Stellar corpses

QuestionEdit

Hi I was wondering if you could help me classify the following as being either being the characteristic of a WHITE DWARF or of a NEUTRON STAR:

1) can have a mass of 1.5 solar masses 2) may be in a binary system that undergoes nova explosions 3) may repeatedly dim and brighten more than once per second 4) may be surrounded by a supernova remnant 5) may be in a binary system that undergoes X-ray bursts 6) may be surrounded by a planetary nebula 7) emits most strongly in visible and ultraviolet

AnswerEdit

Hi, 1) can have a mass of 1.5 solar masses Only a neutron star can do that, as a white dwarf explodes as a type 1-a super nova, the moment its mass exceeds the Chandrashekhar limit of 1.44 solar masses.

2) may be in a binary system that undergoes nova explosions. Truly that can only be a white dwarf. As it orbits the companion, the companion over time swells and becomes a red giant. The dwarf then begins siphoning material off the giant's outer layers. Moment this material hits the dwarf, it gets so compressed and hot, it triggers a fusion reaction and a Nova Burst. This occurs periodicslly and may not fragment the dwarf star.

3) may repeatedly dim and brighten more than once per second. That is a neutron star. As it shrinks, it conserves angular momentum by spinning very fast. Some have periods of milliseconds! The neutron star emits strong radiation along two axes. When the axes point at you, you see a strong beam, which then winks out as it goes out of visual allignment.

4) may be surrounded by a supernova remnant. A neutron star! Because white dwarf stars have planetary nebulas around them. Neutron stars are surrounded by the progenitor supernova debri cloud that speeds away at a few 1000 km/sec! This shock wave meets earlier matter shed by the star in its red giant stage in a couple of decades and sets up a new fire storm (rings of fire). In the case of SN1987A, scientists had predicted this and it was observed also.

5) may be in a binary system that undergoes X-ray bursts This would be a wolf rayet white dwarf binary system. WR 104, has its axis pointed at us. If andwhen it will unleash its Gamma ray burst, it will fry us.

6) may be surrounded by a planetary nebula A white dwarf star.

7) emits most strongly in visible and ultraviolet. An ambiguity there. As the source of the stated emissions is the accretion disk surrounding both of these! However I have heard of accretion disks of black holes more than either neutron stars or white dwarfs. As far as "strong" is concerned, the overall luminosity is low for a white dwarf,as its surface is small. But its surface temperature and absolute luminosity are very high. Temp in range 25 to 35000 deg K. I will settle for the white dwarf on account of its high temperature and absolute luminosity. One never hears much about the luminosity and temperature of a neutron star.

regards Jayen