Download Lecture14

ASTR 1102-002
2008 Fall Semester
Joel E. Tohline, Alumni Professor
Office: 247 Nicholson Hall
[Slides from Lecture14]
Chapter 20: Stellar Evolution:
The Deaths of Stars
and
Chapter 21: Neutron Stars
Excerpt from §21-1
On the morning of July 4, 1054, Yang Wei-T’e
(imperial astronomer to the Chinese court) made
a startling discovery. Just a few minutes before
sunrise, a new and dazzling object ascended
above the eastern horizon.
This “guest star” was so brilliant that it could easily
be seen during broad daylight for the rest of
July!
This “guest star” was visible in the night sky (to the
naked eye) for 21 months.
Excerpt from §21-1
On the morning of July 4, 1054, Yang Wei-T’e
(imperial astronomer to the Chinese court) made
a startling discovery. Just a few minutes before
sunrise, a new and dazzling object ascended
above the eastern horizon.
This “guest star” was so brilliant that it could easily
be seen during broad daylight for the rest of
July!
This “guest star” was visible in the night sky (to the
naked eye) for 21 months.
Excerpt from §21-1
On the morning of July 4, 1054, Yang Wei-T’e
(imperial astronomer to the Chinese court) made
a startling discovery. Just a few minutes before
sunrise, a new and dazzling object ascended
above the eastern horizon.
This “guest star” was so brilliant that it could easily
be seen during broad daylight for the rest of
July!
This “guest star” was visible in the night sky (to the
naked eye) for 21 months.
Crab Nebula
Today, if we look at the location on the sky where
Yang Wei-T’e discovered his “guest star” nearly
1000 years ago, we see a glowing gaseous
nebula that we call the “Crab Nebula”:
– The gaseous debris is expanding away from
its center at a rapid rate;
– projecting this expansion rate backward in
time, we conclude that the nebula originated
from a “point-like explosion” approximately
1000 years ago
Crab Nebula
Crab Nebula
Today, if we look at the location on the sky where
Yang Wei-T’e discovered his “guest star” nearly
1000 years ago, we see a glowing gaseous
nebula that we call the “Crab Nebula”:
– The gaseous debris is expanding away from its center
at a rapid rate;
– projecting this expansion rate backward in time, we
conclude that the nebula originated from a “point-like
explosion” approximately 1000 years ago
Crab Nebula
• At the center of the crab nebula, astronomers
have identified a peculiar, compact star (a
“pulsar”) that …
– At visible wavelengths is difficult to see;
– At radio wavelengths is a powerful “light-house”
beacon that flashes on and off 33 times every second!
Crab Nebula
• Astronomers are convinced that the gas making
up the Crab Nebula is (what is left of) the
outermost layers of a massive star that died
violently (a “supernova explosion”) in the year
1054, and that its central pulsar is a rapidly
rotating neutron star – a compact stellar
remnant, which was once the “core” of the highly
evolved, massive star.
• This illustrates how massive stars die!
Crab Nebula
• Astronomers are convinced that the gas making
up the Crab Nebula is (what is left of) the
outermost layers of a massive star that died
violently (a “supernova explosion”) in the year
1054, and that its central pulsar is a rapidly
rotating neutron star – a compact stellar
remnant, which was once the “core” of the highly
evolved, massive star.
• This illustrates how massive stars die! The
“disaster” alluded to earlier results in an
explosion of cataclysmic proportion.
Supernovae
• Easily (and now frequently) detected in other
galaxies. (Statistically, every galaxy should
display 1-3 supernovae every 100 yrs.)
• The light display from each SN generally can be
categorized as one of several standard “types”:
– Type Ia
– Type Ib, Ic
– Type II
Supernovae
• Easily (and now frequently) detected in other
galaxies. (Statistically, every galaxy should
display 1-3 supernovae every 100 yrs.)
• The light display from each SN generally can be
categorized as one of several standard “types”:
– Type Ia
– Type Ib, Ic
– Type II
What About SNe in Our Galaxy?
• We’ve already discussed the Crab SN, which exploded
in 1054; our distance from the Crab nebula is about 2000
parsecs, and it is approximately 4 pc in diameter.
• Over the past 1000 years, written records indicate that
only 5 SN explosions have been seen (by humans) in
our “Milky Way” Galaxy
– Years 1006, 1054 (Crab), 1181, 1572, 1604
• We’re overdue!
