Hubble Views The Final Frontier For Dark Matter

“This phenomenon of gravitational lensing stretches galaxies into streaks and arcs, magnifying them, and creating multiple images. It also enables us to reconstruct the mass distribution of the cluster, revealing that it’s mostly due to dark matter.”

When you look out at the distant Universe, you can see all sorts of things: stars, galaxies, clusters of galaxies, going as far back into the distant past as our telescopes can image. But where you have the greatest concentrations of mass, an extreme phenomenon emerges: that of gravitational lensing. Any foreground objects lying behind that mass will have their light stretched, magnified and distorted by the intervening matter. Recently, as part of the Hubble Frontier Fields program, the telescope followed-up on galaxy cluster Abell 370, and revealed the most spectacular gravitational lensing signal ever seen in a galaxy cluster. Most importantly, it provides some very strong evidence not only for dark matter’s existence, but for its presence distinct from any galaxies at all.

Come get the full story in images, videos, and no more than 200 words on this edition of Mostly Mute Monday!

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hannahhaifisch

8 years ago

Unusual fluid behavior observed in microgravity

Normally when a liquid is heated above its boiling point, it evaporates, turning into a vapor. But when scientists recently performed an experiment on the International Space Station (ISS), they observed that the vapor near a heat pipe condensed into a liquid even when the temperature was 160 K above the substance’s normal boiling point. The results show that microgravity significantly alters the processes of evaporation and condensation, but the scientists do not yet have a complete explanation for the phenomenon.

The research team, consisting of scientists from Rensselaer Polytechnic Institute and the NASA Glenn Research Center, have published a paper on the surprising observations in a recent issue of Physical Review Letters.

This is not the first time that unexpected behavior in heat pipes, which are devices used to cool components of a spacecraft, has been observed in microgravity. In 2015, many of the same researchers made a related, counterintuitive observation during experiments conducted on the ISS.

At that time, the researchers observed that increasing the heat input to a heat pipe did not cause the device to dry out near the heated end as it does on Earth, but instead it caused liquid accumulation there. At the time, the processes responsible for this phenomenon were not completely understood.

Quantum tunnelling

Tunneling is a quantum mechanical effect. A tunneling current occurs when electrons move through a barrier that they classically shouldn’t be able to move through. In classical terms, if you don’t have enough energy to move “over” a barrier, you won’t. However, in the quantum mechanical world, electrons have wavelike properties. These waves don’t end abruptly at a wall or barrier, but taper off quickly. If the barrier is thin enough, the probability function may extend into the next region, through the barrier! Because of the small probability of an electron being on the other side of the barrier, given enough electrons, some will indeed move through and appear on the other side. When an electron moves through the barrier in this fashion, it is called tunneling.

Quantum mechanics tells us that electrons have both wave and particle-like properties. Tunneling is an effect of the wavelike nature.

The top image shows us that when an electron (the wave) hits a barrier, the wave doesn’t abruptly end, but tapers off very quickly - exponentially. For a thick barrier, the wave doesn’t get past.

The bottom image shows the scenario if the barrier is quite thin (about a nanometer). Part of the wave does get through and therefore some electrons may appear on the other side of the barrier.

Because of the sharp decay of the probability function through the barrier, the number of electrons that will actually tunnel is very dependent upon the thickness of the barrier. The current through the barrier drops off exponentially with the barrier thickness

Source: nanoscience.com | Images: x | x | x

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hannahhaifisch

7 years ago