Starship Asterisk*

[img3="Credit: ESA/Hubble & NASA"]https://cdn.spacetelescope.org/archives ... w1709a.jpg[/img3][hr][/hr]

This NASA/ESA Hubble Space Telescope image showcases the remarkable galaxy UGC 12591. Classified as an S0/Sa galaxy, UGC 12591 sits somewhere between a lenticular and a spiral. It lies just under 400 million light-years away from us in the westernmost region of the Pisces–Perseus Supercluster, a long chain of galaxy clusters that stretches out for hundreds of light-years — one of the largest known structures in the cosmos.

The galaxy itself is also extraordinary: it is incredibly massive. The galaxy and its halo together contain several hundred billion times the mass of the Sun; four times the mass of the Milky Way. It also whirls round extremely quickly, rotating at speeds of up to 1.8 million kilometres per hour!

Observations with Hubble are helping astronomers to understand the mass of UGC 12591, and to determine whether the galaxy simply formed and grew slowly over time, or whether it might have grown unusually massive by colliding and merging with another large galaxy at some point in its past.

Credit: NASA/ESA/Hubble, ALMA (ESO/NAOJ/NRAO), T. Kitayama (Toho Univ, Japan)

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The events surrounding the Big Bang were so cataclysmic that they left an indelible imprint on the fabric of the cosmos. We can detect these scars today by observing the oldest light in the Universe. As it was created nearly 14 billion years ago, this light — which exists now as weak microwave radiation and is thus named the cosmic microwave background (CMB) — has now expanded to permeate the entire cosmos, filling it with detectable photons.

The CMB can be used to probe the cosmos via something known as the Sunyaev-Zel’dovich (SZ) effect, which was first observed over 30 years ago. We detect the CMB here on Earth when its constituent microwave photons travel to us through space. On their journey to us, they can pass through galaxy clusters that contain high-energy electrons. These electrons give the photons a tiny boost of energy. Detecting these boosted photons through our telescopes is challenging but important — they can help astronomers to understand some of the fundamental properties of the Universe, such as the location and distribution of dense galaxy clusters.

This image shows the first measurements of the thermal Sunyaev-Zel’dovich effect from the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile (in blue). Astronomers combined data from ALMA’s 7- and 12-metre antennas to produce the sharpest possible image. The target was one of the most massive known galaxy clusters, RX J1347.5–1145, the centre of which shows up here in the dark “hole” in the ALMA observations. The energy distribution of the CMB photons shifts and appears as a temperature decrease at the wavelength observed by ALMA, hence a dark patch is observed in this image at the location of the cluster.

The NASA/ESA Hubble Space Telescope observed one of most massive known galaxy clusters, RX J1347.5–1145, seen in this Picture of the Week, as part of the Cluster Lensing And Supernova survey with Hubble (CLASH). This observation of the cluster, 5 billion light-years from Earth, helped the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile to study the cosmic microwave background using the thermal Sunyaev-Zel’dovich effect. The observations made with ALMA are visible as the blue-purple hues.

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This image was captured by the NASA/ESA Hubble Space Telescope’s Advanced Camera for Surveys (ACS), a highly efficient wide-field camera covering the optical and near-infrared parts of the spectrum. While this lovely image contains hundreds of distant stars and galaxies, one vital thing is missing — the object Hubble was actually studying at the time!

This is not because the target has disappeared. The ACS actually uses two detectors: the first captures the object being studied — in this case an open star cluster known as NGC 299 — while the other detector images the patch of space just ‘beneath’ it. This is what can be seen here.

Technically, this picture is merely a sidekick of the actual object of interest — but space is bursting with activity, and this field of bright celestial bodies offers plenty of interest on its own. It may initially seem to show just stars, but a closer look reveals many of these tiny objects to be galaxies. The spiral galaxies have arms curving out from a bright centre. The fuzzier, less clearly shaped galaxies might be ellipticals. Some of these galaxies contain millions and millions of stars, but are so distant that all of their starry residents are contained within just a small pinprick of light that appears to be the same size as a single star!

The bright blue dots are very hot stars, sometimes distorted into crosses by the struts supporting Hubble’s secondary mirror. The redder dots are cooler stars, possibly in the red giant phase when a dying star cools and expands.

[img3="Credit: ESO/Petr Horálek"]https://cdn.eso.org/images/screen/potw1707a.jpg[/img3][hr][/hr]

The sky is full of optical phenomena that can make it tricky to get a clear view of the cosmos. These present a frustrating challenge to astronomers, but for astrophotographers they can provide a real feast for the eyes! This stunning image shows the centre of the Milky Way crossed by the eerie glow of zodiacal light, and is full of dust-induced features that obstruct scientific observations — but they look so beautiful it’s difficult to mind too much.

In this image, the centre of the Milky Way appears to be full of inky black gas. In fact, the dark swirling patches are simply the absence of visible light, because huge clouds of dust are obscuring the light from more distant stars. However, just as dust can give the illusion of darkness, it can also give the illusion of light. This is the case with zodiacal light, a fuzzy band of light that we see projected along the constellations of the zodiac. It is caused when sunlight is scattered by the disc of cosmic dust surrounding the inner Solar System. Particularly observant viewers may notice intricate structures within the band of light — notable here is the phenomenon of Gegenschein, the faint elliptical glow at the antisolar point towards the left of the frame. To the right, the bright column of zodiacal light, or “false dawn”, swells up from the horizon.

This image was captured over the course of a night and is the result of sophisticated imaging by ESO Photo Ambassador Petr Horálek, who sought to capture the structure of zodiacal light in a ground-based image like never before. It was taken at ESO’s La Silla Observatory in Chile. Petr Horálek won the title of "Czech Astrophotography of the Month" in January 2017 for his photo. The title is offered by the Czech Astronomical Society and the Czech Astronomical Institute.