APOD and General Astronomy Discussion Forum
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[img3="Credit: ESO / Babak Tafreshi (TWAN)"]https://cdn.eso.org/images/screen/potw1738a.jpg[/img3][hr][/hr]Rising up to block part of the star-studded sky, the New Technology Telescope (NTT) cuts a striking and dramatic figure in this ESO Picture of the Week.
Located at ESO's La Silla Observatory in the Chilean Atacama Desert, the NTT was inaugurated in 1989. It was the first ever telescope to have a computer-controlled main mirror. This 3.58-metre mirror is very flexible and its shape can be continuously changed, allowing astronomers to counteract deformations due to external influences such as wind, temperature and mechanical stress mid-observation in order to see the objects as clearly as possible.
Complementing the NTT’s groundbreaking technology is the innovative design of its housing. Its octagonal dome is relatively small and includes a series of flaps that ventilate the structure with reduced turbulence, allowing air to flow smoothly across the mirror. The dome walls can be opened entirely — as opposed to only opening the roof, as with conventional domes — to reveal large swathes of the southern sky.
This image was taken by ESO Photo Ambassador Babak Tafreshi.
[img3="Credit: ESA/Hubble & NASADespite the advances made in past decades, the process of galaxy formation remains an open question in astronomy. Various theories have been suggested, but since galaxies come in all shapes and sizes — including elliptical, spiral, and irregular — no single theory has so far been able to satisfactorily explain the origins of all the galaxies we see throughout the Universe.
Acknowledgement: Judy Schmidt"]https://cdn.spacetelescope.org/archives ... w1738a.jpg[/img3][hr][/hr]
To determine which formation model is correct (if any), astronomers hunt for the telltale signs of various physical processes. One example of this is galactic coronas, which are huge, invisible regions of hot gas that surround a galaxy’s visible bulk, forming a spheroidal shape. They are so hot that they can be detected by their X-ray emission, far beyond the optical radius of the galaxy. Because they are so wispy, these coronas are extremely difficult to detect. In 2013, astronomers highlighted NGC 6753, imaged here by the NASA/ESA Hubble Space Telescope, as one of only two known spiral galaxies that were both massive enough and close enough to permit detailed observations of their coronas. Of course, NGC 6753 is only close in astronomical terms — the galaxy is nearly 150 million light-years from Earth.
NGC 6753 is a whirl of colour in this image — the bursts of blue throughout the spiral arms are regions filled with young stars glowing brightly in ultraviolet light, while redder areas are filled with older stars emitting in the cooler near-infrared.
[img3="Image Credit: ESO/Jean-Christophe Lambry"]https://cdn.eso.org/images/screen/potw1739a.jpg[/img3][hr][/hr]This spectacular spiral galaxy, known as NGC 1964, resides approximately 70 million light-years away in the constellation of Lepus (The Hare). NGC 1964 has a bright and dense core. This core sits within a mottled oval disc, which is itself encircled by distinct spiral arms speckled with bright starry regions. The brilliant centre of the galaxy caught the eye of the astronomer William Herschel on the night of 20 November 1784, leading to the galaxy’s discovery and subsequent documentation in the New General Catalogue.
In addition to containing stars, NGC 1964 lives in a star-sprinkled section of the sky. In this view from the Wide Field Imager (WFI) — an instrument mounted on the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory, Chile — the star HD 36785 can be seen to the galaxy’s immediate right. Above it reside two other prominent stars named HD 36784 and TYC 5928-368-1 — and the large bright star below NGC 1964 is known as BD-22 1147.
This view of NGC 1964 also contains an array of galaxies, visible in the background. The WFI is able to observe the light from these distant galaxies, and those up to 40 million times fainter than the human eye can see.
[img3="Image Credit: ESA/Hubble & NASA"]https://cdn.spacetelescope.org/archives ... w1739a.jpg[/img3][hr][/hr]The distances to objects in the Universe can differ enormously. The nearest star to us — Proxima Centauri — lies some 4.2 light-years from us, while some incredibly distant galaxies are so far away — 13 billion light-years or more — that they are only visible to us as a result of cosmic tricks of magnification.
The subject of this image, a galaxy called ESO 376-16, sits nearly 23 million light-years from Earth — not that great a distance on a cosmic scale. However, given the galaxy’s relative proximity to us, we know surprisingly little about it. Astronomers are still debating about many of the properties of ESO 376-16, including its morphology. Galaxies are divided into types based on their visual appearance and characteristics; spiral galaxies, like the Milky Way, are flattened discs with curved arms sweeping out from a central nucleus, while irregular galaxies lack a distinct structure and look far more chaotic. On the basis of its rather ill-defined morphology, ESO 376-16 is thought to be either a late-type spiral or a dwarf irregular galaxy.
Despite its mystique, observations of ESO 376-16 have been useful in several studies, including one made with the NASA/ESA Hubble Space Telescope that aimed to create a 3D map of galaxies lying in the vicinity of Earth. Researchers used Hubble to gauge the distance to galaxies including ESO 376-16 by measuring the luminosities of especially bright red-giant-branch stars sitting within the galaxies. They then used their data to generate and calibrate 3D maps of the distribution of galaxies throughout the nearby cosmos.
