Titanium bubbles discovered in supernova could help solve mystery of exploding stars

Titanium has been discovered in the beautiful remnants of the Cassiopeia A supernova about 11,000 light-years away.

This discovery could help scientists understand what leads some giant stars to explode, according to the new study.

Observations of the supernova were made using NASA’s Chandra X-ray Observatory, which has been in operation since 1999, between 2000 and 2018. Scientists recently sifted through the data to understand more about the supernova that has captivated researchers for years.

Cassiopeia A is a giant bubble of hot, expanding gas, and it’s the youngest known remnant from a supernova explosion, dating back 340 years ago, in our Milky Way galaxy. The light from this supernova first reached Earth in the 1670s.

Researchers have used space-based observatories to study Cassiopeia A for years because it’s relatively nearby, astronomically speaking and provides insight into the evolution of the universe. When stars explode, they release their elements into space. Telescopes like Chandra can help unlock which ones Cassiopeia A contributed when it exploded.

The study published Wednesday in the journal Nature.

Release of heavy elements

While stars with masses more than 10 times our sun are known to explode once they run out of fuel, scientists don’t exactly know why this occurs. These explosions have led to the release of heavy elements throughout the universe, like gold and titanium, that are found on Earth.

“Scientists think most of the titanium that is used in our daily lives — such as in electronics or jewelry — is produced in a massive star’s explosion,” said lead study author Toshiki Sato, an assistant professor in the department of physics at Rikkyo University in Tokyo, in a statement. “However, until now scientists have never been able to capture the moment just after stable titanium is made.”

Massive stars run on nuclear power generated by reactions that happen at their core. When this fuel runs out, the star’s center collapses, forming a black hole or a dense object called a neutron star.

If the celestial body becomes a neutron star, a shock wave ripples out from the star, creating new elements as nuclear reactions occur.

When scientists have conducted computer modeling of this phenomenon, they have found that the energy burns up quickly and causes the shock wave to stall. This would prevent a supernova explosion from occurring.

The potential role of neutrinos

New computer simulations suggest a missing element that could allow the supernova to continue: neutrinos.

These ghostly low-mass particles, created when a neutron star forms, could spur on bubbles of elements that rocket away, pushing the shock wave onward and allowing for a supernova.

The explosion that created the Cassiopeia A supernova was likely driven by neutrinos, according to the new study.

Data from Chandra, which observes features in space through X-ray emissions, produced structures shaped like fingers that literally pointed away from the supernova. These structures contained titanium and chromium, along with iron that was previously detected by the space telescope.

The temperature and other conditions needed to create these elements match the speeding bubbles from the computer simulations.

“We have never seen this signature of titanium bubbles in a supernova remnant before, a result that was only possible with Chandra’s incredibly sharp images,” said study coauthor Keiichi Maeda, an associate professor in the department of astronomy at Kyoto University in Japan, in a statement. “Our result is an important step in solving the problem of how these stars explode as supernovae.”

This means that fragments of titanium were created deep within the star as the supernova occurred. The amount of stable titanium produced by this particular supernova exceeds Earth’s total mass, the researchers said.

The findings also support the theory that explosions driven by neutrinos could be used to explain some massive star explosions.