Today's Image

Ten million stars

Fuzzy white ball on a black background.
Image via ESA/CESAR/Wouter van Reeven.

The fuzzy bluish blob in this image is Omega Centauri, a globular cluster of 10 million stars about 15,800 light-years from Earth.

Globular clusters orbit the Milky Way outside the galactic disk. They harbor tens of thousands to millions of stars. Tightly bound by gravity, globular clusters remain intact after 12 billion years. Omega Centauri has a diameter of 230 light-years. Having a mass of 5 million suns, Omega Centauri is 10 times more massive than a typical globular cluster.

According to the European Space Agency (ESA), Omega Centauri is a picture-perfect example of a globular cluster: tightly bound by gravity, it has a very high density of stars at its center and a nearly perfect spherical shape. In addition:

As other globular clusters, Omega Centauri is made up of very old stars and it is almost devoid of gas and dust, indicating star formation in the cluster has long ceased. Its stars have a low proportion of elements heavier than hydrogen and helium, signaling they were formed earlier in the history of the universe than stars like our sun. Unlike in many other globular clusters, however, the stars in Omega Centauri don’t all have the same age and chemical abundances, making astronomers puzzle over the formation and evolution of this cluster. Some scientists have even suggested that Omega Centauri may not be a true cluster at all, but rather the leftovers of a dwarf galaxy that collided with the Milky Way.

Omega Centauri is also special in many other ways, not least because of the sheer number of stars it contains. It is the largest globular cluster in our galaxy, at about 150 light years in diameter, and is also the brightest and most massive of its type, its stars having a combined mass of about four million solar masses.

The image above was captured by Wouter van Reeven, a software engineer at ESA’s European Space Astronomy Centre in Spain, during his recent visit to Chile to observe the July 2019 total solar eclipse. From Chile’s La Silla Observatory, Omega Centauri was high in the sky, presenting the ideal opportunity to photograph it. To create the composition, Wouter combined eight images taken with an exposure time of 10 seconds, seven images of 30 seconds each and another seven images of 60 seconds each. He used a SkyWatcher Esprit 80 ED telescope and a Canon EOS 200D camera.

Bottom line: Image of globular cluster Omega Centauri.


July 30, 2019
Today's Image

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