matter on large scales, but with less small-scale density perturbations.

Galaxy-size density fluctuations get washed out by free-streaming, hot dark matter implies the first objects that can form are huge supercluster-size pancakes, which then fragment into galaxies.

Alternatively, if a dark matter particle is unstable, it could decay into Standard Model particles.

Constraints on dark matter exist from the LEP experiment using a similar principle, but probing the interaction of dark matter particles with electrons rather than quarks.

Dark matter has not yet been identified, many other hypotheses have emerged aiming to explain the observational phenomena that dark matter was conceived to explain.