Starship Asterisk*

[img3="Image Credit: ESA/Hubble & NASA
Acknowledgements: Judy Schmidt"]https://cdn.spacetelescope.org/archives ... w1740a.jpg[/img3][hr][/hr]

At a distance of just 160 000 light-years, the Large Magellanic Cloud (LMC) is one of the Milky Way’s closest companions. It is also home to one of the largest and most intense regions of active star formation known to exist anywhere in our galactic neighbourhood — the Tarantula Nebula. This NASA/ESA Hubble Space Telescope image shows both the spindly, spidery filaments of gas that inspired the region’s name, and the intriguing structure of stacked “bubbles” that forms the so-called Honeycomb Nebula (to the lower left).

The Honeycomb Nebula was found serendipitously by astronomers using ESO’s New Technology Telescope to image the nearby SN1987A, the closest observed supernova to Earth for over 400 years. The nebula’s strange bubble-like shape has baffled astronomers since its discovery in the early 1990s. Various theories have been proposed to explain its unique structure, some more exotic than others.

In 2010, a group of astronomers studied the nebula and, using advanced data analysis and computer modelling, came to the conclusion that its unique appearance is likely due to the combined effect of two supernovae — a more recent explosion has pierced the expanding shell of material created by an older explosion. The nebula’s especially striking appearance is suspected to be due to a fortuitous viewing angle; the honeycomb effect of the circular shells may not be visible from another viewpoint.

[img3="Image Credit: ESO/M. Wittkowski (ESO)"]https://cdn.eso.org/images/screen/potw1740a.jpg[/img3][hr][/hr]

It may not look like much, but this blob shows a remarkable star named V766 Centauri (V766 Cen for short) and its close companion. It was first studied and classified a few years ago by researchers using ESO's Very Large Telescope Interferometer (VLTI) when it was found to be something known as a yellow hypergiant, a massive and luminous type of star that is extremely rare — and extremely big! Measuring over 1400 times the diameter of the Sun, V766 Cen was not only the largest star of its type ever discovered, but also one of the ten largest stars ever found.

However, a recent study has instead suggested that V766 Cen is likely to be in the phase of life just prior to that of a yellow hypergiant: an evolved red supergiant, which is losing mass so fast that it will eventually transition back into a warmer yellow supergiant for a short period of time. Either way, the star is a true behemoth, and of huge interest to scientists wishing to understand more about this unusual stage in the life cycle of stars.

A team of scientists has now used the VLTI again to study V766 Cen in greater detail. Using the array’s four auxiliary telescopes and an instrument mounted on the VLTI known as PIONIER (the Precision Integrated-Optics Near-infrared Imaging ExpeRiment), the team imaged V766 Centauri and its close companion in striking detail. They found this companion to be smaller and cooler than its partner — likely a cool giant or supergiant with a radius of around 650 times that of the Sun. Close companions are thought to be typical for massive stars and are important in the processes of stellar evolution.

This Picture of the Week shows V766 Cen as it was seen over three periods of time. These images actually contain both V766 Cen and its companion — in the first image the companion is passing behind V766 Cen, but in the second and third images the companion is passing in front and is visible as a bright patch.

• Astronomy & Astrophysics 606:L1 (Oct 2017) DOI: 10.1051/0004-6361/201731569
  arXiv.org > astro-ph > arXiv:1709.09430 > 27 Sep 2017

Royal Astronomical Society wrote:

Using multiwavelength kinematic and photometric data we have analysed the gaseous and stellar properties of a previously uncharacterized low-mass star-forming companion and newly discovered stellar stream seen projected against the edge-on spiral galaxy NGC 7241. The companion object was identified serendipitously as an offset velocity component in H α Fabry–Perot observations along the line of sight to NGC 7241, and is most prominent visually in UV and blue wavelengths.

[img3="Credit: ESA/Hubble & NASA"]https://cdn.spacetelescope.org/archives ... w1741a.jpg[/img3][hr][/hr]

As far as galaxies are concerned, size can be deceptive. Some of the largest galaxies in the Universe are dormant, while some dwarf galaxies, such as ESO 553-46 imaged here by the NASA/ESA Hubble Space Telescope, can produce stars at a hair-raising rate. In fact, ESO 553-46 has one of the highest rates of star formation of the 1000 or so galaxies nearest to the Milky Way. No mean feat for such a diminutive galaxy!

