Starship Asterisk*

A huge, dense field completely filled with tiny stars. A few of the star images are a bit
larger than the rest, with visible diffraction spikes; two foreground stars are large and
bright on the right side. Many small galaxies within various shapes and sizes can be
seen hiding behind the stars. In the centre some faint, wispy, dark red gas appears.
(Image Credit: ESA/Webb, NASA & CSA, M. Meixner)

This image shows the irregular galaxy NGC 6822, as observed by the Near-InfraRed Camera (NIRCam) mounted on the NASA/ESA/CSA James Webb Space Telescope. NIRCam probes the near-infrared, which in this case makes it suitable for observing the densely packed star field.

Webb’s near-infrared NIRCam image shows the galaxy’s countless stars in incredible detail. Here, the dust and gas that pervade the galaxy are reduced to translucent red wisps, laying the stars bare for astronomical study. The power of Webb’s ice-cold infrared instruments and the incredible resolution of its primary mirror is necessary to examine stars hidden in dusty environments, and the results as shown here are spectacular.

The brightest stars appear in pale blue and cyan colours in this image, colours which are assigned to the shortest wavelengths of light that NIRCam can detect: red and nearest infrared. The amount of light emitted by any star decreases at longer and longer wavelengths, towards the mid-infrared, so the stars that are more faint to NIRCam also appear more warmly coloured here. A bright blue orb to the lower left of the gas is particularly prominent: this is a globular cluster, packed with stars.

A composite image of NGC 6822 featuring data from both NIRCam and Webb’s Mid-InfraRed Instrument (MIRI) was published for the ESA/Webb Picture of the Month series in July 2023.

Image Credit: Gemini Observatory/NOIRLab/NSF/AURA/J. Chu

---

This image, taken at sunrise, shows the blue shadow of Maunakea in Hawai‘i, home to the Gemini North telescope, tapering into an eerily symmetrical triangle. While Maunakea is vaguely triangular in shape, it is far from a perfect Euclidean pyramid, so why should the shadow appear so symmetrical?

An identical triangular shadow phenomenon can be seen from the tops of many mountains or volcanoes at sunset or sunrise. The key to understanding this effect is that the viewer is staring down a lengthy ‘corridor’ of a sunrise (or sunset) shadow that reaches to the horizon. Even if the massive volcano were a perfect cube, a column, or really any other shape, the resulting shadow would appear to taper off at its summit as this part of the shadow extends far into the distance. You can see a similar effect with parallel railroad lines, hallways, or any other long and straight corridor.

Gemini North is part of the International Gemini Observatory, which is operated by NSF’s NOIRLab.

A galaxy in the centre of a wide view of space. It is surrounded by a variety of differently-shaped small galaxies. A wide and very flat spiral galaxy, and one star with four prominent diffraction spikes, are noticeable. The galaxy itself is a broad horizontal streak of tiny stars, extending left and right from a dense and bright core of stars in the centre. (Image Credit: ESA/Hubble & NASA, R. Tully)

---

This Hubble Picture of the Week includes the pithily-named galaxy SDSS J103512.07+461412.2, visible in the centre of this image as a dispersed sweep of dust and stars with a denser, brighter core. SDSS J103512.07+461412.2 is located 23 million light-years from Earth in the constellation Ursa Major. The seemingly rambling name is because this galaxy was observed as part of the Sloan Digital Sky Survey (SDSS), a massive survey that began in 2000 with the aim of observing and cataloguing vast numbers of astronomical objects. So far, it has recorded several hundred million astronomical objects.

In the early days of astronomy catalogues, astronomers painstakingly recorded individual objects one by one. As an example, the Messier catalogue includes only 110 objects, identified by the astronomer Charles Messier because they were all getting in the way of his comet-hunting efforts. As the Messier catalogue is so limited, it is sufficient to simply refer to those objects as M1 to M110. In contrast, when a survey as massive in scope as the SDSS is involved, and when huge volumes of data need to be processed in an automated manner, the names assigned to objects need to be both longer, and more informative. ...

