This small extract from the VISTA VVV survey of the central parts of the Milky Way shows the famous Trifid Nebula to the right of centre. It appears as faint and ghostly at these infrared wavelengths when compared to the familiar view in visible light. This transparency has brought its own benefits — many previously hidden background objects can now be seen clearly. Among these are two newly discovered Cepheid variable stars (detailed image below) — the first ever spotted on the far side of the galaxy near its central plane. Image credit: ESO/VVV consortium/D. MinnitiA new image taken with ESO’s VISTA survey telescope reveals the famous Trifid Nebula in a new and ghostly light. By observing in infrared light, astronomers can see right through the dust-filled central parts of the Milky Way and spot many previously hidden objects. In just this tiny part of one of the VISTA surveys, astronomers have discovered two unknown and very distant Cepheid variable stars that lie almost directly behind the Trifid. They are the first such stars found that lie in the central plane of the Milky Way beyond its central bulge.The positions of the newly discovered faint Cepheids are marked on this annotated version. Image credit: ESO/VVV consortium/D. MinnitiAs one of its major surveys of the southern sky, the VISTA telescope at ESO’s Paranal Observatory in Chile is mapping the central regions of the Milky Way in infrared light to search for new and hidden objects. This VVV survey (standing for VISTA Variables in the Via Lactea) is also returning to the same parts of the sky again and again to spot objects that vary in brightness as time passes.
A tiny fraction of this huge VVV dataset has been used to create this striking new picture of a famous object, the star formation region Messier 20, usually called the Trifid Nebula because of the ghostly dark lanes that divide it into three parts when seen through a telescope.
This picture compares a new view of the Trifid Nebula in infrared light, from the VVV VISTA survey (top) with a more familiar visible-light view from a small telescope (bottom). The glowing clouds of gas and dust are much less prominent in the infrared view, but many more stars behind the nebula become apparent, including the two newly discovered Cepheid variable stars. Image credit: ESO/VVV consortium/D. Minniti/Gábor TóthThe familiar pictures of the Trifid show it in visible light, where it glows brightly in both the pink emission from ionised hydrogen and the blue haze of scattered light from hot young stars. Huge clouds of light-absorbing dust are also prominent. But the view in the VISTA infrared picture is very different. The nebula is just a ghost of its usual visible-light self. The dust clouds are far less prominent, and the bright glow from the hydrogen clouds is barely visible at all. The three-part structure is almost invisible.
In the new image, as if to compensate for the fading of the nebula, a spectacular new panorama comes into view. The thick dust clouds in the disc of our galaxy that absorb visible light allow through most of the infrared light that VISTA can see. Rather than the view being blocked, VISTA can see far beyond the Trifid and detect objects on the other side of the galaxy that have never been seen before.
By chance this picture shows a perfect example of the surprises that can be revealed when imaging in the infrared. Apparently close to the Trifid in the sky, but in reality about seven times more distant[1], a newly discovered pair of variable stars has been found in the VISTA data. These are Cepheid variables, a type of bright star that is unstable and slowly brightens and then fades with time. This pair of stars, which the astronomers think are the brightest members of a cluster of stars, are the only Cepheid variables detected so far that are close to the central plane, but on the far side of the galaxy. They brighten and fade over a period of eleven days.The Trifid Nebula, or Messier 20, lies in northwestern Sagittarius — a Northern Hemisphere summer constellation rich in deep-sky objects (labelled red). AN graphic by Ade Ashford[1] The Trifid Nebula lies about 5,200 light-years from Earth; the centre of the Milky Way is about 27,000 light-years away, in almost the same direction, and the newly discovered Cepheids are at a distance of about 37,000 light-years.
This image, taken with the Wide Field Planetary Camera 2 on board the NASA/ESA Hubble Space Telescope, shows the globular cluster Terzan 1. Lying around 20,000 light-years from us in the constellation of Scorpius, it is one of about 150 globular clusters belonging to our galaxy, the Milky Way.
The edge-on spiral galaxy captured in this NASA/ESA Hubble Space Telescope image lies about one billion light-years away in the constellation of Eridanus. In 2003, the galaxy was discovered to possess giant jets of superheated gas emitting in the radio part of the spectrum. These jets have long been associated with the cores of giant elliptical galaxies, but are rare in spirals.
This multicoloured swirl of yellow and blue shows a prominent ring of gas near the North Celestial Pole. The pole appears to be fixed in place, while the rest of the night sky slowly circles around it because of Earth’s rotation. This image comes courtesy of ESA’s Planck satellite, which spent years mapping the entire sky in exquisite detail between 2009 and 2013.
