Starship Asterisk*

Image Credit: ESO/Mahdi Zamani

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Powerful lasers leave the dome of one of the four Unit Telescopes of ESO’s Very Large Telescope (VLT) at Paranal Observatory in Chile. The beams reach a layer of the atmosphere about 90 kilometres above the ground, very rich with atoms of sodium. The lasers make the sodium shine, creating artificial stars in the sky. But why?

Earth’s atmosphere distorts light reaching us from cosmic objects, decreasing the sharpness of astronomical observations. This is the same reason why stars seen from Earth appear to “twinkle”.

To correct observations for this effect, astronomers have developed a technology known as adaptive optics, where a flexible mirror is deformed hundreds of times per second to counteract atmospheric turbulence. However, to calculate the necessary corrections, adaptive optics need reference stars close to the observed object. Such stars are not always ideally placed, though, which made astronomers come up with the idea of using lasers to have artificial stars optimally located in the sky any time they are needed.

Fun fact: those sodium atoms are left over from meteoroids which terminated their journey across the Solar System by entering and burning up in the Earth’s atmosphere. So, in a way, when we excite those sodium atoms with lasers we are using space matter to help us observe space!

Image Credit: ESA/Hubble & NASA, E. Wuyts

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This star- and galaxy-studded image was captured by Hubble’s Wide Field Camera 3 (WFC3), using data that were collected for scientific purposes. The object of interest was a galaxy that is visible in the bottom right corner of the image, named SGAS 0033+02. What makes this particular galaxy interesting is a little unusual — it appears not just once in this image, but three times. The thrice-visible galaxy is a little difficult to spot: it appears once as a curved arc and twice more as small round dots around the star.

SGAS 0033+02’s multiple appearances in the same image are not the result of an error, but instead are due to a remarkable phenomenon known as gravitational lensing. Gravitational lensing occurs when the light from a very distant galaxy — such as SGAS 0033+02 — is curved (or ‘lensed’) by the gravity of a massive celestial object that lies in the foreground, between the distant galaxy and the Earth. SGAS 0033+02 was discovered by its namesake, the Sloan Giant Arcs Survey (SGAS), which aimed to identify highly magnified galaxies that were gravitationally lensed by foreground galaxy clusters. SGAS 0033+02 is of special interest because of its highly unusual proximity in the sky to a very bright star. The star is useful, because it can be used to calibrate and correct observations of the lensed SGAS 0033+02.

Image Credit: ESO/VST ATLAS team -- Acknowledgement: Durham Univ/CASU/WFAU

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Just as people at a busy crossroad may accidentally bump into each other, so too can galaxies in the Universe! But in this case, the outcome is more dramatic than a small nudge. When two galaxies clash, they merge into each other, giving birth to a new, bigger one. One example is the NGC 7727 galaxy, shown in this image from ESO’s VLT Survey Telescope (VST) in Chile.

Located 89 million light-years away from Earth in the constellation Aquarius, NGC 7727 is believed to be the result of a clash between two galaxies that occurred about one billion years ago. The consequences of this tremendous cosmic bump are still evident in the peculiar, irregular shape of NGC 7727 and the streams of stars in its outer regions.

The image was taken in visible light as part of the VST-ATLAS survey. The goal of the survey is to map a vast region of the Southern Sky — so large you could fit about 19,000 full moons in it! By studying the galaxies in this region, astronomers aim to shed new light on the nature of dark energy, the mysterious force permeating the Universe and causing its accelerating expansion.

Credits: ESA/Hubble & NASA, J. Lee, PHANGS-HST Team

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In this image the NASA/ESA Hubble Space Telescope peers into the spiral galaxy NGC 1317 in the constellation Fornax, more than 50 million light-years from Earth. This galaxy is one of a pair, but NGC 1317’s rowdy larger neighbour NGC 1316 lies outside Hubble’s field of view. Despite the absence here of its neighbouring galaxy, NGC 1317 is accompanied in this image by two objects from very different parts of the Universe. The bright point ringed with a criss-cross pattern is a star from our own galaxy surrounded by diffraction spikes, whereas the redder elongated smudge is a distant galaxy lying far beyond NGC 1317.

The data presented in this image are from a vast observing campaign of hundreds of observations from Hubble’s Wide Field Camera 3 (WFC3) and Advanced Camera for Surveys (ACS). Combined with data from the ALMA array in the Atacama desert, these observations help astronomers chart the connections between vast clouds of cold gas and the fiercely hot young stars that form within them. ALMA’s unparalleled sensitivity at long wavelengths identified vast reservoirs of cold gas throughout the local Universe, and Hubble’s sharp vision pinpointed clusters of young stars, as well as measuring their ages and masses.

Often the most exciting astronomical discoveries require this kind of telescope teamwork, with cutting-edge facilities working together and providing astronomers with information across the electromagnetic spectrum. The same applies to future telescopes, with Hubble’s observations laying the groundwork for future science with the NASA/ESA/CSA James Webb Space Telescope (JWST).