Early History of Supernovae

S. R. KulkarniCaltech Optical Observatories

Key Papers

• “On Supernovae” Baade & Zwicky (1934a)• “Cosmic Rays From Supernovae” Baade &

Zwicky (1934b)• “On the Search for Supernovae” Zwicky (1938)

BAADE & ZWICKY (1934A)

Novae Facts known by 1934

• Novae occur in our Galaxy at the rate of 30 per year

• Hubble studying novae in M31 (initially to determine distance to M31) and a similar rate is found

• Nova have typical brightness of -6 mag (with a range of 4 mag)

Other Facts known by 1934

• Tycho Nova (AD 1572) was unusually bright • But “pre-cursor” star for Tycho Nova was not

bright• S Andromeda (AD 1885) was very bright– Observed V=7.5 mag– Distance to Modulus to M31, DM=22.2– [Modern Distance Modulus is 24.5]– Peak brightness -14.7 [-17 modern]

Bright Novae (Baade & Zwicky)

• Bright novae are seen in distant nebula• Many of them peak with a brightness similar to the

“host” galaxy– MV = -15

• Last about a month• Observed Radiated light is 1048 erg– Two estimates for total energy release

• The rate is one per several centuries and conservatively one per thousand years (per galaxy)

Energetics: Baade & Zwicky (1934)

• Assume black body radiation from explosion to late times. Assume that we see a small fraction of energy in the optical– Two estimates: 1% to 100% of rest mass of the Sun

• Compute the black body radius at peak and divide by time to get velocity– Velocity = 60,000 km/s or v/c=0.2– This v/c corresponds to 5% of proton rest mass

Baade & Zwicky (1934a)

• Super-novae thus represent transition of ordinary stars into a body much smaller in mass and are different from novae

• Supernovae are catastrophic

THE PALOMAR 18-INCH BEGINS SN SURVEY

Fritz Zwicky (1889-1974)

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SN Spectroscopy

• Wide features seen in SN (a consequence of high ejection velocities)

• Zwicky begins his classification of SN (based on light curves)

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P48

P60

200-inch

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P18

BAADE & ZWICKY (1934B)

Cosmic Rays

• 1912: Hess undertakes high latitude balloon flight and establishes that ionization radiation increases with altitude

• 1920: Millikan coins the term “Cosmic Rays” and argues for a photonic origin

• 1932: Chadwick discovers the neutron • 1936: Hess wins Nobel Prize. Cosmic rays are now

thought to be energetic charged particles (both positive and negative)

• AND OF UNKNOWN ORIGIN

Prior to Baade & Zwicky (1934)

• It was popular to speculate that cosmic rays came from intergalactic space

• B&Z note that cosmic ray energy density to galaxy-light is much larger than the ratio of cosmic rays to Galactic star-light. This, in their view, rules out an IGM or Early Universe explanation for cosmic rays and favors a Galactic origin for Cosmic Rays

• B&Z, noting the large velocity of blast waves, suggest that cosmic rays arise in supernovae

• They compute the supernova energy injection rate and find that the resulting injection energy intensity to be comparable to the the intensity of cosmic rays

• CONCLUSION 1: Cosmic rays arise from supernovae

Conclusion 2:

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Palomar Observatory Museum

First Astronomical Use of Schmidt Camera

• The Schmidt design allows for wide field imaging with large aperture– The field of view of P48 is 47 square degrees!

• Wider field can be obtained by lenses (cf Rotse and others)

• Modern wide field imagers use very complex cameras which require very fine alignment (not easy, cf PS-1, LSST)

MOTIVATING TO THE PALOMAR TRANSIENT FACTORY

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P48Discovery

P60Confirmation

200-inch

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Homework for serious students

• Review the arguments presented in Baade & Zwicky (1934a) which led Baade & Zwicky to infer the explosion energy in supernovae to be between 1% and 100% of the rest mass of the Sun. Do you agree with the two analysis? What are the flaws? (or alternatively could there be SN with so much energy release).