Outside In Stars

The non amateur stuff. Hawking, black holes, that sort of thing

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RMSteele
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Outside In Stars

Post by RMSteele »

A recent study of the Messier 13 globular cluster in Hercules has revealed a larger population of white dwarf stars than expected if they were all the dead, cooling stars that we have assumed them to be. A white dwarf is the remnant of a fairly typical star like our Sun. The white dwarf has run through its internal supply of nuclear fuel, blown off its mostly hydrogen outer layer, and has collapsed under its own gravity to a small, hot, dense remnant about the size of the Earth. However the conclusion is that we can see more white dwarfs in M13 than expected because many of them are warmer (brighter) than they should be because they have managed to initiate nuclear energy production in an outer hydrogen layer. Thus a "normal" star produces energy by nuclear fusion in its core and that energy heats the star from the inside out. Some white dwarfs on the other hand seem to be producing energy at their surfaces that heats them from the outside in. Their active hydrogen envelopes, however, can only delay and not prevent their eventual and inevitable demise. The recent finding has implications for the dating of stellar populations containing white dwarf stars.
Bob
brian livesey
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Re: Outside In Stars

Post by brian livesey »

As we know, globular clusters are very ancient aggregations of stars, but there are oddball globulars that contain what appear to be young blue stars. Astrophysicists concluded that there had been collisions between old stars that resulted in a rejuvenation process, leaving a single blue star.
brian
mikemarotta
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Re: Outside In Stars

Post by mikemarotta »

RMSteele wrote: Thu Sep 09, 2021 10:08 pm A recent study of the Messier 13 globular cluster in Hercules has revealed .... The recent finding has implications for the dating of stellar populations containing white dwarf stars.
brian livesey wrote: Sat Sep 11, 2021 6:15 am ... but there are oddball globulars that contain what appear to be young blue stars. Astrophysicists concluded ...
Thanks! In some ways, I am looking forward to the coming week of cloudy skies so that I can pick up where I left off in an online class in astrophysics from Australian National University through edX.

It is important to understand what you are looking at.
Michael E. Marotta
Explore Scientific 102 mm Refractor
National Geographic 70 mm Refractor
Ploessl oculars 40mm to 6mm 2X Barlow
mike49mercury@gmail.com
brian livesey
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Re: Outside In Stars

Post by brian livesey »

It was Alan Sandage in 1953 who discovered the apparent anomaly of blue stars in ancient clusters. Sandage named them blue stragglers.
brian
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