First proposed in 1977 by physicist Kim Thorne and astronomer Anna Żytkow, a...you know what? Let's just call it a TZO, sounds easier that way. Anyway, a TZO is supposedly a giant or even a supergiant that has swallowed up a neutron star and merged it as the larger star's core. This is a neat idea, as neutron stars are all that remains of a supernova that have become super compressed--on average, a 12-mile-wide object that is half more massive than our own sun. And despite being monstrous, TZOs can live as long as our sun can, and this paragraph from Astronomy explains why:
Ordinary red supergiants, like other stars, are powered by nuclear fusion in their cores. So when that energy runs out, their uncontested gravity causes them to implode before erupting as a supernova. But TZOs can live such long lives because they do not rely on sustained nuclear fusion in their cores to avoid collapse. Instead, a TZO’s neutron star core, which is already extremely compressed, largely prevents the rapid and uncontested gravitational collapse of the surrounding supergiant layers.
Astrobiologists have been looking for stars that are bright enough and long-lasting enough for life to thrive on any planet orbiting that star within a zone suitable enough for surface liquid water. The reason that TZOs were never the focus on that topic is that their very existence remains questionable.
But what if they DO exist?
In this scenario, there are plenty of Earthlike planets orbiting one TZO (starting with one for simplicity's sake) that fit all the criteria for making life possible--plate tectonics, liquid surface water, atmosphere, magnetic field--except that all of them are lacking that one crucial ingredient: Life itself. The star in question is 1200 times brighter than our sun. So in that respect, how far and how wide would the habitable zone of this hybrid star be?