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A mysterious ring of microwaves
06-06-2016 05:01 PM CEST

europeanspaceagency posted a photo:

A mysterious ring of microwaves

Fifty years ago, astronomers discovered a mystery. They called it Loop I. Today, we still have not fully resolved the mystery of how this giant celestial structure formed but we do now have the best image of it, thanks to ESA’s Planck satellite .

Loop I is a nearly circular formation that covers one third of the sky. In reality, it is probably a spherical ‘bubble’ that stretches to more than 100º across, making it wider than 200 full Moons. Its absolute size, however, is extremely uncertain because astronomers do not know how close it is to us: estimates to the centre of the bubble vary from 400 light-years to 25 000 light-years.

What they do know is that the structure shows up in many different wavelengths, from radio waves to gamma rays. Planck sees Loop I in microwaves. This image’s colours reflect the polarisation – the direction in which the microwaves are oscillating.

Our eyes are not sensitive to this information in the visible light, where we perceive only the intensity and colour. Planck, however, can detect all three of these characteristics in the microwaves it targets.

The microwaves detected by Planck are emitted by electrons that are being accelerated by the Galaxy’s magnetic field.

Loop I is most visible in the sky’s northern hemisphere. Astronomers refer to this portion as the north polar spur. It can be seen in this image as the yellow arc. This fades to purple and can be traced into the southern hemisphere, completing the circle. The blue band spanning the image horizontally is the Galactic Plane.

The most popular interpretation places Loop I close to us. If this is correct, it could be related to the ‘Scorpius–Centaurus OB Association’, a region of high-mass star formation that has been active for over 10 million years. Loop I could well be a supernova remnant, a giant bubble hollowed out by the explosion of stars in the OB association.

The stars responsible for Loop I have long since dispersed, so what we see is the ‘smoke’ rather than the ‘fire’ of the explosions.

High-mass stars burn their nuclear fuel so quickly that they live only a few million years before exploding. As these titanic supernovas bloom, their blast waves carve bubbles in the surrounding gas. This compresses the Galaxy’s magnetic field into the bubble ‘walls’, making it stronger and more efficient at accelerating the electrons to produce the observed radiation.

Loop I could well be the combined super-bubble from a number of such cataclysms. As the electrons lose energy and diffuse into the wider Galaxy, so Loop I will eventually fade and disappear. This is likely to take a few million years.

If the loop is more distant, then it could conceivably be the result of an outburst from around the black hole at the centre of the Galaxy.

(A version of the image showing the position of Loop I is available here . The colour represents the direction of polarisation, while the brightness of the colour measures the intensity of polarisation.)

Credit: ESA and the Planck Collaboration

A mysterious hermit
06-06-2016 01:24 PM CEST

europeanspaceagency posted a photo:

A mysterious hermit

The drizzle of stars scattered across this image forms a galaxy known as UGC 4879. UGC 4879 is an irregular dwarf galaxy – as the name suggests, galaxies of this type are a little smaller and messier than their cosmic cousins, lacking the majestic swirl of a spiral or the coherence of an elliptical.

This galaxy is also very isolated. There are about 2.3 million light years between UGC 4879 and its closest neighbour, Leo A, which is about the same distance as that between the Andromeda Galaxy and the Milky Way.

This galaxy’s isolation means that it has not interacted with any surrounding galaxies, making it an ideal laboratory for studying star formation uncomplicated by interactions with other galaxies. Studies of UGC 4879 have revealed a significant amount of star formation in the first 4-billion-years after the Big Bang, followed by a strange nine-billion-year lull in star formation, ended 1-billion-years ago by a more recent reignition. The reason for this behaviour, however, remains mysterious, and the solitary galaxy continues to provide ample study material for astronomers looking to understand the complex mysteries of starbirth throughout the Universe.

Credit: NASA/ESA

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