Starship Asterisk*

Image Credit: Zdeněk Bardon/ESO

---

The technical and engineering achievement behind the astronomical images and discoveries produced by scientists using ESO facilities is exceptionally marvelous. Here we see the fourth Unit Telescope (Yepun) of ESO’s Very Large Telescope (VLT) in Chile, which hosts several advanced instruments, such as MUSE, HAWK-I and ERIS. 

These instruments, engineered to study the mysteries of the Universe, such as planets, stellar nurseries, and supermassive black holes, would never be able to do so without the Adaptive Optics Facility (AOF). One of the components of the AOF is the 4 Laser Guide Star Facility (4LGSF). The lasers are emitted from the four black tubes seen in this image around the telescope’s 8.2-m mirror. Each laser beam is 30 centimeters wide and carries 22 watts of power! As the lasers reach about 90 kilometers into Earth’s atmosphere, they excite sodium atoms, making them glow, just like a star.

Special sensors in each instrument measure the twinkling of these artificial stars in real time. Instructions are sent to the telescope’s deformable secondary mirror, which reshapes at millisecond speeds. This counteracts atmospheric turbulence, delivering crystal clear images.

A dense collection of stars covers the view. Towards the centre the stars become even more dense in a circular region, and also more blue. Around the edges there are some redder foreground stars, and many small stars in the background.

---

Image Credit: ESA/Hubble & NASA, E. Noyola, R. Cohen

---

The scattered stars of the globular cluster NGC 6355 are strewn across this image from the NASA/ESA Hubble Space Telescope. This globular cluster lies less than 50,000 light-years from Earth in the Ophiuchus constellation. NGC 6355 is a galactic globular cluster that resides in our Milky Way galaxy's inner regions.

Globular clusters are stable, tightly bound clusters of tens of thousands to millions of stars, and can be found in all types of galaxy. Their dense populations of stars and mutual gravitational attraction give these clusters a roughly spherical shape, with a bright concentration of stars surrounded by an increasingly sparse sprinkling of stars. The dense, bright core of NGC 6355 was picked out in crystal-clear detail by Hubble in this image, and is the crowded area of stars towards the centre of this image. 

With its vantage point above the distortions of the atmosphere, Hubble has revolutionised the study of globular clusters. It is almost impossible to distinguish the stars in globular clusters from one another with ground-based telescopes, but astronomers have been able to use Hubble to study the constituent stars of globular clusters in detail. This Hubble image of NGC 6355 contains data from both the Advanced Camera for Surveys (ACS) and Wide Field Camera 3 (WFC3).

Click to view full size image

Image Credit ~ Data: KPNO/NOIRLab/NSF/AURA/P. Massey
Processing: T.A. Rector (University of Alaska Anchorage/NSF’s NOIRLab),
M. Zamani (NSF’s NOIRLab) & D. de Martin (NSF’s NOIRLab)

---

This observation captures the variable star HP Tau, which lies more than 550 light-years from Earth in the constellation Taurus. This image was created using data from the Nicholas U. Mayall 4-meter Telescope at Kitt Peak National Observatory (KPNO), a Program of NSF’s NOIRLab. HP Tau is a T Tauri star, a young and chaotic type of star that is settling into a more sedate phase of stellar life known as the main sequence. The length of time that a star spends on the main sequence will depend on its mass. Our Sun, for example, is about halfway through its roughly 10-billion-year main-sequence lifetime.

HP Tau is part of a triple star system — the three separate stars are visible at the center of this image — surrounded by a large arcing reflection nebula. These nebulae, as the name suggests, reflect the light from nearby stars rather than glowing like emission nebulae elsewhere in the Universe.

A faint, scattered collection of cool stars in the form of an irregular galaxy lies right of centre. A disc-shaped galaxy viewed nearly edge-on lies to the left, surrounded by a wide glow. Several smaller galaxies in various orientations cluster around the two. The background is black and mostly empty.

---

Image Credit: ESA/Hubble & NASA, R. Tully

---

This image from the NASA/ESA Hubble Space Telescope features the galaxy LEDA 48062 in the constellation Perseus. LEDA 48062 is the faint, sparse, amorphous galaxy on the right side of this image, and it is accompanied by a more sharply defined neighbour on the left, the large, disc-like lenticular galaxy UGC 8603. A smattering of more distant galaxies also litter the background, and a handful of foreground stars are also visible throughout the image.

Have you ever wondered why the stars in Hubble images are surrounded by four sharp points? These are called diffraction spikes, and are created when starlight diffracts — or spreads around — the support structures inside reflecting telescopes like Hubble. The four spikes are due to the four thin vanes supporting Hubble’s secondary mirror and are only noticeable for bright objects like stars where a lot of light is concentrated on one spot. Darker, more spread-out objects like the galaxies LEDA 48062 and UGC 8603 do not possess visible diffraction spikes. 

Hubble recently spent some time with our galactic neighbours. LEDA 48062 is only around 30 million light-years from the Milky Way, and was therefore included in the observing campaign Every Known Nearby Galaxy. The aim of this campaign was to observe precisely that: every known galaxy within 10 megaparsecs (around 33 million light-years) of the Milky Way. By getting to know our galactic neighbours, astronomers can determine what types of stars reside in various galaxies and also map out the local structure of the Universe.

