How a trickster galaxy fooled us into thinking a supernova was too bright

The gravitational field of the trickster galaxy in the inset magnified a supernova behind it, making it appear 30 times too bright. [Credit: Kavli IPMU / CFHT]

The gravitational field of the trickster galaxy in the inset magnified a supernova behind it, making it appear 30 times too bright. [Credit: Kavli IPMU / CFHT]

Supernovas can be the brightest objects in the whole Universe, sometimes even outshining whole galaxies at their brightest moments. When one pops up that seems too bright, that really can be a cause for head-scratching. Such was the case for supernova PS1-10afx: based on its measured distance from Earth, it was 400 times brighter than expected for an exploding star, or 30 times too bright to be a white dwarf (type Ia) supernova.[*]

While other anomalous superluminous supernovas exist (enough to garner their own acronym: SLSN), this one looked too red. In fact, from its spectrum alone, it looked like a white dwarf supernova, the kind used to measure cosmic expansion. Since we rely on these to explode in very similar ways, a white dwarf supernova 30 times too bright is a problem. However, maybe something else was making it look brighter: a gravitational lens. And this is just what astronomers found, as I explained in Ars Technica:

However, one possibility remained: perhaps the light from this supernova had been magnified by gravitational lensing somewhere between the explosion and Earth. If that’s the case, the anomalous explosion could be an ordinary white dwarf supernova that happened to appear much brighter, instead of a fundamentally new type of event. Robert M. Quimby and colleagues found a galaxy that could be doing the lensing by monitoring the supernova as it faded. While lots of gravitational lenses have been identified, this is the first clear example of magnification of a supernova. [read more…]

Notes

  1. The PS1 in the name PS1-10afx comes from the observatory used to discover it: Panoramic Survey Telescope and Rapid Response System 1 (Pan-STARRS1). The 10 denotes the year 2010 when the supernova was discovered, and the letters indicate how many supernovas were found that year: the first of the year is 10a, the second 10b, the 27th 10aa, etc. I’m feeling too lazy to figure out which one this is, so you can do it yourself.
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