Physics Photo of the Week

May 6, 2011

On April 28, 2011 the American Association of Variable Star Observers sent out an alert notice of a new type Ia supernova in the distant galaxy NGC 2972.  The weather had just cleared after a week of clouds and rain and students were anxious* to observe with the WWC telescope and CCD camera.  The supernova is seen as the bright star in the elongated galaxy in the upper left center of the image.  Zhangwei Jin, Ningbo, Zhejiang, China, and Xing Gao, Urumqi, Xinjiang, China discovered this supernova on April 26, 2011.  At their website,, we can view this galaxy about 2 weeks earlier before the supernova erupted as well as the discovery image.

Supernovae are rather rare events.  It is estimated that in a typical galaxy consisting of 1012 stars there is about one supernova event per century, where a star blows up becoming more than 4 x 109 times (that's 4 billion times) the luminosity of the Sun.

Supernovae, especially type Ia supernovae, are important in astronomy because every type Ia supernova is the same brightness (
4 x 109 times the luminosity of the Sun).  That is because such a supernova explosion occurs when a white dwarf star (in a close binary association with an ordinary star) pulls enough material from the companion star that it reaches the Chandrasekhar limit of 1.4 solar masses upon which it blows up.  Because of the standard brightness, we can use these events to easily calculate the distance to the supernova - hence the distance to the host galaxy.  This supernova is still brightening and expected to reach its maximum brightness in about 2 to 3 weeks.  Estimating the brightness from data available from the AAVSO it is estimated that this galaxy is about 60 million light years distant.  This event happened about the same time that the dinosaurs became extinct on the Earth.
*Students Rashad Ali, Josiah Blocker, Joshua Jenkinson, Kathryn Kipfer, Taylor Moore, and Cristal Stevens helped with the telescope to obtain this image of the supernova on April 28 and April 29, 2011.  I will continue to observe this object through May and June to measure its brightness and to send the data to AAVSO.  On clear nights, people may visit the Spidel Observatory - the yard outside the physics lab.

Physics Photo of the Week is published weekly during the academic year on Fridays by the Warren Wilson College Physics Department.  These photos feature interesting phenomena in the world around us.  Students, faculty, and others are invited to submit digital (or film) photographs for publication and explanation.  Atmospheric phenomena are especially welcome.  Please send any photos to 

All photos and discussions are copyright by Donald Collins or by the person credited for the photo and/or discussion.  These photos and discussions may be used for private individual use or educational use.  Any commercial use without written permission of the photoprovider is forbidden.

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