Clusters of young, hot stars are speckling the galaxy, burning with a fierce blue glow. The intense radiation they produce also causes surrounding gas to light up, which is bright red in this image. The small mass and distinctive colouring of galaxies of this type prompted astronomers to classify them, appropriately, as blue compact dwarfs (BCD).

Lacking the clear core and structure that many larger galaxies — such as the Milky Way — have, BCDs such as ESO 553-46 are composed of many large clusters of stars bound together by gravity. Their chemical makeup is interesting to astronomers, since they contain relatively little dust and few elements heavier than helium, which are produced in stars and distributed via supernova explosions. Such conditions are strikingly similar to those that existed in the early Universe, when the first galaxies were beginning to form.

[img3="Image Credit: ESA/Hubble & NASA"]https://cdn.spacetelescope.org/archives ... w1742a.jpg[/img3][hr][/hr]

This image, captured by the NASA/ESA Hubble Space Telescope, shows what happens when two galaxies become one. The twisted cosmic knot seen here is NGC 2623 — or Arp 243 — and is located about 250 million light-years away in the constellation of Cancer (The Crab).

NGC 2623 gained its unusual and distinctive shape as the result of a major collision and subsequent merger between two separate galaxies. This violent encounter caused clouds of gas within the two galaxies to become compressed and stirred up, in turn triggering a sharp spike of star formation. This active star formation is marked by speckled patches of bright blue; these can be seen clustered both in the centre and along the trails of dust and gas forming NGC 2623’s sweeping curves (known as tidal tails). These tails extend for roughly 50 000 light-years from end to end. Many young, hot, newborn stars form in bright stellar clusters — at least 170 such clusters are known to exist within NGC 2623.

NGC 2623 is in a late stage of merging. It is thought that the Milky Way will eventually resemble NGC 2623 when it collides with our neighbouring galaxy, the Andromeda Galaxy, in four billion years time.

In contrast to the image of NGC 2623 released in 2009 (heic0912), this new version contains data from recent narrow-band and infrared observations that make more features of the galaxy visible.

[img3="Credit: ALMA (ESO/NAOJ/NRAO)/S. Kraus (Univ of Exeter, UK)"]https://cdn.eso.org/images/screen/potw1742a.jpg[/img3][hr][/hr]

This image from the Atacama Large Millimeter/submillimeter Array (ALMA) shows V1247 Orionis, a young, hot star surrounded by a dynamic ring of gas and dust, known as a circumstellar disc. This disc can be seen here in two parts: a clearly defined central ring of matter and a more delicate crescent structure located further out.

The region between the ring and crescent, visible as a dark strip, is thought to be caused by a young planet carving its way through the disc. As the planet orbits around its parent star, its motion creates areas of high pressure on either side of its path, similar to how a ship creates bow waves as it cuts through water. These areas of high pressure could become protective barriers around sites of planet formation; dust particles are trapped within them for millions of years, allowing them the time and space to clump together and grow.

The exquisite resolution of ALMA allows astronomers to study the intricate structure of such a dust trapping vortex for the first time. The image reveals not only the crescent-shaped dust trap at the outer edge of the dark strip, but also regions of excess dust within the ring, possibly indicating a second dust trap that formed inside of the potential planet’s orbit. This confirms the predictions of earlier computer simulations.

Dust trapping is one potential solution to a major stumbling block in current theories of how planets form, which predicts that particles should drift into the central star and be destroyed before they have time to grow to planetesimal sizes (the radial drift problem).

• Astrophysical Journal Letters 848(1):L11 (2017 Oct 10) DOI: 10.3847/2041-8213/aa8edc
  arXiv.org > astro-ph > arXiv:1710.05028 > 13 Oct 2017

geckzilla wrote:That's the kind of thing I'm expecting from Tabby's star, eventually... just a very, very lucky alignment of an unusual disk. Another amazing image from ALMA.

Ann wrote:

geckzilla wrote:That's the kind of thing I'm expecting from Tabby's star, eventually... just a very, very lucky alignment of an unusual disk. Another amazing image from ALMA.

You think Tabby's star is young enough to still have a disk? Or it has a disk even if it isn't young?