Image Credit: ESO/Koss et al.

---

In this Picture of the Week we peer closer into the galaxy UGC 4211, where astronomers have discovered two supermassive black holes on the verge of merging, separated by just 750 lightyears — the closest to have been found to date using multiple wavelengths and less than half of the previous record. They used ESO’s Very Large Telescope (VLT), the Atacama Large Millimeter / submillimeter Array (ALMA), of which ESO is a partner, and other telescopes to detect the bright light produced as the black holes engulf material in their vicinity.

Both of the images shown here were made using data from the MUSE instrument on ESO’s VLT in Chile. The left image shows a classical view of this galaxy, with dust lanes obscuring starlight. The image on the right shows emission from oxygen, nitrogen and hydrogen in blue, green and red respectively. Red indicates areas of star formation, and the bright white central region indicates the presence of two supermassive black holes swallowing material from their surroundings. 

Combining data from the VLT, ALMA and other telescopes, a team led by Michael Koss at Eureka Scientific in the US could identify these two black holes and study them in detail. These black holes likely found each other when their host galaxies collided and merged. Observing this system will help improve our understanding of how galaxies and their supermassive black holes grow as they merge.

• Astrophysical Journal Letters 942(1):L42 (2023 Jan 01) DOI: 10.3847/2041-8213/aca8f0
  arXiv | astro-ph | arXiv:2301.03609 | 09 Jan 2023

Gemini Observatory/NOIRLab/NSF/AURA/Petr Horálek (Institute of Physics in Opava)

---

The extent of our visual field is limited, and can process little information compared to its actual environment. But what would the night sky look like with a much wider field of view, like with a camera?

In this panorama, the Milky Way sets the night ablaze in a bright glowing pillar, dividing the sky in two. On the right, the Gemini South telescope — one half of the International Gemini Observatory, operated by NSF’s NOIRLab — projects its laser guide star into the atmosphere. In the sky above the telescope, from left to right, lie the Small and Large Magellanic Clouds and the star Canopus. On the other end of the image is the SOAR Telescope — part of Cerro Tololo Inter-American Observatory (CTIO), a Program of NOIRLab — with three stars above it forming the semblance of a triangle. The top left vertex is Denebola, the bottom Arcturus, and the top right Spica. There are many more objects in the night sky than these, though it is quite impressive to capture this many with just a panorama. Imagine how much more stunning detail large telescopes like Gemini South and SOAR can discover.

This photo was taken as part of the recent NOIRLab 2022 Photo Expedition to all the NOIRLab sites. A full 360-degree panorama of this image can be viewed here.

Image Credit: Zdeněk Bardon/ESO

---

Since 1979, the 1.54-metre Danish telescope at ESO’s La Silla observatory has been unveiling intricate details about our home galaxy. Stretching over the telescope in this image is the Milky Way and its galactic heart, lighting up the night sky in the Chilean desert. 

The Danish 1.54-m was used in a 15-year long survey published in 2004 to study 14,000 stars in our galaxy, providing the first clues to the turbulent and violent history of the Milky Way. The survey measured the motions of these stars and their distances, as well as their ages and chemical composition. This allowed the creation of a historical map of the Milky Way which revealed a far more complex history of the galaxy than previously expected.

The Milky way cruises the Chilean night sky and looks peaceful in this image, but the survey found traces of a much more dynamic activity in the past. In particular, collisions with other smaller galaxies brought gigantic gas clouds that made the Milky Way come alive with star-formation and supernova explosions, making it the stunning place that we call home. 

Image Credit: ESA/Hubble & NASA, R. Tully

---

A host of astronomical objects throng this image from the NASA/ESA Hubble Space Telescope. Background galaxies ranging from stately spirals to fuzzy ellipticals are strewn across the image, and bright foreground stars much closer to home are also present, surrounded by diffraction spikes. In the centre of the image, the vague shape of the small galaxy UGC 7983 appears as a hazy cloud of light. UGC 7983 is around 30 million light-years from Earth in the constellation Virgo, and is a dwarf irregular galaxy — a type thought to be similar to the very earliest galaxies in the Universe.

This image also conceals an astronomical interloper. A minor asteroid, only a handful of kilometres across, can be seen streaking across the upper left-hand side of this image. The trail of the asteroid is visible as four streaks of light separated by small gaps. These streaks of light represent the four separate exposures that were combined to create this image, the small gaps between each observation being necessary to change the filters inside Hubble’s Advanced Camera for Surveys (ACS). 

Capturing an asteroid was a fortunate side effect of a larger effort to observe every known galaxy close to the Milky Way. When this project was first proposed, roughly 75% of all the Milky Way’s near galactic neighbours had been imaged by Hubble. A group of astronomers proposed using the gaps between longer Hubble observations to capture images of the remaining 25%. The project was an elegantly efficient way to fill out some gaps not only in Hubble's observing schedule, but also in our knowledge of nearby galaxies.