Two Heftiest Stars Found in Milky Way

type size: [A] [A] [A]

June 7, 2007 — The two heaviest stars ever have been discovered in the southern Milky Way galaxy. The double super heavyweights are actually in orbit around each other, and both break the record — 83 times the sun’s mass — for the most massive stars found to date.

The heavier of the two weighs in at a whopping 114 "solar masses," while its little brother is 84 solar masses. The discovery was presented June 7 at the meeting of the Canadian Astronomical Society at the Royal Military College of Canada in Kingston, Ontario.

The two big bruiser stars, which form a binary system called A1, are not only large, they are quite young. This makes sense since it is the largest and brightest of stars that live the briefest, according to stellar theory.

"Their age is about a million years," said astronomer Anthony Moffat of the University of Montreal. They will probably not last beyond two or three million years, he said. Smaller stars like our sun, on the other hand, can burn for many billions of years.

It’s partly this short lifespan that makes these large stars so hard to find, said Robert Lamontagne, a University of Montreal astronomer who was not involved in the discovery.

To hunt down the biggest stars, astronomers need to look closely to the sites where stars are born – stellar clusters. The newfound massive double star system was found in a very dense, young star cluster called NGC 3603 using data from both the Hubble Space Telescope and the Very Large Telescope at the European Southern Observatory in South America. NGC 3603 is located about 20,000 light-years from Earth.

"Our sun was probably born in such a cluster," said Lamontagne, "but its brothers and sisters are spread out over the galaxy now." If there were any giants in our sun’s birth cluster, they died explosively long ago, he said.

What also made the new discovery possible was the fact that there were two stars involved, said Moffat. The interplay between the two provides plenty of data with which to calculate the masses of the stars, he explained. A lone giant would be much harder to weigh.

Another downside of the shorter lifespan of giant stars, from an astronomer’s point of view, is that they are completely outnumbered by their smaller, far older siblings.

"Typical stars are the mass of the sun or even smaller," said Lamontagne.

Large stars, though bright, make up perhaps five or ten percent of the stellar population. But that doesn’t mean the big stars are unimportant, he said. On the contrary, the giants are the factories that make the heaviest elements. Modest stars like our sun can only cook up elements as big as carbon — merely the sixth element out of more than 117.

Astronomers have theorized for years that stars should be able to reach masses of up to 150 times the sun. Beyond that size, the nuclear reactions are so powerful inside a star, they immediately overcome gravity and a star can’t hold together.