• NOTE:
– Dozens of gaseous SN remnants are identifiable in our Galaxy
– Well over a thousand (!) pulsars have been catalogued in our
Galaxy.
What About SNe in Our Galaxy?
• We’ve already discussed the Crab SN, which exploded
in 1054; our distance from the Crab nebula is about 2000
parsecs, and it is approximately 4 pc in diameter.
• Over the past 1000 years, written records indicate that
only 5 SN explosions have been seen (by humans) in
our “Milky Way” Galaxy
– Years 1006, 1054 (Crab), 1181, 1572, 1604
• We’re overdue!
• NOTE:
– Dozens of gaseous SN remnants are identifiable in our Galaxy
– Well over a thousand (!) pulsars have been catalogued in our
Galaxy.
What About SNe in Our Galaxy?
• We’ve already discussed the Crab SN, which exploded
in 1054; our distance from the Crab nebula is about 2000
parsecs, and it is approximately 4 pc in diameter.
• Over the past 1000 years, written records indicate that
only 5 SN explosions have been seen (by humans) in
our “Milky Way” Galaxy
– Years 1006, 1054 (Crab), 1181, 1572, 1604
• We’re overdue!
• NOTE:
– Dozens of gaseous SN remnants are identifiable in our Galaxy
– Well over a thousand (!) pulsars have been catalogued in our
Galaxy.
What About SNe in Our Galaxy?
• We’ve already discussed the Crab SN, which exploded
in 1054; our distance from the Crab nebula is about 2000
parsecs, and it is approximately 4 pc in diameter.
• Over the past 1000 years, written records indicate that
only 5 SN explosions have been seen (by humans) in
our “Milky Way” Galaxy
– Years 1006, 1054 (Crab), 1181, 1572, 1604
• We’re overdue!
• NOTE:
– Dozens of gaseous SN remnants are identifiable in our Galaxy
– Well over a thousand (!) pulsars have been catalogued in our
Galaxy.
SN 1987A
• On February 23, 1987, a supernova was
discovered in the Large Magellanic Cloud
(LMC), a companion galaxy to our Milky Way
some 51,500 pc (168,000 ly) from Earth.
• This supernova (SN 1987A) could easily been
seen (from southern hemisphere) at night w/o
aid of telescope; but was not bright enough to be
seen in the daytime.
• Given the available array of modern telescopes
and detectors, SN 1987A has gave us an
unprecedented “laboratory” for understanding
supernova explosions.
Andromeda Galaxy
Magellanic Clouds
Magellanic Clouds
SMC
LMC
SN 1987A
• On February 23, 1987, a supernova was
discovered in the Large Magellanic Cloud
(LMC), a companion galaxy to our Milky Way
some 51,500 pc (168,000 ly) from Earth.
• This supernova (SN 1987A) could easily been
seen (from southern hemisphere) at night w/o
aid of telescope; but was not bright enough to be
seen in the daytime.
• Given the available array of modern telescopes
and detectors, SN 1987A has gave us an
unprecedented “laboratory” for understanding
supernova explosions.
Large Magellanic Cloud (LMC)
SN 1987 A
SN 1987A
• On February 23, 1987, a supernova was
discovered in the Large Magellanic Cloud
(LMC), a companion galaxy to our Milky Way
some 51,500 pc (168,000 ly) from Earth.
• This supernova (SN 1987A) could easily been
seen (from southern hemisphere) at night w/o
aid of telescope; but was not bright enough to be
seen in the daytime.
• Given the available array of modern telescopes
and detectors, SN 1987A has gave us an
unprecedented “laboratory” for understanding
supernova explosions.
SN 1987 A
Neutrinos from SN 1987A
• Two “particle physics” detectors were in
operation (deep underground) on February 23,
1987.
– Kamiokande detector (Japan)
– IMB (Irvine, Michigan, Brookhaven) detector (U.S.)
• A 12-second “burst” of neutrinos was detected
(12 by Kamiokande; 8 by IMB) 3 hours before
astronomers saw light from the exploding star.
• Actual equivalent of exposure to a “torent of
more than 1016 neutrinos.”
– 100 times the energy the Sun has emitted during its
entire history!
– 100 times that the supernova (1987A) emitted as
light!
Discovery of Pulsars
(neutron stars)