Image Credit: ESO/A. Ghizzi Panizza (www.albertoghizzipanizza.com)

---

It’s hard not to get sucked into this Picture of the Week, taken using a long exposure at ESO’s Paranal Observatory in the Chilean Atacama Desert. Above the mountaintop observatory, a spectacular dance is playing out: imaged over several hours, stars appear to make their way in long arcs, called star trails, across the night sky.

Paranal is home to one of the world’s most advanced optical telescopes: ESO’s Very Large Telescope, or VLT. This flagship facility actually consists of four Unit Telescopes and four smaller movable Auxiliary Telescopes, like the one in the foreground on the right.

But what are those mysterious beams of orange light erupting from one of the Unit Telescopes? Well, they’re for making stars, kind of. The Four Laser Guide Star Facility propagates laser beams^_[1] into the sky, making sodium atoms in the upper atmosphere glow like artificial stars. Each laser delivers 22 watts of power — about 4000 times the maximum allowed for a laser pointer — in a beam that’s about 30 centimetres in diameter. This remarkable display doesn’t just look pretty: the twinkling of these artificial stars is measured in real time and used by the adaptive optics system to correct for the blurring caused by the Earth’s atmosphere so that the telescope can create sharp images.

Credit: DESI Legacy Imaging Surveys/LBNL/DOE & KPNO/CTIO/NOIRLab/NSF/AURA Processing: T.A. Rector (Univ of Alaska Anchorage/NOIRLab), J. Miller (Gemini Obs/NOIRLab), M. Rodriguez (Gemini Obs/NOIRLab) & M. Zamani (NOIRLab

---

Far, far away in the constellation Phoenix, two interacting galaxies meet in an epic battle spanning a hundred thousand light-years, captured here with the Víctor M. Blanco 4-meter Telescope at Cerro Tololo Inter-American Observatory (CTIO), a Program of NSF’s NOIRLab. Collectively known as NGC 454, the upper galaxy is a red elliptical galaxy called NGC 454 E, while below it is NGC 454 W, a blue, gas-rich irregular galaxy. Despite being in the early stages of their interaction, both galaxies already show severe distortion. Remnants of both galaxies have been stretched far beyond their main bodies, from the disarray of both galaxies’ stellar populations at the top right of this image to the globular clusters forming at NGC 454 W’s bottom-left side. Dust lanes from the dynamic interaction cross NGC 454 E, and NGC 454 W barely looks like the disk galaxy it was thought to be. The early merger is further evidenced by the veil of a low surface brightness halo surrounding the galaxies as well as the myriad of young stars that populate the system. Now gravitationally bound together, the fight of NGC 454 will end when the two galaxies eventually combine into one.

This interacting pair was captured by the Dark Energy Camera (DECam) made by the US Department of Energy as part of the Dark Energy Spectroscopic Instrument (DESI) Legacy Imaging Surveys.

bystander wrote: ↑Tue Sep 19, 2023 3:18 pm A Peculiar Proceeding
ESA Hubble Picture of the Week | 2023 Sep 18

A pair of merging galaxies. The galaxy on the left has a large, single spiral arm curving out from the core and around to below it, with very visible glowing dust and gas. The right galaxy has a bright core but only a bit of very faint material. A broad curtain of gas connects the two galaxies’ cores and hangs beneath them. A few small stars and galaxies are scattered around the black background. (Credit: ESA/Hubble & NASA, J. Dalcanton)

---

This Hubble Picture of the Week — taken using NASA/ESA Hubble Space Telescope’s Advanced Camera for Surveys (ACS) — shows Arp 107, a celestial object that comprises a pair of galaxies in the midst of a collision. The larger galaxy (in the left of this image) is an extremely energetic galaxy type known as a Seyfert galaxy, which house active galactic nuclei at their cores. Seyfert galaxies are notable because despite the immense brightness of the active core, radiation from the entire galaxy can be observed. This is evident in this image, where the spiraling whorls of the whole galaxy are readily visible. The smaller companion is connected to the larger by a tenuous-seeming ‘bridge’, composed of dust and gas. The colliding galactic duo lie about 465 million light-years from Earth.

