A wide-field view of the Sculptor dwarf galaxy

Wide-field image of the sky around the Sculptor Dwarf GalaxyThis image of the sky around the Sculptor Dwarf Galaxy, a close neighbour of our galaxy, the Milky Way, was created from pictures from the Digitized Sky Survey 2. Despite their close proximity, both galaxies have very distinct histories and characters. Credit: ESO/Digitized Sky Survey 2

This galaxy is much smaller and older than the Milky Way, making it a valuable subject for studying both star and galaxy formation in the early Universe. However, due to its faintness, studying this object is no easy task. The Sculptor Dwarf Galaxy — also known as the Sculptor Dwarf Elliptical or the Sculptor Dwarf Spheroidal — is a dwarf spheroidal galaxy, and is one of the fourteen (and counting) known satellite galaxies orbiting the Milky Way. These galactic hitchhikers are located close by in the Milky Way’s extensive halo, a spherical region extending far beyond our galaxy’s spiral arms. As indicated by its name, this galaxy is located in the southern constellation of Sculptor and lies about 280 000 light-years away from Earth. Despite its proximity, the galaxy was only discovered in 1937, as its stars are faint and spread thinly across the sky. Although difficult to pick out, the Sculptor Dwarf Galaxy was among the first faint dwarf galaxies found orbiting the Milky Way. The tiny galaxy’s shape intrigued astronomers at the time of its discovery, but nowadays dwarf spheroidal galaxies play a more important role in allowing astronomers to dig deeply into the Universe’s past. The Milky Way, like all large galaxies, is thought to have formed from the build-up of smaller galaxies during the early days of the Universe. If some of these small galaxies still remain today, they should now contain many extremely old stars. The Sculptor Dwarf Galaxy fits the bill as a primordial galaxy, thanks to a large number of ancient stars, visible in this image taken by the Wide Field Imager camera, installed on the 2.2-metre MPG/ESO telescope at ESO’s La Silla Observatory. Astronomers can determine the age of stars in the galaxy because their light carries the signatures of only a small quantity of heavy chemical elements. These heavy elements accumulate in galaxies with successive generations of stars. A low level of heavy elements thus indicates that the average age of the stars in the Sculptor Dwarf Galaxy is high. This quantity of old stars makes the Sculptor Dwarf Galaxy a prime target for studying the earliest history of star formation. In a recent study, astronomers combined all the data available for the galaxy to create the most accurate star formation history ever determined for a dwarf spheroidal galaxy. This analysis revealed two distinct groups of stars in the galaxy. The first, predominant group is the older population, which is lacking in heavier elements. The second, smaller population, in contrast, is rich with heavy elements: this youthful stellar population is concentrated toward the galaxy’s core.

There has been a great abundance of interesting solar system news lately so it is time for a round-up. Recent investigations of the extreme trans-Neptunian object 2012 VP113 and its orbital alignment with that of Sedna and certain other, nearer objects have sparked new speculations concerning a putative large planet in the very outer reaches of the solar system. The difference this time is that the postulated planet is thought to be rocky and too cold to have been observed by the WISE survey. Moving sunward, it is now thought that the abundance of water on Earth is primordial, rather than having been delivered by the bombardment of comets and asteroids at a somewhat later epoch:

Fragments of Earth’s earliest rock, preserved unchanged deep in the mantle until they were coughed up by volcanic eruptions, suggest that our planet has had water from the very beginning. If so, that raises the likelihood that water – one of the key prerequisites for life – could be native to other planets, too. The origin of Earth’s water has long been a mystery to planetary scientists, because the young sun would have burned hot enough to vaporise any ice that was present as dust coalesced to form our planet. Scientists therefore assumed that newborn Earth must have formed from dry material and acquired its water through bombardment by objects from more distant, icy reaches of the solar system.

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