Astronomy and Cosmology News

Have they not considered Del's whiskers? For shame.

'brightness is being reduced by clouds of whiskers.'

Dark matter maybe?

Regards JD.

'brightness is being reduced by clouds of whiskers.'

Sounds like my facial complexion after not shaving for two days.

Great. I can see the newspaper headlines now:

"OUTER SPACE FULL OF NEEDLES AND WHISKERS! SO MANY THAT STARS ARE OBSCURED! EARTH FACING PIERCING & ENTANGLEMENT DOOM???"

Perhaps now we've finally found that elusive dark matter!

Nice reply! I also found a recent article discussing how one can discern whether a massive body is a neutron star (having a physical surface), and one that has no physical surface (black hole event horizon) by gas and other matter falling into/onto the surface of a neutron star, vs. into a black hole. Thanks, Jorrie.

Hi Cardio,

Can you provide a link to the article?

-John

You beat me to it. I give you a vote.

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The American astronomer Vera Rubin studied the rotation of spiral galaxies by measuring the degree of red- (and blue-) shift as a function of distance from a galactic center. The relative rotation rates of different parts of a galaxy indicate the distribution of mass within the galaxy -- assuming that the majority of the mass is contained within the radiative confines of the galaxy (but not necessarily being that which is visible).

It should be noted that the dynamic mass should indicate a galaxy's true mass, as its presence is inferred from its gravitational influence on the galaxy as a whole. It is not so simple for estimates of the luminous mass.

To measure the latter, the assumption is made that all the mass of the galaxy (or the galaxy cluster) is made of luminous stars. These stars radiate, and if one knows their distribution (mass, number, age, etc), the visible light is then a potentially viable way to estimate the mass. This is no easy task.

By analyzing a spiral galaxy's spectrum - specifically the physical distribution and degree to which aggregate stellar spectra undergo red-shift - it is possible to deduce the rotational rate of various parts of a galaxy. A plot of red-shift versus distance from the galactic center should follow a curve, reaching a maximum a few kilo-parsecs from the center. This is followed by a Keplerian decrease with the stars at the outermost rim having the lowest orbital velocities. The curve is a direct representation of the total distribution of matter in the galaxy. Until recently, this was the assumption.

However, Rubin observed that the stars located at the periphery of the Andromeda Galaxy (and other spirals) appear to orbit too fast. But not only are they too fast, their velocities remain nearly independent of the distance from the galactic center! The rotation curve of some spiral galaxies is nearly flat. In these galaxies orbital velocities do not decrease as one moves away from the barycenter. Many other, similar observations were carried out in the 1980s, reinforcing those made by Rubin. These observations raised deep questions about the distribution of mass within a galaxy because the distribution of orbital velocities is (or should be) a measure of a galaxy's dynamic mass. No assumption about the age or the stars' mass distribution is necessary as is the case with estimates of luminous mass.

One explanation might be to assume the existence of a huge non-visible matter halo surrounding the galaxies; a halo which would represent up to 90% of the galaxy's total mass. In this scenario the galaxy's visible stars are located relatively near the galactic center, with the bulk of the (invisible) mass extending well beyond. In such a scenario the distribution of orbital velocities, as observed, would be expected to remain more or less constant as the bulk of the visible matter is actually quite near the galaxy's barycenter. Hence the birth of the "Dark Matter" theory.

The existence of dark matter has the advantage of simplicity, but at the cost of introducing a new and inexplicable form of matter which cannot be directly observed. Its properties remain almost completely unknown and largely speculative. It has the properties of mass but does not interact with EM radiation at all. The observation of spiral galaxies at other wavelengths is an ongoing effort to identify the existence and distribution of other, possibly "conventional" matter that might just as easily explain these anomalies.

But even if the additional mass is represented, say, by swarms of nearly-invisible brown dwarfs, protostars and other objects (excluding interstellar gas, whose absorption spectra can be directly measured), this itself introduces yet another problem that demands explanation. Why would the outer reaches of many galaxies favor such populations? So many objects, in fact, that they constitute nearly 90% of a given galaxy's mass? This strikes me as pretty far-fetched.

Back to the topic on hand: I suspect - and it is only a hunch - that Type 1a "standard candles" are incorrectly modelled and so photometric measurements of these supernovae suggest SN distances that are not on par with reality. I am more inclined to suspect a flawed model than introduce a new and previously unknown form of matter/energy.

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