Samantha Rae

Universe’s largest structure caught in the act of forming

“The Universe forms a vast cosmic web where filaments interconnect, with matter flowing along them into a nexus. At the centers of these intersections, the most massive galaxy clusters form. Over time, more clusters fall in, creating the largest structures of all. The Hubble Space Telescope recently observed one of them, MACS J0717, revealing four separate clusters in the collision process.”

When it comes to the largest bound cosmic structures, it doesn’t get any bigger than galaxy clusters. Unless, that it, you consider when multiple galaxy clusters merge together. Located at the intersections of cosmic dark matter filaments, smaller clusters flow into the larger clusters located at such a nexus. When we get very lucky, colliding clusters can be seen. Recently, scientists have located a cosmic smash-up between four such clusters in the large structure MACS J0717.5+3745. One of the clusters within is moving so quickly – 3,000 km/s – that the light within it gets shifted thanks to the speed of the electrons within it. X-ray, radio and optical/IR data combine to reveal a treasure trove of information, including active galaxies, a separation between normal and dark matter and even information about the inflows along the cosmic filaments.

Awesome 3D-Printed Miniature Solar Systems That Fit On Your Desk Table

London-based boutique Little Planet Factory makes adorable miniature 3d-printed plants and moons, which you can use as decor for your desk or even to play with. They have collections of moons, solitary planets to even entire solar systems.

Find the solar system in their Etsy shop.

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Recent Claims Invalid: Emergent Gravity Might Deliver A Universe Without Dark Matter

“The real challenge for emergent gravity, I think, is not galactic rotation curves. That is the one domain where we already know that modified gravity – at last some variants thereof – work well. The real challenge is to also explain structure formation in the early universe, or any gravitational phenomena on larger (tens of millions of light years or more) scales.”

When it comes to galaxies, clusters of galaxies or the largest-scales on the Universe, dark matter is absolutely required. There’s no way to explain colliding galaxy clusters, correlations between different galaxies, the filamentary structure of the Universe or the fluctuations in the Cosmic Microwave Background without it. But it isn’t just dark matter that hopes to solve these problems, and there’s a new contender in town: emergent gravity. 20 years ago, Ted Jacobson proposed, after noting similarities between gravitation and thermodynamics, that gravity might be an emergent phenomenon. Erik Verlinde has run with it, producing a formalism to get dark matter and dark energy-like effects out of a Universe where a new kind of entropy exists. Recently, it’s made predictions for galactic rotation curves, and with marginal successes, may be poised to test those larger scales.