Neutron stars/pulsars and black holes on HR diagram

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r.jenkins
Posts: 11
Joined: Sat May 01, 2010 10:43 pm

Neutron stars/pulsars and black holes on HR diagram

Postby r.jenkins » Sat Sep 18, 2010 5:31 pm

Hi,

As high mass stars approach their death to become neutron stars, black holes etc, what direction on the HR diagram do they head and where do they end up resting (relative to the HR diagram because they are obviously not on it anymore)?

Thanks

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joe
Posts: 745
Joined: Fri Aug 29, 2003 11:57 am
Location: Sydney

Re: Neutron stars/pulsars and black holes on HR diagram

Postby joe » Fri Sep 24, 2010 2:45 pm

Gday R.Jenkins,

I'll refer this one on to one of my astrophysicist colleagues. I've only seen HR diagrams used for optical quantification.

For a normal star, nearly all radiation is photons, most of them visible. For neutron stars, most is Xrays. So their spectrum in the visible would be pretty flat (see
http://www.phys.unsw.edu.au/~jw/FAQ.html#black )
and so they are 'white' in a sense.

Temperature? VERY hot, especially soon after collapse, so way way off the HR diagram to the right.

Black holes are also complicated. Classical Netownian BHs don't radiate light. I don't think that Hawking radiation has been observed. Further, some of us would demur that Hawking temperature at the moment has only metaphorical status: the argument that it is the same as thermodynamic temperature is elegant but not, it seems to me, rigorous.

So, when a star goes nova and shoots up to pas the top right corner of a HR diagram, I'd say that the NSs and BHs don't come back! Well the right of a HR diagram

Joe


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