“Cloud D” in Nearby Dwarf Galaxy –Obscures Spectacular Cluster of Massive Stars Billion Xs Brighter Than Our Sun






The star cluster is buried within a massive gas cloud dubbed "Cloud D" in the NGC 5253 dwarf galaxy, and, although it's a billion times brighter than our sun, is barely visible, hidden by its own hot gases and dust. The star cluster contains more than 7,000 massive "O" stars: the most brilliant stars extant, each a million times more luminous than our sun.

NGC 5253 is one of the nearest of the known blue compact dwarf galaxies. It is located 11 million light-years away the constellation Centaurus. The galaxy is considered part of the Centaurus A/Messier 83 group of galaxies, which includes the famous radio galaxy Centaurus A and the spiral galaxy Messier 83. Previous studies have suggested the possibility that its peculiar nature could result from a close encounter with its closer neighbor, Messier 83.

The newly-discovered star cluster is buried within a supernebula in NGC 5253, and contains more than 7,000 massive O-type stars – the most luminous of all known stars – and has one billion times the luminosity of our Sun, but is invisible in ordinary light, hidden by its own hot gases.

"Cloud D is an incredibly efficient star and soot factory," says Prof. Sara Beck of TAU's Department of Astronomy and Astrophysics and co-author of the research, recently published in Nature. "This cloud has created a huge cluster of stars, and the stars have created an unprecedented amount of dust."

For the study, Prof. Beck collaborated with Prof. Jean Turner, Chair of UCLA's Department of Physics and Astronomy, and a team of researchers at the Submillimeter Array, a joint project of the Smithsonian Astrophysical Observatory and the Academia Sinica Institute of Astronomy and Astrophysics, on Hawaii's Mauna Kea.

"Extreme and extraordinary things are happening right in our very own astronomical neighborhood," Prof. Beck says. "In astrophysics we assume that, unless proven otherwise, basic processes are the same everywhere. But here we're witnessing globular cluster formation — a process which we assumed was 'turned off' in our galaxy ten billion years ago — occurring today in a nearby galaxy."

According to the researchers, NGC 5253 is home to hundreds of large star clusters. The most spectacular cluster, cocooned in the massive Cloud D, is about three million years old, remarkably young in astronomical terms. The proportion of gas clouds, which eventually become stars, varies in different parts of the universe. In the Milky Way, for example, less than 5 percent of gas in clouds the size of Cloud D transforms into stars." In the newly discovered Cloud D, however, the rate appears to be least ten times greater.

"This discovery is not an isolated find, but the temporary culmination of a long search which began with a faint radio emission in 1996," Prof. Beck observes. "We have been working for almost twenty years on extreme star formation. Along the way, we started asking why these clusters were being born at a precise time and a certain place. We are still hard at work on this, so this certainly isn't the end of the road for us."

NGC 5253 has approximately nine times as much dark matter as visible matter — a much higher rate than the inner parts of the Milky Way. In coming years, the cloud could be destroyed by stars that become supernovae, which would spin all of the gas and elements created by the stars into interstellar space.

Our Milky Way Galaxy has not formed gigantic star clusters for billions of years. It is still forming new stars, but not in nearly such large numbers. Some astronomers had believed that such giant star clusters could form only in the early Universe.

Prof. Beck said her team is continuing to study and monitor the galaxy using the Atacama Large Millimeter/submillimeter Arrray in Chile.

The Daily Galaxy via American Friends of Tel Aviv University


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