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Q&A: Supernova Remnants and Neutron Stars
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Q:
An article I read says a pulsar is 1,615 years old - the Chinese
saw something 1,600 years ago...and astronomers say the pulsar
was born in the year (Earth year) 386. But then the article
states that the "1,600 year old pulsar is 15,000 light years
away from Earth!" Doesn't that mean that what the Chinese saw in
the sky was an event that took place at least 15,000 years ago?
So if you add 1,600 to 15,000 you get a pulsar about 16,600
years old?
A:
The age of 1615 years for the pulsar refers to the age of the
outburst in the source. Assuming a distance of 15,000 light
year, the light took 15,000 years to get here, so the Chinese
astronomers observed the outburst 15,000 years after it
occurred. Since it's the evolution of the source that is of
primary interest, astronomers talk about the age SINCE the
outburst was observed. Our information for this source is always
15,000 years out of date. It's similar to finding a series of
photographs of a child in a 100 year-old time capsule. We could
see how the child was developing back then, even though he/she
may no longer be alive.
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