Each year, astronomers discover new explosions in the Milky Way that cause faint stars to erupt and emit much more light than the sun before they disappear again. But our galaxy is so large and dusty that no one knows how many of these eruptions occur along its vast domain, where they release newly coined chemical elements into space.
Now, by detecting infrared light from explosions, which penetrates dust better than visible light, Caltech astronomer Kishalay De and his colleagues have estimated the frequency with which these explosions occur in the Milky Way. Knowing the rate of novae is vital in determining how much these explosions have contributed to the chemical composition of the galaxy by creating new elements.
The updated balance puts the rate at 46, 13 or 13 years a year, the team reported on Jan. 11 on arXiv.org. Previous estimates of the new rate ranged from just 10 a year to 300.
A new one emerges from a binary star: two surrounding stars. One is a white dwarf, a dense star that is as small as Earth but about as massive as the sun. After the white dwarf receives gas from its mate, the gas explodes causing the faint star to glow brightly. The new one does not destroy the star, unlike a supernova, which marks the death of a star.
After observing the sky from the Palomar Observatory in California for 17 months, De and his colleagues detected 12 new explosions. By estimating the number of explosions lost, astronomers deducted the annual new rate. Its rate is similar, but more accurate, to that reported four years ago by Allen Shafter, an astronomer at San Diego State University who set the annual new rate between 27 and 81.
“They’re doing a wonderful job,” says Bradley Schaefer, an astrophysicist at Louisiana State University in Baton Rouge, who points out that looking for infrared wavelengths is ideal for finding distant explosions hidden by galaxy dust. "They have a lot of really good data."
The most accurate rate helps confirm estimates of how much these explosions have altered the chemical composition of the galaxy. In this regard, it is difficult for a mere newcomer to compete with a supernova explosion that, while rare, releases many more elements of new production than a new one. But if the annual new rate is around 50, then certain scarce isotopes on Earth, such as lithium-7, carbon-13, nitrogen-15 and oxygen-17, have emerged partially or mostly in new explosions, says Sumner Starrfield , an Arizona State University astronomer in Tempe who did not participate in this study. The explosions then animated these isotopes before other nuclear reactions could destroy them.