Telescopes see rare moment of donor star giving new life to ‘zombie’ star

6 Mar 2018

A fast-spinning electron star sucking in material from a neighbouring red giant. Image: NASA/Dana Berry

Is it possible for a zombie to return to the land of the living? Yes, when we look to the distant universe.

It seems that, as we add more powerful telescopes to our astronomical catalogue, we are capturing more and more rare events in deep space.

The latest one was first seen by the European Space Agency’s (ESA) Integral space observatory in August of last year, but the peculiar findings have just been published to the journal Astronomy & Astrophysics.

Future Human

At the time, a massive x-ray flare was detected from an unknown source somewhere in the crowded centre of our Milky Way galaxy, leading to astronomers training their telescopes in that direction.

These observations later revealed a strongly magnetised and slowly rotating neutron star that appeared to be feeding on material from a nearby red giant star, which was once up to eight times larger than our sun but had now reached the end stage of its life.

The neutron star, however, was once even larger, at up to 30 solar masses. After racing through its fuel and exploding in a supernova, it left a spinning stellar ‘zombie’ with a strong magnetic field that packs 1.5 solar masses into a space just 10km across.

While pairings of stars are relatively common in the universe, this discovery of a paired red giant star and neutron star is incredibly rare, as no more than 10 are known to science.

Artist impression depicting winds from a red giant star impacting a neutron star to create prolonged x-ray emission. GIF: ESA

A puzzling event

Readings from the pair reveal some other peculiarities, including the fact that the neutron star spins almost every two hours – very slow compared with other neutron stars, which can spin many times per second.

It also showed that it had a strong magnetic field, which typically points to a young neutron star; a red giant is much older, making this a bizarre couple to have grown up together.

“It might be that either the neutron star magnetic field does not decay substantially with time after all, or the neutron star actually formed later in the history of the binary system,” said Enrico Bozzo, who led the study.

“That would mean it collapsed from a white dwarf into a neutron star as a result of feeding off the red giant over a long time, rather than becoming a neutron star as a result of a more traditional supernova explosion of a short-lived massive star.”

Colm Gorey was a senior journalist with Silicon Republic