We owe our existence to a star that exploded long, long ago.
That's the conclusion of a study that aimed to solve the mystery of why our solar system is enriched in a rare form of oxygen.
The study suggests that the sun and the material for what became the eight major planets formed in the vicinity of one or more supernovas and were enriched in the matter that stellar explosions left behind, including that strange type of oxygen.
Astronomers can probe the galaxy for signatures of different elements and their isotopes (atoms that have the same number of protons, but a different number of neutrons) to see how they vary from region to region. They have long known that the solar system has a peculiarly high ratio of the two rarest forms of oxygen, but haven't known exactly why.
"This has been a problem for a long time," said study author Edward Young of UCLA, who announced the finding Thursday at the 215th meeting of the American Astronomical Society in Washington, D.C.
Some researchers initially thought the discrepancy between the ratio of those oxygen isotopes seen in the solar system and those elsewhere in the galaxy was a matter of measurement error. Another possibility was that while values for the solar system came from the observations of one star — the sun — those for other parts of the galaxy came from stars across large swaths of the Milky Way.
Now scientists have been able to determine the oxygen isotope ratios for individual star systems elsewhere in the galaxy, and the new measurements matched up with previous ones.
"They confirm that the solar system is indeed unusual," Young said. It "sticks out like a sore thumb above the rest."
So something must have enriched the neighborhood where the solar system formed with these rare types of oxygen.
"And in this case I think it's supernovae that are the culprit," Young said.
To get the values of oxygen isotopes that exist in the solar system, you would have to mix the material from the small supernova of an early star with the normal galactic background material, Young said.
Knowing what kind of environment our solar system formed in tells us more about how our solar system compares to other planetary systems in the galaxy.
The astronomers detected their pairs by noting their relative motion to each other. When something moves away from an observer, its light appears redder, or red-shifted (this shift in wavelength is known as the Doppler effect). And when an object moves toward an observer, its light appears bluer.
So the researchers measured the relative velocities of apparent black holes inside distant galaxies and found some sets that appeared to be very close to each other — about 3,000 light-years apart, or one-eighth the distance from the sun to the center of the Milky Way — indicating they were gravitationally-bound in pairs.