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Massive stars discovered

Using a combination of instruments on ESO's Very Large Telescope, astronomers have discovered the most massive stars to date, one weighing at birth more than 300 times the mass of the Sun, or twice as much as the currently accepted limit of 150 solar masses. The existence of these monsters – millions of times more luminous than the Sun, losing mass through very powerful winds – may provide an answer to the question "how massive can stars be?"

A team of astronomers led by Paul Crowther, Professor of Astrophysics at the University of Sheffield, has used ESO's Very Large Telescope (VLT), as well as archival data from the NASA/ESA Hubble Space Telescope, to study two young clusters of stars, NGC 3603 and RMC 136a in detail.

NGC 3603 is a cosmic factory where stars form frantically from the nebula's extended clouds of gas and dust, located 22 000 light-years away from the Sun.

RMC 136a (more often known as R136) is another cluster of young, massive and hot stars, which is located inside the Tarantula Nebula, in one of our neighbouring galaxies, the Large Magellanic Cloud, 165 000 light-years away.

The team found several stars with surface temperatures over 40 000 degrees, more than seven times hotter than our Sun, and a few tens of times larger and several million times brighter. Comparisons with models imply that several of these stars were born with masses in excess of 150 solar masses. The star R136a1, found in the R136 cluster, is the most massive star ever found, with a current mass of about 265 solar masses and with a birth weight of as much as 320 times that of the Sun.

In NGC 3603, the astronomers could also directly measure the masses of two stars that belong to a double star system, as a validation of the models used. The stars A1, B and C in this cluster have estimated masses at birth above or close to 150 solar masses.

Very massive stars produce very powerful outflows. "Unlike humans, these stars are born heavy and lose weight as they age," says Paul Crowther. "Being a little over a million years old, the most extreme star R136a1 is already 'middle-aged' and has undergone an intense weight loss program, shedding a fifth of its initial mass over that time, or more than fifty solar masses."

If R136a1 replaced the Sun in our Solar System, it would outshine the Sun by as much as the Sun currently outshines the full Moon. "Its high mass would reduce the length of the Earth's year to three weeks, and it would bathe the Earth in incredibly intense ultraviolet radiation, rendering life on our planet impossible," says Raphael Hirschi from Keele University, who belongs to the team.

These super heavyweight stars are extremely rare, forming solely within the densest star clusters. Distinguishing the individual stars – which has now been achieved for the first time – requires the exquisite resolving power of the VLT's infrared instruments.

Understanding how high mass stars form is puzzling enough, due to their very short lives and powerful winds, so that the identification of such extreme cases as R136a1 raises the challenge to theorists still further. "Either they were born so big or smaller stars merged together to produce them," explains Crowther.

Stars between about 8 and 150 solar masses explode at the end of their short lives as supernovae, leaving behind exotic remnants, either neutron stars or black holes. Having now established the existence of stars weighing between 150 and 300 solar masses, the astronomers' findings raise the prospect of the existence of exceptionally bright, "pair instability supernovae" that completely blow themselves apart, failing to leave behind any remnant and dispersing up to ten solar masses of iron into their surroundings. A few candidates for such explosions have already been proposed in recent years.

Not only is R136a1 the most massive star ever found, but it also has the highest luminosity too, close to 10 million times greater than the Sun. "Owing to the rarity of these monsters, I think it is unlikely that this new record will be broken any time soon," concludes Crowther.

(Download the research paper ESO1030).

ESO Press Release

Recent news

top story: March newsletter of the ASSA Deep-Sky Section, featuring 47 Tuc on the cover. — "Nightfall" (2015 April) is the current newsletter of the Deep-Sky Observing Section of the Astronomical Society of Southern Africa.

A globular cluster in the realm of the galaxies — A rare gem - a bright globular cluster in the realm of the galaxies.

The Dark Emu rises, in pursuit of the Magellanic Clouds — The beautiful complex of dark nebulosity along the southern Milky Way appears like an ancient monster, its serpentine neck reaching out as if to gobble up the Magellanic Clouds.

Massive star forming region in the Small Magellanic Cloud — Dale Liebenberg images NGC 346, a gigantic star forming region in the SMC.

Flocculent Galaxy in Southern Leo — Dale Liebenberg images the spiral galaxy NGC 3521 in southern Leo.

Ancient open cluster in Lyra — Anthony Ayiomamitis images the old open cluster NGC 6791.

Golden Coin Galaxy — Dale Liebenberg images the Golden Coin, NGC 4945 in Centaurus.

NGC 2467 in Puppis — Dale Liebenberg images NGC 2467 in Puppis.

Last but not least - Messier 103 — Anthony Ayiomamitis images Messier 103 in Cassiopeia.

The Arkenstone of Thrain — Dale Liebenberg images Messier 22, the "Arkenstone of Thrain" according to Burnham.

ConCards available — A handy set of beginner's star charts, "Constellation Cards" are now available for free download.

Deep sky celebrations — Three deep sky observers of yore have birthdays this week: William Herschel (1738), the Fourth Earl of Rosse, and Stephane Javelle.

Necklace Nebula featured on APOD — The recently-discovered planetary nebula nicknamed the Necklace Nebula, recently featured on APOD.

Methuselah Nebula featured on APOD — The old bipolar planetary nebula MWP1, a.k.a. Methuselah Nebula, is today's APOD.

New deepsky book from CUP — Deep sky author Wolfgang Steinicke's latest book, "Observing and Cataloguing Nebulae and Star Clusters: From Herschel to Dreyer's New General Catalogue", has just been published by Cambridge University Press.

NGC 1365 in infrared (ESO VLT) — The bright barred spiral galaxy NGC 1365 in Fornax has been imaged in the infrared with the ESO VLT telescope.

New HST image of eta Carinae Nebula — New observations, combined with images made in 2005, show beautiful detail in part of the extensive eta Carinae Nebula.

First planetary in open cluster found — A team of astronomers from Australia, the UK, the USA and France have discovered the first planetary nebula known to be associated with a galactic open cluster.

NGC 300 in Sculptor imaged at ESO — The bright spiral galaxy NGC 300 has been imaged with the MPG/ESO 2.2-meter telescope at the La Silla Observatory in Chile.

Superwind galaxy NGC 4666 — A remarkable galaxy with very vigorous star formation has been newly imaged on the MPG/ESO 2.2-meter telescope at the La Silla Observatory in Chile.

News archives

All earlier news items can be browsed in the archives.

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As Nelson swept the seas you sweep the skies, leaving little for those who may come after you.
Letter from Thomas Maclear to John Herschel,
Royal Observatory, April 5, 1834

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