Starship Asterisk*

Image Credit: ESO/Yuri Beletsky (LCO)

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Humans have gazed up at the skies for a very long time, fascinated by the flowing shape of the Milky Way, the bright lights of the stars and planets, and the dark patches that obscure regions of sky. Different cultures had various names for these features; this Picture of the Week shows one object that has taken on several different identities over time, alongside an antenna of the Atacama Large Millimeter/submillimeter Array (ALMA).

At the very top of the frame, within the band of the Milky Way, lies a pair of bright stars. These form part of Crux (The Southern Cross), one of the most recognisable constellations in the southern sky. Just below Crux, a dark, irregular shape is silhouetted against the central band of our galaxy. This is a prominent dark nebula lying just 600 light-years away: a giant cloud of molecules so dense it blocks out the light of anything behind it.

The name of this dark blob, however, depends on your culture. It is most popularly known as the Coalsack Nebula, but others identify it as a giant celestial bird. It is of great importance in Aboriginal Australian astronomy, where it is said to be the head of an emu stretching across the sky — a “constellation” made up not of stars, but of dust. Inca astronomers instead named the patch Yutu, referring to a shy, partridge-like bird species found in South America (the Tinamou).

Nebulae such as the Coalsack cannot be penetrated by visible light, but the stars and galaxies obscured by them often shine through in millimetre and submillimetre wavelengths. This region of the electromagnetic spectrum is explored by ALMA, an array with 66 antennas located in northern Chile.

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

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This week’s Hubble/ESA Picture of the Week features NGC 7678 — a galaxy located approximately 164 million light-years away in the constellation of Pegasus (The Winged Horse). With a diameter of around 115 000 light-years, this bright spiral galaxy is a similar size to our own galaxy (the Milky Way), and was discovered in 1784 by the German-British astronomer William Herschel.

The Atlas of Peculiar Galaxies is a catalogue which was produced in 1966 by the American astronomer Halton Arp. NGC 7678 is among the 338 galaxies presented in this catalogue, which organises peculiar galaxies according to their unusual features. Catalogued here as Arp 28, this galaxy is listed together with six others in the group “spiral galaxies with one heavy arm”.

Image Credit: ESO

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This gently glowing area of sky is actually a hot bubble of hydrogen gas — named Sh 2-305 — that has been bombarded by intense radiation from nearby stars. Such gas clouds are known as emission nebulae, or HII regions (pronounced “H-two”). The radiation in question is in the ultraviolet part of the spectrum and is thought to emanate from at least two O-type stars, and likely several others. This stellar class is the brightest and hottest that we know of — such stars can be up to 90 times as massive as the Sun, and an incredible one million times as bright.

Together with five neighbouring bubbles, Sh 2-305 belongs to a giant complex of dense clouds of dust and gas and, on a larger scale, an enormous ring called the GS234-02 star-forming supershell (located in the Perseus arm of the Milky Way, in the constellation of Puppis).

This image was obtained under the ESO Cosmic Gems programme, an outreach initiative to produce images of interesting, intriguing or visually attractive objects using ESO telescopes, for the purposes of education and public outreach. The programme makes use of telescope time that cannot be used for science observations. All data collected may also be suitable for scientific purposes, and are made available to astronomers through ESO’s science archive.

Image Credit: ESA/Hubble & NASA, Z. Levay

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This Picture of the Week revisits the Veil Nebula, a popular subject for Hubble images! This object was featured in a previous Hubble photo release, but now new processing techniques have been applied, bringing out fine details of the nebula’s delicate threads and filaments of ionised gas.

To create this colourful image, observations taken by Hubble's Wide Field Camera 3 instrument through 5 different filters were used. The new post-processing methods have further enhanced details of emissions from doubly ionised oxygen (seen here in blues), ionised hydrogen and ionised nitrogen (seen here in reds).

The Veil Nebula lies around 2100 light-years from Earth in the constellation of Cygnus (The Swan), making it a relatively close neighbour in astronomical terms. Only a small portion of the nebula was captured in this image.

The Veil Nebula is the visible portion of the nearby Cygnus Loop, a supernova remnant formed roughly 10 000 years ago by the death of a massive star. The Veil Nebula’s progenitor star — which was 20 times the mass of the Sun — lived fast and died young, ending its life in a cataclysmic release of energy. Despite this stellar violence, the shockwaves and debris from the supernova sculpted the Veil Nebula’s delicate tracery of ionised gas — creating a scene of surprising astronomical beauty.