Stellar corpse reveals origin of radioactive molecules

Astronomers using ALMA and NOEMA have made the first definitive detection of a radioactive molecule in interstellar space. The radioactive part of the molecule is an isotope of aluminium. The observations reveal that the isotope was dispersed into space after the collision of two stars, that left behind a remnant known as CK Vulpeculae. This is the first time that a direct observation has been made of this element from a known source. Previous identifications of this isotope have come from the detection of gamma rays, but their precise origin had been unknown.

The team, led by Tomasz Kaminski (Harvard-Smithsonian Center for Astrophysics, Cambridge, USA), used the Atacama Large Millimeter/submillimeter Array (ALMA) and the NOrthern Extended Millimeter Array (NOEMA) to detect a source of the radioactive isotope aluminium-26. The source, known as CK Vulpeculae, was first seen in 1670 and at the time it appeared to observers as a bright, red "new star". Though initially visible with the naked eye, it quickly faded and now requires powerful telescopes to see the remains of this merger, a dim central star surrounded by a halo of glowing material flowing away from it.

348 years after the initial event was observed, the remains of this explosive stellar merger have led to the clear and convincing signature of a radioactive version of aluminum, known as aluminium-26. This is the first unstable radioactive molecule definitively detected outside of the Solar System. Unstable isotopes have an excess of nuclear energy and eventually decay into a stable form.

"This first observation of this isotope in a star-like object is also important in the broader context of galactic chemical evolution," notes Kaminski. "This is the first time an active producer of the radioactive nuclide aluminum-26 has been directly identified."

Kaminski and his team detected the unique spectral signature of molecules made up of aluminum-26 and fluorine (26AlF) in the debris surrounding CK Vulpeculae, which is about 2000 light-years from Earth. As these molecules spin and tumble through space, they emit a distinctive fingerprint of millimetre-wavelength light, a process known as rotational transition. Astronomers consider this the "gold standard" for detections of molecules.

The observation of this particular isotope provides fresh insights into the merger process that created CK Vulpeculae. It also demonstrates that the deep, dense, inner layers of a star, where heavy elements and radioactive isotopes are forged, can be churned up and cast into space by stellar collisions.

"We are observing the guts of a star torn apart three centuries ago by a collision," remarked Kaminski.

The astronomers also determined that the two stars that merged were of relatively low mass, one being a red giant star with a mass somewhere between 0.8 and 2.5 times that of our Sun.

Being radioactive, aluminium-26 will decay to become more stable and in this process one of the protons in the nucleus decays into a neutron. During this process, the excited nucleus emits a photon with very high energy, which we observe as a gamma ray.

Previously, detections of gamma ray emission have shown that around two solar masses of aluminium-26 are present across the Milky Way, but the process that created the radioactive atoms was unknown. Furthermore, owing to the way that gamma rays are detected, their precise origin was also largely unknown. With these new measurements, astronomers have definitively detected for the first time an unstable radioisotope in a molecule outside of our Solar System.

At the same time, however, the team have concluded that the production of aluminium-26 by objects similar to CK Vulpeculae is unlikely to be the major source of aluminium-26 in the Milky Way. The mass of aluminium-26 in CK Vulpeculae is roughly a quarter of the mass of Pluto, and given that these events are so rare, it is highly unlikely that they are the sole producers of the isotope in the Milky Way galaxy. This leaves the door open for further studies into these radioactive molecules.

Research paper

Related Links
European Southern Observatory
Stellar Chemistry, The Universe And All Within It

Tweet

Thanks for being there;
We need your help. The SpaceDaily news network continues to grow but revenues have never been harder to maintain.

With the rise of Ad Blockers, and Facebook - our traditional revenue sources via quality network advertising continues to decline. And unlike so many other news sites, we don't have a paywall - with those annoying usernames and passwords.

Our news coverage takes time and effort to publish 365 days a year.

If you find our news sites informative and useful then please consider becoming a regular supporter or for now make a one off contribution.

SpaceDaily Monthly Supporter
$5+ Billed Monthly

paypal only

SpaceDaily Contributor
$5 Billed Once

credit card or paypal

Young galaxy's halo offers clues to its growth and evolution
Maunakea HI (SPX) Jul 25, 2018
A team of astronomers has discovered a new way to unlock the mysteries of how the first galaxies formed and evolved. In a study published in Astrophysical Journal Letters, lead author Dawn Erb of the University of Wisconsin-Milwaukee and her team - for the very first time - used new capabilities at W. M. Keck Observatory on Maunakea, Hawaii to examine Q2343-BX418, a small, young galaxy located about 10 billion light years away from Earth. This distant galaxy is an analog for younger galaxies ... read more