Starship Asterisk*

Susanna Kohler wrote:

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Look closely at this radio image (click for the full view!) and you might see why scientists have named this phenomenon a radio “harp”. These remarkable near-parallel lines of emission — which are seemingly sorted by length, so that they resemble a harp with radio-emitting strings — span several light-years and can be spotted in the center regions of our galaxy. In a new study led by Timon Thomas (Leibniz-Institute for Astrophysics Potsdam), a team of scientists argues that this cosmic music is caused by a massive star or a pulsar (a magnetized neutron star) plunging through an ordered magnetic field in the galactic center. As the star crosses (moving upward, in the image above) bundles of field lines, it discharges high-energy cosmic rays that travel in either direction along the bundles, emitting radio waves. Thomas and collaborators use observations of these radio harps to study how cosmic rays propagate along magnetic fields.

• Astrophysical Journal Letters 890(2):L18 (2020 Feb 20) DOI: 10.3847/2041-8213/ab7237
• arXiv.org > astro-ph > arXiv:1912.08491 > 18 Dec 2019

Credit: ESA/Hubble & NASA, A. Riess et al.

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This image of an archetypal spiral galaxy was captured by the NASA/ESA Hubble Space Telescope.

The subject of this image is known as NGC 691, and it can be found some 120 million light-years from Earth. This galaxy was one of thousands of objects discovered by astronomer William Herschel during his prolific decades-long career spent hunting for, characterising, and cataloguing a wide array of the galaxies and nebulae visible throughout the night sky — almost 200 years before Hubble was even launched.

The intricate detail visible in this Picture of the Week would likely be extraordinary to Herschel. Hubble was able to capture an impressive level of structure within NGC 691’s layers of stars and spiralling arms — all courtesy of the telescope’s high-resolution Wide Field Camera 3.

Credit: ESO/M. Marsset et al/MISTRAL algorithm (ONERA/CNRS)

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A new study led by Pierre Vernazza (Laboratoire d’Astrophysique de Marseille, France) conducted using ESO facilities has observed the asteroid Pallas for the first time at extremely high angular resolution. The asteroid could be successfully observed in such great detail thanks to the Adaptive-Optics (AO)-fed SPHERE imager on the Very Large Telescope (VLT).

German astronomer Heinrich Wilhelm Matthäus Olbers first discovered Pallas on 28 March 1802. Named for the Greek goddess Pallas Athene, the asteroid — along with many other asteroids discovered in the 19th century — was initially classified as a planet. As time passed and technology improved, Pallas was later reclassified as an asteroid. Today it is famous for being the third-largest asteroid in the Solar System, with an average diameter of 512 km.

Although Pallas is the largest known asteroid in the Solar System after Ceres and Vesta, it is the only one of these large asteroids that has not been visited by a spacecraft. This is due to its orbit, which has an unusually high inclination to the plane of the Earth’s orbit — which means it is particularly challenging to land a spacecraft on.

These new images show that the surface of Pallas displays very interesting topographic features suggesting a violent collisional history. Numerous large craters are found in both hemispheres of Pallas, forming a surface resembling a golf ball. The two distinct large impact basins on its surface could also be related to a family-forming impact — a collision which caused an original object to fracture into several separate bodies. The bright spot which appears in the southern hemisphere of Pallas (right image) is also very reminiscent of the salt deposits on Ceres. ...

• Nature Astronomy (online 10 Feb 2020) DOI: 10.1038/s41550-019-1007-5

Image Credit: ESA/Hubble & NASA

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TheNASA/ESA Hubble Space Telescope is no stranger to spiral galaxies. The telescope has brought us some of the most beautiful images ever taken of our spiral neighbours — and this Picture of the Week, which features a galaxy known as NGC 4689, is no exception.

However, seen almost face on, NGC 4689 appears less like a majestic spiral and more like a smudged fingerprint on the sky. No matter how good the image quality, there is little contrast between the spiralling arms of stars, gas, and dust, and the less dense areas in between. This is because NGC 4689 is something known as an “anaemic galaxy”, a galaxy that contains only quite small quantities of the raw materials needed to produce stars. This means that star formation is quelled in NGC 4689, and the pinwheeling, bustling arms are less bright than those belonging to other Hubble muses.

Despite this subtlety when compared to its brash, spotlight-stealing relatives, NGC 4689 retains an otherworldly charm, its delicately glowing material standing out subtly from the surrounding darkness of space.

Image Credit: Yuri Beletsky (LCO)/ESO

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Located deep in the Chilean Atacama Desert, far from the light pollution associated with human activity, is ESO’s Paranal Observatory: a world-leading research site that enjoys some of the darkest skies on Earth. Paradoxically, it is this extreme darkness that allows the sky to light up in technicolour in this image.

The striking radiant light visible in the sky here is a phenomenon called airglow, which lends a magical appearance to the already breathtaking night sky. As the name suggests, airglow is a faint glow in the air created as atoms and molecules in the atmosphere combine and emit radiation. It is only visible in regions where the sky is dark enough that artificial lights do not overwhelm it. This phenomenon was the subject of ESOcast 78.

This perspective was captured from the site of VISTA, the Visible and Infrared Survey Telescope for Astronomy. The trail of faint yellow lights along the ground leads towards Cerro Paranal, the mountain in the centre of the image, where ESO’s Very Large Telescope (VLT) is just about discernible at the top. The bright band of stars that forms our home galaxy, the Milky Way, appears to arc over the mountain, infused with the colours of the atmosphere.

Susanna Kohler wrote:

You’re looking at a 55’ x 55’ Deep Sky Survey image of the Rosette Nebula (click for the full view), a large, spherical, star-forming region located about 5,200 light-years away. In a recent study led by Koraljka Mužić (University of Lisbon, Portugal), a team of scientists has used the Gemini South telescope in Chile to obtain near-infrared images from deep in the heart of the nebula. Zooming in on a region of less than 25 square light-years (the central cyan-outlined region in the photos above and to the right), Mužić and collaborators have imaged the center of NGC 2244, a young, high-density stellar cluster forming massive stars. In their study, the authors seek to understand how low-mass stars and brown dwarfs form and evolve among their high-mass siblings in these extreme environments.

• Astrophysical Journal 881(1):79 (2019 Aug 10) DOI: 10.3847/1538-4357/ab2da4
• arXiv.org > astro-ph > arXiv:1907.00617 > 01 Jul 2019 (v1), 30 Jul 2019 (v2)