APOD and General Astronomy Discussion Forum
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Around 60 million light-years away, in the constellation Virgo, the two galaxies NGC4567 and NGC4568, nicknamed the Butterfly Galaxies due to their wing-like structure, are beginning to collide and merge into each other. This is depicted in this picture captured by the FOcal Reducer and low dispersion Spectrograph 2 (FORS2) instrument, which is mounted on ESO’s Very Large Telescope (VLT) at the Paranal Observatory in the Chilean Andes.
Galaxy collisions are not unusual in the Universe. We may imagine them to be violent and catastrophic, but in reality they are surprisingly peaceful, like a waltz performed by stars, gas and dust, choreographed by gravity. This kind of collision and merger is also thought to be the eventual fate of the Milky Way, which scientists believe will undergo a similar interaction with our neighbouring galaxy Andromeda.
FORS2 is often nicknamed Paranal’s “Swiss Army knife” for its incredible versatility, and it’s in fact one of our most demanded instruments. Besides capturing images like this one it can also take spectra of up to several tens of cosmic objects simultaneously, or study polarised light.
This image was created as part of the ESO Cosmic Gems programme, an outreach initiative to produce images of interesting, intriguing or visually attractive objects using ESO telescopes, for the purposes of education and public outreach. The programme makes use of telescope time that cannot be used for science observations. All data collected may also be suitable for scientific purposes, and are made available to astronomers through ESO’s science archive.
The subject of this image is a group of three galaxies, collectively known as NGC 7764A. They were imaged by the NASA/ESA Hubble Space Telescope, using both its Advanced Camera for Surveys (ACS) and Wide Field Camera 3 (WFC3). The two galaxies in the upper right of the image appear to be interacting with one another — indeed, the long trails of stars and gas extending from them both give the impression that they have both just been struck at great speed, thrown into disarray by the bowling-ball-shaped galaxy to the lower left of the image. In reality, however, interactions between galaxies happen over very long time periods, and galaxies rarely collide head-on with one another. It is also unclear whether the galaxy to the lower left is actually interacting with the other two, although they are so relatively close in space that it seems possible that they are. By happy coincidence, the collective interaction between these galaxies have caused the two on the upper right to form a shape, which from our Solar System's perspective, ressembles the starship known as the USS Enterprise from Star Trek!
NGC 7764A, which lies about 425 million light years from Earth in the constellation Phoenix, is a fascinating example of just how awkward astronomical nomenclature can be. The three galaxies are individually referred to as NGC 7764A1, NGC 7764A2 and NGC 7764A3, and just to be really difficult, an entirely separate galaxy, named NGC 7764, sits in the skies about a Moon’s distance (as seen from Earth) away. This rather haphazard naming makes more sense when we consider that many of the catalogues for keeping track of celestial bodies were compiled well over 100 years ago, long before modern technology made standardising scientific terminology much easier. As it is, many astronomical objects have several different names, or might have names that are so similar to other objects’ names that they cause confusion.
Construction on the world’s biggest eye on the sky, ESO’s Extremely Large Telescope (ELT) is making progress! After a significant slow-down of the building works due to the COVID-19 pandemic — including almost a year of complete site closure — works resumed in mid-2021. As this image from January 2022 shows, the foundations of the mammoth 39-m telescope have been laid, taking us one step closer to uncovering some of the most elusive mysteries of the Universe.
The first forms of the ELT’s spectacular dome are taking shape. The immense structure will be about 80 metres high, with a diameter of about 88 metres, roughly equivalent to the area of a football pitch. To the left you can see the scaffolding and the first formwork of the dome’s pier. The pier will be surrounded by a circular auxiliary building, and its concrete foundation is almost complete. The various electrical, thermal, and hydraulic plants used to operate the ELT will be housed here. The entire structure will rest on shock absorbers, already installed and aligned, to protect against major earthquakes and other vibrations.
In front of the dome, next to where the entrance will be, the eagle-eyed observer can spot a deep pit, which will host a special tower to test and calibrate the telescope’s M4 mirror. This mirror, which is a fundamental component of the adaptive optics system of the ELT, can be quickly deformed to correct for turbulence in the Earth’s atmosphere, as well as vibrations caused by the telescope’s motion and the wind. When finished, this will be the largest adaptive mirror ever made for a telescope, allowing ESO’s ELT to see the Universe in unprecedented detail.
The dwarf galaxy NGC 1705 is featured in this image from the NASA/ESA Hubble Space Telescope. This diminutive galaxy lies in the southern constellation Pictor, and is approximately 17 million light-years from Earth. NGC 1705 is a cosmic oddball — it is small, irregularly shaped, and has recently undergone a spate of star formation known as a starburst.
Despite these eccentricities, NGC 1705 and other dwarf irregular galaxies like it can provide valuable insights into the overall evolution of galaxies. Dwarf irregular galaxies tend to contain few elements other than hydrogen or helium, and are considered to be similar to the earliest galaxies that populated the Universe.
The data shown in this image come from a series of observations designed to unveil the interplay between stars, star clusters, and ionised gas in nearby star-forming galaxies. By observing a specific wavelength of light known as H-alpha with Hubble’s Wide Field Camera 3, astronomers aimed to discover thousands of emission nebulae — regions created when hot, young stars bathe the clouds of gas surrounding them in ultraviolet light, causing them to glow.
This is not the first time that NGC 1705 has been imaged by Hubble — astronomers peered into the heart of the galaxy in 1999 using Hubble’s workhorse camera at the time, the Wide Field Planetary Camera 2. This instrument was replaced with the Wide Field Camera 3 during the fifth and final Space Shuttle mission to Hubble in 2009, and the newer instrument has provided a richer and far more detailed portrait of NGC 1705 than the 1999 observation.
