Two explosions observed in 2004 and 2006 in a galaxy 78 million light years from Earth were part of the fiery death of one of the most massive stars known to exist, astronomers said on Wednesday.
Writing in the journal Nature, the scientists described the supernova death of a star estimated to be 50 to 100 times as massive as our sun in a galaxy called UGC4904 in the Lynx constellation. A supernova is a gigantic explosion that marks the demise of a star.
The researchers said Japanese astronomer Koichi Itagaki discovered a faint celestial explosion that remained visible for about 10 days in 2004, then detected a second, much more powerful explosion two years later.
"In the 2004 outburst episode, the star lost a significant amount of the external mantle, while in the 2006 episode its heart collapsed, likely forming a black hole, while the rest of the star exploded as a very luminous supernova," Andrea Pastorello of the Queen's University Belfast in Northern Ireland, one of the researchers, said by e-mail.
Pastorello and other researchers determined that the two explosions were in the exact same place. This marked the first time a double explosion like this has been observed, adding to the understanding of the life cycle of stars, they said.
Their conclusions backed similar findings of other scientists reported in the journal Astrophysics.
The 2004 explosion and any other prior outbursts like it probably stripped the star of most of its initial material, hydrogen and helium, leaving it about 15 to 25 times more massive than the sun before its 2006 supernova, Pastorello said.
The researchers believe the 2004 outburst was like one seen in another very massive star called Eta Carinae in the 1850s. Astronomers believe Eta Carinae, located 7,500 light years away within our own Milky Way galaxy, could go supernova — in other words explode and die — at any time.
"Although it may be tomorrow, it may be in 100,000 years," Pastorello said.
A light year is about 6 trillion miles, the distance light travels in a year.