# Tag Info

4

Then, shouldn't this sphere be detectable via the way it lenses light coming from galaxies that lie behind it (relative to earth). Similarly, a mass of dark matter within our own galaxy, should be detectable via the way it lenses light from stars that lie behind it ( again relative to earth). Has anything like this ever been observed? Yes, it should do ...

2

Your title asks about dark matter, while the question asks about dark energy. The two are very different! I'd guess you mean to ask about dark energy because this does behave differently from matter (as far as gravity is concerned dark matter behaves just like ordinary matter). If so, the answer is that dark energy does not behave like exotic matter and ...

0

Absolutely not. Dark matter has the same gravitational effects as regular matter it just doesn't interact electromagnetically. We expected a certain amount of dark matter, such a neutrinos, bit there weren't enough neutrinos so it seemed like there must be something else besides things like neutrinos. Something that interacts in the normal way ...

0

Rod Vance's answer explains why your proposed explanation seems unlikely to many. I'd like to explain what the observations you allude to really show. The correlation between black hole mass and stellar velocities is known as the M-sigma relation. First, note that it does not involve the outer stars in the galaxy. While it is true that the outer stars (and ...

-2

The mass which fills 'empty' space is beginning to be referred to as the 'dark mass' in order to distinguish it from the baggage associated with dark matter. 'Dark Energy/Dark Mass: The Slient Truth' https://tienzengong.wordpress.com/2015/04/22/dark-energydark-mass-the-silent-truth/ "That is, all that we are certain about [is] the dark mass, not dark ...

2

Like most proposals, it is possible of course; in physics we must ultimately test proposals experimentally. In the meantime (i.e. in this case whilst waiting for experimental observation and study of dark matter here on Earth), one must resort to assessing plausibility in the light of what we already know. There are two ways your proposal, if true, could ...

1

The critical density is an observable quantity. $$\rho_C = \frac{3H_0^2}{8\pi G},$$ where $H_0$ is the present-day value of the Hubble parameter. $H_0$ is known (observationally) from a variety of methods to be 69 km/s per Mpc, with an accuracy of about 1 per cent. So to answer your question as posed, the critical density has a confidence interval of about ...

3

For a real answer, each particle would have to be discussed individually and that might get long. Dark matter possibly being Neutrinos has certainly been proposed and in many ways, Neutrino's lack of interaction makes them a good candidate, as they are essentially "dark" - though "invisible" is perhaps a more accurate term and Neutrinos fly through stuff ...

2

The de Broglie wavelengths of freely propagating particles (i.e. forget interactions) are redshifted by the expansion of the universe. Another way of saying this is that their peculiar momenta with respect to a co-moving local volume decrease as the inverse of the scale factor. As neutrinos have a non-zero mass (perhaps 0.1 eV - see Battye & Moss 2014, ...

0

One astrophysical constraint is that dark matter particles must not be produced in too large numbers in stars. Suppose that the reaction $\gamma + Ze^+ \to \gamma + Ze^+ + D$ or something similar, is allowed where $D$ is a dark matter particle. Since a star is opaque to photons, that energy stays in the star, but the dark matter particle escapes, like ...

6

Good question! I agree with the two restrictions on dark matter (DM) that you mentioned. In total I would mention four main restrictions: It must be non-luminous: In practice this means no coupling (or extremely weak) to $U(1)_{em}$ and no coupling to $SU(3)_c$. We know it cannot interact with the strong force because e.g. radiation of gluons would ...

3

This new paper addresses exactly this question, albeit with simulations. Here's a partial breakdown of the distribution of matter in the Universe, summarized from the above paper: Dark matter makes up about 26% of the critical energy density budget of the Universe, while "baryonic matter" (which is jargon for "visible matter" and includes all baryons as ...

2

We don't know what caused inflation, and we don't know what dark matter is. You'll appreciate that this makes a definitive answer to your question somewhat elusive. However it's generally believed that the matter we see around us today was created at the end of inflation by the decay of the inflaton field. This included both baryonic and dark matter, though ...

2

No-one knows what dark matter and dark energy are, so any comments on your question are necessarily speculative. Having said this, dark matter is generally considered to be just matter and the adjective dark is not meant to signify anything mysterious but merely that it doesn't interact with electromagnetic radiation or charge. The most popular suggestion ...

2

There are 4 general contributors to the mass density of our co-moving patch of what may be a larger universe: (1) Visible baryonic matter (including clouds of baryonic matter which may be visible only as shadows blocking galaxies). NASA estimates 4.6% of all matter is baryonic (http://map.gsfc.nasa.gov/universe/uni_matter.html). (2) Dark matter (not ...

3

The integrated local interstellar cosmic ray energy density is claimed by Webber (1998) to be about 1.8 ev/cm$^3$. The energy density of dark matter (mostly rest mass energy) in the solar system is thought to be around $0.43\pm0.1$ GeV/cm$^{3}$ (Salucci et al. 2010). Both numbers likely have quite big error bars, but as you can see, there is an 8-9 orders ...

4

Disk galaxies don't rotate like solid bodies (think frisbee), but rather rotate differentially (think whirlpool). The rotation speed as a function of radius is called a rotation curve, and is often interpreted as a measurement of the mass profile of a galaxy, as: $$v_c(R) = \sqrt{\frac{GM(<R)}{R}}$$ where $M(<R)$ is the total mass enclosed$^1$ within ...

2

Part of the LHC program is to find new particles that can be what dark matter is: very weakly interacting particles. This will show that an extension to the standard model would be correct. This will follow the pattern: "for every particle there exists an antiparticle", or a particle can be the antiparticle for itself, so yes, in this case there will be ...

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