Three centuries ago, a pair of stars collided about 2,000 light-years from Earth, spewing their innards into space. Amazingly, we’ve now been able to study the result of this collision – and find something rather unique in the process.
In a study published in the journal Nature Astronomy, scientists said they managed to observe a radioactive version of aluminum from the explosion, the isotope 26Al (aluminum monofluoride). This is the first time an unstable radioactive molecule, one that survives on a short time scale in the tens of thousands of years, has been found beyond the Solar System.
“We are observing the guts of a star torn apart three centuries ago by a collision,” lead author Tomasz Kaminski from the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts said in a statement. “How cool is that?”
The molecule was spotted using two radio telescopes, the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile and the Northern Extended Millimeter Array (NOEMA) in the French Alps.
The telescopes were trained on CK Vulpeculae, which is a remnant of the aforementioned stellar collision 2,000 light-years away. It was seen in 1670, described by observers at the time as a bright new star in the sky, visible to the naked eye.
We can only see it now with telescopes, but we can tell quite a bit about it. While both of the stars were relatively low in mass compared to the rest of the universe, one was a red giant with a mass 0.8 to 2.5 times that of our Sun.
It’s not quite clear what happened to the stars after the collision, although there is some suggestion one (or both) exploded as a nova. Surrounding the collision zone is a cloud of dust and gas resulting from the impact.
The major finding here though is that isotope of aluminum. It’s an atom with 13 protons and 13 neutrons, and we think there is just three Suns’ worth of it in the Milky Way. The amount found here was about a quarter of the mass of Pluto.
We’ve detected 26Al in space as far back as 1984, but we’ve never been sure where it’s coming from. This study seems to suggest stellar mergers play a part, but there's a catch. The amount spotted was too low to account for all the 26Al in our galaxy, as stellar mergers are rare.
However, the astronomers note they could only spot the atoms of 26Al that were also bound to fluorine; there might be more that we can’t see yet. And other mergers may emit more of the stuff than we can see here.
“So this is not a closed issue and the role of mergers may be non-negligible,” said Kaminski.