Arp 107 is part of a catalogue of 338 galaxies known as the Atlas of Peculiar Galaxies, which was compiled in 1966 by Halton Arp. It was observed by Hubble as part of an observing programme that specifically sought to fill in an observational ‘gap’, by taking limited observations of members of the Arp catalogue. Part of the intention of the observing programme was to provide the public with images of these spectacular and not-easily-defined galaxies, and as such, it has provided a rich source for Hubble Pictures of the Week. In fact, several recent releases, including this one and this one, have made use of observations from the same observing programme.

A pair of merging galaxies. The galaxy on the left has a large, single spiral arm curving out from the core and around to below it, with very visible glowing dust and gas. The right galaxy has a bright core but only a bit of very faint material. A broad curtain of gas connects the two galaxies’ cores and hangs beneath them. A few small stars and galaxies are scattered around the black background. (Credit: ESA/Hubble & NASA, J. Dalcanton)

---

This Hubble Picture of the Week — taken using NASA/ESA Hubble Space Telescope’s Advanced Camera for Surveys (ACS) — shows Arp 107, a celestial object that comprises a pair of galaxies in the midst of a collision. The larger galaxy (in the left of this image) is an extremely energetic galaxy type known as a Seyfert galaxy, which house active galactic nuclei at their cores. Seyfert galaxies are notable because despite the immense brightness of the active core, radiation from the entire galaxy can be observed. This is evident in this image, where the spiraling whorls of the whole galaxy are readily visible. The smaller companion is connected to the larger by a tenuous-seeming ‘bridge’, composed of dust and gas. The colliding galactic duo lie about 465 million light-years from Earth.

Arp 107 is part of a catalogue of 338 galaxies known as the Atlas of Peculiar Galaxies, which was compiled in 1966 by Halton Arp. It was observed by Hubble as part of an observing programme that specifically sought to fill in an observational ‘gap’, by taking limited observations of members of the Arp catalogue. Part of the intention of the observing programme was to provide the public with images of these spectacular and not-easily-defined galaxies, and as such, it has provided a rich source for Hubble Pictures of the Week. In fact, several recent releases, including this one and this one, have made use of observations from the same observing programme.

ESO/A. Chomez et al.

---

This Picture of the Week shows the unique stellar system HIP 81208, as captured by ESO’s Very Large Telescope (VLT) in Chile. Astronomers thought HIP 81208 was a system consisting of a massive central star (A, the central bright spot), a brown dwarf (B) circling around it, and a low-mass star (C) orbiting further away. However, a new study has revealed a never-before-seen hidden gem: an object (Cb), approximately 15 times more massive than Jupiter, orbiting around the smaller of the two stars (C).

The discovery of Cb means that HIP 81208 is a uniquely intriguing system with two stars and two smaller bodies orbiting each one –– in other words, a hierarchical quadruple system. The mass of the newly found Cb object places it right at the border between planets and brown dwarfs –– failed stars that are not massive and hot enough to fuse hydrogen into helium.

The hidden giant Cb was spotted when a team of astronomers, led by A. Chomez of the Paris Observatory, re-analysed archival data from the Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) instrument installed on the VLT. While many other instruments use indirect methods to hunt for far-flung worlds, SPHERE uses a technique known as direct imaging: what we see here is an actual image of the system. Indeed, this is the first hierarchical quadruple system to be found using direct imaging, which will prove invaluable to understanding how complex systems like this one form and evolve.

• Astronomy & Astrophysics 676:L10 (Aug 2023) DOI: 10.1051/0004-6361/202347044
• arXiv > astro-ph > arXiv:2307.01195 > 03 Jul 2023