Massive 9-gigapixel VISTA image reveals galactic ‘bulge’ in stunning detail

Astronomers working at the European Southern Observatory released a glorious 9-gigapixel image of the centre of our galaxy today, which is a composite mosaic of pictures taken by VISTA, the Visible and Infrared Survey Telescope for Astronomy, located on Paranal Mountain, in northern Chile.

The full image is massive — 108,500 pixels wide by 81,500 long. If it was printed out as a good quality photo, it would be over 9 metres long and nearly 7 metres tall. The collection of images that went into making it were taken over the past 2 years, as part of the VISTA Variables in the Via Lactea (VVV) survey (Via Lactea is Milky Way in Latin). The compiled image contains about 173 million different astronomical objects, around 84 million of which are confirmed stars.

"By observing in detail the myriads of stars surrounding the centre of the Milky Way we can learn a lot more about the formation and evolution of not only our galaxy, but also spiral galaxies in general," said Roberto Saito, an astronomer with the Pontificia Universidad Católica de Chile, who leads the study that produced the new image, according to an ESO statement.

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A 'zoomable' version of the image can be found at this link. It shows what the galaxy looks like in the infrared part of the spectrum, taking advantage of how infrared light gets around the galaxy more easily than visible light.

"Observations of the bulge of the Milky Way are very hard because it is obscured by dust," says Dante Minniti, also from Pontificia Universidad Catolica de Chile, who co-authored the study. "To peer into the heart of the galaxy, we need to observe in infrared light, which is less affected by the dust."

To see just how big a difference the change in spectrum makes, a comparison of the infrared and visible light versions of this image can be found here.

The astronomers on the team used the image to produce a colour-magnitude diagram — a graph where each star is plotted by colour vs brightness. This particular graph is the first that's ever been done for the galactic 'bulge', and has 10 times the number of stars on any past study of its kind.

According to the ESO statement: "One interesting result revealed in the new data is the large number of faint red dwarf stars. These are prime candidates around which to search for small exoplanets using the transit method."

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The transit method is when astronomers watch for a star to dim sharply as a planet orbiting the star passes in front of it (from our point of view). These faint red dwarf stars are the best candidates to search for planets because, compared to more massive stars, they experience the greatest drop in brightness as a planetary transit happens.

"One of the other great things about the VVV survey is that it's one of the ESO VISTA public surveys. This means that we're making all the data publicly available through the ESO data archive, so we expect many other exciting results to come out of this great resource," said Saito.

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