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Lecture 10

Introduction to Astronomy-Lecture 10 Notes!.docx

Course Code
PCS 181
Margaret Buckby

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Pulsation Explanation:
A neutron “Star” (NS) is the compacted core of a star that had a magnetic field.
The neutron “Star” has Strong magnetic field which directs charged particles to the
North or South magnetic poles.
The particles continuing strike the surface of the NS, creating polar “hot spots”.
These “hot spots” radiate over a wide range of wavelengths …visible and invisible.
If the NS is properly oriented with respect to Earth, we detect the beams of radiation
emitted by the “hot spots” as the NS rotates on its axis.
This is the “Lighthouse Effect”.
If we detect these pulses, we call the object a “pulsar”.
However, a pulsar is a neutron “star”…
BUT every neutron “star” is NOT a pulsar.
Typical Neutron “Star”:
Mass range: 1.4 Mo < MNS < ~3Mo.
Size: ~20 to 100 km across ~about the size of a city.
Density is similar to that of an atomic nucleus ~1017 kg/m3 to 1018kg/m3.
Temperature: ~10 x 106 k on surface.
Period = 0.1 to 4s.
We know of ~500 pulsars.
Supernova 1987A:
Discovered/reported from Chile by Ian Shelton, an observer from the University of
SN1987A occurred in the Large Magellanic cloud, an irregular galaxy near out own at
~170,000 ly distance.
The progenitor star was a blue giant star, Sanduleak.
Huge neutrino bursts were detected by Earth-based equipment.
This particular SN event has been studied from the actual explosion to the present day.
Death of very Massive Stars:
These are > ~25 Mo.
<~5% of Stars are >~4Mo.
Star undergoes several Red Giant phases, producing ever-heavier elements in the core.
When star has an iron core, it explodes in a Supernova event…BUT
If the collapsed core is >~3 Mo, it cannot resist the pull of gravity and collapses to a
Black Hole Singularity.
Black Hole:
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