Stars and more stars: Hubble never stops surprising. An amazing picture of the globular cluster M55

 Even the great astronomer Charles Messier, author of the homonymous and famous catalogue, had difficulty observing the globular cluster M55 when he composed his catalogue of nebulae and star clusters. It was initially identified in 1752 by a French astronomer in South Africa, but Messier catalogued it in 1778. This is because, while Messier 55 is large and bright, but lacks a dense nucleus and many of its stars are rather weak, making it difficult to observe in sub-optimal conditions.

For northern hemisphere observers, M55 is located below the sky, so the view is hampered by a thicker layer of the atmosphere, as well as light and air pollution. Although the photo above shows only part of M55, the entire cluster appears spherical because the intense gravitational pull of the stars unites them. Hubble’s clear view over Earth’s atmosphere resolves the individual stars in this cluster.

Credit: NASA, ESA, A. Sarajedini (Florida Atlantic University), and M. Libralato (STScI, ESA, JWST);  Image processing: Gladys Kober

Even in the sky with little light pollution, seen with binoculars, the cluster will only show up as a round misty place. Small telescopes can solve some stars in M55, while larger aperture telescopes easily detect low-magnitude stars. The star cluster is located in the southern part of the constellation of Sagittarius and is more easily spotted in August. The following image shows the image taken from the smaller Earth (bottom left) taken from the Digital Sky Survey and shows the area of M55 observed by Hubble.

Credit: NASA, ESA, A. Sarajedini (Florida Atlantic University), M. Libralato (STScI, ESA, JWST), and Digital Sky Survey; Image processing: Gladys Kober

The globular cluster is located at approximately 20,000 light-years and has a diameter of approximately 100 light-years. It holds approximately 100,000 stars with 55 variable stars whose brightness varies.

Source: NASA