A "zombie star" observed in September 2014 challenges astronomers' understanding of star formation and death. The stellar object refuses to die even though it has exploded many times.

When astronomers working at the Las Cumbres Observatory in California first observed the supernova called PTF14hls, they thought the object was just like others of its kind. After a closer look at the light of the explosion, however, they noticed something strange about the supernova.

Supernova

Stars that are more than eight times more massive than the sun end their lives in explosions known as supernova, one of the most energetic phenomena in the universe. Supernova that form from supermassive stars often rise to their peak brightness before fading over a period of about 100 days.

PTF14hls, however, fluctuated by brightening and dimming far longer than 100 days. Astronomers observed that after 100 days, the supernova still looked like it was 30 days old. Even after two years, the star's spectrum still looked as if it were 60 days old.

When the supernova recently emerged from behind the sun, researchers found that it was still bright even after about three years. The object, however, only had one-hundredth of its peak brightness, which suggests it could finally be fading out.

Also Exploded In 1954

Researchers also looked at the archival data and found that the same star also exploded in 1954 but managed to survive the catastrophic event before exploding again and continuing to survive.

The star's mass is 50 times that of the sun. The explosion is likewise the longest-lived ever observed. The researchers said that it could be the most massive supernova astronomers have so far observed, and the size of the explosion could be to blame as to why the supernova defies current understanding on how stars die.

Researchers will continue to monitor the supernova. It will become more transparent as its light fades and it expands. This will allow researchers to take a closer look at it.

Study researcher Iair Arcavi, from the University of California, Santa Barbara, said that the Hubble Space Telescope is set to observe this supernova, and the telescope's increased resolution should allow astronomers to see what the neighboring stars of the supernova look like.

"I'd like to know how common these explosions are. Was this a super rare beast, or will we find more now that we know what to look for?" Arcavi said.

The findings were published in the journal Nature on Nov. 8.