Question

What are the similarities between a nova and an X-ray burster? What are the differences?

Answer 1

Similarity:

1. Both Nova and X-ray burster involve an evolving star in a close binary system shedding mass onto a compact, previously more massive binary companion which has already shed its outer layers to become a white dwarf (nova) or a neutron star (x-ray burster).

Differences:

2. In the nova, hydrogen accumulates on the white dwarf’s surface until it ignites in a short-lived (several days) but violent fusion reaction on the white dwarf’s surface. Most of the mass of the hydrogen layer (only a tiny fraction of the white dwarf’s total mass) is ejected.

3. In the X-ray burster, Hydrogen falls onto the neutron star’s surface and instantly fuses to form helium, producing a continuous creation of weak x-rays, but eventually the accumulating helium layer on the neutron star fuses in a brief (several seconds) outburst of x-rays which give the burster its name. Both of these outbursts will occur repeatedly as mass transfer continues after the described outbursts.

4. In the case of the nova, the subsequent outburst typically occurs years, decades, centuries or even millennia later.

5. The next outburst of an x-ray burster typically occurs only hours or days later. The much shorter period until the next outburst, compared with a nova, is a consequence of the much smaller surface area of a neutron star as compared with a white dwarf which accumulates the critical thickness of a layer necessary for the next outburst in a much shorter period of time.

THANKS