Astronomers discover dozens of massive stars launched from young star cluster R136

Astronomers used data from Europe’s Gaia space telescope to discover 55 high-speed stars launched from the young star cluster R136 in the Large Magellanic Cloud, a satellite galaxy of the Milky Way. This increases tenfold the number of “runaway stars” known in this region. The team of astronomers, including Simon Portegies Zwart of the Leiden Observatory, published their results this week in Nature.

When star clusters form, near-collisions of closely packed and crisscrossing newborn stars can cause stars to be ejected from the young cluster. The astronomers, led by UvA Ph.D. student Mitchel Stoop, discovered that the young cluster R136 had launched up to a third of its most massive stars over the past few million years, at higher speeds at 100,000 km/h. These stars travel up to 1,000 light years from their birthplace before exploding as a supernova at the end of their life, producing a neutron star or black hole.

But Stoop and his colleagues made another surprising discovery: There was not just one period in which stars were dynamically ejected, but two. Stoop explains: “The first episode occurred 1.8 million years ago, when the cluster formed, and corresponds to the ejection of stars during the formation of the cluster. The second episode occurred only 200,000 years ago and had very different characteristics. The fleeing stars in this second episode move more slowly and are not projected in random directions like in the first episode, but in a preferred direction. »

“We believe that the second episode of projected stars was due to the interaction of R136 with another nearby cluster (which was only discovered in 2012). The second episode could predict that the two clusters will mix and merge in the near future.” says co-author Alex de Koter (UvA).

Massive stars eventually explode as supernovas. During their lifetime, they are extremely bright – up to a million times brighter than the sun – and emit primarily ultraviolet light that ionizes surrounding hydrogen gas. They only live a short time (millions of years) and normally still explode in the star forming region in which they were born. Such a star-forming region consists of clouds of gas and dust that dampen the effect of massive stars on their surroundings.

This is the first time that such a large number (55) of high-speed stars from a single cluster have been discovered. R136 is a very special cluster, containing hundreds of thousands of stars including the most massive stars known (up to 300 times the mass of the sun). It is part of – and is the “prima donna” – the largest star-forming region we know of within a radius of five million light years.

“Now that we have discovered that a third of massive stars are ejected from their regions of birth early in their lives and that they exert their influence beyond these regions, the impact of massive stars on the structure and the The evolution of galaxies is probably much more important than previously thought. It is even possible that runaway stars formed in the early universe made an important contribution to what is known as reionization. universe caused by ultraviolet light”, explains co-author Lex Kaper (UvA).

The astronomers used data from ESA’s Gaia telescope, which measures the positions, distances and velocities of more than a billion stars. Gaia is located far beyond the Moon, at a distance of 1.5 million kilometers from Earth. The team’s main goal was to test the limits of Gaia’s capabilities. R136 is located in the Large Magellanic Cloud, a sister galaxy to the Milky Way, at a distance of 160,000 light years. This is extremely far away by Gaia’s measurements.

“R136 has only just formed (1.8 million years ago) so the runaway stars might not yet be so far away that it becomes impossible to identify them. If you can find a large number of these stars, you can make reliable statistical statements. This worked beyond our expectations and we are extremely satisfied with the results. Discovering something new is always a pleasure for a scientist,” concludes De Koter.

Furthermore, during his doctoral research (1946), the Dutch astronomer Adriaan Blaauw (April 12, 1914 – December 1, 2010) discovered the first indications of the existence of runaway stars, stars moving at high speed in the Milky Way. Using data from ESA’s Hipparcos space mission, co-led by Blaauw, and now from Gaia, star clusters and the movements of fleeing stars can be studied in detail.