From Caltech: “The Shape of Star Explosions”

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From Caltech

March 11, 2021
Whitney Clavin
(626) 395‑1944
wclavin@caltech.edu

Caltech Palomar 200 inch Hale Telescope, Altitude 1,713 m (5,620 ft), located in San Diego County, California, U.S.A.

New polarization instrument at Palomar Observatory delivers first results.

When massive stars end their lives in fiery explosions called supernovae, their ashes fly outward to form expanding clouds of debris. While these clouds may look roughly spherical, astronomers think that star explosions are in fact lopsided events in which different amounts of material shoot outward in different directions.


Three-Dimensional Core-Collapse Supernova (highest resolution).

Now, astronomers have a new tool to better understand the asymmetrical shapes of supernova explosions, and thus how stars explode in the first place. An instrument called “WIRC+Pol,” located at Caltech’s 200-inch Hale Telescope at Palomar Observatory, has delivered its first science results, which show that a supernova called SN 2018hna exploded in a shape more like an ellipse than a sphere, similar to the well-studied supernova remnant called SN 1987A.

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The WIRC+Pol instrument in the 200-inch Hale dome at Palomar. Credit: K. Tinyanont/Caltech.

“We believe all supernovae explode asymmetrically but we need an instrument like this to confirm that theory and to teach us more about how stars explode as well as the environments they explode into,” says Samaporn (Kaew) Tinyanont (MS ’17, PhD ’20), lead author of a new study reporting the findings in the journal Nature Astronomy. Tinyanont helped commission the WIRC+Pol instrument as part of his PhD thesis. His advisors were Caltech astronomy professors Mansi Kasliwal (MS ’07, PhD ’11) and Dimitri Mawet; Mawet is also affiliated with NASA-JPL/Caltech(US), which is managed by Caltech for the National Aeronautics and Space Administration(US).

WIRC+Pol, which was designed to study brown dwarfs and supernovae, is an adaptation of a previous instrument that operated at Palomar called the Wide-Field Infrared Camera. With these modifications, WIRC+Pol now has the ability to capture spectra of polarized light, hence its name. When light from a supernova explosion scatters off the supernova’s debris clouds, that light can become polarized, which means that some of the light waves become oriented in the same direction. The more asymmetrical the explosion, the more the light will be polarized. Thus, the degree of the light’s polarization, as measured from Earth, can be used to determine the shape of the explosion.

WIRC+Pol employs a thin sheet of liquid crystal polymer called polarization grating to split infrared light from an object into different polarization signals. Infrared light works better than optical light in polarization instruments because infrared light is not blocked by dust that causes contaminating polarization signatures. The infrared light beams with different polarization signals are simultaneously further split into different wavelengths to create the spectra. The efficiency of the new polarization grating is much higher compared with traditional gratings used previously. WIRC+Pol is the first instrument that employs a polarization grating on a large telescope, and the first with the sensitivity to observe supernovae.

“The vast majority of supernovae that are not in our own Milky Way and the nearby Magellanic Clouds are so far away that they appear as a point in our images even with the highest power telescopes. Polarization allows us to infer the shape of these supernovae.”

See the full article here.


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The California Institute of Technology(US) is a private research university in Pasadena, California. The university is known for its strength in science and engineering, and is one among a small group of institutes of technology in the United States which is primarily devoted to the instruction of pure and applied sciences.

Caltech was founded as a preparatory and vocational school by Amos G. Throop in 1891 and began attracting influential scientists such as George Ellery Hale, Arthur Amos Noyes, and Robert Andrews Millikan in the early 20th century. The vocational and preparatory schools were disbanded and spun off in 1910 and the college assumed its present name in 1920. In 1934, Caltech was elected to the Association of American Universities, and the antecedents of National Aeronautics and Space Administration (US)’s Jet Propulsion Laboratory, which Caltech continues to manage and operate, were established between 1936 and 1943 under Theodore von Kármán.

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