Starship Asterisk*

[img3="Credit: ESA/Hubble & NASA"]https://cdn.spacetelescope.org/archives ... w1651a.jpg[/img3][hr][/hr]

On a clear evening in April of 1789, the renowned astronomer William Herschel continued his unrelenting survey of the night sky, hunting for new cosmic objects — and found cause to celebrate! Lengthening his impressive list of cosmic discoveries yet again, the astronomer spotted this bright spiral galaxy, named NGC 4707, lurking in the constellation of Canes Venatici (The Hunting Dog). NGC 4707 lies roughly 22 million light-years from Earth.

Over two centuries later, the NASA/ESA Hubble Space Telescope is able to view the same galaxy in far greater detail than Herschel could, allowing us to appreciate the intricacies and characteristics of NGC 4707 as never before. This striking image comprises observations from Hubble’s Advanced Camera for Surveys (ACS), one of a handful of high-resolution instruments currently aboard the space telescope.

Herschel himself reportedly described NGC 4707 as a “small, stellar” galaxy; while it is classified as a spiral (type Sm), its overall shape, centre, and spiral arms are very loose and undefined, and its central bulge is either very small or non-existent. It instead appears as a rough sprinkling of stars and bright flashes of blue on a dark canvas, as if a pointillist painter had dotted the cosmos with small pinpricks of bright paint.

The blue smudges seen across the frame highlight regions of recent or ongoing star formation, with newborn stars glowing in bright, intense shades of cyan and turquoise.

[img3="Credit: ESA/Hubble & NASA
Acknowledgement: Judy Schmidt (geckzilla)"]https://cdn.spacetelescope.org/archives ... w1652a.jpg[/img3][hr][/hr]

This galaxy has a far more exciting and futuristic classification than most — it is a megamaser. Megamasers are intensely bright, around 100 million times brighter than the masers found in galaxies like the Milky Way. The entire galaxy essentially acts as an astronomical laser that beams out microwave emission rather than visible light (hence the ‘m’ replacing the ‘l’).

This megamaser is named IRAS 16399-0937, and is located over 370 million light-years from Earth. This NASA/ESA Hubble Space Telescope image belies the galaxy’s energetic nature, instead painting it as a beautiful and serene cosmic rosebud. The image comprises observations captured across various wavelengths by two of Hubble’s instruments: the Advanced Camera for Surveys (ACS), and the Near Infrared Camera and Multi-Object Spectrometer (NICMOS).

NICMOS’s superb sensitivity, resolution, and field of view gave astronomers the unique opportunity to observe the structure of IRAS 16399-0937 in detail. They found that IRAS 16399-0937 hosts a double nucleus — the galaxy’s core is thought to be formed of two separate cores in the process of merging. The two components, named IRAS 16399N and IRAS 16399S for the northern and southern parts respectively, sit over 11 000 light-years apart. However, they are both buried deep within the same swirl of cosmic gas and dust and are interacting, giving the galaxy its peculiar structure.

The nuclei are very different. IRAS 16399S appears to be a starburst region, where new stars are forming at an incredible rate. IRAS 16399N, however, is something known as a LINER nucleus (Low Ionization Nuclear Emission Region), which is a region whose emission mostly stems from weakly-ionised or neutral atoms of particular gases. The northern nucleus also hosts a black hole with some 100 million times the mass of the Sun!

[img3="Credit: ALMA (ESO/NAOJ/NRAO); A. Isella; B. Saxton (NRAO/AUI/NSF)"]https://cdn.eso.org/images/screen/potw1652a.jpg[/img3][hr][/hr]

Our Solar System formed out of a huge, primordial cloud of gas and dust. The vast majority of that cloud formed the Sun, while the leftover disc of rotating material around it eventually coalesced into the orbiting planets we know — and live on — today.

Astronomers can observe similar processes happening around other stars in the cosmos. This splendid Picture of the Week shows a disc of rotating, leftover material surrounding the young star HD 163296. Using the observing power of the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, astronomers have been able to discern specific features in the disc, including concentric rings of material surrounding the central star. They were even able to use ALMA to obtain high-resolution measurements of the gas and dust constituents of the disc. With these data they could infer key details of the formation history of this young stellar system.

The three gaps between the rings are likely due to a depletion of dust and in the middle and outer gaps astronomers also found a lower level of gas. The depletion of both dust and gas suggests the presence of newly formed planets, each around the mass of Saturn, carving out these gaps on their brand new orbits.