Scientists have found the “smoking gun" evidence that a massive star exploded in a lopsided manner, with ejected material flying in one direction and the core of the star going the other way. The key was titanium-44, which is a radioactive form of titanium that is usually produced in the very heart of a particular type of star explosion called Type II or core-collapse supernovae.
"Stars are spherical objects, but apparently the process by which they die causes their cores to be turbulent, boiling and sloshing around in the seconds before their demise. We are learning that this sloshing leads to asymmetrical explosions," said lead author Steve Boggs of the University of California, Berkeley.
While observing the supernova remnant called 1987A, researchers were able to study direction-dependent frequency changes—or Doppler shifts—of energy from titanium-44 and probe into the mechanisms of a deteriorating star. The findings, published in the journal Science, provides the best evidence yet that Type II supernovae are inherently asymmetrical.
“The NuSTAR (Nuclear Spectroscopic Telescope Array) data revealed that, surprisingly, most of the material is moving away from us," said Fiona Harrison, the principal investigator of NuSTAR at the California Institute of Technology in Pasadena in a statement.
The study found titanium-44 to be moving away with a velocity of 1.6 million mph (2.6 million kilometers per hour). While previous research has hinted at the lopsided nature of the blast, the observatory's sharp high-energy X-ray vision has provided researchers with the most precise measurements of titanium-44 yet.
“Radioactive titanium-44 glows in the X-rays no matter what and is only produced in the explosion,” said Brian Grefenstette, a co-author of the study at Caltech. "This means that we don’t have to worry about how the environment influenced the observations. We are able to directly observe the material ejected in the explosion."
Christian Ott, a professor of theoretical physics at Caltech who was not involved in study, says in a statement that these findings combined with previous research could provide an important clue to why some supernovae collapse into neutron stars and others into a black hole to form a space-time singularity. He suggests that the asymmetrical fashion the star explodes in can produce a dual effect, where the star explodes in one direction and the remainder of it continues to collapse in all other directions.
Supernova 1987A is 166,000 light-years away and was first detected in 1987 when light from the blast that created the remnant reached Earth. As the findings unravel the mysteries of these supernovae, researchers hope further studies by NuSTAR and other telescopes will provide additional information on their warped nature.